Effects of forest amount and fragmentation on different bird guilds reveal strategies of forest restoration in Three Gorges Reservoir area of Yangtze River, China

The construction of the Three Gorges Dam Project had changed the forest landscapes and threatened the bird diversity of the Three Gorges Reservoir (TGR) area. For restoring degraded ecosystems and protecting biodiversity, the government has carried out a series of ecological projects in recent years, which has significantly restored the forest of the TGR area. However, the fragmentation of forest landscapes in the TGR area was not clearly improved by these ecological projects, and we were concerned that some birds might be impacted. Therefore, in this research, we studied the effects of forest amount and fragmentation on diversity of different bird guilds, to develop the effective strategies of forest restoration for bird preservation in the TGR area. We first selected a series of forest landscapes where forest amount and fragmentation were independent of each other to conduct bird surveys, and then used structural equation models to examine their direct and indirect effects on species richness and relative abundance of four bird guilds (vertical-profile generalists, understory birds, edge users and ground users). The results showed that forest amount had direct positive effects on diversity of all bird guilds, and fragmentation had indirect negative effects on diversity of vertical-profile generalists and understory birds that was mediated through vegetation condition. We believe that to increase forest amount in the landscapes undoubtedly plays an important role in bird conservation. Meanwhile, we also need to be alert to the threats that fragmentation may pose to birds by reducing forest quality. We suggest that optimizing landscape configuration and improving forest quality should both be emphasized while restoring the forest. For example, restoring the areas between forest patches preferentially to increase connectivity in the landscapes, and transforming the degraded mono-specific forests into mixed forests through replanting to optimize the stand structure.