Limited increases in savanna carbon stocks over decades of fire suppression

Zhou, Yuehan; Singh, Jenia; Butnor, John R.; Coetsee, Corli; Boucher, Peter; Case, Madelon F.; Hockridge, Evan G.; Davies, Andrew B.; Staver, A. Carla

doi:10.1038/s41586-022-04438-1

Cited by 55 publications

(56 citation statements)

References 52 publications

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“…Land fragmentation disrupts fire regimes and restricts animal movements (Rosan et al, 2019; Stevens et al, 2017) with the global burned area having declined by 25% in the last two decades, and where the largest decreases occurred in tropical grassy ecosystems (Andela et al, 2017). Long‐term fire exclusion experiments demonstrate encroachment (Woinarski et al, 2004; Zhou et al, 2022), while fire suppression policies have favored encroachment in regions such as the Cerrado (Abreu et al, 2017). By altering light and water availability, fire regimes, herbivory, soil characteristics, or competition for space, encroachment can affect different plant taxonomic and functional groups.…”

Section: Introductionmentioning

confidence: 99%

Encroachment diminishes herbaceous plant diversity in grassy ecosystems worldwide

Wieczorkowski

Lehmann

2022

Global Change Biology

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Woody encroachment is ubiquitous in grassy ecosystems worldwide, but its global impacts on the diversity of herbaceous plants that characterise and define these ecosystems remain unquantified. The pervasiveness of encroachment is relatively easily observed via remote sensing, but its impacts on plant diversity and richness below the canopy can only be observed via field‐based studies. Via a meta‐analysis of 42 field studies across tropical to temperate grassy ecosystems, we quantified how encroachment altered herbaceous species richness, and the richness of forbs, C3 graminoids and C4 graminoids. Across studies, the natural logarithm of the response ratio (lnRR) of herbaceous species richness ranged from −3.33 to 0.34 with 87% of encroached ecosystems negatively impacted. Assessment of the extent of encroachment, duration of encroachment, mean annual rainfall, latitude, and continent demonstrated that only extent of encroachment had relevance in the data (univariate model including a random effect of study explained 45.4% of variance). The global weighted mean lnRR of species richness decreased from −0.245 at <33% of woody cover increase, to −0.562 at 33%–66%, and to −0.962 at >66%. Continued encroachment results in substantial loss of herbaceous diversity at medium and high extents, with a loss of richness that is not replaced. Although all functional groups are significantly negatively impacted by encroachment, forb richness is relatively more sensitive than graminoid richness, and C4 graminoid richness relatively more than C3 graminoid richness. Although no geographic or climatic correlates had relevance in the data, encroachment as an emergent product of global change coalesces to decrease ground layer light availability, lead to loss of fire and grazers, and alter hydrology and soils. Encroachment is accelerating and grassy ecosystems require urgent attention to determine critical woody cover thresholds that facilitate diverse and resilient grassy ecosystems.

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Section: Introductionmentioning

confidence: 99%

Encroachment diminishes herbaceous plant diversity in grassy ecosystems worldwide

Wieczorkowski

Lehmann

2022

Global Change Biology

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“…Sustained active fire exclusion leads to tree encroachment and ultimately conversion of savanna to forest, resulting in dramatic losses in herbaceous diversity (Abreu et al, 2017; Stevens et al, 2017). The loss of herbaceous diversity can represent a significant loss of belowground carbon stocks, given that many herbaceous plants maintain large belowground storage organs (Fidelis, Di Santi lyra & Pivelllo, 2013; Ottaviani et al, 2020; Zhou et al, 2022).…”

Section: Discussionmentioning

confidence: 99%

Flammability in tropical savannas: Variation among growth forms and seasons in Cerrado

2022

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Bradstock, 2010), which is the capacity of different plants and its components to burn and sustain a flame after encountering an ignition source (Anderson, 1970;Pausas, Keeley, & Schwilk, 2017). The most fire-prone ecosystems globally are tropical savannas (Bond & Van Wilgen, 1996;Simpson et al., 2016), covering about 20% of the Earth's land surface, due to the combination of highly seasonal rainfall and a continuous herbaceous layer that is typically dominated

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“…On the root economics space (Bergmann et al, 2020), savanna plant species may tend to allocate more carbon belowground and to develop root traits that are long-lived and well-protected in a frequently burned environment (Figure 1B). There is robust evidence from both experimental studies and field observations that savanna plant species experiencing frequent fires have a larger root mass fraction than those growing free from fires both at the individual species level and ecosystem level (Figure 1C, Table 1) (Boonman et al, 2020;Teixeira et al, 2022;Zhou et al, 2022). Likewise, savanna plant species persisting through frequent fires generally store large amounts of non-structural carbohydrates in specialized root organs (e.g., lignotubers) (Wigley et al, 2009;Clarke et al, 2016;Diaz-Toribio and Putz, 2021), which are critical to support root bud banks and the ability of root sucker for postfire resprouting (Charles-Dominique et al, 2015;da Silva et al, 2020).…”

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confidence: 86%

Root traits in response to frequent fires: Implications for belowground carbon dynamics in fire-prone savannas

Zhou

2023

Front. Plant Sci.

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Predicting how belowground carbon storage reflects changes in aboveground vegetation biomass is an unresolved challenge in most ecosystems. This is especially true for fire-prone savannas, where frequent fires shape the fraction of carbon allocated to root traits for post-fire vegetation recovery. Here I review evidence on how root traits may respond to frequent fires and propose to leverage root traits to infer belowground carbon dynamics in fire-prone savannas. Evidently, we still lack an understanding of trade-offs in root acquisitive vs. conservative traits in response to frequent fires, nor have we determined which root traits are functionally important to mediate belowground carbon dynamics in a frequently burned environment. Focusing research efforts along these topics should improve our understanding of savanna carbon cycling under future changes in fire regimes.

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Limited increases in savanna carbon stocks over decades of fire suppression

Cited by 55 publications

References 52 publications

Encroachment diminishes herbaceous plant diversity in grassy ecosystems worldwide

Encroachment diminishes herbaceous plant diversity in grassy ecosystems worldwide

Flammability in tropical savannas: Variation among growth forms and seasons in Cerrado

Root traits in response to frequent fires: Implications for belowground carbon dynamics in fire-prone savannas

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