Resumen de Importancia de las interacciones bióticas entre plantas de comunidades vegetales gipsícolas para la conservación y restauración de ecosistemas yesíferos

Ana María Foronda Vázquez

• Los suelos de yeso presentan limitaciones físicas y químicas para el desarrollo vegetal, como una baja disponibilidad de agua y macronutrientes esenciales, altas concentraciones de sulfato y calcio que pueden llegar a ser tóxicas para las plantas, o costras superficiales que impiden la penetración de las raíces. Sin embargo, estos suelos albergan comunidades vegetales especializadas, raras y ricas en especies adaptadas a estas condiciones (gipsófitos), que son de gran importancia para la conservación de la biodiversidad mundial. A pesar de su relevancia, estos hábitats suelen estar degradados y/o fragmentados debido a actividades antrópicas como la agricultura intensiva, el sobrepastoreo o la minería. La restauración de ecosistemas gipsícolas degradados es un proceso difícil debido a las duras condiciones ambientales, que limitan la regeneración de la vegetación.

  La regeneración y la persistencia de la comunidad vegetal en estos ambientes estresantes dependen de la capacidad de establecimiento y supervivencia de las plantas, que son fases críticas en estos ambientes. Las plantas en las primeras etapas de su vida son altamente vulnerables al estrés ambiental (especialmente las plantas menos adaptadas al yeso, gipsovagos) y a menudo necesitan la presencia de plantas nodrizas para germinar y sobrevivir hasta la etapa adulta. En general, las plantas que actúan como nodrizas son arbustos que mejoran las condiciones micro-ambientales bajo su dosel, creando microhábitats favorables para el establecimiento de especies menos adaptadas al estrés, formando así parches de vegetación ricos en especies. Los arbustos pueden presentar una doble función positiva en la comunidad, ya que también captan y acumulan semillas bajo su dosel, donde las condiciones serán favorables a su germinación. La facilitación puede ser un proceso clave en la restauración de ecosistemas gipsícolas degradados, ya que promovería la sucesión de las plantas y, por tanto, la regeneración espontánea de la comunidad vegetal. Por tanto, es necesario identificar las especies clave que ejercen efectos positivos significativos en la comunidad, ya sea mediante la captura de semillas o facilitando el establecimiento de plantas, y habrían de tenerse en cuenta en planes de conservación y restauración.

  Además de la facilitación, las interacciones negativas entre plantas (conocidas como interferencia) también influyen en la composición y estructura de las comunidades vegetales. Una vez que las plántulas facilitadas son adultas, pueden ejercer un efecto adverso sobre las plantas nodrizas a través de la competencia por los recursos escasos. Para eliminar plantas vecinas potencialmente competidoras, hay algunas especies que liberan compuestos con efectos adversos sobre el establecimiento y crecimiento de otras plantas. Esto conduciría a un empobrecimiento de especies en su vecindad y, como consecuencia, estas plantas pueden llegar a ser localmente dominantes en las comunidades gipsícolas. El balance neto de las interacciones depende de las especies involucradas y de las condiciones ambientales. Hay investigaciones que postulan que mientras que en ambientes con más estrés ambiental la facilitación tomaría mayor relevancia, en ambientes con estrés moderado dominaría la interferencia. Sin embargo, otras sugieren una predominancia de la interferencia en condiciones de elevado estrés, por ejemplo debido a un aumento de la competencia por los recursos escasos o a la intensificación de los efectos fitotóxicos.

  El objetivo de la tesis es investigar el papel de los arbustos gipsófitos y gipsovagos en la estructuración de la diversidad vegetal en las comunidades gipsícolas para identificar especies clave para la conservación y restauración de estos ecosistemas. A diferencia de la mayoría de estudios sobre interacciones bióticas entre plantas, centrados en los efectos de una especie sobre otra, esta tesis doctoral aporta conocimiento sobre el balance neto que tienen las interacciones a nivel de comunidad. Dado que las plantas son organismos sésiles y que las interacciones bióticas ocurren entre individuos vecinos, los patrones espaciales de la vegetación pueden ser buenos indicadores para inferir el balance neto de las interacciones entre plantas de la comunidad. El estudio se ha abordado desde distintas perspectivas, tanto a nivel observacional evaluando la estructura espacial de la comunidad, como a nivel experimental testando el efecto que tienen ciertas especies clave en el establecimiento de otras. Los experimentos complementan a los datos observacionales, ya que ayudan a desentrañar los mecanismos por los cuáles las plantas influyen en el patrón espacial de la comunidad. El estudio se realizó en el Valle Medio del Ebro (NE de España), que comprende uno de los mayores afloramientos de yeso de Europa. En el área de estudio existe un gradiente de aridez de norte a sur, facilitando la evaluación de las interacciones bajo distintos niveles de estrés ambiental.

  Los datos observacionales recogidos en el capítulo 1 sirvieron para destacar la relevancia que tienen las interacciones positivas en la comunidad vegetal tanto desde el punto de vista de las plantas facilitadas como de las facilitadoras. Se encontró que independientemente de su estrategia de vida (gipsófitos o gipsovagos), las plantas de las comunidades gipsícolas se ven favorecidas por la presencia de plantas adultas para establecerse. En este capítulo se identificaron especies con un papel positivo sobre la riqueza y abundancia de plantas en la comunidad. Como especies de estudio se seleccionaron los arbustos más abundantes en la comunidad vegetal, siendo tres gipsófitos (Gypsophila struthium, Ononis tridentata y Helianthemum squamatum), y tres gipsovagos (Cistus clusii, Rosmarinus officinalis y Thymus vulgaris). A excepción de H. squamatum, los arbustos estudiados tienen un papel positivo en el establecimiento de otras plantas con respecto a áreas abiertas. Se observó que estos arbustos mejoran las condiciones micro-ambientales bajo su dosel, lo que podría ser el mecanismo subyacente que favorece el establecimiento de plantas en esos micrositios. Sin embargo, se encontraron diferencias significativas entre las especies estudiadas en la capacidad de facilitación. Los gipsófitos G.struthium y O. tridentata albergan más plantas bajo su dosel que los otros arbustos, estructurando parches ricos en especies en su vecindad.

  En el capítulo 2 se estudió la capacidad que tienen estos arbustos como fuentes y sumideros de semillas y, por tanto, como estructuradores del banco de semillas del suelo en estas comunidades vegetales. De entre las especies estudiadas, el arbusto G. struthium es el que acumula más riqueza y abundancia de semillas bajo su dosel, debido a que su arquitectura y tamaño le permite captar y acumular más semillas que otras plantas (sumidero de semillas). Además, este arbusto actúa como fuente de semillas a través de las plantas que alberga bajo su dosel (capítulo 1), que aportan semillas al suelo de las áreas vecinas. El papel significativo que G. struthium ejerce como sumidero y como fuente de semillas favorece la formación de un banco de semillas estructurado en parches en áreas vecinas. Existiría un mecanismo de retroalimentación positiva, ya que las semillas acumuladas en las cercanías de G. struthium también encontrarían condiciones micro-ambientales favorables a su germinación, por tanto, formando parches de vegetación ricos en especies.

  Por otro lado, en el capítulo 1 se observó que, a pesar de tener arquitectura de nodriza y mejorar las condiciones micro-ambientales bajo su dosel de igual manera que los gipsófitos G. struthium y O. tridentata, los arbustos gipsovagos R. officinalis y C. clusii albergan menor riqueza y abundancia de plantas que los anteriores. Ambas especies son localmente dominantes en las comunidades vegetales gipsícolas del Valle Medio del Ebro. Estas observaciones sugieren que estos arbustos gipsovagos pueden tener efectos adversos sobre ciertas especies vecinas, potencialmente causados por una mayor capacidad competitiva o por interferencia química. Mientras que la interferencia química de R. officinalis ha sido demostrada en otras comunidades vegetales, no existen evidencias de que C. clusii ejerza efectos químicos negativos sobre la vegetación (aunque sí existen trabajos que demuestran efectos químicos negativos de otras especies del mismo género). En el capítulo 3 de esta tesis se combinaron datos observacionales en campo con datos obtenidos de un experimento de siembra en invernadero para estudiar el posible mecanismo de interferencia que este arbusto podría estar ejerciendo sobre las especies cohabitantes en la comunidad. Se observó que la germinación y la supervivencia de algunas especies se veían afectadas negativamente por los extractos acuosos de hojas y raíces de C. clusii, coincidiendo con lo observado bajo condiciones naturales. Complementariamente, en los extractos acuosos se encontraron compuestos comúnmente considerados con potencial fitotóxico. Estos resultados evidenciaron que C. clusii ejerce un papel químico negativo en plantas vecinas y que este efecto es especie-específico.

  Dado que los ecosistemas gipsícolas se encuentran a menudo degradados por las actividades humanas, se hace necesario elaborar planes de restauración eficientes para devolver el ecosistema al estado inicial. Recientemente se está considerando a la facilitación como un mecanismo crucial para la restauración de ecosistemas. Una de las mayores aportaciones de la tesis ha sido la identificación de G. struthium como especie clave el mantenimiento de la diversidad por su papel significativo como nodriza. En el capítulo 4 se estudió la idoneidad de este arbusto como planta nodriza en la restauración de ecosistemas gipsícolas degradados por la minería. Por un lado, un trabajo observacional en una cantera de yeso confirmó la aparición de G. struthium como especie pionera en canteras de yeso, que ya había sido demostrada anteriormente por otros investigadores. Otros especialistas edáficos (gipsófitos) también aparecieron como pioneros en la comunidad vegetal. Por otro lado, un experimento de plantación y siembra bajo el dosel de G. struthium en un vertedero de yeso confirmó su papel positivo sobre el establecimiento y crecimiento de otras plantas de interés para la restauración de comunidades vegetales gipsícolas. Este experimento desveló que la mejora de las condiciones micro-ambientales podría ser el mecanismo subyacente de la facilitación que ejerce este arbusto. Este trabajo puso en valor el uso de plantas que aparecen como pioneras en la comunidad como plantas nodrizas para la restauración, lo que mejoraría la sucesión vegetal espontánea y la persistencia de la comunidad vegetal.

  Los distintos capítulos que componen esta tesis mejoran el entendimiento de las interacciones entre plantas a nivel de comunidad y destacan el papel clave que tienen ciertas especies que son abundantes en la estructuración de la diversidad en las comunidades vegetales gipsícolas del Valle Medio del Ebro. Aunque se han identificado especies que tienen un efecto negativo en el establecimiento de ciertas especies (por ejemplo C. clusii), la tesis pone de manifiesto que el balance neto de las interacciones a nivel de comunidad es positivo. Por un lado, se ha demostrado que las plantas necesitan ser facilitadas para establecerse bajo las condiciones extremas que suponen los ambientes de yeso. Por otro lado, se han identificado arbustos con un claro papel de nodriza, que estructuran la vegetación en parches ricos en especies a su alrededor. En general, el arbusto que ha demostrado tener un papel más positivo en balance neto de las interacciones es el gipsófito G. struthium (seguido del gipsófito O. tridentata), tanto por su papel de nodriza como por su capacidad de formar bancos de semillas abundantes y ricos en especies. Este arbusto aparece como pionero en las comunidades vegetales gipsícolas, que junto a su papel positivo en el establecimiento de plantas, pone en valor su uso en los planes de restauración de ecosistemas de yeso degradados por la minería.

