Landscape disturbances influence local plant diversity beyond stand-scale effects in a North American boreal forest

Natural and anthropogenic disturbances are major threats to biodiversity worldwide, with important consequences for forest ecosystems. Landscape characteristics play a central role in shaping diversity–disturbance relationships by capturing ecological processes that operate beyond the local stand scale. However, when disturbances co-occur across multiple spatial scales, their combined effects are difficult to predict, and interactions among scales may either mitigate or amplify their impacts on biodiversity. Here, we tested how spatiotemporal characteristics of disturbances measured at the landscape-level interact with stand-level disturbances to shape plant alpha and beta diversity across one quarter-hectare plots in the boreal forest of Alberta, Canada. Using a multi-scale approach, we evaluated how time since disturbance, weighted by the proportion of area affected by fire, forest harvesting, and seismic lines, explained variation in plant diversity beyond the stand-level effects typically associated with succession after wildfires. We found that species richness was primarily shaped by a dominant negative effect of seismic lines. Specifically, plots with more recent and extensive seismic line networks within a 1-km radius exhibited lower local species richness. Species turnover between randomly paired plots was largely explained by stand-level effects of recent fire moderated by the effect of the surrounding disturbance mosaic, although no single disturbance type emerged as a relevant predictor. Finally, multivariate analyses indicated that nearly all species responding significantly to seismic lines were negatively affected by this disturbance. In the context of accelerating forest cover change driven by human activities, understanding how interacting disturbances across scales shape local biodiversity is essential for informing forest management and conservation. Our results indicate that in boreal forests, a system subject to ongoing natural resource extraction, anthropogenic disturbances associated with oil and gas development can outweigh natural disturbances, resulting in a dominant negative effect on plant diversity. This highlights that landscape-scale patterns of disturbance can be as important as, or more important than, local stand-scale disturbances in structuring plant diversity in a stand. Together, these findings underscore the need to adopt a landscape-level perspective when managing and restoring ecosystems exposed to multiple, interacting disturbances.