The role of fire in preventing transitions from a grass dominated state to a bush thickened state in arid savannas

Joubert, David; Smit, G.N.; Hoffman, M. Timm

doi:10.1016/j.jaridenv.2012.06.012

Cited by 54 publications

(42 citation statements)

References 30 publications

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“…Both these highly palatable perennial grasses are common in the T. prunioides shrubland (Strohbach, 2014) and are usually planted for hay and pasture (van Oudtshoorn, 2016;Sweet & Burke, 2006). The expansion of monoculture farming in the Tsumeb region, particularly from the 1980s (Lau & Reiner, 1993), is also suggested by decreases in charcoal flux and Gelasinospora signals (Figures 2 and 3) toward zone 3, which in turn suggest the suppression of wildfire and/or the reduction of controlled fires to conserve pastures for livestock (Joubert, Smit, & Hoffman, 2012). …”

Section: Fire Managementmentioning

confidence: 99%

“…For example, while climate shifts are considered the main driver of changes in the grass/woody vegetation ratio on a long timescale (Gil-Romera et al, 2010;Scott et al, 1991), changes in grazing pressure and fire, besides stochastic variations in rainfall, are thought to drive decadal-scale variability (Gillson, 2004;van Rooyen et al, 2018). Interestingly, different studies have shown that precipitation, fire, and herbivory may have different effects on encroacher species, and thus a different effect on savanna stability (Joubert et al, 2008;Joubert, Smit, & Hoffman, 2012. Hence, disentangling triggers that induce changes of state, as well as understanding stabilizing feedbacks, requires long time series with adequate taxonomic resolution.…”

Section: Introductionmentioning

confidence: 99%

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Vegetation state changes in the course of shrub encroachment in an African savanna since about 1850 CE and their potential drivers

Tabares

Zimmermann

Dietze

et al. 2019

Ecology and Evolution

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1. Shrub encroachment has far-reaching ecological and economic consequences in many ecosystems worldwide. Yet, compositional changes associated with shrub encroachment are often overlooked despite having important effects on ecosystem functioning.2. We document the compositional change and potential drivers for a northern Namibian Combretum woodland transitioning into a Terminalia shrubland. We use a multiproxy record (pollen, sedimentary ancient DNA, biomarkers, compoundspecific carbon (δ 13 C) and deuterium (δD) isotopes, bulk carbon isotopes (δ 13 Corg), grain size, geochemical properties) from Lake Otjikoto at high taxonomical and temporal resolution.3. We provide evidence that state changes in semiarid environments may occur on a scale of one century and that transitions between stable states can span around 80 years and are characterized by a unique vegetation composition. We demonstrate that the current grass/woody ratio is exceptional for the last 170 years, as supported by n-alkane distributions and the δ 13 C and δ 13 Corg records. Comparing vegetation records to environmental proxy data and census data, we infer a complex network of global and local drivers of vegetation change. While our δD record suggests physiological adaptations of woody species to higher atmospheric pCO 2 concentration and drought, our vegetation records reflect the impact of broadscale logging for the mining industry, and the macrocharcoal record suggests a decrease in fire activity associated with the intensification of farming. Impact of selective grazing is reflected by changes in abundance and taxonomical composition of grasses and by an increase of nonpalatable and trampling-resistant taxa.In addition, grain-size and spore records suggest changes in the erodibility of soils because of reduced grass cover. | 963TABARES ET Al.

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Section: Fire Managementmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Vegetation state changes in the course of shrub encroachment in an African savanna since about 1850 CE and their potential drivers

Tabares

Zimmermann

Dietze

et al. 2019

Ecology and Evolution

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“…Independent of elephant effects, savanna regions are being increasingly recognized as critical to the regulation of the terrestrial carbon cycle (Ahlström et al, ; Poulter et al, ) and many savannas are undergoing rapid rates of woody vegetation growth and encroachment (Archer et al, ; Asner, Elmore, Olander, Martin, & Harris, ; Poulter et al, ; Stevens, Lehmann, Murphy, & Durigan, ; but see Brandt et al, ) due to changing fire and rainfall regimes (Joubert, Smit, & Hoffman, ; Kulmatiski & Beard, ), altered herbivore populations (Daskin, Stalmans, & Pringle, ; Roques, O'Connor, & Watkinson, ), and increased levels of atmospheric CO 2 that favor tree growth (Buitenwerf, Bond, Stevens, & Trollope, ; Higgins & Scheiter, ; but see Archer, Schimel, & Holland, ). Woody vegetation growth and encroachment could therefore compensate for potential elephant effects on savanna carbon stocks.…”

