Plant community shifts along tree canopy cover gradients in grazed Patagonian Nothofagus antarctica forests and grasslands

Abstract

Nothofagus antarctica forests at the Chilean Patagonia are valued for both their ecological and livestock production value. Despite their importance, there is not enough information about the understory associated to these forests. Previous studies have reported the dependence of the understory on the light intensity reaching the sward. Thus, our objective was to study the effect of the tree canopy cover on the plant community composition and productivity of the forests´ understory. We established four experimental sites along a 100-km transect covering an area of 700 km² in Southern Chilean Patagonia. 73 1-m² metal exclusion cages (quadrats) were randomly distributed along tree cover gradients on the sites. Bare soil, litter and understory cover were registered. Plant botanical composition was also recorded. At the end of the growing season plant biomass was harvested to estimate yield. Species frequency and abundance were analyzed. Species richness and biodiversity were determined. We found 37 species distributed in 20 families. Woody species represented 13.5%, grasses 24.3% and forbs 62.2% of the total. Species richness was higher in grasslands than forests. There was a trend in decreasing biodiversity when increasing tree canopy cover. Differences in yield between grasslands and open forests were not significant. High forage value species presented higher abundance in open forests than grasslands. We conclude that open forests of N. antarctica have higher grazing potential than their associated grasslands. These findings support the facilitation effect of trees over understory species reported previously.