Temporal variability in seed production and pre-dispersal seed predation in Nothofagus forests under silvopastoral use

R SOLER ESTEBAN; JM ESPELTA; MV LENCINAS; G MARTÍNEZ PASTUR

University of Evora

Congreso; World Congress Silvo-pastoral Systems.; 2016

University of Evora

Seed-predator interactions may be crucial in agroforestry systems as the maintenance of tree component over time (e.g. natural regeneration) may be influenced by seed availability. However, the results of this interaction may depend on life-history traits of predators (e.g. specificity, life span, dispersal ability), as well as the modifications produced by forest thinning (e.g. canopy cover). The aim of this study was to assess the temporal variability in seed production of N. antacrtica in southern Patagonia forests (Argentina), and the consequences on pre-dispersal seed predation by different seed predators differing in the above-mentioned attributes: insects and birds. We established seed traps (n=10 per site) in primary, secondary and silvopastoral used stands. From 2008 to 2015, we collected and classified the fallen seeds into: (i) insect depredated, (ii) bird depredated, or (iii) sound seeds. N. antarctica showed strong among-year variation in mature seed production but the effect of forest type was not significant. Seed predation (total, by insects or by birds) was also strongly influenced by years but not by forest type. While seed predation by insects increased during small crop years (e.g. 2011), bird predation was higher during larger crop year (e.g. 2010). We observed a negative relationship between the proportion of total seed predation and the ratio of mature seeds, indicating the potential satiation-starvation effect on predators by fluctuating seed production through. This effect was significant for both primary and silvopastoral stands, but only marginal for secondary forests. Concerning the identity of the seed predator, mean percentage of seeds depredated by birds showed a strong negative relationship with the proportion of seeds depredated by insects. This was mainly noticeable in years when insect predation reached high levels (20-40% of total seed crop) and bird predation did not almost occur. . Finally, we detected a negative relationship between the variability in seed production (measured as the population-level coefficient of variation) and the percentage of seeds depredated. This pattern was observed for total predation and the proportion of insect predation (significant correlation), but no for birds predation. In sum our results highlight that silvopastoral use did not affect seed production or predation trends, although it could depend on the intensity of thinning (