Journal Article

Plant species richness-environment relationships across the Subantarctic-Patagonian transition zone

Ezcurra, Cecilia, Ruggiero, Adriana, Speziale, Karina Lilian

2010

Overview

To evaluate the relative importance of climate, productivity, environmental heterogeneity, biotic associations and habitat use by cattle to account for the species richness of trees, shrubs and herbs across the Subantarctic-Patagonian transition. An area of c. 150 x 150 km, within the transition zone between the Subantarctic and Patagonian subregions on the eastern slope of the Andes (c. 39-42° S, 70-72° W). All vascular plants found at each one of 50 (10 x 10 m) sampling plots were counted to estimate the local tree, shrub and herb species richness. Path analysis was used to evaluate the relationship between the richness of the three life-forms and plant cover, dried litter biomass, mean annual temperature, annual precipitation, daily temperature range, substrate heterogeneity and number of faecal pats. Principal coordinates of neighbour matrices was used to model the spatial autocorrelation of the data. Total plant species richness showed a unimodal pattern of spatial variation across the transition. Richness responded positively to indirect effects of precipitation mediated through plant cover, but there was a negative overall effect of precipitation on richness towards the west of the transition, most strongly for trees. An increase in substrate heterogeneity promoted a local increase in herb and shrub richness; the richness of trees increased in sites with steeper slopes. Canopy closure had a direct negative impact on herb richness; it also increased the local accumulation of litter, which negatively affected shrub and herb richness. The impact of habitat use by cattle negatively affected herb richness in areas to the east of the biogeographical transition. We suggest that the importance of indirect climatic effects mediated by vegetation cover can account for species richness patterns across this transition, most strongly for woody species, which supports the productivity hypothesis. The southern temperate forests towards the west may represent a deviation from the predictions of the water-energy dynamics hypothesis. Dissimilar spatial patterns of variation in the richness of woody and herbaceous species, and their different responses to climatic and heterogeneity variables across the transition, suggest that plant life-form influences the plant species richness-environment relationships.

• Publisher: Oxford, UK : Blackwell Publishing Ltd,Blackwell Publishing Ltd,Blackwell Publishing,Blackwell
• Subject: Andes region / Animal and plant ecology / Animal, plant and microbial ecology / atmospheric precipitation / autocorrelation / Biogeography / Biological and medical sciences / biomass / canopy / cattle / climate / Climate models / Diverse determinants of diversity / Eastern Andes / eigenvector-based spatial filtering / floristic diversity / Forest ecology / Fundamental and applied biological sciences. Psychology / General aspects / habitat preferences / Herbs / longitudinal gradient / partial regression / path analysis / Plants / Precipitation / prediction / productivity / Rain / Shrubs / Species / species diversity / Steppes / Synecology / temperate forests / temperature / topographic slope / trees / vascular plants / vegetation cover / water-energy dynamics / woody plants