Understanding the effects of spatial scaling on the relationship between urban structure and biodiversity

Consideration of spatial dependence in heterogeneous urban landscapes is crucial for understanding how urban landscapes shape biodiversity. However, understanding the linkage between urban landscape patterns, both vertically and horizontally, and urban-dwelling bird species at various spatial scales remains an unsolved question. Here, we investigated how patterns of vertical and horizontal urban landscape structure influence urban-dwelling bird species at various spatial scales in the Chicago Region. We utilize a high-density Airborne Laser Scanning (ALS) dataset to exam ALS-derived metrics (foliage height diversity, canopy openness, and building volume) in relation to bird diversity. Our results show that LiDAR-derived metrics exhibited significant variation across spatial scales. The negative impact of building volume on bird species is greatest at the smallest scale (slope = -0.24 at 50 m radius), but its effect declined as the scale increased (slope = 0.00 at 500 m radius). Foliage height diversity did not influence bird diversity at small spatial scales but shows a positive effect on bird diversity over 150 m radius (slope = 0.05 to 0.11). Canopy openness changed its sign of slope from negative to positive as the buffer radius increased (between 150 and 200 m buffer radii), indicating that openness may have different roles depending on the spatial scale. Based on our findings, a buffer radius of 150-200 m was concluded to be the threshold distinguishing local and landscape-level variables in this study. In general, horizontal landscape patterns have a stronger influence on urban biodiversity than vertical structures. However, our findings suggest that enhancing the vertical complexity of canopy structures in existing green spaces could be an effective strategy for sustaining bird diversity in urban areas, particularly where expanding green spaces is not feasible. Our study enhances the understanding of urban biodiversity dynamics and provides practical implications for urban landscape management and planning.