Consistent shifts in Alpine plant traits along a mesotopographical gradient
Résumé
Despite an increasing interest in the study of functional diversity, there have been few attempts to link plant traits, habitat variation, and community structure in Alpine landscapes. These interrelationships were examined along a snowmelt and growing-season-length gradient determined by mesotopographical variations. The study site was chosen so as to encompass much of the floristic beta diversity encountered at the Alpine belt of the southwestern Alps. A three-table ordination technique, named RLQ, was used to unravel on a quantitative basis the co-structure of a plot-by-environmental-variable table, a plot-by-species table, and a species-by-traits table. The main covariations between traits and habitat were (1) an increased specific leaf area (SLA) and leaf nitrogen content on a mass basis (N-mass) in late-meting sites, (2) a trend toward upright and thick leaves in the most exposed, physically disturbed, early-melting sites, and (3) an increasing leaf area in the middle of the gradient, which also exhibits small-scale disturbance due to the Alpine marmot. The interplay of intermediate snow-melting dates and intense zoogenic disturbance appears to promote plant diversity and the persistence of species whose mean-elevation distribution is located much below the study site. The adaptive value of trait attributes along the mesotopographical gradient is discussed within the broader context of plant strategies in temperate Alpine grasslands.