  A pesar de haber identificado que los arbustos gipsófitos son clave en la conservación y restauración de las comunidades vegetales gipsícolas del Valle del Ebro, hacen falta futuros trabajos para ampliar el conocimiento de las interacciones entre plantas en los ecosistemas gipsícolas. Para poder generalizar nuestras conclusiones, se hace necesario realizar trabajos paralelos en comunidades vegetales gipsícolas de otras regiones bajo diversas condiciones ambientales y en las que están implicadas otras especies. Además, sería interesante desarrollar trabajos experimentales bajo condiciones naturales a nivel de comunidad, para permitir sacar conclusiones firmes sobre los mecanismos subyacentes que generan los patrones observados en esta tesis. Asimismo, se hace necesario comprobar experimentalmente la idoneidad de otras especies que aparecen como pioneras para su uso como nodrizas en la restauración de ecosistemas gipsícolas.

  Abdul-Kareem, A.W., McRae, S.G., 1984. The effects on topsoil of long-term storage in stockpiles. Plant Soil 76, 357–363. https://doi.org/10.1007/BF02205593 Aerts, R., Maes, W., November, E., Behailu, M., Poesen, J., Deckers, J., Hermy, M., Muys, B., 2006. Surface runoff and seed trapping efficiency of shrubs in a regenerating semiarid woodland in northern Ethiopia. CATENA 65, 61–70. https://doi.org/10.1016/j.catena.2005.09.004 Aguiar, M.R., Sala, O.E., 1999. Patch structure, dynamics and implications for the functioning of arid ecosystems. Trends in Ecology & Evolution 14, 273–277. https://doi.org/10.1016/S0169-5347(99)01612-2 Aguiar, M.R., Sala, O.E., 1997. Seed distribution constrains the dynamics of the patagonian steppe. Ecology 78, 93–100. https://doi.org/10.1890/0012-9658(1997)078[0093:SDCTDO]2.0.CO;2 Alados, C.L., Gotor, P., Ballester, P., Navas, D., Escos, J.M., Navarro, T., Cabezudo, B., 2006. Association between competition and facilitation processes and vegetation spatial patterns in alpha steppes. Biological Journal of the Linnean Society 87, 103–113. https://doi.org/10.1111/j.1095-8312.2006.00559.x Albert, M.J., Iriondo, J.M., Pérez-García, F., 2002. Effects of temperature and pretreatments on seed germination of nine semiarid species from NE Spain. Israel Journal of Plant Sciences 50, 103–112. https://doi.org/10.1560/3HT7-P4UB-GA7N-PB3F Alguacil, M.M., Torrecillas, E., Roldán, A., Díaz, G., Torres, M.P., 2012. Perennial plant species from semiarid gypsum soils support higher AMF diversity in roots than the annual Bromus rubens. Soil Biology and Biochemistry 49, 132–138. https://doi.org/10.1016/j.soilbio.2012.02.024 Alías, J.C., Sosa, T., Escudero, J.C., Chaves, N., 2006. Autotoxicity against germination and seedling emergence in Cistus ladanifer L. Plant Soil 282, 327–332. https://doi.org/10.1007/s11104-005-6066-y Allington, G.R.H., Valone, T.J., 2010. Reversal of desertification: The role of physical and chemical soil properties. Journal of Arid Environments 74, 973–977. https://doi.org/10.1016/j.jaridenv.2009.12.005 Aragón, C.F., Albert, M.J., Giménez-Benavides, L., Luzuriaga, A.L., Escudero, A., 2007. Environmental Scales on the Reproduction of a Gypsophyte: A Hierarchical Approach. Ann Bot 99, 519–527. https://doi.org/10.1093/aob/mcl280 Aragón, C.F., Escudero, A., Valladares, F., 2008. Stress-induced dynamic adjustments of reproduction differentially affect fitness components of a semi-arid plant. Journal of Ecology 96, 222–229. https://doi.org/10.1111/j.1365-2745.2007.01320.x Aragón, C.F., Méndez, M., Escudero, A., 2009. Survival costs of reproduction in a short-lived perennial plant: Live hard, die young. American Journal of Botany 96, 904–911. https://doi.org/10.3732/ajb.0800223 Armas, C., Pugnaire, F.I., 2009. Ontogenetic shifts in interactions of two dominant shrub species in a semi-arid coastal sand dune system. Journal of Vegetation Science 20, 535–546. https://doi.org/10.1111/j.1654-1103.2009.01055.x Armas, C., Pugnaire, F.I., 2005. Plant interactions govern population dynamics in a semi-arid plant community. Journal of Ecology 93, 978–989. https://doi.org/10.1111/j.1365-2745.2005.01033.x Arroyo, A.I., Pueyo, Y., Pellissier, F., Ramos, J., Espinosa-Ruiz, A., Millery, A., Alados, C.L., 2018. Phytotoxic effects of volatile and water soluble chemicals of Artemisia herba-alba. Journal of Arid Environments 151, 1–8. https://doi.org/10.1016/j.jaridenv.2017.11.010 Arroyo, A.I., Pueyo, Y., Saiz, H., Alados, C.L., 2015. Plant-plant interactions as a mechanism structuring plant diversity in a Mediterranean semi-arid ecosystem. Ecology and Evolution 5, 5305–5317. https://doi.org/10.1002/ece3.1770 Bąbel, M., 2012. Facies and depositional environments of the Nida Gypsum deposits (Middle Miocene, Carpathian Foredeep, southern Poland). Geological Quarterly 43, 405–428.

  Badía-Villas, D., del Moral, F., 2016. Soils of the Arid Areas, in: Gallardo, J.F. (Ed.), The Soils of Spain, World Soils Book Series. Springer International Publishing, Cham, pp. 145–161. https://doi.org/10.1007/978-3-319-20541-0_4 Ballesteros, M., Cañadas, E.M., Foronda, A., Fernández-Ondoño, E., Peñas, J., Lorite, J., 2012. Vegetation recovery of gypsum quarries: short-term sowing response to different soil treatments. Appl Veg Sci 15, 187–197. https://doi.org/10.1111/j.1654-109X.2011.01166.x Ballesteros, M., Cañadas, E.M., Foronda, A., Peñas, J., Valle, F., Lorite, J., 2014. Central role of bedding materials for gypsum-quarry restoration: An experimental planting of gypsophile species. Ecological Engineering 70, 470–476. https://doi.org/10.1016/j.ecoleng.2014.06.001 Ballesteros, M., Cañadas, E.M., Marrs, R.H., Foronda, A., Martín-Peinado, F.J., Lorite, J., 2017. Restoration of Gypsicolous Vegetation on Quarry Slopes: Guidance for Hydroseeding under Contrasting Inclination and Aspect. Land Degrad. Develop. n/a-n/a. https://doi.org/10.1002/ldr.2740 Ballesteros, M., Foronda, A., Cañadas, E.M., Peñas, J., Lorite, J., 2013. Conservation status of the narrow endemic gypsophile Ononis tridentata subsp. crassifolia in southern Spain: effects of habitat disturbance. Oryx 47, 199–202. https://doi.org/10.1017/S0030605312001688 Barney, J.N., Sparks, J.P., Greenberg, J., Whitlow, T.H., Guenther, A., 2008. Biogenic volatile organic compounds from an invasive species: impacts on plant–plant interactions. Plant Ecol 203, 195–205. https://doi.org/10.1007/s11258-008-9529-4 Barrajón-Catalán, E., Fernández-Arroyo, S., Roldán, C., Guillén, E., Saura, D., Segura-Carretero, A., Micol, V., 2011. A systematic study of the polyphenolic composition of aqueous extracts deriving from several Cistus genus species: evolutionary relationship. Phytochem. Anal. 22, 303–312. https://doi.org/10.1002/pca.1281 Belnap, J., Büdel, B., Lange, O.L., 2003. Biological Soil Crusts: Characteristics and Distribution, in: Belnap, Jayne, Lange, Otto L. (Eds.), Biological Soil Crusts: Structure, Function, and Management, Ecological Studies. Springer Berlin Heidelberg, Berlin, Heidelberg, pp. 3–30. https://doi.org/10.1007/978-3-642-56475-8_1 Belnap, J., Lange, O.L., 2001. Biological soil crusts: structure, function and management. Ecological Studies Series, Springer-Verlag, Berlin.

  Berdugo, M., Soliveres, S., Maestre, F.T., 2014. Vascular Plants and Biocrusts Modulate How Abiotic Factors Affect Wetting and Drying Events in Drylands. Ecosystems 17, 1242–1256. https://doi.org/10.1007/s10021-014-9790-4 Bertin, C., Yang, X., Weston, L.A., 2003. The role of root exudates and allelochemicals in the rhizosphere. Plant and Soil 256, 67–83. https://doi.org/10.1023/A:1026290508166 Bertness, M.D., Callaway, R., 1994. Positive interactions in communities. Trends in Ecology & Evolution 9, 191–193. https://doi.org/10.1016/0169-5347(94)90088-4 Bewick, V., Cheek, L., Ball, J., 2004. Statistics review 12: Survival analysis. Crit Care 8, 389–394. https://doi.org/10.1186/cc2955 Boukhris, M., Lossaint, P., 1975. Aspects ecologiques de la nutrition minerale des plantes gypsicoles de Tunisie. Rev Ecol Biol Sol.

  Bowker, M.A., 2007. Biological Soil Crust Rehabilitation in Theory and Practice: An Underexploited Opportunity. Restoration Ecology 15, 13–23. https://doi.org/10.1111/j.1526-100X.2006.00185.x Bowker, M.A., Mau, R.L., Maestre, F.T., Escolar, C., Castillo-Monroy, A.P., 2011. Functional profiles reveal unique ecological roles of various biological soil crust organisms. Functional Ecology 25, 787–795. https://doi.org/10.1111/j.1365-2435.2011.01835.x Boyadgiev, T.G., Verheye, W.H., 1996. Contribution to a utilitarian classification of gypsiferous soil. Geoderma 74, 321–338. https://doi.org/10.1016/S0016-7061(96)00074-2 Boyle, M., Frankenberger, W.T., Stolzy, L.H., 1989. The Influence of Organic Matter on Soil Aggregation and Water Infiltration. Journal of Production Agriculture 2, 290–299. https://doi.org/10.2134/jpa1989.0290 Bradshaw, A., 1997. Restoration of mined lands—using natural processes. Ecological Engineering 8, 255–269. https://doi.org/10.1016/S0925-8574(97)00022-0 Braun-Blanquet, J., Bolòs, O., 1958. Les groupements végétaux du bassin moyen de l’Ebre et leur dynamisme. Anales de la Estación Experimental de Aula Dei 5, 1–266.

  Bray, J.R., 1963. Root production and the estimation of net productivity. Canadian Journal of Botany 41, 65–72.

  Bray, R.H., Kurtz, L.T., 1945. Determination of total, organic, and available forms of phosphorus in soils. Soil Science 59, 39–46.

