“In a tree by the brook, there’s a songbird who sings”: Woodlands in an agricultural matrix maintain functionality of a wintering bird community

The agricultural matrix has increasingly been recognized for its potential to supplement Protected Areas (PAs) in biodiversity conservation. This potential is highly contextual, depending on composition and spatial configuration of matrix elements and their mechanistic relationship with biological communities. We investigate the effects of local vegetation structure, and proximity to a PA on the site-use of different guilds in a wintering bird community within the PA, and in wooded land-use types in the surrounding matrix. We used occupancy models to estimate covariate–guild relationships and predict site-use. We also compared species richness (estimated through capture–recapture models) and species naïve site-use between the PA and the matrix to evaluate taxonomic changes. We found that tree cover did not limit the site-use of most guilds of the community, probably due to high canopy cover across all chosen sites. Exceptions to this were guilds comprising generalist species. Shrub cover and bamboo cover had important effects on some woodland-associated guilds, suggesting a change in limiting factors for site-use under adequate tree cover. Site-use across the matrix was high for all analyzed guilds. This was found to be due to three non-exclusive reasons: (i) presence of one or more ubiquitous species (found all across the landscape) within some guilds, (ii) redundancy of species within guilds that buffered against a decrease in site-use, and (iii) turnover in guild composition/abundances to more generalist species from PA to matrix. Estimated species richness was higher in the matrix (107± 11; mean ± SE) than in the PA (90± 7), which may have been in part due to the addition of generalist species in the matrix. Understanding factors that limit biological communities is crucial to better managing the ever-increasing matrix for biodiversity conservation. Our study provides insights into the effects of different components of vegetation structure on the bird community in wooded land-use types in the matrix. We highlight the value of woodlands surrounding PAs in maintaining multiple guilds, and hence, the functionality of a wintering bird community. However, we caution that the matrix may fall short in retaining some specialized species of the community.

农业生境矩阵（agricultural matrix）在生物多样性保护中补充保护区（Protected Areas，PAs）的潜力日益受到学界认可。该潜力具有高度情境依赖性，取决于生境矩阵组分的组成与空间配置，及其与生物群落的作用机制关系。本研究针对保护区内及周边农业生境矩阵中林地型土地利用类型的越冬鸟类群落，探究本地植被结构、与保护区的距离对不同生态功能群（guilds）位点利用的影响。我们采用占用模型（occupancy models）估算协变量-功能群关系并预测位点利用情况；同时通过标志重捕模型（capture–recapture models）估算物种丰富度（species richness），并对比保护区与农业生境矩阵的物种原生位点利用度（naïve site-use），以评估类群组成变化。

研究发现，林木覆盖并未限制该群落多数功能群的位点利用，这可能源于所有所选样地均具备较高的冠层覆盖度；仅由广食性物种组成的功能群为例外。灌丛覆盖与竹类覆盖对部分与林地相关的功能群具有显著影响，表明在林木覆盖充足的条件下，位点利用的限制因子会发生改变。所有被分析的功能群在农业生境矩阵中的位点利用度均较高，究其原因可归纳为三点（无排他性）：(i) 部分功能群内存在一种或多种广布物种（在整个研究景观中均有分布）；(ii) 功能群内物种存在功能冗余，可缓冲位点利用度的下降；(iii) 从保护区到农业生境矩阵，功能群组成与多度发生更替，群落偏向广食性物种。

估算得到的物种丰富度在农业生境矩阵中为107±11（平均值±标准误），高于保护区的90±7，这部分原因可能是农业生境矩阵中新增了广食性物种。明确限制生物群落的关键因子，对于优化不断扩张的农业生境矩阵以服务生物多样性保护至关重要。本研究揭示了植被结构的不同组分对农业生境矩阵中林地型土地利用类型内鸟类群落的影响，强调了保护区周边林地在维持多类功能群、进而保障越冬鸟类群落功能完整性方面的价值。但同时需警惕：农业生境矩阵可能难以留存群落中的部分特化物种。