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

1. Tropical 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 unknown.

2. Using over two decades of bird surveys from Borneo's largest logged forest restoration project, we quantified occupancy patterns for 171 species across primary, naturally regenerating and actively restored logged forests spanning a 30+ year post-logging chronosequence.

3. Forest-dependent, threatened and near-threatened species generally declined through time in actively restored areas, whereas many species in naturally regenerating forests progressively recovered towards primary forest levels. Between 14% and 39% (9–25 of 64) of 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 ~23% below primary forest even 50 years after harvests (versus ~3% higher with natural regeneration).

4. Arboreal insectivores, frugivores and predatory species appeared most negatively affected by active restoration, with 27%–49% (17–30 of 62) arboreal gleaning insectivores, 13%–31% (5–12 of 39) arboreal frugivores and 20%–33% (3–5 of 15) predatory species having higher occupancy in naturally regenerating than actively restored forests. Sallying insectivores also showed a possible but uncertain response (6%–41%; 1–7 of 17 species), whereas ground-associated frugivores and insectivores were largely unaffected by restoration treatment.

5. Concerningly, even 50 years post-logging, 28%–64% (14–32 of 50) of species highly dependent on forests remained below primary forest occupancy in actively restored forest (versus 0%–6%; 0–3 of 50 with natural regeneration), suggesting persistent negative impacts of vine-cutting and/or tree planting activities on avian populations.

6. Synthesis and applications. 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.