Connectivity with primary forest determines the value of secondary tropical forests for bird conservation

Predicted species extinctions caused by the destruction and degradation of tropical primary forest may be at least partially mitigated by the expansion of regenerating secondary forest. However, the conservation value of secondary forest remains controversial, and potentially underestimated, since most previous studies have focused on young, single-aged, or isolated stands. Here we use point count surveys to compare tropical forest bird communities in 20–120-yr-old secondary forest and primary forest stands in central Panama, with varying connectivity between secondary forest sites and extensive primary forest. We found that species richness and other metrics of ecological diversity, as well as the combined population density of all birds, reached a peak in younger (20-yr-old) secondary forests, and appeared to decline in older secondary forest stands. This counter-intuitive result can be explained by the greater connectivity between younger secondary forests and extensive primary fores...热带原生林（tropical primary forest）遭破坏与退化所引发的预估物种灭绝情况，或可通过再生次生林（regenerating secondary forest）的扩张得到至少部分缓解。然而，次生林（secondary forest）的保护价值仍存在争议且可能被低估——因此前多数研究仅聚焦于幼龄、单龄或孤立林分（stands）。本研究采用点计数调查法（point count surveys），对比巴拿马中部20至120年生次生林与原生林林分中的热带森林鸟类群落，且次生林样地与大面积原生林之间的连通性存在差异。研究发现，物种丰富度及其他生态多样性指标，连同所有鸟类的总种群密度，均在幼龄（20年生）次生林中达到峰值，而在老龄次生林分中似乎呈下降趋势。这一反直觉的结果可通过幼龄次生林与大面积原生林之间更强的连通性得到解释……