Competition effects of grazing-modified herbaceous vegetation on growth, survival and water relations of lenga (Nothofagus pumilio) seedlings in a temperate forest of Patagonia, Argentina

Abstract

In this study, we determined the competition effects of herbaceous vegetation on survival, growth, and plant water relations of planted lenga (Nothofagus pumilio) seedlings under field and nursery conditions in western Patagonia, Argentina. In the field, thirty (1.5 × 1.5 m) plots were randomly set in a grazing-free exclosure built in a typical grazing-degraded lenga canopy gap mainly colonized by non-native herbs and grasses (empastado). Herbaceous aerial and root biomass was removed in half of the plots (non-competition treatment, NCT), while the others (competition treatment, CT), remained undisturbed. Four similarly-sized lenga seedlings were planted per plot. In the nursery, 120 lenga seedlings were planted in individual pots containing soil of the field study site, and set to a factorial experiment including two competition levels (CT and NCT) and two watering regimes: normal (simulating average rains during the growing season, 500 mm, NW), and high (equivalent to 1000 mm, HW). During three growing seasons, we determined seedling survival, growth, and plant and soil water status of both experiments. Higher survival and growth, and better plant water status values were obtained in NCT as compared to CT in both experiments. In the nursery, HW did not improve survival and growth as compared to NW. In restoration trials implying grazing-degraded areas, increases in lenga seedling survival and growth could be achieved by reducing nearby competition of grasses and herbs, while extra watering appears unnecessary. However, limitations in the experimental design (pseudo-replication), limits generalization of results to other forest ecosystems with similar structural and functional characteristics.