2023 Volume 28 Issue 1 Article ID: 2222
Biodiversity provides a foundation for the cultural value and ecosystem services of plants in urban forests. Although urban forests in Japan differ from those in well-studied montane areas in many ways (e.g. fragmentation by artificial elements), conifer plantations remain major components. Birds play important roles in urban forests, providing pest control and contributing to plant reproduction through seed dispersal. However, the effects of fruit availability and forest and landscape structures on bird community composition have not been studied in conifer plantations in urban forests. Therefore, we investigated the extent to which birds use conifer plantations as habitat in an urban landscape and how stand structure, landscape configuration, and fruit availability affect the local abundance and species richness of birds. We compared the effects among different bird species and considered conservation strategies to promote bird diversity in urban forests. We established 18 study sites in Tsukuba, Ibaraki Prefecture, Japan: six plantations consisting only of conifer trees (denoted 'plantation') and 12 consisting of conifers mixed with broadleaf trees (denoted 'mixed forest'). At each site, we conducted 27 15-minute bird censuses just after dawn during January - November 2021. The basal area (BA) and mean diameter at breast height (DBH) of the trees at each site and the areas and edge lengths of forests within a 200-m radius around each site were considered variables that might influence local bird communities. In total, 27 bird species were recorded, and the six most abundant species were analysed. We categorised the 27 species into six functional groups in terms of body length and fruit preference. Habitat-selection analysis revealed that most functional groups and species were significantly more abundant and species richness was greater in mixed forests than in plantations. A binomial mixture model showed that the forest area around a site had a positive effect on most functional groups and species, whereas BA and the forest-edge length around a site had negative effects on some. DBH had either positive (e.g. Japanese pygmy wood- pecker, Yungipicus kizuki) or negative (e.g. long-tailed tit, Aegithalos caudatus) effects, depending on the functional group and species. Fruit availability had no significant effect on any functional group or species. These results imply that, to conserve bird community diversity it is important to maintain large non-fragmented forests in urban spaces. It would also be effective to increase the complexity of conifer plantations in terms of their local structure (e.g. mixture of broadleaf trees) and spatial heterogeneity (e.g. mosaic of young and old stands).