  Brooker, R.W., 2006. Plant–plant interactions and environmental change. New Phytologist 171, 271–284. https://doi.org/10.1111/j.1469-8137.2006.01752.x Brooker, R.W., Maestre, F.T., Callaway, R.M., Lortie, C.L., Cavieres, L.A., Kunstler, G., Liancourt, P., Tielbörger, K., Travis, J.M.J., Anthelme, F., Armas, C., Coll, L., Corcket, E., Delzon, S., Forey, E., Kikvidze, Z., Olofsson, J., Pugnaire, F., Quiroz, C.L., Saccone, P., Schiffers, K., Seifan, M., Touzard, B., Michalet, R., 2008. Facilitation in plant communities: the past, the present, and the future. Journal of Ecology 96, 18–34. https://doi.org/10.1111/j.1365-2745.2007.01295.x Bullock, J.M., Moy, I.L., 2004. Plants as seed traps: inter-specific interference with dispersal. Acta Oecologica 25, 35–41. https://doi.org/10.1016/j.actao.2003.10.005 Burgess, S.S.O., Adams, M.A., Turner, N.C., White, D.A., Ong, C.K., 2001. Tree roots: conduits for deep recharge of soil water. Oecologia 126, 158–165. https://doi.org/10.1007/s004420000501 Byers, J.E., Cuddington, K., Jones, C.G., Talley, T.S., Hastings, A., Lambrinos, J.G., Crooks, J.A., Wilson, W.G., 2006. Using ecosystem engineers to restore ecological systems. Trends in Ecology & Evolution 21, 493–500. https://doi.org/10.1016/j.tree.2006.06.002 Caballero, I., Olano, J.M., Escudero, A., Loidi, J., 2008. Seed bank spatial structure in semi-arid environments: beyond the patch-bare area dichotomy. Plant Ecol 195, 215–223. https://doi.org/10.1007/s11258-007-9316-7 Caballero, I., Olano, J.M., Loidi, J., Escudero, A., 2003. Seed bank structure along a semi-arid gypsum gradient in Central Spain. Journal of Arid Environments 55, 287–299. https://doi.org/10.1016/S0140-1963(03)00029-6 Caballero, R., Bustos, A., Román, R., 2001. Soil Salinity under Traditional and Improved Irrigation Schedules in Central Spain. Soil Science Society of America Journal 65, 1210–1218. https://doi.org/10.2136/sssaj2001.6541210x Cáceres, Y., Llambí, L.D., Rada, F., 2015. Shrubs as foundation species in a high tropical alpine ecosystem: a multi-scale analysis of plant spatial interactions. Plant Ecology & Diversity 8, 147–161. https://doi.org/10.1080/17550874.2014.960173 Callaway, R.M., 2007a. Direct mechanisms for facilitation, in: Positive Interactions and Interdependence in Plant Communities. Springer Netherlands, pp. 15–116. https://doi.org/10.1007/978-1-4020-6224-7_2 Callaway, R.M., 2007b. Indirect Mechanisms for Facilitation, in: Positive Interactions and Interdependence in Plant Communities. Springer Netherlands, pp. 117–177. https://doi.org/10.1007/978-1-4020-6224-7_3 Callaway, R.M., 1998. Are Positive Interactions Species-Specific? Oikos 82, 202–207. https://doi.org/10.2307/3546931 Callaway, R.M., Kikodze, D., Chiboshvili, M., Khetsuriani, L., 2005. Unpalatable Plants Protect Neighbors from Grazing and Increase Plant Community Diversity. Ecology 86, 1856–1862.

  Callaway, R.M., Ridenour, W.M., 2004. Novel weapons: invasive success and the evolution of increased competitive ability. Frontiers in Ecology and the Environment 2, 436–443. https://doi.org/10.1890/1540-9295(2004)002[0436:NWISAT]2.0.CO;2 Callaway, R.M., Walker, L.R., 1997. Competition and Facilitation: A Synthetic Approach to Interactions in Plant Communities. Ecology 78, 1958–1965. https://doi.org/10.1890/0012-9658(1997)078[1958:CAFASA]2.0.CO;2 Cañadas, E.M., Ballesteros, M., Valle, F., Lorite, J., 2014. Does gypsum influence seed germination? Turk J Bot 38, 141–147.

  Cañadas, E.M., Jiménez, M.N., Valle, F., Fernández-Ondoño, E., Martín-Peinado, F., Navarro, F.B., 2010. Soil–vegetation relationships in semi-arid Mediterranean old fields (SE Spain): Implications for management. Journal of Arid Environments 74, 1525–1533. https://doi.org/10.1016/j.jaridenv.2010.06.007 Casby-Horton, S., Herrero, J., Rolong, N.A., 2015. Chapter Four - Gypsum Soils—Their Morphology, Classification, Function, and Landscapes, in: Sparks, D.L. (Ed.), Advances in Agronomy. Academic Press, pp. 231–290. https://doi.org/10.1016/bs.agron.2014.10.002 Castells, E., Peñuelas, J., Valentine, D.W., 2004. Are phenolic compounds released from the Mediterranean shrub Cistus albidus responsible for changes in N cycling in siliceous and calcareous soils? New Phytologist 162, 187–195. https://doi.org/10.1111/j.1469-8137.2004.01021.x Castillejo, J.M., Castelló, R., 2010. Influence of the Application Rate of an Organic Amendment (Municipal Solid Waste [MSW] Compost) on Gypsum Quarry Rehabilitation in Semiarid Environments. Arid Land Research and Management 24, 344–364. https://doi.org/10.1080/15324982.2010.502920 Castro, J., Romero-García, A.T., 1999. Dormancy and germination in Cistus clusii (Cistaceae): effect of biotic and abiotic factors.

  Castroviejo, S., Laínz, M., López González, G., Montserrat, T., Muñoz Garmendia, F., Paiva, J., Villar, L., Aedo, C., Cirujano, S., Morales, R., n.d. 1986–2012. Flora Ibérica. Plantas vasculares de la Penìnsula Ibérica e Islas Baleares 1–8.

  Cavieres, L.A., Badano, E.I., 2009. Do facilitative interactions increase species richness at the entire community level? Journal of Ecology 97, 1181–1191. https://doi.org/10.1111/j.1365-2745.2009.01579.x Cavieres, L.A., Badano, E.I., Sierra-Almeida, A., Gómez-González, S., Molina-Montenegro, M.A., 2006. Positive interactions between alpine plant species and the nurse cushion plant Laretia acaulis do not increase with elevation in the Andes of central Chile. New Phytologist 169, 59–69. https://doi.org/10.1111/j.1469-8137.2005.01573.x Cavieres, L.A., Brooker, R.W., Butterfield, B.J., Cook, B.J., Kikvidze, Z., Lortie, C.J., Michalet, R., Pugnaire, F.I., Schöb, C., Xiao, S., Anthelme, F., Björk, R.G., Dickinson, K.J.M., Cranston, B.H., Gavilán, R., Gutiérrez-Girón, A., Kanka, R., Maalouf, J.-P., Mark, A.F., Noroozi, J., Parajuli, R., Phoenix, G.K., Reid, A.M., Ridenour, W.M., Rixen, C., Wipf, S., Zhao, L., Escudero, A., Zaitchik, B.F., Lingua, E., Aschehoug, E.T., Callaway, R.M., 2014. Facilitative plant interactions and climate simultaneously drive alpine plant diversity. Ecol Lett 17, 193–202. https://doi.org/10.1111/ele.12217 Cerrillo, M.I., Dana, E.D., Castro, H., Rodríguez-Tamayo, M.L., Mota, J.F., 2002. Selección de áreas prioritarias para la conservación de flora gipsícola en el sureste de la Península Ibérica. Revista chilena de historia natural 75, 395–408. https://doi.org/10.4067/S0716-078X2002000200010 Chacón-Labella, J., de la Cruz, M., Escudero, A., 2016. Beyond the classical nurse species effect: diversity assembly in a Mediterranean semi-arid dwarf shrubland. J Veg Sci 27, 80–88. https://doi.org/10.1111/jvs.12337 Chaves, M.M., Pereira, J.S., Maroco, J., Rodrigues, M.L., Ricardo, C.P.P., Osório, M.L., Carvalho, I., Faria, T., Pinheiro, C., 2002. How Plants Cope with Water Stress in the Field? Photosynthesis and Growth. Ann Bot 89, 907–916. https://doi.org/10.1093/aob/mcf105 Chaves, N., Escudero, J.C., 1997. Allelopathic effect of Cistus ladanifer on seed germination. Functional Ecology 11, 432–440. https://doi.org/10.1046/j.1365-2435.1997.00107.x Chaves, N., Sosa, T., Alias, J.C., Escudero, J.C., 2003. Germination inhibition of herbs in Cistus ladanifer L. soils: possible involvement of allelochemicals. Allelopathy Journal 11, 31–42.

  Chesson, P., Gebauer, R.L.E., Schwinning, S., Huntly, N., Wiegand, K., Ernest, M.S.K., Sher, A., Novoplansky, A., Weltzin, J.F., 2004. Resource pulses, species interactions, and diversity maintenance in arid and semi-arid environments. Oecologia 141, 236–253. https://doi.org/10.1007/s00442-004-1551-1 Chowhan, N., Singh, H.P., Batish, D.R., Kohli, R.K., 2011. Phytotoxic effects of β-pinene on early growth and associated biochemical changes in rice. Acta Physiol Plant 33, 2369–2376. https://doi.org/10.1007/s11738-011-0777-x Connell, J.H., Slatyer, R.O., 1977. Mechanisms of Succession in Natural Communities and Their Role in Community Stability and Organization. The American Naturalist 111, 1119–1144. https://doi.org/10.1086/283241 Coomes, D.A., Grubb, P.J., 2000. Impacts of root competition in forests and woodlands: a theoretical framework and review of experiments. Ecological Monographs 70, 171–207. https://doi.org/10.1890/0012-9615(2000)070[0171:IORCIF]2.0.CO;2 Cornelissen, J.H.C., Lavorel, S., Garnier, E., Díaz, S., Buchmann, N., Gurvich, D.E., Reich, P.B., Steege, H. ter, Morgan, H.D., Heijden, M.G.A. van der, Pausas, J.G., Poorter, H., 2003. A handbook of protocols for standardised and easy measurement of plant functional traits worldwide. Aust. J. Bot. 51, 335–380. https://doi.org/10.1071/bt02124 Creus, J., Ferraz, J., 1995. Irregularidad pluviométrica y continentalidad térmica en el valle medio del Ebro.

  Csontos, P., 2007. Seed banks: ecological definitions and sampling considerations. Community Ecology 8, 75–85. https://doi.org/10.1556/ComEc.8.2007.1.10 Cuadrat, J.M., Saz, M.A., Vicente-Serrano, S.M., 2007. Atlas climático de Aragón. Gobierno de Aragón.

  Dana, E.D., Mota, J.F., 2006. Vegetation and soil recovery on gypsum outcrops in semi-arid Spain. Journal of Arid Environments 65, 444–459. https://doi.org/10.1016/j.jaridenv.2005.08.009 Dawson, T.E., 1993. Hydraulic lift and water use by plants: implications for water balance, performance and plant-plant interactions. Oecologia 95, 565–574. https://doi.org/10.1007/BF00317442 De Almeida, L.F.R., Frei, F., Mancini, E., De Martino, L., De Feo, V., 2010. Phytotoxic Activities of Mediterranean Essential Oils. Molecules 15, 4309–4323. https://doi.org/10.3390/molecules15064309 de la Cruz, M., Romao, R.L., Escudero, A., Maestre, F.T., 2008. Where do seedlings go? A spatio-temporal analysis of seedling mortality in a semi-arid gypsophyte. Ecography 31, 720–730. https://doi.org/10.1111/j.0906-7590.2008.05299.x De Micco, V., Aronne, G., 2012. Morpho-Anatomical Traits for Plant Adaptation to Drought, in: Aroca, R. (Ed.), Plant Responses to Drought Stress: From Morphological to Molecular Features. Springer Berlin Heidelberg, Berlin, Heidelberg, pp. 37–61. https://doi.org/10.1007/978-3-642-32653-0_2 Delgado-Baquerizo, M., Maestre, F.T., Gallardo, A., Bowker, M.A., Wallenstein, M.D., Quero, J.L., Ochoa, V., Gozalo, B., García-Gómez, M., Soliveres, S., García-Palacios, P., Berdugo, M., Valencia, E., Escolar, C., Arredondo, T., Barraza-Zepeda, C., Bran, D., Carreira, J.A., Chaieb, M., Conceição, A.A., Derak, M., Eldridge, D.J., Escudero, A., Espinosa, C.I., Gaitán, J., Gatica, M.G., Gómez-González, S., Guzman, E., Gutiérrez, J.R., Florentino, A., Hepper, E., Hernández, R.M., Huber-Sannwald, E., Jankju, M., Liu, J., Mau, R.L., Miriti, M., Monerris, J., Naseri, K., Noumi, Z., Polo, V., Prina, A., Pucheta, E., Ramírez, E., Ramírez-Collantes, D.A., Romão, R., Tighe, M., Torres, D., Torres-Díaz, C., Ungar, E.D., Val, J., Wamiti, W., Wang, D., Zaady, E., 2013. Decoupling of soil nutrient cycles as a function of aridity in global drylands. Nature 502, 672–676. https://doi.org/10.1038/nature12670 Demoly, J.-P., Montserrat, P., 1990. Cistus L., in: Castroviejo, S. (Eds.) Flora Ibérica. Real Jardín Botánico, CSIC, Madrid, pp. 319–337.

