Black pine (pinus nigra arn.) Growth at different time scales: global change effects / crecimiento del pino laricio (pinus nigra arn.) En distintas escalas temporales: efectos del cambio global
- Autores: Darío Martín Benito
- Directores de la Tesis: Isabel Cañellas Rey de Viñas (dir. tes.), Miren del Río Gaztelurrutia (codir. tes.)
- Lectura: En la Universidad Politécnica de Madrid ( España ) en 2009
- Idioma: español
- Tribunal Calificador de la Tesis: Luis Alfonso Gil Sánchez (presid.), María del Mar Génova Fuster (secret.), Jordi Martínez Vilalta (voc.), Jesús Julio Camarero Martínez (voc.), Hans Beeckman (voc.)
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- Resumen
Black pine (Pinus nigra Arn.) is one of the most important forest tree species in the Mediterranean basin where it plays an important ecological, economic and social role. Therefore, it is essential to increase our knowledge on the functioning of these forests and their interactions with climate in a global change scenario. In this study, we have analysed black pine growth, climate-growth relationship, and growth trends during the last century in a latitudinal transect along the mountain ranges of the eastern Iberian Peninsula. The importance of analysing several spatial and temporal scales requires the use of different types of data and methodologies that complement each other and thus attain a deeper knowledge of the processes and factors that are more influential for growth. Because of the great human influence on these forest systems, we also analysed the effect of competition on growth and climate-growth relationships in order to establish in the near future different management alternatives that may assure their sustainability.
First, we have developed a dynamic dominant-height growth model for three regions in Spain using stem analysis data for the model fitting and permanent sample plot inventory data for model validation. The final model selected has an interregional character, i.e. it can be used for all regions without increasing the prediction errors. Forest site productivity synchronously changed during the last 150 years in the three regions studied. Although a probable climatic cause can be hypothesised for these changes, the causal relationship can not be unequivocally established.
Using tree-ring analysis we observed that black pine growth was mainly affected by autumn-spring precipitations (positive) and summer temperatures (negative), as could be expected in a Mediterranean climate. However, climate-growth relationships were not stable through time. In addition, we observed increasing water stress from south to north in its distribution area during the last decades and a general growth decay in these forests caused by rising temperatures and decreasing temperatures. However, certain individuals showed divergent growth trends (i.e. positive). The frequency of these divergent trees in a region was inversely related to forest productivity and most likely also to intra-regional genetic diversity.
Analysis of intra-specific competition between trees of different crown classes showed that climate sensitivity was greater in suppressed trees, whose radial growth was less affected by drought but took longer to recover pre-drought growth, than dominant trees. Therefore, tree-rings evidenced that certain degree of shelter from canopy trees buffers the effect of climate, although it might increase drought-stress in certain cases.
The effect of reducing stand density was explored through basal area increments and water use efficiency (WUE) analysis in an afforested stand. Growth in the thinned stand increased compared to the control stand. Thinning also increased tree mean sensitivity to temperatures but reduced sensitivity to precipitations. Increased growth was caused by an increment in available resources for each tree and not to increases of WUE which could limit the positive effects of thinnings as an adaptation tool for climate change if temperatures and/or precipitations exceed certain thresholds.
Finally, a wood anatomical and dendrochronological analysis of black pine was carried out to reduce the temporal scale of the climate-growth relationships. These results were also compared with a similar analysis in Scots pine (Pinus sylvestris L.), an ecologically close species which forms mixed forests with black pine. Climatic variables recorded by anatomical features were in many cases different from those recorded by tree-ring width. This allowed for the more precise identification of those periods of the year that most influenced radial growth and to analyse basic process of growth such as number and width of tracheids. In black pine, higher ratios of cell-wall thickness to cell-lumen width seemed to confer greater safety against drought-induced cavitation than in Scots pine.
These results, although partial, are an important advance in our knowledge of the factors that influence black pine growth and the general trends that it might follow in the near future. This way, we will be able to develop and implement forest management practices which could be real sustainable alternatives truly adapted to the actual global change scenario.
