Savanna fire regimes depend on grass trait diversity

Simpson, Kimberley J.; Archibald, Sally; Osborne, Colin P.

doi:10.1016/j.tree.2022.04.010

Cited by 12 publications

(9 citation statements)

References 71 publications

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“…Most notably, longleaf pine savannas occur in regions with less seasonality in rainfall compared to tropical savannas on other continents (see Figure S1 in Supporting Information). Because seasonal drought is considered a necessary condition for fire in other tropical savanna regions, the role of plant traits, such as the flammability of wiregrass and longleaf pine's long needles, help explain convergent fire regimes in climatically dissimilar regions (Archibald et al, 2018; Fill et al, 2012; Platt et al, 2016; Simpson et al, 2022).…”

Section: The Unique Climate and Structure Of Longleaf Pine Savannasmentioning

confidence: 99%

“…Because seasonal drought is considered a necessary condition for fire in other tropical savanna regions, the role of plant traits, such as the flammability of wiregrass and longleaf pine's long needles, help explain convergent fire regimes in climatically dissimilar regions (Archibald et al, 2018;Fill et al, 2012;Platt et al, 2016;Simpson et al, 2022).…”

Section: P Palustris Southern United Statesmentioning

confidence: 99%

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Longleaf pine savannas reveal biases in current understanding of savanna biogeography

Pau,

Griffith,

Zampieri

et al. 2023

Global Ecol Biogeogr

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Biased understanding of savanna biogeographyGrasslands and savannas exist across a wide range of climates. Mesic savannas, with highly variable tree densities, are particularly misunderstood and understudied in comparison to arid and semi‐arid savannas. North America contains historically extensive mesic savannas dominated by longleaf pine. Longleaf pine savannas may have once been the largest savanna type on North America, yet these ecosystems have been overlooked in global syntheses. Excluding these “Forgotten Ecosystems” from global syntheses biases our understanding of savanna biogeography and distribution.Evolutionary history and distinct climate of longleaf savannasWe assessed the evolutionary history and biogeography of longleaf pine savannas. We then harmonize plot data from longleaf savannas with plot data from valuable existing global synthesis of savannas on other continents. We show that longleaf pine savannas occur in a strikingly distinct climate space compared to savannas on Africa, Australia, and South America, and are unique in having wide ranging tree basal areas.Future directionsGrass‐dominated ecosystems are increasingly recognized as being ancient and biologically diverse, yet threatened and undervalued. A new synthesis of savanna ecosystems considering their full range of distributions is needed to understand their ecology and conservation status. Interestingly, the closest analogues to North American savannas and their relatives in Mesoamerica and the Caribbean may be Asian savannas, which also contain mesic fire‐driven pine savannas and have been similarly neglected in existing global syntheses.

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Section: The Unique Climate and Structure Of Longleaf Pine Savannasmentioning

confidence: 99%

Section: P Palustris Southern United Statesmentioning

confidence: 99%

Longleaf pine savannas reveal biases in current understanding of savanna biogeography

Pau,

Griffith,

Zampieri

et al. 2023

Global Ecol Biogeogr

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“…Existing research typically only focuses on the relationship between climatic pressures and vegetation response, without accounting for the influence of ecosystem characteristics on how vegetation responds to different stressors. Furthermore, most recent studies on these environmental characteristics are site‐specific and rely on limited data (de Oliveira et al., 2019; Hartnett et al., 2013; Simpson et al., 2022; Van Coller et al., 2021; Wigley‐Coetsee & Staver, 2020). A comprehensive understanding of the interplay between ecosystem characteristics and pressures requires an expanded analysis framework.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, savanna landscapes are inherently heterogeneous (Levick et al., 2012). The response to similar drivers may vary among savanna landscapes due to underlying ecosystem characteristics, including climate, solar radiation, soil traits, topography, vegetation type and soil moisture (Cardoso et al., 2022; Simpson et al., 2022). Existing research typically only focuses on the relationship between climatic pressures and vegetation response, without accounting for the influence of ecosystem characteristics on how vegetation responds to different stressors.…”

Section: Introductionmentioning

confidence: 99%

Wetness severity increases abrupt shifts in ecosystem functioning in arid savannas

