Tropical grassy biomes: linking ecology, human use and conservation

Lehmann, Caroline E. R.; Parr, Catherine L.

doi:10.1098/rstb.2016.0329

Cited by 77 publications

(68 citation statements)

References 78 publications

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“…Similarly, savannas store large amounts of carbon and are essential in supporting millions of people through ecosystem services, farming and tourism (Lehmann & Parr, 2016;Scurlock & Hall, 1998), which could be directly affected by woody encroachment (Table 1).…”

Section: Climate Change Impacts On Ecosystem Services and Biodiversitymentioning

confidence: 99%

Woody plant encroachment intensifies under climate change across tundra and savanna biomes

Criado

Myers‐Smith

Bjorkman

et al. 2020

Global Ecol Biogeogr

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144

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Aim Biomes worldwide are shifting with global change. Biomes whose extents are limited by temperature or precipitation, such as the tundra and savanna, may be particularly strongly affected by climate change. While woody plant encroachment is prevalent across both biomes, its relationship to temperature and precipitation change remains unknown. Here, we quantify the degree to which woody encroachment is related to climate change and identify its main associated drivers. Location Tundra and savanna biomes. Time period 1992 ± 20.27–2010 ± 5.62 (mean ± SD). 1876–2016 (range). Major taxa studied Woody plants (shrubs and trees). Methods We compiled a dataset comprising 1,089 records from 899 sites of woody plant cover over time and attributed drivers of woody cover change across these two biomes. We calculated cover change in each biome and assessed the degree to which cover change corresponds to concurrent temperature and precipitation changes using multiple climate metrics. Finally, we conducted a quantitative literature review of the relative importance of attributed drivers of woody cover change. Results Woody encroachment was widespread geographically and across climate gradients. Rates of woody cover change (positive or negative) were 1.8 times lower in the tundra than in the savanna (1.8 vs. 3.2%), while rates of woody cover increase (i.e., encroachment) were c. 1.7 times lower in the tundra compared with the savanna (3.7 vs. 6.3% per decade). In the tundra, magnitudes of woody cover change did not correspond to climate, while in the savanna, greater cover change corresponded with increases in precipitation. We found higher rates of woody cover change in wetter versus drier sites with warming in the tundra biome, and higher rates of woody cover change in drier versus wetter sites with increasing precipitation in the savanna. However, faster rates of woody cover change were not associated with more rapid rates of climate change across sites, except for maximum precipitation in the savanna. Main conclusions Woody encroachment was positively related to warming in the tundra and increased rainfall in the savanna. However, cover change rates were not predicted by rates of climate change, which can be partially explained by climate interactions in both biomes. Additional likely influences include site‐level factors, time‐lags, plant‐specific responses, and land use and other non‐climate drivers. Our findings highlight the complex nature of climate change impacts in biomes limited by seasonality, which should be accounted for to realistically estimate future responses across open biomes under global change scenarios.

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Section: Climate Change Impacts On Ecosystem Services and Biodiversitymentioning

confidence: 99%

Woody plant encroachment intensifies under climate change across tundra and savanna biomes

Criado

Myers‐Smith

Bjorkman

et al. 2020

Global Ecol Biogeogr

Self Cite

144

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“…Ecological theory would suggest exclusion of one or the other life forms and not their coexistence, which is a defining characteristic of savanna (Sankaran et al, 2004). Over the last 5 decades, numerous mechanisms have been proposed to explain tree-grass coexistence (Bond, 2008;Lehmann and Parr, 2016;Ratnam et al, 2011;Scholes and Archer, 1997;Walter and Burnett, 1971). Contrasting conceptual models have been largely supported by empirical evidence, but no single model has emerged that provides a generic mechanism explaining coexistence across the three continents of the tropical savanna biome (Lehmann et al, 2014).…”

Section: Conceptual Models Of Tree and Grass Coexistencementioning

confidence: 99%

Challenges and opportunities in land surface modelling of savanna ecosystems

et al. 2017

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Abstract. The savanna complex is a highly diverse global biome that occurs within the seasonally dry tropical to subtropical equatorial latitudes and are structurally and functionally distinct from grasslands and forests. Savannas are open-canopy environments that encompass a broad demographic continuum, often characterised by a changing dominance between C 3 -tree and C 4 -grass vegetation, where frequent environmental disturbances such as fire modulates the balance between ephemeral and perennial life forms. Climate change is projected to result in significant changes to the savanna floristic structure, with increases to woody biomass expected through CO 2 fertilisation in mesic savannas and increased tree mortality expected through increased rainfall interannual variability in xeric savannas. The complex interaction between vegetation and climate that occurs in savannas has traditionally challenged terrestrial biosphere models (TBMs), which aim to simulate the interaction between the atmosphere and the land surface to predict responses of vegetation to changing in environmental forcing. In this review, we examine whether TBMs are able to adequately represent savanna fluxes and what implications potential deficiencies may have for climate change projection scenarios that rely on these models. We start by highlighting the defining characteristic traits and behaviours of savannas, how these differ across continents and how this information is (or is not) represented in the structural framework of many TBMs. We highlight three dynamic processes that we believe directly affect the water use and productivity of the savanna system: phenology, root-water access and fire dynamics. Following this, we discuss how these processes are represented in many current-generation TBMs and whether they are suitable for simulating savanna fluxes.Finally, we give an overview of how eddy-covariance observations in combination with other data sources can be usedPublished by Copernicus Publications on behalf of the European Geosciences Union. 4712 R. Whitley et al.: Land surface modelling of savanna ecosystems in model benchmarking and intercomparison frameworks to diagnose the performance of TBMs in this environment and formulate road maps for future development. Our investigation reveals that many TBMs systematically misrepresent phenology, the effects of fire and root-water access (if they are considered at all) and that these should be critical areas for future development. Furthermore, such processes must not be static (i.e. prescribed behaviour) but be capable of responding to the changing environmental conditions in order to emulate the dynamic behaviour of savannas. Without such developments, however, TBMs will have limited predictive capability in making the critical projections needed to understand how savannas will respond to future global change.

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“…Consequently, many effective techniques to restore temperate grasslands have been developed (Perrow & Davy, ; Jordan, ; Kiehl et al ., ; Freudenberger & Gibson‐Roy, ; Török et al ., ; Aronson, ; Marshall, Williams & Morgan, ). By contrast, recognition of the conservation values of tropical old‐growth grasslands has only emerged recently (Overbeck et al ., , , ; Bond & Parr, ; Laurance et al ., ; Parr et al ., ; Fernandes, ; Lehmann & Parr, ; Ratnam et al ., ; Silveira et al ., ), or where concern has existed, conservation emphasis has been placed on the management of populations of charismatic animals (African megafauna) or agricultural conversion (e.g. Ratter, Ribeiro & Bridgewater, ), rather than ecosystem restoration (but see Fernandes, ; Strassburg et al ., ).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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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.

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Tropical grassy biomes: linking ecology, human use and conservation

Cited by 77 publications

References 78 publications

Woody plant encroachment intensifies under climate change across tundra and savanna biomes

Woody plant encroachment intensifies under climate change across tundra and savanna biomes

Challenges and opportunities in land surface modelling of savanna ecosystems

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

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