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

SPEZIALE, K.; RUGGIERO, A.; EZCURRA, C.

JOURNAL OF BIOGEOGRAPHY

Wiley-Blackwell

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

0305-0270

Aim:  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.Location:  An area of ca. 150 x 150 km, within the transition zone between the Subantarctic and Patagonian subregions, on the eastern slope of the Andes (approx. 39º S- 42ºS, 70ºW- 72ºW).Methods:  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 fecal pats. Principal coordinates of neighbour matrices (PCNM) was used to model the spatial autocorrelation of the data.Results:  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 negative direct 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.Main conclusions:  We suggest the importance of indirect climatic effects mediated by vegetation cover to 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 be a deviation of 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.