Sixteen hundred years of increasing tree cover prior to modern deforestation in Southern Amazon and Central Brazilian savannas

Wright, Jamie L.; Bomfim, Barbara; Wong, Corrine I; Marimon-Júnior, Ben Hur; Marimon, Beatriz Schwantes; Silva, Lucas C. R.

doi:10.1111/gcb.15382

Cited by 22 publications

(15 citation statements)

References 66 publications

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“…It is important to acknowledge that (a) nucleation will likely be weaker where frequent fires reduce canopy size and kill recruits, and that (b) forest expansion over savannas and grasslands can also proceed by alternate mechanisms, with the forest gradually expanding as a wave front or with tree density and cover simultaneously increasing in the whole area (Favier et al., 2004; Wright et al., 2021). However, the woody encroachment driven by nucleation that we described here for the first time in the Cerrado may be a widespread phenomenon in the whole biome wherever fire is suppressed, particularly in landscape mosaics where forest patches share the space with open savannas.…”

Section: Discussionmentioning

confidence: 99%

Section: Factors Explaining the Effectiveness Of Nucleation Among Nur...mentioning

confidence: 99%

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Facilitation by isolated trees triggers woody encroachment and a biome shift at the savanna–forest transition

Abreu

Durigan

Melo

et al. 2021

Journal of Applied Ecology

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1. Woody encroachment into grassy biomes is a global phenomenon, often resulting in a nearly complete turnover of species, with savanna specialists being replaced by forest-adapted species. Understanding the mechanisms involved in this change is important for devising strategies for managing savannas.2. We examined how isolated trees favour woody encroachment and species turnover by overcoming dispersal limitation and environmental filtering. In a savanna released from fire in south-eastern Brazil (Cerrado), we sampled woody plants establishing under 40 tree canopies and in paired treeless plots. These trees comprised eight species selected for habitat preference (savanna or forest) and dispersal syndrome (bird dispersed or not). We recorded dimensions of each tree, dispersal syndrome and habitat preference of recruits, and quantified the physical environment within each plot, aiming at a mechanistic understanding of woody encroachment.3. We found clear evidence that isolated trees cause nucleation and drive changes in functional composition of savanna. Effectiveness as nucleator differed among species, but was unrelated to their functional guilds (habitat preference or dispersal syndrome). The density of saplings in nuclei was partially explained by soil moisture (+), daily temperature amplitude (−) and sum of bases (−). 4. Our results indicate that isolated trees act first as perches, strongly favouring bird-dispersed species. They then act as nurse trees, considerably changing the environment in favour of forest-adapted recruits. In the long term, as the nuclei expand and merge, savanna specialists tend to disappear and the savanna turns into a low-diversity forest. Synthesis and applications.Fire suppression has allowed the nucleation process and consequently the woody encroachment and fast replacement of savanna specialists by forest species in the Cerrado. By elucidating the mechanisms behind woody encroachment, we recommend using prescribed fires to burn forest seedlings and to reduce tree canopy size wherever the management goal is to maintain the typical savanna structure and composition.

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Section: Discussionmentioning

confidence: 99%

Section: Factors Explaining the Effectiveness Of Nucleation Among Nur...mentioning

confidence: 99%

Facilitation by isolated trees triggers woody encroachment and a biome shift at the savanna–forest transition

Abreu

Durigan

Melo

et al. 2021

Journal of Applied Ecology

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“…a combination of pollen records, phytolith, and δ 13 C values), there was a shift in land use from savanna to forests in the last 6 ka years in areas of the transition between Cerrado and Mata Atlântica biomes in southeastern Brazil (Behling & Lichte, 1997; Gouveia et al, 2002; Ledru et al, 2016). Notably, the shift from a dry period (12–6 ka year BP) to more humid conditions (starting 6 ka year BP) led to the expansion of forest fragments (Mata Atlântica biome) over savannas (Cerrado biome) only in the gradual transition between rainforest and savannas (Scheel‐Ybert et al, 2003; Ledru et al, 2009; Arruda et al, 2018; Wright et al, 2021).…”

Section: Discussionmentioning

confidence: 99%

“…Notably, the shift from a dry period (12-6 ka year BP) to more humid conditions (starting 6 ka year BP) led to the expansion of forest fragments (Mata Atlântica biome) over savannas (Cerrado biome) only in the gradual transition between rainforest and savannas (Scheel-Ybert et al, 2003;Ledru et al, 2009;Arruda et al, 2018;Wright et al, 2021).…”

