This paper is a preliminar one on objectives of a new project in terrestrial ecology and on the characteristics of selected study area. The project is being drived by Ecology departments of Universitat de Barcelona and Universitat Autonoma de Barcelona, and is embodied in a larger one on nutrient cycles in forest ecosystems. The parameters measured and their relationships are exposed and future developments briefly discussed. The La Castanya valley is included in the Montseny nature park, a Biosphere Reserve, in a Mediterranean mountain stage with relatively humid climate but with great interanual fluctuation. The bedrock is nearly all constituted by paleozoic shales and valley-side slopes are pronounced (30%) . There is a soil catena from litosols to rankers and brown acid soils that can be lixiviated in some places. Vegetation is a green oak mountain forest (Quercetum ilicis mediterraneo-montanum) in nearly all the valley. There are, however, some grasslands and a beech forest near the summits and also a little Taxus baccata trees clump. The green oak forest is a young one, in a regeneration stage, after a very intensive explotation period (wood for fuel and coal making) interrupted some years ago, and an early farming period. In the experimental plot direct insolation is lowered by topographic position and the soil is colluvial, deep but with loose rocks at surface. Herb and shrub layer are poor, being the young Quercus ilex also dominants. The experimental plot surface is 0,22 ha, including 450 trees (more than 5 cm dbh) between 7 and 12 m high. The branch system has a lowe layer level, with a few horizontal branches, and a higher one with near vertical branches. The major axis is not clearly defined, as it divides in two or three over 2,5-4 m.
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