Persistent declines in forest-dependent birds following active restoration of logged tropical forest in Borneo

Abstract

O_LITropical forest restoration is critical for mitigating biodiversity loss and climate change, including in forests impacted by selective logging. Active restoration through liana cutting and enrichment tree planting can substantially accelerate carbon recovery, potentially reducing economic pressures to convert logged forests. But its long-term biodiversity impacts remain largely unknown. C_LIO_LIUsing over two decades of bird survey data from Borneos largest logged-forest restoration project, we quantified occupancy patterns for 176 species across primary, naturally regenerating, and actively restored logged forests spanning a 30+ year post-logging chronosequence. C_LIO_LIForest-dependent, threatened and near-threatened species generally declined through time in actively restored areas, whereas many species in naturally regenerating forests progressively recovered toward primary forest levels. Between 17-40% of 66 threatened or near-threatened species had consistently lower occupancies in actively restored than in naturally regenerating forest. Across species of global conservation concern, median occupancies in restored areas remained [~]22% below primary forest even 50 years after harvests, compared with only [~]6% lower under natural regeneration. C_LIO_LIArboreal insectivores, frugivores, and predatory species appeared most negatively affected by active restoration, with 27-49% of arboreal gleaning insectivores (of 62), 13-30% of arboreal frugivores (of 40), and one-third of predatory species (of 15) showing higher occupancy in naturally regenerating forests. Sallying insectivores also showed a possible but uncertain response, whereas ground-associated frugivores and insectivores were largely unaffected by restoration treatment. C_LIO_LIConcerningly, even 50 years post-logging, up to 52% of 50 high forest-dependency species retained distinct occupancies in actively restored compared with primary forest, suggesting persistent negative impacts of vine-cutting and/or tree planting activities on avian populations. C_LIO_LISynthesis and applications. Our findings indicate that despite substantial carbon benefits, active restoration within selectively logged forests may impede the recovery of forest-dependent biodiversity. This challenges the common assumption embedded within nature-based climate solutions that carbon and biodiversity outcomes will necessarily align. Nonetheless, despite the persistent declines in bird communities, actively restored forests continued to provide key habitat for many species. Active interventions may thus still contribute to broader biodiversity conservation objectives if they protect logged areas from conversion, potentially via carbon payments. C_LI