Section: Scenario 1: Vegetation Adding Large Quantities Of Carbon Int...mentioning

confidence: 99%

Carbon stocks in umbric ferralsols driven by plant productivity and geomorphic processes, not by mineral protection

Martinez

Silva

Calegari

et al. 2021

Earth Surf Processes Landf

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Umbric ferralsols (UF) have organic carbon stocks within the first 1 m of soil profile depth that are nearly double the size (~19 kg C m−2) compared to the average carbon stocks of all other ferralsols (~10 kg C m−2). Here, we investigate processes that allow UF to gain and maintain such extraordinary carbon stocks. Using the International Soil Research and Information Center database, complemented with recently published datasets, we show that the carbon saturation capacity of the clay + silt fractions in UF (22.8 ± 5.7 g C kg−1 soil, n = 59) does not exceed the carbon saturation capacity in other ferralsols (23.3 ± 6.2 g C kg−1 soil, n = 165), thus eliminating a particularly retentive mineral matrix as a possible explanation. Rather, carbon stocks were correlated with the thickness of A horizons (106 ± 49 cm, n = 59 in umbric versus 35 ± 22 cm, n = 165 in non‐umbric ferralsols). We subsequently hypothesized that differences in A‐horizon thickness arose from two pedogenic scenarios: (i) superior carbon accrual resulting from a unique vegetation cover capable of allocating large quantities of carbon to belowground plant organs; and (ii) geomorphic processes that led to carbon burial. We evaluated the plausibility of these scenarios considering landscape history and associated carbon flux rates, hillslope position, as well as δ13C values and Ti/Zr ratios for subsets of ferralsol profiles studied by us in a region that encompasses latitudes from 26 to 7°S in eastern Brazil. We found that exceptional carbon stocks were most prevalent in the gradual transition zone (ecotone) between savanna and rainforest, likely resulting from erosion–deposition processes, historic changes of vegetation cover composed of grasses and arboreal elements, and active bioturbation. We suggest that attempts to sequester carbon in non‐umbric ferralsols will be most successful if they emulate or promote the biotic and abiotic processes prevalent in the savanna/rainforest ecotone.

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“…An alternative possibility is that savanna-forest boundaries may be highly dynamic over longer time-scales (Schwartz et al, 1986, West et al ., 2000, Staver et al , 2017, Aleman et al 2019) and in response to changing climate or climate events (Hirota el al , 2010, Breman et al, 2012, Beckett & Bond, 2019, Wright et al, 2021, Sato et al , 2021). Spatially explicit modelling work has argued that fires at the savanna-forest boundary can have major effects on the biogeographic distribution of biomes (Staver et al , 2011b, van de Leemput et al , 2015, Goel et al , 2020a, Goel et al , 2020b, Wuyts et al , 2019) and local observations confirm that boundaries are sometimes dynamic through time (Brook & Bowman, 2006, Silva et al , 2008, Ibanez et al , 2013, Beckett & Bond, 2019).…”

Section: Introductionmentioning

confidence: 99%

Pathways of savannization in a mesic African savanna-forest mosaic following an extreme fire

Beckett

Charles‐Dominique

et al. 2021

Preprint

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Typically, savannas experience frequent fires, which limit tree cover and promote flammable grass accumulation, whereas forests form dense canopies that exclude fires by reducing C4-grass fuel loads and creating a humid microclimate. However, extreme fires occasionally burn into forests. Although these are known to kill forest trees and can make repeat fires more likely, the long-term consequences of an extreme fire event for forest structure and potential forest savannization remain largely unknown. Here, we analysed whether an extreme fire event could, alone, alter forest species composition, vegetation structure, and fire regimes, or whether successive fires after an initial extreme fire event were necessary to trigger a biome transition. We found that forests that only burned once recovered, whereas those that burned again following an initial extreme fire event underwent a transition from closed-canopy forests to open, grassy systems. Our results suggest that, while extreme fires set the stage for a biome transition, subsequent fires are necessary for flammable grasses to colonise and establish, ultimately resulting in a savanna fire regime.

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Sixteen hundred years of increasing tree cover prior to modern deforestation in Southern Amazon and Central Brazilian savannas

Cited by 22 publications

References 66 publications

Facilitation by isolated trees triggers woody encroachment and a biome shift at the savanna–forest transition

Facilitation by isolated trees triggers woody encroachment and a biome shift at the savanna–forest transition

Carbon stocks in umbric ferralsols driven by plant productivity and geomorphic processes, not by mineral protection

Pathways of savannization in a mesic African savanna-forest mosaic following an extreme fire

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