Abstract
Forest degradation has gained global attention for its role in exacerbating biodiversity loss and climate change, yet indicators, baselines, and thresholds of degradation remain under debate. Maintaining key forest characteristics within bounds of natural variability offers a strategy to sustain ecological integrity and to provide potential measures of degradation. We used forest inventories, satellite-derived information, and government planning guidelines to evaluate five potential indicators of forest degradation during 2012-2021 for public forests in boreal northeastern Ontario, Canada. We tested two contrasting hypotheses (natural disturbance emulation vs. timber maximization) by comparing observed values against those from two reference landscapes: one shaped by empirical estimates of natural fire disturbance regimes and one by forest management aimed at maximizing timber volumes. All indicators fell outside bounds of natural variability from natural landscapes and were more consistent with timber maximization. Specifically, compared to natural landscapes, some forest types were disturbed at substantially higher rates; the proportion of forest >100 years old was significantly lower (22.4% on average vs. 53.5% in a natural landscape); and modelled boreal caribou and American marten habitats were highly fragmented and substantially reduced (12% for boreal caribou and 36% for American marten vs. corresponding percentages of 73% vs. 76% in a natural landscape). Government planning targets for natural variability targets also were lower than, and did not overlap with, empirical estimates. Continued degradation of biodiversity and ecological services is likely unless management approaches are altered.