Vermeulen,

Verbist,

Van Meerbeek

et al. 2024

Global Change Biology

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The accelerating pace of climate change has led to unprecedented shifts in surface temperature and precipitation patterns worldwide, with African savannas being among the most vulnerable regions. Understanding the impacts of these extreme changes on ecosystem health, functioning and stability is crucial. This paper focuses on the detection of breakpoints, indicative of shifts in ecosystem functioning, while also determining relevant ecosystem characteristics and climatic drivers that increase susceptibility to these shifts within the semi‐arid to arid savanna biome. Utilising a remote sensing change detection approach and rain use efficiency (RaUE) as a proxy for ecosystem functioning, spatial and temporal patterns of breakpoints in the savanna biome were identified. We then employed a novel combination of survival analysis and remote sensing time series analysis to compare ecosystem characteristics and climatic drivers in areas experiencing breakpoints versus areas with stable ecosystem functioning. Key ecosystem factors increasing savanna breakpoint susceptibility were identified, namely higher soil sand content, flatter terrain and a cooler long‐term mean temperature during the wet summer season. Moreover, the primary driver of changes in ecosystem functioning in arid savannas, as opposed to wetter tropical savannas, was found to be the increased frequency and severity of rainfall events, rather than drought pressures. This research highlights the importance of incorporating wetness severity metrics alongside drought metrics to comprehensively understand climate–ecosystem interactions leading to abrupt shifts in ecosystem functioning in arid biomes. The findings also emphasise the need to consider the underlying ecosystem characteristics, including soil, topography and vegetation composition, in assessing ecosystem responses to climate change. While this research primarily concentrated on the southern African savanna as a case study, the methodological robustness of this approach enables its application to diverse arid and semi‐arid biomes for the assessment of climate–ecosystem interactions that contribute to abrupt shifts.

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“…The desiccation of leaf material could lead to dehydration of the entire above‐ground portion of the plant. Given that foliage moisture content and total biomass are linked to fire intensity and its rate of spread (Simpson et al, 2022), the linkages between drought tolerance and plant size could massively impact ecosystem fire dynamics.…”

Section: Introductionmentioning

confidence: 99%

Coordination of hydraulic and morphological traits across dominant grasses in eastern Australia

et al. 2023

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Leaf hydraulic traits characterize plant drought tolerance and responses to climate change. Yet, plant hydraulics are biased towards northern hemisphere woody species. We collected rhizomes of several perennial grass species along a precipitation gradient in eastern Australia and grew them in an experimental pot study to investigate potential trade‐offs between drought tolerance and plant morphology. We measured the following leaf hydraulic traits: the leaf water potential (Ψleaf) at 50% and 88% loss of leaf hydraulic conductance (P50Kleaf and P88Kleaf), the Ψleaf at 50% loss of stomatal conductance (P50gs), leaf turgor loss point (TLP), leaf dry matter content (LDMC), leaf modulus of elasticity (ε), and the slope of the relationship between predawn and midday Ψleaf. We also measured basal area, tiller density, seed head density, root collar diameter, plant height, and aboveground biomass of each individual. As expected, grass species varied widely in leaf‐level drought tolerance, with loss of 88% hydraulic conductance occurring at a Ψleaf ranging from −1.52 to −4.01 MPa. However, all but one species lost leaf turgor, and most reached P50gs before this critical threshold. Taller more productive grass species tended to have drought vulnerable leaves characterized by low LDMC and less negative P88Kleaf. Species with greater tiller production experienced stomatal closure and lost turgor at more negative Ψleaf. Although our sample size was limited, we found no relationships between these species' traits and their climate of origin. Overall, we identified important hydraulic and morphological trade‐offs in Australian grasses that were surprisingly similar to those observed for woody plants: (1) xylem of taller species was less drought tolerant and (2) turgor loss occurs and stomatal closure begins before significant loss of Kleaf. These data build upon a small yet growing field of grass hydraulics and may be informative of species responses to further drought intensification in Australia. Read the free Plain Language Summary for this article on the Journal blog.

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Savanna fire regimes depend on grass trait diversity

Cited by 12 publications

References 71 publications

Longleaf pine savannas reveal biases in current understanding of savanna biogeography

Longleaf pine savannas reveal biases in current understanding of savanna biogeography

Wetness severity increases abrupt shifts in ecosystem functioning in arid savannas

Coordination of hydraulic and morphological traits across dominant grasses in eastern Australia

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