The eco‐evolutionary history of Madagascar presents unique challenges to tropical forest restoration

Abstract

High biodiversity and endemism combined with persistently high deforestation rates mark Madagascar as one of the hottest biodiversity hot spots. Contemporary rising interest in large-scale reforestation, both globally and throughout Madagascar itself, presents a promising impetus for forest restoration and biodiversity conservation across the island. However, Madagascar may face unique restoration challenges due to its equally unique eco-evolutionary trajectory, which must be understood to enable successful ecological restoration. We conducted a systematic review of potential barriers to restoration for terrestrial forest biomes (rain forests, dry forests, and subhumid highland forests) in Madagascar. Our results indicate that aboveground biomass recovery of Malagasy forests appears to be slower than other tropical forests. We suggest four key synergistic factors that inhibit restoration in Madagascar: (a) lack of resilience to shifting nutrient and fire regimes arising from widespread high-intensity shifting cultivation; (b) predominance of nutrient-poor, highly weathered ferralitic soils; (c) vulnerability of regenerating native trees to competition with invasive species due to their evolutionary isolation; and (d) low seed dispersal into regenerating forests due to the unique dependence of Malagasy trees on dispersal by forest-dependent endangered or extinct primates. However, we note that rigorous experimental study of regenerating forests in Madagascar is currently lacking. There are great opportunity and need for such research to disentangle drivers and interactions inhibiting forest restoration. These studies would enable reforestation practitioners to effectively capitalize on current global momentum to implement the large-scale restoration necessary for the conservation of Madagascar's numerous endemic species.

Lavaka (erosional gullies) provide productive patch environments for flora and farming in Madagascar's grassy highlands

“…Although seen as poster children for landscape degradation, in fact they provide not only patch environments for a wide range of shrub and tree species but also agricultural opportunities for hardscrabble tanety farmers. Despite decades of reforestation discourse (e.g., Baohanta et al, 2012;Culbertson et al, 2022;Holloway, 2004;World Wildlife Fund, 2020), the grass-roots crop cultivation and agroforestry practices that we describe, as well as the role that lavaka play in providing refugia and fire protection for a wide range of plants, have not hitherto been included in that thinking. We hope that our analysis will help bring these ideas forward.…”

“…Reforestation efforts are prominent in Madagascar, promoted and aided by the Malagasy government, NGOS and international aid organisations (e.g., USAID, 2022; World Bank, 2016, 2021). Success has been limited, however, in part because of a variety of challenges to forest establishment in the grassy highlands; as summarised by Culbertson et al (2022), these include the nutrient poverty of upland soils as well as the vulnerability of young trees. Lavaka have two roles to play that have been little recognised and under‐exploited: their utility as ‘tree banks’ for local people (i.e., artisanal agroforestry) and as effective small‐scale reforestation sites.…”

“…Reforestation or afforestation projects in the grassy highlands tend to have low success rates, and this is attributed to a range of factors, including less soil moisture retention and lower nutrient concentrations (Culbertson et al, 2022; Miandrimanana et al, 2019; Pareliussen et al, 2006). This problem is not unique to Madagascar, and is a recognised problem in tropical environments throughout the world (Ota et al, 2020).…”

Recolonization of secondary forests by locally extinct fauna through the lens of range expansion: Four open questions

“…Lastly, the duration of forest succession will also mediate these ecological processes. For instance, systems adapted to high levels of disturbance such as hurricane‐prone regions or some types of dry forests may experience faster rates of succession decreasing time to initial colonization and the amount of time that individuals experience density independence (Culbertson et al, 2022).…”