  Dhima, K., Vasilakoglou, I., Garane, V., Ritzoulis, C., Lianopoulou, V., Panou-Philotheou, E., 2010. Competitiveness and Essential Oil Phytotoxicity of Seven Annual Aromatic Plants. Weed Science 58, 457–465. https://doi.org/10.1614/WS-D-10-00031.1 D’Odorico, P., Bhattachan, A., Davis, K.F., Ravi, S., Runyan, C.W., 2013. Global desertification: Drivers and feedbacks. Advances in Water Resources, 35th Year Anniversary Issue 51, 326–344. https://doi.org/10.1016/j.advwatres.2012.01.013 Dominguez Lozano, F., Carlos Moreno Saiz, J., Sainz Ollero, H., 2005. Biological properties of the endemic and threatened shrub in Iberia Vella pseudocytisus subsp. paui Gómez Campo (Cruciferae) and implications for its conservation. JOURNAL FOR NATURE CONSERVATION-JENA- 13, 17–30.

  Dorning, M., Cipollini, D., 2006. Leaf and root extracts of the invasive shrub Lonicera maackii inhibit seed germination of three herbs with no autotoxic effects. Plant Ecol 184, 287–296. https://doi.org/10.1007/s11258-005-9073-4 Ehlers, B.K., Charpentier, A., Grøndahl, E., 2014. An allelopathic plant facilitates species richness in the Mediterranean garrigue. J Ecol 102, 176–185. https://doi.org/10.1111/1365-2745.12171 Elorza, M.G., Santolalla, F.G., 1998. Geomorphology of the Tertiary gypsum formations in the Ebro Depression (Spain). Geoderma 87, 1–29. https://doi.org/10.1016/S0016-7061(98)00065-2 Escavy, J.I., Herrero, M.J., Arribas, M.E., 2012. Gypsum resources of Spain: Temporal and spatial distribution. Ore Geology Reviews 49, 72–84. https://doi.org/10.1016/j.oregeorev.2012.09.001 Escudero, A., 2009. 1520 Vegetación gipsícola mediterránea (Gypsophiletalia). VV. AA., Bases ecológicas preliminares para la conservación de los tipos de hábitat de interés comunitario en España.

  Escudero, A, Albert, M.J., Pita, J.M., Pérez-García, F., 2000. Inhibitory effects of Artemisia herba-alba on the germination of the gypsophyte Helianthemum squamatum. Plant Ecology 148, 71–80. https://doi.org/10.1023/A:1009848215019 Escudero, A., Carnes, L.F., Pérez-Garcı́a, F., 1997. Seed germination of gypsophytes and gypsovags in semi-arid central Spain. Journal of Arid Environments 36, 487–497. https://doi.org/10.1006/jare.1996.0215 Escudero, A., Iriondo, J.M., Olano, J.M., Rubio, A., Somolinos, R.C., 2000. Factors affecting establishment of a gypsophyte: the case of Lepidium subulatum (Brassicaceae). Am. J. Bot. 87, 861–871.

  Escudero, A., Palacio, S., Maestre, F.T., Luzuriaga, A.L., 2015. Plant life on gypsum: a review of its multiple facets. Biol Rev 90, 1–18. https://doi.org/10.1111/brv.12092 Escudero, A., Romao, R.L., de la Cruz, M., Maestre, F.T., 2005. Spatial pattern and neighbour effects on Helianthemum squamatum seedlings in a Mediterranean gypsum community. Journal of Vegetation Science 16, 383–390. https://doi.org/10.1111/j.1654-1103.2005.tb02377.x Escudero, A., Somolinos, R.C., Olano, J.M., Rubio, A., 1999. Factors controlling the establishment of Helianthemum squamatum, an endemic gypsophile of semi-arid Spain. Journal of Ecology 87, 290–302. https://doi.org/10.1046/j.1365-2745.1999.00356.x Espigares, T., Moreno-de las Heras, M., Nicolau, J.M., 2011. Performance of Vegetation in Reclaimed Slopes Affected by Soil Erosion. Restoration Ecology 19, 35–44. https://doi.org/10.1111/j.1526-100X.2009.00546.x Eswaran, H., Gong, Z.-T., 1991. Properties, Genesis, Classification, and Distribution of Soils with Gypsum. Occurrence, Characteristics, and Genesis of Carbonate, Gypsum, and Silica Accumulations in Soils sssaspecialpubl, 89–119. https://doi.org/10.2136/sssaspecpub26.c6 European Commission, 1992. Council directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora. European Community, Brussels, Belgium.

  FAO, F. and A.O. of the U.N., 2006. Guidelines for soil description. FAO Rome.

  Faulkner, H., Ruiz, J., Zukowskyj, P., Downward, S., 2003. Erosion risk associated with rapid and extensive agricultural clearances on dispersive materials in southeast Spain. Environmental Science & Policy, Socio-economic Factors in Soil Erosion and Conservation 6, 115–127. https://doi.org/10.1016/S1462-9011(02)00126-0 Flores, J., Jurado, E., 2003. Are nurse-protégé interactions more common among plants from arid environments? Journal of Vegetation Science 14, 911–916. https://doi.org/10.1111/j.1654-1103.2003.tb02225.x Foronda, A., Pueyo, Y., Arroyo, A.I., Saiz, H., Giner, M. de la L., Alados, C.L., 2019. The role of nurse shrubs on the spatial patterning of plant establishment in semi-arid gypsum plant communities. Journal of Arid Environments 160, 82–90. https://doi.org/10.1016/j.jaridenv.2018.09.003 Fowler, N., 1986. The Role of Competition in Plant Communities in Arid and Semiarid Regions. Annu. Rev. Ecol. Syst. 17, 89–110. https://doi.org/10.1146/annurev.es.17.110186.000513 Gagliardo, R.W., Chilton, W.S., 1992. Soil transformation of 2(3H)-benzoxazolone of rye into phytotoxic 2-amino-3H-phenoxazin-3-one. J Chem Ecol 18, 1683–1691. https://doi.org/10.1007/BF02751095 García, D., Zamora, R., 2003. Persistence, multiple demographic strategies and conservation in long-lived Mediterranean plants. Journal of Vegetation Science 14, 921–926. https://doi.org/10.1658/1100-9233(2003)014[0921:PMDSAC]2.0.CO;2 García-Fayos, P., Bochet, E., Cerdà, A., 2010. Seed removal susceptibility through soil erosion shapes vegetation composition. Plant Soil 334, 289–297. https://doi.org/10.1007/s11104-010-0382-6 Geist, H.J., Lambin, E.F., 2004. Dynamic Causal Patterns of Desertification. BioScience 54, 817–829. https://doi.org/10.1641/0006-3568(2004)054[0817:DCPOD]2.0.CO;2 Gelman, A., Hill, J., 2006. Data analysis using regression and multilevel/hierarchical models. Cambridge university press.

  Giraudoux, P., Giraudoux, M.P., 2017. Package ‘pgirmess.’ Gobierno de Aragón RD 181/2005, n.d. DECRETO 181/2005, de 6 de septiembre, del Gobierno de Aragón, por el que se modifica parcialmente el Decreto 49/1995, de 28 de marzo, de la Diputación General de Aragón, por el que se regula el Catálogo de Especies Amenazadas de Aragón.

  Goldberg, D.E., Barton, A.M., 1992. Patterns and Consequences of Interspecific Competition in Natural Communities: A Review of Field Experiments with Plants. The American Naturalist 139, 771–801. https://doi.org/10.1086/285357 Gómez, L., Zamora, R., Hódar, J.A., Gómez, J.M., Castro, J., Radoglou, K., 2001. Facilitation of tree seedlings by shrubs in Sierra Nevada (SE Spain): disentangling the mechanisms., in: Proceedings International Conference Forest Research: A Challenge for an Integrated European Approach, Thessaloniki, Greece, 27 August-1 September 2001, Volume I. NAGEF-Forest Research Institute, pp. 395–400.

  Gómez-Aparicio, L., 2009. The role of plant interactions in the restoration of degraded ecosystems: a meta-analysis across life-forms and ecosystems. Journal of Ecology 97, 1202–1214. https://doi.org/10.1111/j.1365-2745.2009.01573.x Gómez-Aparicio, L., Gómez, J.M., Zamora, R., Boettinger, J.L., Ezcurra, E., 2005. Canopy vs. soil effects of shrubs facilitating tree seedlings in Mediterranean montane ecosystems. Journal of Vegetation Science 16, 191–198. https://doi.org/10.1658/1100-9233(2005)016[0191:CVSEOS]2.0.CO;2 Gómez-Aparicio, L., Zamora, R., Gómez, J.M., Hódar, J.A., Castro, J., Baraza, E., 2004. Applying Plant Facilitation to Forest Restoration: A Meta-Analysis of the Use of Shrubs as Nurse Plants. Ecological Applications 14, 1128–1138. https://doi.org/10.1890/03-5084 Goodall, D.W., 1952. Quantitative aspects of plant distribution. Biological Reviews 27, 194–242. https://doi.org/10.1111/j.1469-185X.1952.tb01393.x Grigore, M.N., Toma, C., Zamfirache, M.-M., Boscaiu, M., 2011. Anatomical considerations on Spanish gypsophytes. Where is their place within plant ecology? Analele Stiintifice ale Universitatii" Al. I. Cuza" din Iasi 57, 31.

  Grime, J.P., 2006. Plant Strategies, Vegetation Processes, and Ecosystem Properties. John Wiley & Sons.

  Grøndahl, E., Ehlers, B.K., 2008. Local adaptation to biotic factors: reciprocal transplants of four species associated with aromatic Thymus pulegioides and T. serpyllum. Journal of Ecology 96, 981–992. https://doi.org/10.1111/j.1365-2745.2008.01407.x Gross, N., Boerger, L., Soriano-Morales, S.I., Le Bagousse-Pinguet, Y., Quero, J.L., Garcia-Gomez, M., Valencia-Gomez, E., Maestre, F.T., 2013. Uncovering multiscale effects of aridity and biotic interactions on the functional structure of Mediterranean shrublands. Journal of Ecology 101, 637–649. https://doi.org/10.1111/1365-2745.12063 Gross, N., Kunstler, G., Liancourt, P., De Bello, F., Suding, K.N., Lavorel, S., 2009. Linking individual response to biotic interactions with community structure: a trait-based framework. Functional Ecology 23, 1167–1178. https://doi.org/10.1111/j.1365-2435.2009.01591.x Guerrero-Campo, J., 1998. Respuestas de la vegetación y de la morfología de las plantas a la erosión del suelo: Valle del Ebro y Prepirineo aragonés. Consejo de Protección de la Naturaleza de Aragón.

  Guerrero-Campo, J., Alberto, F., Hodgson, J., Garcı́a-Ruiz, J.M., Montserrat-Martı́, G., 1999. Plant community patterns in a gypsum area of NE Spain. I. Interactions with topographic factors and soil erosion. Journal of Arid Environments 41, 401–410. https://doi.org/10.1006/jare.1999.0492 Guo, Q., Rundel, P.W., Goodall, D.W., 1998. Horizontal and vertical distribution of desert seed banks: patterns, causes, and implications. Journal of Arid Environments 38, 465–478. https://doi.org/10.1006/jare.1997.0353 Hall, S.L., Barton, C.D., Baskin, C.C., 2010. Topsoil Seed Bank of an Oak–Hickory Forest in Eastern Kentucky as a Restoration Tool on Surface Mines. Restoration Ecology 18, 834–842. https://doi.org/10.1111/j.1526-100X.2008.00509.x Harper, Jl., White, J., 1974. The demography of plants. Annual review of ecology and systematics 5, 419–463.

