Stability in tapia woodlands amid non‐native expansion: Integrating traditional ecological knowledge and remote sensing to track 73 years of tree cover in Madagascar

Afromontane ecosystems, characterised by mosaics of fire-adapted grassy ecosystems and fire-sensitive forests, are biodiversity hotspots facing escalating pressures from non-native species, climate and land-use change. Madagascar's Central Highlands is one such hotspot, hosting woodlands dominated by endemic Uapaca bojeri (tapia) which are important to local livelihoods and biodiversity conservation. Despite their social–ecological importance, multi-decadal dynamics of tree cover remain poorly understood, particularly differential responses from native versus non-native tree species to socio-ecological drivers.
We investigated tree cover trajectories across the Central Highlands by integrating ground-based vegetation surveys (40 plots), historical remote sensing analysis (80 sites) spanning 73 years (1949–2022), and traditional ecological knowledge (TEK) documented through 32 focus groups with 114 members of community forest management associations. We examined whether native tapia woodlands declined as has been widely assumed, how non-native forestry species (Pinus spp. and Eucalyptus spp.) spread and the factors driving these dynamics.
Tapia woodlands showed multi-decadal (1949–2022) structural stability confirmed by both remote sensing (−0.52% change, 𝑝 = 0.0810) and TEK shared during 81% of focus groups. TEK revealed compositional change within superficially stable tapia stands, with losses of companion species.
Non-native forestry species cover increased substantially (+17.4%, 𝑝 < 0.001) over the same period, with expansion accelerating after 1991. Expansion was greatest near roads, with model predictions indicating +26% total increase at roadside sites compared to sites far from roads over 73 years (Year × Distance to Road: β = −0.152, 𝑝 = 0.002).
Synthesis. Tapia woodlands demonstrate structural resilience, challenging widespread narratives of human-driven deforestation in the Central Highlands of Madagascar, although compositional losses of companion species reveal that not all biodiversity within stable canopies is equally conserved. Meanwhile, rapid non-native encroachment poses increasing threats to ecosystem services that rural communities depend on. Integrating TEK with remote sensing facilitated detection of compositional losses and offers a transferable framework for monitoring heterogeneous landscapes that have been challenging to monitor using conventional methods.