Empar Carrillo

Timberline structure and limited tree recruitment in the Catalan Pyrenees

Background: Pyrenean timberlines, lowered to various extents through ancient land use, are expected to rise due to abandonment of land use and climate warming. Aims: To provide a comprehensive survey of the timberline in the Catalan Pyrenees, at the landscape, plant community, and tree population levels. Methods: We assessed the present location of timberlines by means of GIS techniques and characterised the treeline ecotone in 12 representative plots, where we took small phytosociological relevés (surface cover type, vegetation structure and species cover) and studied the regeneration of Pinus uncinata (seedlings and saplings). Results: The potential timberline was mostly found between 2300 and 2400 m a.s.l., with complex variation in these values due to bioclimatic and topographic diversity. Most of the present timberline was found at far lower altitudes than its potential location. Present forests reached the potential timberline about 25% along its total length. At natural or semi-natural treelines, the transition from subalpine forest to open alpine landscapes was relatively sharp. It was formed by the irregular alternation of two or three contrasting plant community types (forest, dwarf-shrub, grassland). Most Pinus regeneration was recorded where vegetation mosaics occurred on a fine scale. The highest numbers of Pinus seedlings and saplings were found emerging from bare ground or litter in small vegetation gaps. Over recent years Pinus recruitment showed very slow growth and a strong limitation in reaching the pole stage. Conclusions: In Pyrenean treeline ecotones situated near to their potential altitudes, recruitment and growth of existing Pinus uncinata seedlings and saplings is unlikely to produce pronounced infilling and thus perceptible changes in high-altitude forest cover.

Functional Plant Traits and Species Assemblage in Pyrenean Snowbeds

In mid-latitude mountains, snowbeds often consist of small, scattered alpine belt units that host many plants of high biogeographic interest. Because most snowbed species are weak competitors, it is important to study the dissemination and persistence of their seeds to better understand their population dynamics. This study analyzed the snowbed flora of the Central Pyrenees using 11 morpho-functional traits, mostly related to seed function. The seeds of most plants found in snowbeds are small or very small, they have ovoid to elliptical shapes, and have no attributes related to dispersal. When only snowbed specialists (i.e., with a phytosociological optimum in snowbed habitats) are considered, three strategy groups become apparent: i) annuals or pauciennials producing abundant small seeds prone to accumulate in the soil; ii) chamaephytes or hemicryptophytes that produce anemochorous seeds; and iii) other perennials – mainly hemicryptophytes – with no specific seed traits. In the first two groups, the extant populations are maintained either by permanent soil seed banks or by means of vegetative persistence and dispersal. The lack of specific traits in the third group suggests that these plants could be more sensitive to direct competitive exclusion from non-chionophilous species under a changing climatic scenario in which snowbeds tend to disappear.

Assessing the natural interest of the landscapes of Andorra, a mountain country under contrasted land use changes

Abstract In this paper, we present a method for analysing the landscape, using the example of Andorra, through assessing the interest of the CORINE units recognised. The starting point was a map of habitats previously drawn at the 1:25,000 scale, on infrared orthoimages. It includes some 3,000 polygons, identified by 103 legend units based on the CORINE habitats. Diversity, naturalness, endemicity, rarity and other attributes of each habitat were evaluated a priori and then combined with site features (analysed through the GIS Arclnfo) to yield a global evaluation for each legend unit. This enabled us to produce a map showing a few levels of natural interest in the landscape of Andorra and to draw the attention to main tendencies of change, which are, when compared with similar neighbouring Pyrenean valleys, not so affected by human activity.