Spatial patterns of saproxylic beetles shortly after fire in the northern boreal forest

Wildfires generate large, spatially heterogeneous patches in boreal forests, providing a unique opportunity to investigate the spatial pattern of saproxylic beetle colonization. In this study, we analyzed spatial patterns of beetle assemblages within a 76,483 ha wildfire in northern Québec in 2005. Using a spatial modeling approach (Principal Coordinate of Neighboring Matrices, PCNM), we examined how beetle abundance patterns were structured at different spatial scales and whether these patterns were explained by plot-level variables, landscape-scale burn severity, or proximity to potential source habitats. Our results showed that most common saproxylic species exhibited significant spatial structure, primarily at a very large scale (> 2 km), with additional contributions from medium and small scales. These patterns were largely explained by environmental variables, particularly landscape-level attributes such as fire severity, rather than by distance to potential source habitats. While some mycophagous species showed reduced abundance with increasing distance from a recent (2002) burn, overall, distance to unburned or previously burned areas did not strongly constrain colonization. Our findings suggest that early post-fire beetle colonizers possess high dispersal capacities, allowing them to track suitable habitats across large distances. At a close proximity to suitable habitats, fine-scale environmental conditions, such as local fire severity and substrate characteristics, also played an important role, especially for xylophagous and predaceous species. These findings indicate that post-fire saproxylic beetle colonization is driven by a complex interplay of large-scale environmental heterogeneity and species-specific responses to fine-scale habitat features. Our study underscores the importance of incorporating broad spatial extents when studying post-fire colonization dynamics and highlights how spatial modeling can help disentangle the relative influence of environmental structure and dispersal processes.