The road to recovery: a synthesis of outcomes from ecosystem restoration in tropical and sub-tropical Asian forests

Abstract

Current policy is driving renewed impetus to restore forests to return ecological function, protect species, sequester carbon and secure livelihoods. Here we assess the contribution of tree planting to ecosystem restoration in tropical and sub-tropical Asia; we synthesize evidence on mortality and growth of planted trees at 176 sites and assess structural and biodiversity recovery of co-located actively restored and naturally regenerating forest plots. Mean mortality of planted trees was 18% 1 year after planting, increasing to 44% after 5 years. Mortality varied strongly by site and was typically ca 20% higher in open areas than degraded forest, with height at planting positively affecting survival. Size-standardized growth rates were negatively related to species-level wood density in degraded forest and plantations enrichment settings. Based on community-level data from 11 landscapes, active restoration resulted in faster accumulation of tree basal area and structural properties were closer to old-growth reference sites, relative to natural regeneration, but tree species richness did not differ. High variability in outcomes across sites indicates that planting for restoration is potentially rewarding but risky and context-dependent. Restoration projects must prepare for and manage commonly occurring challenges and align with efforts to protect and reconnect remaining forest areas. The abstract of this article is available in Bahasa Indonesia in the electronic supplementary material. This article is part of the theme issue ‘Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration’.

Fifteen essential science advances needed for effective restoration of the world's forest landscapes

“…Therefore, more work is needed to understand the relative importance of the multiple drivers of restoration success, and how they interact. In this theme issue, wind damage in Vietnam is shown to be more detrimental to forest recovery where past disturbance and land-use change have been greatest [ 68 ], while planted seedling survival across Southeast Asian sites was highly variable, but particularly connected to habitat condition at time of planting [ 69 ]. Similarly, new data in the theme issue from Brazil show an increase in forest restoration success with soil quality and proximity to forests [ 70 ].…”

“…In this theme issue, a critique of the widely employed Framework Species Approach shows that procedures for selecting species are inconsistent and ill-defined [ 96 ]. Accordingly, new data in the theme issue show that plantings are often species-poor [ 69 ], which may be partly due to limited infrastructure to access local seed sources or limited knowledge of nursery practices for a broad set of species. The same study also shows that planting success varied with prior land use, which may alter species suitability.…”

“…However, we also see in the theme issue that for other regions, e.g. Southeast Asia, information on competitive thresholds is too limited to draw conclusions for management [ 69 ].…”

“…Banin et al . [ 69 ] show that active restoration tends to increase rates of basal area accumulation, relative to naturally regenerating forests in Asian forests, but the effect is variable across landscapes. More knowledge is also needed about the implications of landscape mosaics for selecting restoration methods, to ensure that FLR landscapes are not managed with broad-brush approaches.…”

“…Longitudinal studies lasting morer than 5 years are rare among the published restoration literature [ 69 ] but are urgently needed to understand the mechanisms, ecosystem service flow and other long-term outcomes of forest restoration and management [ 155 ]. Assessing recovery rates using chronosequences does not offer the same level of information provided by long-term studies and can be misleading [ 164 ].…”