Forest structural responses to site characteristics and silvicultural intensity shape caribou habitat suitability in stands of Ontario's boreal forest

Woodland caribou ( Rangifer tarandus caribou) depend on mature conifer forests that provide abundant forage and refuge from predation. However, large-scale forest management and other anthropogenic disturbances throughout the boreal region in Canada have altered forest composition and structure, raising concerns regarding caribou habitat suitability. However, a variety of silvicultural intensive treatments and tools may be used to offset negative effects of forest management and even promote caribou habitat. We used the NEBIE (Natural, Extensive, Basic, Intensive, Elite) silviculture trial network to evaluate how a gradient of silvicultural intensities affects forest structural attributes and habitat suitability for woodland caribou across four sites in Ontario, Canada. We quantified basal area, stem density, canopy closure, and leaf area index from 20th year post-harvest field measurements and airborne lidar from the four boreal NEBIE installations. We used this data to develop a structure-based habitat suitability model with two sub-indices (forage availability and predator avoidance) to estimate the effects of site characteristics and silvicultural intensity on regenerating structural attributes consistent with caribou habitat. Habitat suitability was greatest in Sioux Lookout (0.83), followed by Kapuskasing (0.68), Dryden (0.56), and Timmins (0.19). Highly intensive silviculture treatments provided the highest suitability due to higher conifer basal area and lower canopy closure compared to less intense silviculture — but this effect was site-dependent. Overall, low-intensity approaches may be sufficient in lower productivity conifer forests, while in more productive mixedwood systems, even aggressive treatment intensity may be insufficient to create suitable caribou habitat conditions. The outcomes of silviculture strategies are strongly dependent on-site characteristics. The outcomes highlight the need for site-specific silviculture planning for successful caribou recovery strategies, rather than uniform application of treatment intensities across landscapes.