Section: Introductionmentioning

confidence: 99%

Elephants limit aboveground carbon gains in African savannas

Davies

Asner

2019

Global Change Biology

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Understanding the drivers of vegetation carbon dynamics is essential for climate change mitigation and effective policy formulation. However, most efforts focus on abiotic drivers of plant biomass change, with little consideration for functional roles performed by animals, particularly at landscape scales. We combined repeat airborne Light Detection and Ranging with measurements of elephant densities, abiotic factors, and exclusion experiments to determine the relative importance of drivers of change in aboveground woody vegetation carbon stocks in Kruger National Park, South Africa. Despite a growing elephant population, aboveground carbon density (ACD) increased across most of the landscape over the 6‐year study period, but at fine scales, bull elephant density was the most important factor determining carbon stock change, with ACD losses recorded only where bull densities exceeded 0.5 bulls/km2. Effects of bull elephants were, however, spatially restricted and landscape dependent, being especially pronounced along rivers, at mid‐elevations, and on steeper slopes. In contrast, elephant herds and abiotic drivers had a comparatively small influence on the direction or magnitude of carbon stock change. Our findings demonstrate that animals can have a substantive influence on regional‐scale carbon dynamics and warrant consideration in carbon cycling models and policy formulation aimed at carbon management and climate change mitigation.

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“…Periods of occupation should be relatively short, and adequate rest periods should be allowed between successive grazing periods (Kirkman, 2002a;2002b). Fire should definitely not be applied in the more arid areas as an aid to increase animal production, but rather to eradicate undesirable plant encroachment (Trollope, 2009;Joubert et al, 2012). According…”

Section: General Conclusion and Management Aspects After Burningmentioning

confidence: 99%

“…These conditions seldom become a problem in arid and semi-arid rangelands and, therefore, burning is deemed to be unnecessary (Snyman, 2003a). On the other hand, the abundance of undesirable shrub and tree encroachment in arid and semi-arid areas can also successfully be controlled by fire (Zimmerman et al, 2010;Joubert et al, 2012;O'Connor et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Short-Term Responses of Southern African Semi-Arid Rangelands to Fire: A Review of Impact on Plants

Snyman

2014

Arid Land Research and Management

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The influence of fire on the ecosystem in the higher rainfall ''sour'' rangeland areas of southern Africa has been well established; however, less information is available for arid and semi-arid ''sweet'' rangeland areas. Sour and sweet rangeland areas can be defined as receiving higher and lower than approximately 600 mm of rainfall, respectively. This review uses a South African case study (experimental plot data) to elevate the research on short-term fire responses in arid and semi-arid climates. Burned rangeland took at least two full growing seasons to recover in terms of above-and belowground phytomass production and water-use efficiency (WUE). The initial advantage in quality (crude protein) accompanying fire did not neutralize the reduction in half of the aboveground phytomass production and poor WUE occurring in the first season following the fire. The belowground growth was more sensitive to burning than aboveground growth. Seasonal aboveground phytomass production loss to fire which was a function of the amount and distribution of rainfall varied between 238 and 444 kg ha À1 for semi-arid rangeland. The importance of correct timing in the utilization of burned semi-arid rangeland, with respect to sustained high production, cannot be overemphasized. In arid and semi-arid rangeland areas, fire as a management tool is questionable if there is no specific purpose for it, which also can increase ecological and financial risk management in the short-term.

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The role of fire in preventing transitions from a grass dominated state to a bush thickened state in arid savannas

Cited by 54 publications

References 30 publications

Vegetation state changes in the course of shrub encroachment in an African savanna since about 1850 CE and their potential drivers

Vegetation state changes in the course of shrub encroachment in an African savanna since about 1850 CE and their potential drivers

Elephants limit aboveground carbon gains in African savannas

Short-Term Responses of Southern African Semi-Arid Rangelands to Fire: A Review of Impact on Plants

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