The role of abiotic and biotic factors in functional structure and processes of alpine subshrub communities

Abstract

Species occurrence is subjected to the particular ecological constraints of each site where species that can become dominant exert strong influence on community structure and functioning. Given the harsh environmental conditions in alpine areas and the low number of woody species able to support them, we wanted to study the effect of the main abiotic (environmental conditions related to topographical situation and bedrock type) and biotic (functional type of the dominant species) factors on functional structure and processes of alpine subshrub communities. In 24 study sites, we collected aboveground biomass and raw litter. Biomass was sorted into functional groups (shrubs, graminoids, forbs, bryophytes, lichens), which, in turn, were separated into photosynthetic and structural compartments. We characterized community structure in terms of biomass allocation of functional groups, estimated leaf primary production and litter persistence, and performed analyses of variance for each of the factors considered. Our results showed that community structure is driven mainly by the functional type of the dominant species, although abiotic factors are also relevant. Production depends on abiotic conditions. It is constrained by low temperatures in northern exposures and by low water availability in permeable bedrock types. Litter decomposition depends on environmental conditions and the dominant species characteristics. It is limited by dry conditions in southern slopes and by the thick and N-poor leaves of evergreen subshrubs. In summary, the few alpine woody species able to build specific communities in the Pyrenees grow in particular topographical situations, where they become crucial drivers of ecosystem structure and functioning.