Growth of Festuca pallescens in Silvopastoral Systems in Patagonia, Part 1: Positive Balance between Competition and Facilitation

Silvopastoral systems may overyield compared to monocultures as a result of higher resource capture and/or facilitation effects of the trees on the pastures. Festuca pallescens (St. Ives) Parodi, a forage species of Patagonia, is vulnerable to water deficit, suggesting that it may benefit from the facilitative effects of trees. Radiation (PPFD), temperature, relative humidity (RH) and soil water distribution during the growing season were measured under different tree cover levels in ponderosa pine-based silvopastoral systems. PPFD decreased with increasing tree cover, and the decrease was lower in the positions under than between tree crowns. No significant differences were observed for temperature, RH nor for soil water content between treatments. Pre-dawn water potential of grasses during the growing season showed similar high values in all treatments. However, cumulative water stress was slightly lower in high tree cover treatments than in open situations. Leaf water potential of the grasses during the day was always lower in open grassland than in forested plots. The growth of the grasses showed no significant differences between treatments, but mean growth tended to decrease in the more densely planted treatments. We concluded that F. pallescens is a species that is biologically sound for use in silvopastoral systems, because the balance between facilitation and competition can be positive under the semiarid conditions of Patagonia.