Grassland productivity and diversity on a tree cover gradient in Nothofagus pumilio in NW Patagonia

Extensive areas of primary forests of lenga (Nothofagus pumilio (Poepp et Endl.) Krasser) have been transformed into grasslands over the past few decades. In Chile's Aysén region, grazing in remnant forests is common practice but there is little empirical evidence of tree-understorey interactions therein. In an attempt to establish a scientific basis for silvopastoral implementation, the relationship between lenga cover and grassland productivity, quality and species richness was examined. Tree cover was quantified in 14 (20 × 20 m) sites where aboveground herbaceous biomass was evaluated monthly throughout two growing seasons. Herbage quality and plant species richness were measured once at the peak of biomass production in the second year. We discuss radiation transmitted through the canopy and water supply as drivers of the tree-understorey relationship. Changes in herbaceous species composition and richness with varying tree cover are described. Despite interannual differences, scattered trees or medium-density forests allow higher productivity than open areas, as well as an acceptable nutritive value and preservation of native species. Although further studies are required, our results suggest that presence of lenga trees within grazing areas can be an advantageous alternative in terms of biodiversity and productivity, to traditional grazing systems in open grasslands.