Fire prevents woody encroachment only at higher‐than‐historical frequencies in a South African savanna

Case, Madelon F.; Staver, A. Carla

doi:10.1111/1365-2664.12805

Cited by 82 publications

(111 citation statements)

References 64 publications

(203 reference statements)

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“…Amid concerns that woody encroachment has become increasingly harder to control in savannas (Buitenwerf et al. , Case and Staver ), drought may serve as a harsh counterbalance, countering one form of vegetation transformation with another.…”

Section: Discussionmentioning

confidence: 99%

“…Amidst this uncertainty, savannas are already changing for other reasons: in recent decades, savannas around the world have experienced widespread woody encroachment (increasing woody biomass and cover), a trend likely driven by factors such as fire suppression and increasing atmospheric CO 2 (Naito and Cairns , Stevens et al. , , Case and Staver ). Will more intense drought exacerbate this trend, or mitigate it?…”

Section: Introductionmentioning

confidence: 99%

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Severe drought limits trees in a semi‐arid savanna

Case

Coetsee

Nzima

et al. 2019

Ecology

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Increasingly frequent and severe droughts under climate change are expected to have major impacts on vegetation worldwide. However, research to date has focused on tree vulnerability to drought in forests. Less is known about trees and drought in savannas, where a sparse tree layer coexists with grass. These tree–grass interactions (often mediated by fire and herbivory) shape savanna tree ecology, and confound predictions of how strongly drought might affect trees. On the one hand, drought is physiologically stressful, which could harm trees and be exacerbated by herbivore impacts; on the other hand, trees adapted to semiarid savannas might be relatively drought tolerant, and the considerable impacts of drought on grass could even benefit trees via reduced grass competition and fire risk, especially in the year following a drought. Here, we sought to understand the net effects of severe drought on the savanna tree layer, and how fire and herbivory mediate these effects. We monitored tree growth, mortality, and community structure for 2 yr within existing long‐term fire and herbivory experiments across a drought‐severity contrast, following a major drought in Kruger National Park, South Africa. Overall, severe drought was a major stressor for trees. Tree mortality rates in most species increased by an order of magnitude in the year following drought, and slower growth rates for some persisted for 2 yr. At the community level, this translated into substantial decreases in tree densities. Herbivory and fire did little either to mitigate or exacerbate drought effects on trees, and overall, drought swamped effects of herbivory and fire that have otherwise been observed. However, species differed in their responses to drought, with some dominant encroaching species especially vulnerable. We suggest that increasing drought frequency and severity could drastically alter savanna vegetation by repeatedly killing off trees.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Severe drought limits trees in a semi‐arid savanna

Case

Coetsee

Nzima

et al. 2019

Ecology

Self Cite

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“…A critical question in understanding savanna vegetation dynamics is how global‐scale factors interact with the local environment (Case & Staver, ). Previous research has debated the role of fire vs local edaphic factors in determining vegetation structure in northern Australia (Bowman, ; Craig, ; Douglas et al., ; Ondei et al., ).…”

Section: Discussionmentioning

confidence: 99%

Forgotten impacts of European land‐use on riparian and savanna vegetation in northwest Australia

Connor

Schneider

Trezise

et al. 2017

J Vegetation Science

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Questions Fire and livestock grazing are regarded as current threats to biodiversity and landscape integrity in northern Australia, yet it remains unclear what biodiversity losses and habitat changes occurred in the 19–20th centuries as livestock and novel fire regimes were introduced by Europeans. What baseline is appropriate for assessing current and future environmental change? Location Australia's Kimberley region is internationally recognized for its unique biodiversity and cultural heritage. The region is home to some of the world's most extensive and ancient rock art galleries, created by Aboriginal peoples since their arrival on the continent 65,000 years ago. The Kimberley is considered one of Australia's most intact landscapes and its assumed natural vegetation has been mapped in detail. Methods Interpretations are based on a continuous sediment record obtained from a waterhole on the Mitchell River floodplain. Sediments were analysed for geochemical and palynological proxies of environmental change and dated using 210Pb and 14C techniques. Results We show that the present‐day vegetation in and around the waterhole is very different to its pre‐European counterpart. Pre‐European riparian vegetation was dominated by Antidesma ghaesembilla and Banksia dentata, both of which declined rapidly at the beginning of the 20th century. Soon after, savanna density around the site declined and grasses became more prevalent. These vegetation shifts were accompanied by geochemical and biological evidence for increased grazing, local burning, erosion and eutrophication. Conclusions We suggest that the Kimberley region's vegetation, while maintaining a ‘natural’ appearance, has been altered dramatically during the last 100 years through grazing and fire regime changes. Landscape management should consider whether the current (impacted) vegetation is a desirable or realistic baseline target for biodiversity conservation.

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“…However, species functional traits may influence survival during fire, for example, while zoophagous and phytophagous arthropods are highly resilient to the effects of fire, mortality was higher for ground-litter saprophagous species (Moretti, Bello, Roberts, & Potts, 2009). Over the postfire period, fire usually transforms landscapes into more open habitat, which may change species composition over time (Case & Staver, 2017). In addition, long-term recolonization of burned habitat may be affected by transformation processes of the habitat, as the newly transformed habitat may yield different species composition.…”

Section: Introductionmentioning

confidence: 99%

Refuges from fire maintain pollinator–plant interaction networks

Adedoja

Dormann

Kehinde

et al. 2019

Ecology and Evolution

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Fire is a major disturbance factor in many terrestrial ecosystems, leading to landscape transformation in fire‐prone areas. Species in mutualistic interactions are often highly sensitive to disturbances like fire events, but the degree and complexity of their responses are unclear. We use bipartite insect–flower interaction networks across a recently burned landscape to explore how plant–pollinator interaction networks respond to a recent major fire event at the landscape level, and where fire refuges were present. We also investigate the effectiveness of these refuges at different elevations (valley to hilltop) for the conservation of displaced flower‐visiting insects during fire events. Then, we explore how the degree of specialization of flower‐visiting insects changes across habitats with different levels of fire impact. We did this in natural areas in the Greater Cape Floristic Region (GCFR) biodiversity hotspot, which is species rich in plants and pollinators. Bees and beetles were the most frequent pollinators in interactions, followed by wasps and flies. Highest interaction activity was in the fire refuges and least in burned areas. Interactions also tracked flower abundance, which was highest in fire refuges in the valley and lowest in burned areas. Interactions consisted mostly of specialized flower visitors, especially in refuge areas. The interaction network and species specialization were lowest in burned areas. However, species common to at least two fire classes showed no significant difference in species specialization. We conclude that flower‐rich fire refuges sustain plant–pollinator interactions, especially those involving specialized species, in fire‐disturbed landscape. This may be an important shelter for specialized pollinator species at the time that the burned landscape goes through regrowth and succession as part of ecosystem recovery process after a major fire event.

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Fire prevents woody encroachment only at higher‐than‐historical frequencies in a South African savanna

Cited by 82 publications

References 64 publications

Severe drought limits trees in a semi‐arid savanna

Severe drought limits trees in a semi‐arid savanna

Forgotten impacts of European land‐use on riparian and savanna vegetation in northwest Australia

Refuges from fire maintain pollinator–plant interaction networks

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