  Hawkesford, M., Horst, W., Kichey, T., Lambers, H., Schjoerring, J., Møller, I.S., White, P., 2012. Chapter 6 - Functions of Macronutrients, in: Marschner, P. (Ed.), Marschner’s Mineral Nutrition of Higher Plants (Third Edition). Academic Press, San Diego, pp. 135–189. https://doi.org/10.1016/B978-0-12-384905-2.00006-6 Heanes, D.L., 1984. Determination of total organic‐C in soils by an improved chromic acid digestion and spectrophotometric procedure. Communications in Soil Science and Plant Analysis 15, 1191–1213. https://doi.org/10.1080/00103628409367551 Heerdt, G.N.J.T., Verweij, G.L., Bekker, R.M., Bakker, J.P., 1996. An Improved Method for Seed-Bank Analysis: Seedling Emergence After Removing the Soil by Sieving. Functional Ecology 10, 144–151. https://doi.org/10.2307/2390273 Hermans, C., Hammond, J.P., White, P.J., Verbruggen, N., 2006. How do plants respond to nutrient shortage by biomass allocation? Trends in Plant Science 11, 610–617. https://doi.org/10.1016/j.tplants.2006.10.007 Hernández, I., Alegre, L., Munné-Bosch, S., 2004. Drought-induced changes in flavonoids and other low molecular weight antioxidants in Cistus clusii grown under Mediterranean field conditions. Tree Physiol 24, 1303–1311. https://doi.org/10.1093/treephys/24.11.1303 Herranz, J.M., Ferrandis, P., Copete, M.A., Duro, E.M., Zalacaín, A., 2005. Effect of allelopathic compounds produced by Cistus ladanifer on germination of 20 Mediterranean taxa. Plant Ecol 184, 259–272. https://doi.org/10.1007/s11258-005-9071-6 Herrero, J., Artieda, O., Hudnall, W.H., 2009. Gypsum, a Tricky Material. Soil Science Society of America Journal 73, 1757–1763. https://doi.org/10.2136/sssaj2008.0224 Herrero, J., Porta, J., 2000. The terminology and the concepts of gypsum-rich soils. Geoderma 96, 47–61. https://doi.org/10.1016/S0016-7061(00)00003-3 Herrero, J., Snyder, R.L., 1997. Aridity and irrigation in Aragon, Spain. Journal of Arid Environments 35, 535–547. https://doi.org/10.1006/jare.1996.0222 Hobbs, R.J., Walker, L.R., Walker, J., 2007. Integrating Restoration and Succession, in: Walker, L.R., Walker, J., Hobbs, R.J. (Eds.), Linking Restoration and Ecological Succession, SPRINGER SERIES ON ENVIRONMENTAL MANAGEMENT. Springer New York, New York, NY, pp. 168–179. https://doi.org/10.1007/978-0-387-35303-6_8 Holzapfel, C., Mahall, B.E., 1999. Bidirectional facilitation and interference between shrubs and annuals in the mojave desert. Ecology 80, 1747–1761. https://doi.org/10.1890/0012-9658(1999)080[1747:BFAIBS]2.0.CO;2 Holmgren, M. and Scheffer, M., 2010. Strong facilitation in mild environments: the stress gradient hypothesis revisited. Journal of Ecology, 98: 1269-1275.

  Hooper, D.U., Chapin, F.S., Ewel, J.J., Hector, A., Inchausti, P., Lavorel, S., Lawton, J.H., Lodge, D.M., Loreau, M., Naeem, S., Schmid, B., Setälä, H., Symstad, A.J., Vandermeer, J., Wardle, D.A., 2005. Effects of Biodiversity on Ecosystem Functioning: A Consensus of Current Knowledge. Ecological Monographs 75, 3–35. https://doi.org/10.1890/04-0922 Hopfensperger, K.N., 2007. A review of similarity between seed bank and standing vegetation across ecosystems. Oikos 116, 1438–1448. https://doi.org/10.1111/j.0030-1299.2007.15818.x Hothorn, T., Bretz, F., Westfall, P., 2008. Simultaneous inference in general parametric models. Biom. J. 50, 346–363. https://doi.org/10.1002/bimj.200810425 Hsiao, T.C., 1973. Plant responses to water stress. Annual review of plant physiology 24, 519–570.

  Huang, J., Yu, H., Guan, X., Wang, G., Guo, R., 2016. Accelerated dryland expansion under climate change. Nature Climate Change 6, 166–171. https://doi.org/10.1038/nclimate2837 Inderjit, 1996. Plant phenolics in allelopathy. The Botanical Review 186–202.

  Inderjit, Callaway, R.M., 2003. Experimental designs for the study of allelopathy. Plant and Soil 256, 1–11. https://doi.org/10.1023/A:1026242418333 Inderjit, Del Moral, R., 1997. Is separating resource competition from allelopathy realistic? Bot. Rev 63, 221–230. https://doi.org/10.1007/BF02857949 Inderjit, Duke, S.O., 2003. Ecophysiological aspects of allelopathy. Planta 217, 529–539. https://doi.org/10.1007/s00425-003-1054-z Jackman, S., Kleiber, C., Zeileis, A., 2007. Regression Models for Count Data in R (Working Paper). WWZ, University of Basel.

  Jensen, C.G., Ehlers, B.K., 2010. Genetic variation for sensitivity to a thyme monoterpene in associated plant species. Oecologia 162, 1017–1025. https://doi.org/10.1007/s00442-009-1501-z Jilani, G., Mahmood, S., Chaudhry, A.N., Hassan, I., Akram, M., 2008. Allelochemicals: sources, toxicity and microbial transformation in soil —a review. Ann. Microbiol. 58, 351–357. https://doi.org/10.1007/BF03175528 Jones, C.G., Lawton, J.H., Shachak, M., 1997. Positive and Negative Effects of Organisms as Physical Ecosystem Engineers. Ecology 78, 1946–1957. https://doi.org/10.1890/0012-9658(1997)078[1946:PANEOO]2.0.CO;2 Jones, C.G., Lawton, J.H., Shachak, M., 1994. Organisms as Ecosystem Engineers, in: Ecosystem Management. Springer New York, pp. 130–147. https://doi.org/10.1007/978-1-4612-4018-1_14 Khabou, W., Hajji, B., Zouari, M., Rigane, H., Abdallah, F.B., 2014. Arbuscular mycorrhizal fungi improve growth and mineral uptake of olive tree under gypsum substrate. Ecological Engineering 73, 290–296. https://doi.org/10.1016/j.ecoleng.2014.09.054 Kirmer, A., Tischew, S., Ozinga, W.A., Lampe, M.V., Baasch, A., Groenendael, J.M.V., 2008. Importance of regional species pools and functional traits in colonization processes: predicting re-colonization after large-scale destruction of ecosystems. Journal of Applied Ecology 45, 1523–1530. https://doi.org/10.1111/j.1365-2664.2008.01529.x Kruckeberg, A.R., 1986. An Essay: The Stimulus of Unusual Geologies for Plant Speciation. Systematic Botany 11, 455–463. https://doi.org/10.2307/2419082 Kruse, M., Strandberg, M., Strandberg, B., 2000. Ecological effects of allelopathic plants-a review. NERI Technical Report 315.

  Langenheim, J.H., 1994. Higher plant terpenoids: a phytocentric overview of their ecological roles. Journal of chemical ecology 20, 1223–1280.

  Lasanta, T., Garcı́a-Ruiz, J.M., Pérez-Rontomé, C., Sancho-Marcén, C., 2000. Runoff and sediment yield in a semi-arid environment: the effect of land management after farmland abandonment. CATENA 38, 265–278. https://doi.org/10.1016/S0341-8162(99)00079-X Lázaro-Nogal, A., Matesanz, S., Gimeno, T.E., Escudero, A., Valladares, F., 2012. Fragmentation modulates the strong impact of habitat quality and plant cover on fertility and microbial activity of semiarid gypsum soils. Plant Soil 358, 213–223. https://doi.org/10.1007/s11104-012-1184-9 Leck, M.A., 2012. Ecology of Soil Seed Banks. Elsevier.

  Liancourt, P., Callaway, R.M., Michalet, R., 2005. Stress tolerance and competitive-response ability determine the outcome of biotic interactions. Ecology 86, 1611–1618.

  Linhart, Y.B., Gauthier, P., Keefover-Ring, K., Thompson, J.D., 2015. Variable phytotoxic effects of Thymus vulgaris (Lamiaceae) terpenes on associated species. International Journal of Plant Sciences 176, 20–30. https://doi.org/10.1086/678772 Loidi, J. (Ed.), 2017. The vegetation of the Iberian Peninsula. Volume 1: ..., Plant and vegetation. Springer, Cham, Switzerland.

  Loidi, J., Costa, M., 1997. Sintaxonomía de los matorrales gipsícolas españoles. Fitosociologia 32, 221–227.

  López, R.P., Squeo, F.A., Armas, C., Kelt, D.A., Gutiérrez, J.R., 2016. Enhanced facilitation at the extreme end of the aridity gradient in the Atacama Desert: a community-level approach. Ecology 97, 1593–1604. https://doi.org/10.1890/15-1152.1 López‐Moreno, J.I., Vicente‐Serrano, S.M., Angulo‐Martínez, M., Beguería, S., Kenawy, A., 2010. Trends in daily precipitation on the northeastern Iberian Peninsula, 1955–2006. International Journal of Climatology 30, 1026–1041. https://doi.org/10.1002/joc.1945 López-Peralta, A.M., Maria Sanchez, A., Luzuriaga, A.L., Escudero, A., 2016. Factors driving species assemblage in Mediterranean soil seed banks: from the large to the fine scale. Ann. Bot. 117, 1221–1228. https://doi.org/10.1093/aob/mcw039 Luzuriaga, A.L., Escudero, A., Olano, J.M., Loidi, J., 2005. Regenerative role of seed banks following an intense soil disturbance. Acta Oecologica 27, 57–66. https://doi.org/10.1016/j.actao.2004.09.003 Luzuriaga, A.L., Sánchez, A.M., López-Angulo, J., Escudero, A., 2018. Habitat fragmentation determines diversity of annual plant communities at landscape and fine spatial scales. Basic and Applied Ecology 29, 12–19. https://doi.org/10.1016/j.baae.2018.03.008 Machı́n, J., Navas, A., 1998. Spatial analysis of gypsiferous soils in the Zaragoza province (Spain), using GIS as an aid to conservation. Geoderma 87, 57–66. https://doi.org/10.1016/S0016-7061(98)00071-8 Maestre, F.T., Bautista, S., Cortina, J., Bellot, J., 2001. Potential for using facilitation by grasses to establish shrubs on a semiarid degraded steppe. Ecological Applications 11, 1641–1655. https://doi.org/10.1890/1051-0761(2001)011[1641:PFUFBG]2.0.CO;2 Maestre, F.T., Callaway, R.M., Valladares, F., Lortie, C.J., 2009. Refining the stress-gradient hypothesis for competition and facilitation in plant communities. Journal of Ecology 97, 199–205.

