Resilience and restoration of tropical and subtropical grasslands, savannas, and grassy woodlands

Abstract

Despite growing recognition of the conservation values of grassy biomes, our understanding of how to maintain and restore biodiverse tropical grasslands (including savannas and open‐canopy grassy woodlands) remains limited. To incorporate grasslands into large‐scale restoration efforts, we synthesised existing ecological knowledge of tropical grassland resilience and approaches to plant community restoration. Tropical grassland plant communities are resilient to, and often dependent on, the endogenous disturbances with which they evolved – frequent fires and native megafaunal herbivory. In stark contrast, tropical grasslands are extremely vulnerable to human‐caused exogenous disturbances, particularly those that alter soils and destroy belowground biomass (e.g. tillage agriculture, surface mining); tropical grassland restoration after severe soil disturbances is expensive and rarely achieves management targets. Where grasslands have been degraded by altered disturbance regimes (e.g. fire exclusion), exotic plant invasions, or afforestation, restoration efforts can recreate vegetation structure (i.e. historical tree density and herbaceous ground cover), but species‐diverse plant communities, including endemic species, are slow to recover. Complicating plant‐community restoration efforts, many tropical grassland species, particularly those that invest in underground storage organs, are difficult to propagate and re‐establish. To guide restoration decisions, we draw on the old‐growth grassland concept, the novel ecosystem concept, and theory regarding tree cover along resource gradients in savannas to propose a conceptual framework that classifies tropical grasslands into three broad ecosystem states. These states are: (1) old‐growth grasslands (i.e. ancient, biodiverse grassy ecosystems), where management should focus on the maintenance of disturbance regimes; (2) hybrid grasslands, where restoration should emphasise a return towards the old‐growth state; and (3) novel ecosystems, where the magnitude of environmental change (i.e. a shift to an alternative ecosystem state) or the socioecological context preclude a return to historical conditions.

The restoration species pool for restoring tropical landscapes: assessment of the largest Brazilian supply chain

“…Despite the remarkable diversity of the restoration species pool we studied, the representation of regional floras was biased under several aspects. While both Atlantic Forest and Cerrado species were available in plant nurseries, there was an underrepresentation of savannas’ specialists, which may lead to afforestation and to other negative consequences for the native diversity of the grassy biomes of Cerrado (Overbeck et al 2013; Veldman et al 2015a, 2015b; Abreu et al 2017; Buisson et al 2018). Furthermore, the restoration species pool constituted a narrow spectrum of growth forms that lack or underrepresent lianas, epiphytes and herbs; in the Atlantic Forest and Cerrado biomes, these growth forms exceed 2 to 7 times the number of tree species (BFG 2015).…”

Tailoring restoration interventions to the grassland‐savanna‐forest complex in central Brazil

“…; Furley & Ratter ; Furley ; Villalobos‐Vega et al ). Woody species from tropical savannas have deep roots (approximately 15 m; Canadell et al ) so shallow soils prevent colonization by most woody species, especially trees (Ribeiro & Walter ; Amaral et al ; Buisson et al ), acting as a barrier to most grassland‐savanna transitions.…”

Pine savanna plant community disassembly after fire suppression

“…In fire-maintained savannas, community disassembly is often caused by altered fire regimes (e.g. Buisson et al, 2019). Species losses from changes in fire frequency, intensity, and season are particularly severe in non-edaphic savannas where frequent fires are required to prevent colonization of fire-intolerant species and to maintain understorey plant diversity (Bond, 2016;Kirkman & Mitchell, 2006;Myers, 1990;Veldman, 2016).…”