Synergistic Effect of Anthropogenic Disturbances on Offspring Demography of &i&Pentadesma butyracea&/i& (Clusiaceae), a Threatened Tree Species in Benin (West-Africa)

摘要

Understanding how ecological differences and anthropogenic disturbances synergistically drive population dynamics decline is critical for optimal management strategy definition. Main anthropogenic disturbances such as habitat size reduction, fire and non-timber forest harvest affect demographic processes but our understanding of their interaction effects in contrasted ecological conditions is limited. We investigated the interaction effects of fruit harvest, fire, gallery forest size and distance to streambed on density, recruitment, survival and growth of Pentadesma butyracea offspring in dry and moist ecological conditions. We randomly selected in each ecological region six P . butyracea populations. We then established in each population, 10 subplots of 100 m ~( 2 ) within 1 ha to assess offspring demographic performance from 2015 to 2017. Results showed that fire suppressed the positive effect of large habitat size and amplified the negative effect of increasing local aridity on offspring growth. Fire and harvest synergistically reduced growth whereas offspring growth was resilient to fire in moist ecological region. Moist ecological conditions mitigated the negative effect of harvest on growth. Harvest mitigated the surprise negative effect of large habitat size on survival. However, in large gallery size, high harvest limited clonal recruitment and growth. There was a positive interaction effect between harvest and distance to streambed on survival (High harvest, Z = 2.045, p = 0.041, Medium, Z = 2.060, p = 0.039) but a negative interaction effect on growth (High, t = -2.357, p < 0.05, Medium, t = -1.403, p > 0.05). Clonal offspring grew faster than sexual offspring in high harvest populations. In moist region, offspring survived better in large gallery forest size. In 2017, survival and growth were lower in large gallery forest. In 2017, offspring growth was higher near the riverbed where the survival rate low. This study suggests that management strategies should consider the interaction effects of anthropogenic disturbances and climatic conditions.