  Maestre, F.T., Cortina, J., 2005. Remnant shrubs in Mediterranean semi-arid steppes: effects of shrub size, abiotic factors and species identity on understorey richness and occurrence. Acta Oecologica-International Journal of Ecology 27, 161–169. https://doi.org/10.1016/j.actao.2004.11.003 Maestre, F.T., Eldridge, D.J., Soliveres, S., Kéfi, S., Delgado-Baquerizo, M., Bowker, M.A., García-Palacios, P., Gaitán, J., Gallardo, A., Lázaro, R., Berdugo, M., 2016. Structure and Functioning of Dryland Ecosystems in a Changing World. Annual Review of Ecology, Evolution, and Systematics 47, 215–237.

  Maestre, F.T., Escolar, C., Ladron De Guevara, M., Quero, J.L., Lazaro, R., Delgado-Baquerizo, M., Ochoa, V., Berdugo, M., Gozalo, B., Gallardo, A., 2013. Changes in biocrust cover drive carbon cycle responses to climate change in drylands. Global Change Biology 19, 3835–3847. https://doi.org/10.1111/gcb.12306 Maestre, F.T., Quero, J.L., Gotelli, N.J., Escudero, A., Ochoa, V., Delgado-Baquerizo, M., García-Gómez, M., Bowker, M.A., Soliveres, S., Escolar, C., García-Palacios, P., Berdugo, M., Valencia, E., Gozalo, B., Gallardo, A., Aguilera, L., Arredondo, T., Blones, J., Boeken, B., Bran, D., Conceição, A.A., Cabrera, O., Chaieb, M., Derak, M., Eldridge, D.J., Espinosa, C.I., Florentino, A., Gaitán, J., Gatica, M.G., Ghiloufi, W., Gómez-González, S., Gutiérrez, J.R., Hernández, R.M., Huang, X., Huber-Sannwald, E., Jankju, M., Miriti, M., Monerris, J., Mau, R.L., Morici, E., Naseri, K., Ospina, A., Polo, V., Prina, A., Pucheta, E., Ramírez-Collantes, D.A., Romão, R., Tighe, M., Torres-Díaz, C., Val, J., Veiga, J.P., Wang, D., Zaady, E., 2012. Plant Species Richness and Ecosystem Multifunctionality in Global Drylands. Science 335, 214–218. https://doi.org/10.1126/science.1215442 Maestre, F.T., Valladares, F., Reynolds, J.F., 2006. The stress-gradient hypothesis does not fit all relationships between plant-plant interactions and abiotic stress: further insights from arid environments. Journal of Ecology 94, 17–22. https://doi.org/10.1111/j.1365-2745.2005.01089.x Maestre, F.T., Valladares, F., Reynolds, J.F., 2005. Is the change of plant-plant interactions with abiotic stress predictable? A meta-analysis of field results in arid environments. Journal of Ecology 93, 748–757. https://doi.org/10.1111/j.1365-2745.2005.01017.x Mall, U., Singh, G.S., 2014. Soil Seed Bank Dynamics: History and Ecological Significance in Sustainability of Different Ecosystems, in: Environment and Sustainable Development. Springer, New Delhi, pp. 31–46. https://doi.org/10.1007/978-81-322-1166-2_3 Martínez-Duro, E., Ferrandis, P., Escudero, A., Luzuriaga, A. l., Herranz, J. m., 2010. Secondary old-field succession in an ecosystem with restrictive soils: does time from abandonment matter? Applied Vegetation Science 13, 234–248. https://doi.org/10.1111/j.1654-109X.2009.01064.x Martínez-Duro, E., Ferrandis, P., Herranz, J.M., 2009. Factors controlling the regenerative cycle of Thymus funkii subsp. funkii in a semi-arid gypsum steppe: A seed bank dynamics perspective. Journal of Arid Environments 73, 252–259. https://doi.org/10.1016/j.jaridenv.2008.10.011 Martinez-Duro, E., Luzuriaga, A.L., Ferrandis, P., Escudero, A., Herranz, J.M., 2012. Does aboveground vegetation composition resemble soil seed bank during succession in specialized vegetation on gypsum soil? Ecol Res 27, 43–51. https://doi.org/10.1007/s11284-011-0870-z Martínez-Hernández, F., Pérez-García, F.J., Garrido-Becerra, J.A., Mendoza-Fernández, A.J., Medina-Cazorla, J.M., Martínez-Nieto, M.I., Calvente, M.E.M., Poveda, J.F.M., 2011. The distribution of Iberian gypsophilous flora as a criterion for conservation policy. Biodivers Conserv 20, 1353–1364. https://doi.org/10.1007/s10531-011-0031-2 Matesanz, S., Escudero, A., Valladares, F., 2009. Impact of three global change drivers on a Mediterranean shrub. Ecology 90, 2609–2621. https://doi.org/10.1890/08-1558.1 Matesanz, S., García-Fernández, A., Limón-Yelmo, A., Gómez-Fernández, A., Escudero, A., 2018. Comparative landscape genetics of gypsum specialists with naturally-patchy distributions reveal their resilience to anthropogenic fragmentation. Perspectives in Plant Ecology, Evolution and Systematics 34, 1–9. https://doi.org/10.1016/j.ppees.2018.07.001 Matesanz, S., Valladares, F., 2007. Improving revegetation of gypsum slopes is not a simple matter of adding native species: Insights from a multispecies experiment. Ecological Engineering 30, 67–77. https://doi.org/10.1016/j.ecoleng.2007.01.005 Mélanie, R.-D., 2008. Social Costs of Desertification in Africa: The Case of Migration, in: Lee, C., Schaaf, T. (Eds.), The Future of Drylands. Springer Netherlands, pp. 569–581.

  Merlo, M.E., Mota, J.F., Cabello, J., Alemán, M.M., 1998. La gipsofilia en plantas: un apasionante edafismo. Investigación y Gestión 3, 103–112.

  Meyer, S.E., 1986. The ecology of gypsophile endemism in the eastern Mojave Desert. Ecology 67, 1303–1313. https://doi.org/10.2307/1938686 Meyer, S.E., Garcia-Moya, E., 1989. Plant community patterns and soil moisture regime in grypsum grasslands of north central Mexico. Journal of arid environments 16, 147–155.

  Michalet, R., 2006. Is facilitation in arid environments the result of direct or complex interactions? New Phytologist 169, 3–6. https://doi.org/10.1111/j.1468-8137.2006.01617.x Michalet, R., Bagousse‐Pinguet, Y.L., Maalouf, J.-P., Lortie, C.J., 2014. Two alternatives to the stress-gradient hypothesis at the edge of life: the collapse of facilitation and the switch from facilitation to competition. Journal of Vegetation Science 25, 609–613. https://doi.org/10.1111/jvs.12123 Miller, J.R., Hobbs, R.J., 2007. Habitat Restoration—Do We Know What We’re Doing? Restoration Ecology 15, 382–390. https://doi.org/10.1111/j.1526-100X.2007.00234.x Miriti, M.N., 2006. Ontogenetic shift from facilitation to competition in a desert shrub. Journal of Ecology 94, 973–979. https://doi.org/10.1111/j.1365-2745.2006.01138.x Molina‐Montenegro, M.A., Badano, E.I., Cavieres, L.A., 2008. Positive interactions among plant species for pollinator service: assessing the ‘magnet species’ concept with invasive species. Oikos 117, 1833–1839. https://doi.org/10.1111/j.0030-1299.2008.16896.x Montserrat-Martí, G., Palacio, S., Milla, R., Giménez-Benavides, L., 2011. Meristem Growth, Phenology, and Architecture in Chamaephytes of the Iberian Peninsula: Insights into a Largely Neglected Life Form. Folia Geobot 46, 117–136. https://doi.org/10.1007/s12224-010-9073-6 Moore, M.J., Mota, J.F., Douglas, N.A., Olvera, H.F., Ochoterena, H., 2014. The ecology, assembly and evolution of gypsophile floras. Plant ecology and evolution in harsh environments’.(Eds N Rajakaruna, RS Boyd, T Harris) pp 97–128.

  Morales-Soto, A., Oruna-Concha, M.J., Elmore, J.S., Barrajón-Catalán, E., Micol, V., Roldán, C., Segura-Carretero, A., 2015. Volatile profile of Spanish Cistus plants as sources of antimicrobials for industrial applications. Industrial Crops and Products 74, 425–433. https://doi.org/10.1016/j.indcrop.2015.04.034 Moreno, J.C., 2010. Lista Roja 2008 de la flora vascular española.

  Moret-Fernández, D., Herrero, J., 2015. Effect of gypsum content on soil water retention. Journal of Hydrology 528, 122–126. https://doi.org/10.1016/j.jhydrol.2015.06.030 Mortimore, M., Anderson, S., Cotula, L., Davies, J., Faccer, K., Hesse, C., Morton, J., Nyangena, W., Skinner, J., Wolfangel, C., 2009. Dryland Opportunies: A new paradigm for people, ecosystems and development. International Union for Conservation of Nature (IUCN).

  Mota, J.F., Sánchez-Gómez, P., Guirado, J.S., 2011. Diversidad vegetal de las yeseras ibéricas. El reto de los archipiélagos edáficos para la biología de la conservación. ADIF-Mediterráneo Asesores Consultores, Almería.

  Mota, J.F., Sola, A.J., Dana, E.D., Jiménez-Sánchez, M.L., 2003a. Plant succession in abandoned gypsum quarries in SE Spain. Phytocoenologia 33, 13–28. https://doi.org/10.1127/0340-269X/2003/0033-0013 Mota, J.F., Sola, A.J., Jiménez-Sánchez, M.L., Pérez-García, F., Merlo, M.E., 2004. Gypsicolous flora, conservation and restoration of quarries in the southeast of the Iberian Peninsula. Biodiversity and Conservation 13, 1797–1808. https://doi.org/10.1023/B:BIOC.0000035866.59091.e5 Munné-Bosch, S., Jubany-Marí, T., Alegre, L., 2003. Enhanced photo- and antioxidative protection, and hydrogen peroxide accumulation in drought-stressed Cistus clusii and Cistus albidus plants. Tree Physiol 23, 1–12. https://doi.org/10.1093/treephys/23.1.1 Nathan, R., Katul, G.G., Horn, H.S., Thomas, S.M., Oren, R., Avissar, R., Pacala, S.W., Levin, S.A., 2002. Mechanisms of long-distance dispersal of seeds by wind. Nature 418, 409–413. https://doi.org/10.1038/nature00844 Nathan, R., Muller-Landau, H.C., 2000. Spatial patterns of seed dispersal, their determinants and consequences for recruitment. Trends in Ecology & Evolution 15, 278–285. https://doi.org/10.1016/S0169-5347(00)01874-7 Navarro-Cano, J.A., Ferrer-Gallego, P.P., Laguna, E., Ferrando, I., Goberna, M., Valiente-Banuet, A., Verdú, M., 2016. Restoring phylogenetic diversity through facilitation. Restor Ecol 24, 449–455. https://doi.org/10.1111/rec.12350 Navarro-Cano, J.A., Goberna, M., Valiente-Banuet, A., Montesinos-Navarro, A., García, C., Verdú, M., 2014. Plant phylodiversity enhances soil microbial productivity in facilitation-driven communities. Oecologia 174, 909–920. https://doi.org/10.1007/s00442-013-2822-5 Navarro-Cano, J.A., Verdú, M., García, C., Goberna, M., 2015. What nurse shrubs can do for barren soils: rapid productivity shifts associated with a 40 years ontogenetic gradient. Plant Soil 388, 197–209. https://doi.org/10.1007/s11104-014-2323-2 Navas, A., 1999. Los suelos de Monegros.

  Navas, A., 1991. Application of simulated rainfall for atudying runoff yield and erosive behaviour of gypsiferous soils, in: Soil Erosion Studies in Spain, 1991, ISBN 84-87779-04-2, Págs. 181-190. Presented at the Soil erosion studies in Spain, Geoforma, pp. 181–190.

