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

SPEZIALE, KARINA LILIAN; RUGGIERO, ADRIANA; EZCURRA, CECILIA

JOURNAL OF BIOGEOGRAPHY

Blackwell's-Wiley

Lugar: Oxford; Año: 2010 vol. 37 p. 449 - 464

0305-0270

ABSTRACTAim To evaluate the relative importance of climate, productivity, environmentalheterogeneity, biotic associations and habitat use by cattle to account for thespecies richness of trees, shrubs and herbs across the Subantarctic–Patagoniantransition.Location An area of c. 150 · 150 km, within the transition zone betweenthe Subantarctic and Patagonian subregions on the eastern slope of the Andes(c. 39–42 S, 70–72 W).Methods All vascular plants found at each one of 50 (10 · 10 m) sampling plotswere counted to estimate the local tree, shrub and herb species richness. Pathanalysis was used to evaluate the relationship between the richness of the threelife-forms and plant cover, dried litter biomass, mean annual temperature, annualprecipitation, daily temperature range, substrate heterogeneity and number offaecal pats. Principal coordinates of neighbour matrices was used to model thespatial autocorrelation of the data.Results Total plant species richness showed a unimodal pattern of spatialvariation across the transition. Richness responded positively to indirect effects ofprecipitation mediated through plant cover, but there was a negative overall effectof precipitation on richness towards the west of the transition, most strongly fortrees. An increase in substrate heterogeneity promoted a local increase in herb andshrub richness; the richness of trees increased in sites with steeper slopes. Canopyclosure had a direct negative impact on herb richness; it also increased the localaccumulation of litter, which negatively affected shrub and herb richness. Theimpact of habitat use by cattle negatively affected herb richness in areas to the eastof the biogeographical transition.Main conclusions We suggest that the importance of indirect climatic effectsmediated by vegetation cover can account for species richness patterns across thistransition, most strongly for woody species, which supports the productivityhypothesis. The southern temperate forests towards the west may representa deviation from the predictions of the water–energy dynamics hypothesis.Dissimilar spatial patterns of variation in the richness of woody and herbaceousspecies, and their different responses to climatic and heterogeneity variablesacross the transition, suggest that plant life-form influences the plant speciesrichness–environment relationships.