  Nielsen, J.A., Frew, R.D., Whigam, P.A., Callaway, R.M., Dickinson, K.J.M., 2015. Germination and growth responses of co-occurring grass species to soil from under invasive Thymus vulgaris. Allelopathy Journal 35, 139–152.

  Noy-Meir, I., 1973. Desert Ecosystems: Environment and Producers. Annual Review of Ecology and Systematics 4, 25–51. https://doi.org/10.1146/annurev.es.04.110173.000325 Oksanen, J., Guillaume Blanchet, F., Kindt, R., Legendre, P., 2017. others. 2016. vegan: Community ecology package. R package version 2.3–5.

  Olano, J. m., Caballero, I., Loidi, J., Escudero, A., 2005. Prediction of plant cover from seed bank analysis in a semi-arid plant community on gypsum. Journal of Vegetation Science 16, 215–222. https://doi.org/10.1111/j.1654-1103.2005.tb02358.x Olano, J.M., Caballero, I., Escudero, A., 2012. Soil seed bank recovery occurs more rapidly than expected in semi-arid Mediterranean gypsum vegetation. Ann Bot 109, 299–307. https://doi.org/10.1093/aob/mcr260 Oviedo, R., Faife-Cabrera, M., Noa-Monzón, A., Arroyo, J., Valiente-Banuet, A., Verdú, M., 2014. Facilitation allows plant coexistence in Cuban serpentine soils. Plant Biol J 16, 711–716. https://doi.org/10.1111/plb.12116 Padilla, F.M., Pugnaire, F.I., 2006. The role of nurse plants in the restoration of degraded environments. Frontiers in Ecology and the Environment 4, 196–202. https://doi.org/10.1890/1540-9295(2006)004[0196:TRONPI]2.0.CO;2 Palacio, S., Aitkenhead, M., Escudero, A., Montserrat-Martí, G., Maestro, M., Robertson, A.H.J., 2014a. Gypsophile chemistry unveiled: Fourier Transform Infrared (FTIR) spectroscopy provides new insight into plant adaptations to gypsum soils. PLoS ONE 9, e107285. https://doi.org/10.1371/journal.pone.0107285 Palacio, S., Azorín, J., Montserrat-Martí, G., Ferrio, J.P., 2014b. The crystallization water of gypsum rocks is a relevant water source for plants. Nat Commun 5, 4660. https://doi.org/10.1038/ncomms5660 Palacio, S., Escudero, A., Montserrat-Martí, G., Maestro, M., Milla, R., Albert, M.J., 2007. Plants living on gypsum: beyond the specialist model. Ann Bot 99, 333–343. https://doi.org/10.1093/aob/mcl263 Palacio, S., Millard, P., Montserrat-Martí, G., 2006. Aboveground biomass allocation patterns within Mediterranean sub-shrubs: A quantitative analysis of seasonal dimorphism. Flora - Morphology, Distribution, Functional Ecology of Plants 201, 612–622. https://doi.org/10.1016/j.flora.2006.02.002 Parsons, R.F., 1976. Gypsophily in Plants-A Review. The American Midland Naturalist 96, 1–20. https://doi.org/10.2307/2424564 Paterno, G.B., Siqueira Filho, J.A., Ganade, G., 2016. Species-specific facilitation, ontogenetic shifts and consequences for plant community succession. J. Veg. Sci. 27, 606–615. https://doi.org/10.1111/jvs.12382 Pausas, J.G., Bonet, A., Maestre, F.T., Climent, A., 2006. The role of the perch effect on the nucleation process in Mediterranean semi-arid oldfields. Acta Oecologica-International Journal of Ecology 29, 346–352. https://doi.org/10.1016/j.actao.2005.12.004 Pedrocchi Renault, C., 1998. Ecología de los Monegros. Instituto de Estudios Altoaragoneses, Diputación de Huesca.

  Pedrol, N., González, L., Reigosa, M.J., 2006. Allelopathy and abiotic stress, in: Allelopathy. Springer, pp. 171–209.

  Pérez-García, F., González-Benito, M.E., 2006. Seed germination of five Helianthemum species: Effect of temperature and presowing treatments. Journal of Arid Environments 65, 688–693. https://doi.org/10.1016/j.jaridenv.2005.10.008 Perry, G.L.W., Miller, B.P., Lamont, B.B., Enright, N.J., 2016. Community-level spatial structure supports a model of stochastic geometry in species-rich shrublands. Oikos n/a-n/a. https://doi.org/10.1111/oik.03680 Pietrasiak, N., Regus, J.U., Johansen, J.R., Lam, D., Sachs, J.L., Santiago, L.S., 2013. Biological soil crust community types differ in key ecological functions. Soil Biology and Biochemistry 65, 168–171. https://doi.org/10.1016/j.soilbio.2013.05.011 Pinheiro, J., Bates, D., DebRoy, S., Sarkar, D., 2007. Linear and nonlinear mixed effects models. R package version 3, 57.

  Porta, J., 1998. Methodologies for the analysis and characterization of gypsum in soils: A review. Geoderma 87, 31–46. https://doi.org/10.1016/S0016-7061(98)00067-6 Prach, K., 2003. Spontaneous succession in Central-European man-made habitats: What information can be used in restoration practice? Applied Vegetation Science 6, 125–129. https://doi.org/10.1111/j.1654-109X.2003.tb00572.x Prach, K., Hobbs, R.J., 2008. Spontaneous Succession versus Technical Reclamation in the Restoration of Disturbed Sites. Restoration Ecology 363–366. https://doi.org/10.1111/j.1526-100X.2008.00412.x@10.1111/(ISSN)1526-100X.2525thAnniversaryVI Prăvălie, R., 2016. Drylands extent and environmental issues. A global approach. Earth-Science Reviews 161, 259–278. https://doi.org/10.1016/j.earscirev.2016.08.003 Pueyo, Y., 2005. Evaluación de los factores ambientales y del uso antrópico como condicionantes de la conservación de la vegetación del sector central de la Depresión del Ebro. Universidad de Zaragoza.

  Pueyo, Y., Alados, C.L., 2007. Effects of fragmentation, abiotic factors and land use on vegetation recovery in a semi-arid Mediterranean area. Basic and Applied Ecology 8, 158–170. https://doi.org/10.1016/j.baae.2006.03.009 Pueyo, Y., Alados, C.L., Barrantes, O., 2006. Determinants of Land Degradation and Fragmentation in Semiarid Vegetation at Landscape Scale. Biodivers Conserv 15, 939–956. https://doi.org/10.1007/s10531-004-2936-5 Pueyo, Y., Alados, C.L., Barrantes, O., Komac, B., Rietkerk, M., 2008. Differences in gypsum plant communities associated with habitat fragmentation and livestock grazing. Ecological Applications 18, 954–964. https://doi.org/10.1890/07-1770.1 Pueyo, Y., Alados, C.L., García-Ávila, B., Kéfi, S., Maestro, M., Rietkerk, M., 2009. Comparing Direct Abiotic Amelioration and Facilitation as Tools for Restoration of Semiarid Grasslands. Restoration Ecology 17, 908–916. https://doi.org/10.1111/j.1526-100X.2008.00474.x Pueyo, Y., Alados, C.L., Maestro, M., Komac, B., 2007. Gypsophile vegetation patterns under a range of soil properties induced by topographical position. Plant Ecol 189, 301–311. https://doi.org/10.1007/s11258-006-9185-5 Pueyo, Y., Moret-Fernández, D., Arroyo, A.I., de Frutos, A., Kéfi, S., Saiz, H., Charte, R., Giner, M. de la L., Alados, C.L., 2016. Plant nurse effects rely on combined hydrological and ecological components in a semiarid ecosystem. Ecosphere 7, n/a-n/a. https://doi.org/10.1002/ecs2.1514 Pueyo, Y., Moret-Fernández, D., Saiz, H., Bueno, C.G., Alados, C.L., 2012. Relationships Between Plant Spatial Patterns, Water Infiltration Capacity, and Plant Community Composition in Semi-arid Mediterranean Ecosystems Along Stress Gradients. Ecosystems 16, 452–466. https://doi.org/10.1007/s10021-012-9620-5 Pugnaire, F.I., Lázaro, R., 2000. Seed Bank and Understorey Species Composition in a Semi-arid Environment: The Effect of Shrub Age and Rainfall. Ann Bot 86, 807–813. https://doi.org/10.1006/anbo.2000.1240 Pugnaire, F.I., Luque, M.T., 2001. Changes in plant interactions along a gradient of environmental stress. Oikos 93, 42–49. https://doi.org/10.1034/j.1600-0706.2001.930104.x Quirantes, J., 1978. Estudio sedimentológico y estratigráfico del Terciario continental de los Monegros. Zaragoza, ed. Institución Fernando El Católico (CSIC), Diputación Provincial de Zaragoza.

  R Core Team, 2017. R: A language and environment for statistical computing.

  Rajakaruna, N., 2004. The Edaphic Factor in the Origin of Plant Species. International Geology Review 46, 471–478. https://doi.org/10.2747/0020-6814.46.5.471 Ramón, P., Velázquez, E., Escudero, A., Cruz, M. de la, 2018. Environmental heterogeneity blurs the signature of dispersal syndromes on spatial patterns of woody species in a moist tropical forest. PLOS ONE 13, e0192341. https://doi.org/10.1371/journal.pone.0192341 Rao, A.V., Tak, R., 2001. Influence of mycorrhizal fungi on the growth of different tree species and their nutrient uptake in gypsum mine spoil in India. Applied Soil Ecology 17, 279–284. https://doi.org/10.1016/S0929-1393(01)00136-6 Rausch, T., Wachter, A., 2005. Sulfur metabolism: a versatile platform for launching defence operations. Trends in Plant Science 10, 503–509. https://doi.org/10.1016/j.tplants.2005.08.006 Rayburn, A.P., Wiegand, T., 2012. Individual species–area relationships and spatial patterns of species diversity in a Great Basin, semi-arid shrubland. Ecography 35, 341–347. https://doi.org/10.1111/j.1600-0587.2011.07058.x Reisman-Berman, O., 2007. Age-related change in canopy traits shifts conspecific facilitation to interference in a semi-arid shrubland. Ecography 30, 459–470. https://doi.org/10.1111/j.0906-7590.2007.05066.x Reynolds, J.F., Stafford Smith, D.M., Lambin, E.F., Turner, B.L., Mortimore, M., Batterbury, S.P.J., Downing, T.E., Dowlatabadi, H., Fernandez, R.J., Herrick, J.E., Huber-Sannwald, E., Jiang, H., Leemans, R., Lynam, T., Maestre, F.T., Ayarza, M., Walker, B., 2007. Global desertification: Building a science for dryland development. Science 316, 847–851. https://doi.org/10.1126/science.1131634 Rice, E.L., 1984. Allelopathy, 2 nd. ed. ed. Academic Press, New York.

  Ridenour, W., Callaway, R., 2001. The relative importance of allelopathy in interference: the effects of an invasive weed on a native bunchgrass. Oecologia 126, 444–450. https://doi.org/10.1007/s004420000533 Rivas-Martínez, S., Costa, M., 1970. Comunidades gipsícolas del centro de España. Instituto Botánico Antonio José Cavanilles.

  Romão, R.L., Escudero, A., 2005. Gypsum physical soil crusts and the existence of gypsophytes in semi-arid central Spain. Plant Ecol 181, 127–137. https://doi.org/10.1007/s11258-005-5321-x Rouchy, J.M., Caruso, A., 2006. The Messinian salinity crisis in the Mediterranean basin: A reassessment of the data and an integrated scenario. Sedimentary Geology, The Messinian Salinity Crisis Revisited 188–189, 35–67. https://doi.org/10.1016/j.sedgeo.2006.02.005 Rubio, A., Escudero, A., 2000. Small-scale spatial soil-plant relationship in semi-arid gypsum environments. Plant and Soil 220, 139–150. https://doi.org/10.1023/A:1004764411116 Ruiz, J.M., López-Cantarero, I., Rivero, R.M., Romero, L., 2003. Sulphur Phytoaccumulation in Plant Species Characteristic of Gypsiferous Soils. International Journal of Phytoremediation 5, 203–210. https://doi.org/10.1080/713779220 Ruiz, N., Ward, D., Saltz, D., 2002. Calcium oxalate crystals in leaves of Pancratiumsickenbergeri: constitutive or induced defence? Functional Ecology 16, 99–105. https://doi.org/10.1046/j.0269-8463.2001.00594.x Saiz, H., Alados, C.L., 2012. Changes in Semi-Arid Plant Species Associations along a Livestock Grazing Gradient. PLOS ONE 7, e40551. https://doi.org/10.1371/journal.pone.0040551 Saiz, H., Alados, C.L., Pueyo, Y., 2014. Plant–plant spatial association networks in gypsophilous communities: the influence of aridity and grazing and the role of gypsophytes in its structure. Web Ecology 14, 39–49. https://doi.org/10.5194/we-14-39-2014 Schenk, H.J., 2006. Root competition: beyond resource depletion. Journal of Ecology 94, 725–739. https://doi.org/10.1111/j.1365-2745.2006.01124.x Schöb, C., Kammer, P.M., Kikvidze, Z., 2012. Combining observational and experimental methods in plant–plant interaction research. Plant Ecology & Diversity 5, 27–36. https://doi.org/10.1080/17550874.2012.674067 Schöb, C., Prieto, I., Armas, C., Pugnaire, F.I., 2014. Consequences of facilitation: one plant’s benefit is another plant’s cost. Funct Ecol 28, 500–508. https://doi.org/10.1111/1365-2435.12185 Schreiber, B.C., Tabakh, M.E., 2000. Deposition and early alteration of evaporites. Sedimentology 47, 215–238. https://doi.org/10.1046/j.1365-3091.2000.00002.x Sharma, K.D., Kumar, S., Gough, L.P., 2001. Rehabilitation of Gypsum-Mined Lands in the Indian Desert. Arid Land Research and Management 15, 61–76. https://doi.org/10.1080/15324980119929 Sharp, R.E., Davies, W.J., 1989. a restricted supply of water. Plants under stress: biochemistry, physiology and ecology and their application to plant improvement 39, 71.

  Siegel, S., Castellan, N.J., 1988. Nonparametric systems for the behavioural sciences. McGraw Hill International Editions.

  Smit, C., Ouden, J., Díaz, M., 2008. Facilitation of Quercus ilex recruitment by shrubs in Mediterranean open woodlands. Journal of Vegetation Science 19, 193–200.

  Smit, C., Ouden, J.D., Müller‐Schärer, H., 2006. Unpalatable plants facilitate tree sapling survival in wooded pastures. Journal of Applied Ecology 43, 305–312. https://doi.org/10.1111/j.1365-2664.2006.01147.x Smith, R.S., Rushton, S.P., 1994. The Effects of Grazing Management on the Vegetation of Mesotrophic (Meadow) Grassland in Northern England. Journal of Applied Ecology 31, 13–24. https://doi.org/10.2307/2404595 Sokal, R.R., Rohlf, F.J., 1995. Biometry: the principles of statistics in biological research. New York, NY: WH Freeman and Co.

  Soliveres, S., DeSoto, L., Maestre, F.T., Olano, J.M., 2010. Spatio-temporal heterogeneity in abiotic factors modulate multiple ontogenetic shifts between competition and facilitation. Perspectives in Plant Ecology, Evolution and Systematics 12, 227–234. https://doi.org/10.1016/j.ppees.2010.02.003 Soliveres, S., Eldridge, D.J., Maestre, F.T., Bowker, M.A., Tighe, M., Escudero, A., 2011. Microhabitat amelioration and reduced competition among understorey plants as drivers of facilitation across environmental gradients: Towards a unifying framework. Perspectives in Plant Ecology, Evolution and Systematics 13, 247–258. https://doi.org/10.1016/j.ppees.2011.06.001 Soliveres, S., Maestre, F.T., 2014. Plant–plant interactions, environmental gradients and plant diversity: a global synthesis of community-level studies. Perspectives in Plant Ecology, Evolution and Systematics 16, 154–163. https://doi.org/10.1016/j.ppees.2014.04.001 Sørensen, T., 1948. A method of establishing groups of equal amplitude in plant sociology based on similarity of species and its application to analyses of the vegetation on Danish commons. Biol. Skr. 5, 1–34.

  Soriano, A., Sala, O.E., Perelman, S.B., 1994. Patch structure and dynamics in a Patagonian arid steppe. Vegetatio 111, 127–135. https://doi.org/10.1007/BF00040332 Sosa, T., Valares, C., Alías, J.C., Lobón, N.C., 2010. Persistence of flavonoids in Cistus ladanifer soils. Plant Soil 337, 51–63. https://doi.org/10.1007/s11104-010-0504-1 Sprent, J.I., Gehlot, H.S., 2010. Nodulated legumes in arid and semi-arid environments: are they important? Plant Ecology & Diversity 3, 211–219. https://doi.org/10.1080/17550874.2010.538740 Srivastava, R.K., Jozewicz, W., 2001. Flue Gas Desulfurization: The State of the Art. Journal of the Air & Waste Management Association 51, 1676–1688. https://doi.org/10.1080/10473289.2001.10464387 Tarayre, M., Thompson, J.D., Escarré, J., Linhart, Y.B., 1995. Intra-specific variation in the inhibitory effects of Thymus vulgaris (Labiatae) monoterpenes on seed germination. Oecologia 101, 110–118. https://doi.org/10.1007/BF00328907 Tewksbury, J.J., Lloyd, J.D., 2001. Positive interactions under nurse-plants: spatial scale, stress gradients and benefactor size. Oecologia 127, 425–434. https://doi.org/10.1007/s004420000614 Thanos, C.A., Georghiou, K., Kadis, C., Pantazi, C., 1992. Cistaceae: a plant family with hard seeds. Israel Journal of Botany 41, 251–263. https://doi.org/10.1080/0021213X.1992.10677232 Therneau, T.M., 2014. A Package for Survival Analysis in S. R package version 2.38 2.37-7.

  Thiede, D.A., Augspurger, C.K., 1996. Intraspecific Variation in Seed Dispersion of Lepidium campestre (Barassicaceae). American Journal of Botany 83, 856–866. https://doi.org/10.2307/2446262 Thompson, J.D., Chalchat, J.C., Michet, A., Linhart, Y.B., Ehlers, B., 2003. Qualitative and quantitative variation in monoterpene co-occurrence and composition in the essential oil of Thymus vulgaris chemotypes. Journal of Chemical Ecology 29, 859–880. https://doi.org/10.1023/A:1022927615442 Thompson, K., 2000. The functional ecology of soil seed banks. Seeds: the ecology of regeneration in plant communities 2, 215–235.

  Tielbörger, K., Kadmon, R., 2000. Temporal Environmental Variation Tips the Balance Between Facilitation and Interference in Desert Plants. Ecology 81, 1544–1553. https://doi.org/10.1890/0012-9658(2000)081[1544:TEVTTB]2.0.CO;2 Tilman, D., 1994. Competition and Biodiversity in Spatially Structured Habitats. Ecology 75, 2–16. https://doi.org/10.2307/1939377 Tirado, R., I. Pugnaire, F., 2005. Community structure and positive interactions in constraining environments. Oikos 111, 437–444. https://doi.org/10.1111/j.1600-0706.2005.14094.x Tirado, R., Pugnaire, F.I., 2003. Shrub spatial aggregation and consequences for reproductive success. Oecologia 136, 296–301. https://doi.org/10.1007/s00442-003-1264-x Tsubo, M., Nishihara, E., Nakamatsu, K., Cheng, Y., Shinoda, M., 2012. Plant volatiles inhibit restoration of plant species communities in dry grassland. Basic and Applied Ecology 13, 76–84. https://doi.org/10.1016/j.baae.2011.11.005 Valiente-Banuet, A., Ezcurra, E., 1991. Shade as a Cause of the Association Between the Cactus Neobuxbaumia Tetetzo and the Nurse Plant Mimosa Luisana in the Tehuacan Valley, Mexico. Journal of Ecology 79, 961–971. https://doi.org/10.2307/2261091 Valiente-Banuet, A., Verdú, M., 2008. Temporal shifts from facilitation to competition occur between closely related taxa. Journal of Ecology 96, 489–494. https://doi.org/10.1111/j.1365-2745.2008.01357.x Valladares, F., Pearcy, R.W., 2002. Drought can be more critical in the shade than in the sun: a field study of carbon gain and photo-inhibition in a Californian shrub during a dry El Niño year. Plant, Cell & Environment 25, 749–759. https://doi.org/10.1046/j.1365-3040.2002.00856.x Venable, D.L., Brown, J.S., 1988. The Selective Interactions of Dispersal, Dormancy, and Seed Size as Adaptations for Reducing Risk in Variable Environments. The American Naturalist 131, 360–384. https://doi.org/10.1086/284795 Verdú, M., Traveset, A., 2005. Early emergence enhances plant fitness: a phylogenetically controlled meta-analysis. Ecology 86, 1385–1394. https://doi.org/10.1890/04-1647 Verdú, M., Valiente‐Banuet, A., 2008. The Nested Assembly of Plant Facilitation Networks Prevents Species Extinctions. The American Naturalist 172, 751–760. https://doi.org/10.1086/593003 Vicente-Serrano, S.M., Zouber, A., Lasanta, T., Pueyo, Y., 2012. Dryness is accelerating degradation of vulnerable shrublands in semiarid Mediterranean environments. Ecological Monographs 82, 407–428. https://doi.org/10.1890/11-2164.1 Vilà, M., Sardans, J., 1999. Plant competition in mediterranean-type vegetation. Journal of Vegetation Science 10, 281–294. https://doi.org/10.2307/3237150 Vokou, D., Vareltzidou, S., Katinakis, P., 1993. Effects of aromatic plants on potato storage: sprout suppression and antimicrobial activity. Agriculture, ecosystems & environment 47, 223–235.

  Volaire, F., Barkaoui, K., Norton, M., 2014. Designing resilient and sustainable grasslands for a drier future: Adaptive strategies, functional traits and biotic interactions. European Journal of Agronomy 52, 81–89. https://doi.org/10.1016/j.eja.2013.10.002 Weiner, J., 1990. Asymmetric competition in plant populations. Trends in Ecology & Evolution 5, 360–364. https://doi.org/10.1016/0169-5347(90)90095-U Whitehead, D.C., Dibb, H., Hartley, R.D., 1983. Bound phenolic compounds in water extracts of soils, plant roots and leaf litter. Soil Biology and Biochemistry 15, 133–136. https://doi.org/10.1016/0038-0717(83)90092-5 Wiegand, T., Gunatilleke, C.V.S., Gunatilleke, I.A.U.N., Huth, A., 2007. How individual species structure diversity in tropical forests. PNAS 104, 19029–19033. https://doi.org/10.1073/pnas.0705621104 Wiegleb, G., Felinks, B., 2001. Primary succession in post-mining landscapes of Lower Lusatia — chance or necessity. Ecological Engineering 17, 199–217. https://doi.org/10.1016/S0925-8574(00)00159-2 Zhang, C., Fu, S., 2010. Allelopathic effects of leaf litter and live roots exudates of Eucalyptus species on crops. Allelopathy J 26, 91–100.

  Zhang, Y., Belnap, J., 2015. Growth responses of five desert plants as influenced by biological soil crusts from a temperate desert, China. Ecol Res 30, 1037–1045. https://doi.org/10.1007/s11284-015-1305-z