Persistent Effects of Chemicals Used to Control Shrub Densification in Semi-Arid Savanna

Bezuidenhout, H.; Kraaij, Tineke; Baard, Johan A.

doi:10.5539/esr.v4n1p31

Cited by 5 publications

(16 citation statements)

References 13 publications

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“…A. mellifera, on the other hand, requires exceptionally good rainfall in order to produce large crops of viable seed, while seeds may be absent, sterile or highly predated in years with low or moderate rainfall (Joubert et al 2013;Bezuidenhout et al, 2015). This possibly explains why we do not see a recovery in A. mellifera numbers within the time frame of this study.…”

Section: Discussioncontrasting

confidence: 39%

Some ecological side-effects of chemical and physical bush clearing in a southern African rangeland ecosystem

Haussmann

Kalwij

Bezuidenhout

2016

South African Journal of Botany

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1 Highlights Some ecological side-effects of bush thickening treatments were evaluated  No effect on non-targeted tree species was found 24-36 months post treatment  Both treatments were colonized by undesired sagebush Pechuel-loeschea leubnitziae  Perennial grass species were particularly abundant in physically treated sites  A side-effect of arborocide treatment: facilitating fast-growing, undesired species 2 AbstractBush thickening is a major concern to farmers of arid and semi-arid rangelands; reactive intervention remains the norm. Here we compared some of the short-term ecological implications of chemical and physical removal of the bush encroacher Acacia mellifera in the central Highland savanna of Namibia. We selected 21 invaded sites, 7 had been chemically cleared, 7 had been physically cleared and 7 had never been cleared. From each site, we recorded grass species composition, as well as the densities of A. mellifera, the undesired perennial shrub Pechuel-loeschea leubnitziae and a non-targeted tree A. erioloba, 24-30 months post-treatment.We fitted one-way ANOVA models to test for the effect of treatment on grass species richness and density of targeted and non-targeted tree species. A Canonical Correspondence Analysis was used to determine how treatment affected grass species composition. While both treatments reduced the density of the bush encroacher, P. leubnitziae effectively replaced A. mellifera in chemically treated sites, where die-back presumably happened faster and nutrient and water competition decreased more rapidly. In such sites, perennial grass species were effectively outcompeted by P. leubnitiziae.

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Section: Discussioncontrasting

confidence: 39%

Some ecological side-effects of chemical and physical bush clearing in a southern African rangeland ecosystem

Haussmann

Kalwij

Bezuidenhout

2016

South African Journal of Botany

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“…Due to the global nature of some of the determinants of woody encroachment, as well as the legacy of historical land‐use practises, the options available to managers to prevent or reverse the process are limited. Mechanical (Brudvig & Asbjornsen ) or chemical (Bezuidenhout, Kraaij & Baard ) control methods are sometimes employed, but are expensive, unfeasible over large areas and often ecologically undesirable. An alternative is to manipulate and actively manage the locally controllable determinants, by reducing grazing pressure, increasing browsing and promoting an appropriate fire regime (Staver et al .…”

Section: Introductionmentioning

confidence: 99%

An examination of the potential efficacy of high‐intensity fires for reversing woody encroachment in savannas

Smit

Asner

Govender

et al. 2016

Journal of Applied Ecology

103

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1. Frequent fires are often proposed as a way of preventing woody encroachment in savannas, yet few studies have examined whether high-intensity fires can effectively reverse woody encroachment. 2. We applied successive fire treatments to examine the effect of fire intensity on woody vegetation structure. The treatments included early dry season, low-intensity fires; late dry season, higher-intensity fires; and an unburnt control. We used pre-and post-fire airborne LiDAR to compare vegetation structural changes brought about by fires of different intensity. 3. Early dry season fires were of lower intensity (1400-2100 kW m À1 ) than late dry season fires (2500-4300 kW m À1 ). The two treatments also differed in terms of fuel consumed, scorch heights and char heights, indicating that clear differences in fire intensity and severity were achieved. 4. After 4 years and two fire applications, relative woody cover increased by between 20 and 110% in different height categories following low-intensity and control treatments and declined by between 3 and 70% following high-intensity fire treatments. Declines were markedly higher following two repeated high-intensity fires than following a high and then a moderate-intensity fire. Because woody shrubs in lower height classes can recover rapidly, repeated high-intensity fires would be needed to maintain lower cover. 5. Tall trees are often assumed to be unaffected by fires. However, we found that the rate of tree loss was directly related to fire intensity, where 36% of trees were lost following repeated high-intensity fires, compared to 22% after a high-and then a moderate-intensity fire and 6% after two low-intensity fires (3% without fire). 6. Synthesis and applications. Using LiDAR data we show that high-intensity fires can, at least in the short term, significantly reduce woody cover in South African savannas. The use of repeated high-intensity fires simultaneously causes both a positive (reduction in cover of short shrubs) and a negative (loss of tall trees) outcome, and managers need to make tradeoffs when contemplating the use of fire intensity to achieve specific goals. One potential solution may be to repeatedly apply high-intensity treatments to some areas, and not to others. This could generate a heterogeneous landscape where grasses become dominant and tall trees become scarce in some places, but in others, tall trees persist (or at least decline at slower rates), and shorter woody shrubs increase in dominance. Whether this would be acceptable, or practical, remains to be tested.

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“…Various localized management interventions are implemented to reduce woody cover encroachment. These include mechanical clearing, poisoning of woody plants (sometimes through aerial spraying) (Bezuidenhout et al 2015) or changed fire regimes (increased fire intensity and frequency) (Smit et al 2016). Even though these interventions may sometimes be successful at a local scale in reducing woody cover, there are trade-offs, and they may have to be continuously repeated since the driver of change (i.e., increased carbon dioxide) is not addressed (Table 3).…”

Section: Current Management Options and The Nffmentioning

confidence: 99%

“…On the other hand, aerial poisoning on savanna systems was identified as the only management option negatively impacting nature for its potential to remove non-target species (Bezuidenhout et al 2015). In some cases, benefits will be context dependent within the NN component.…”

Section: Cross-case Study Comparisonmentioning

confidence: 99%

Managing biodiversity in the Anthropocene: discussing the Nature Futures Framework as a tool for adaptive decision-making for nature under climate change

Palacios‐Abrantes

Badhe²,

Bamford

et al. 2022

Sustain Sci

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Conservation approaches to social-ecological systems have largely been informed by a framing of preserving nature for its instrumental societal benefits, often ignoring the complex relationship of humans and nature and how climate change might impact these. The Nature Futures Framework (NFF) was developed by the Task Force on scenarios and models of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services as a heuristic approach that appreciates the diverse positive values of nature and its contribution to people. In this overview, we convene a group of experts to discuss the NFF as a tool to inform management in social-ecological systems facing climate change. We focus on three illustrative case studies from the global south across a range of climate change impacts at different ecological levels. We find that the NFF can facilitate the identification of trade-offs between alternative climate adaptation pathways based on different perspectives on the values of nature they emphasize. However, we also identify challenges in adopting the NFF, including how outputs can be translated into modeling frameworks. We conclude that using the NFF to unpack diverse management options under climate change is useful, but that there are still gaps where more work needs to be done to make it fully operational. A key conclusion is that a range of multiple perspectives of people’s values on nature could result in adaptive decision-making and policy that is resilient in responding to climate change impacts in social-ecological systems.

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Persistent Effects of Chemicals Used to Control Shrub Densification in Semi-Arid Savanna

Cited by 5 publications

References 13 publications

Some ecological side-effects of chemical and physical bush clearing in a southern African rangeland ecosystem

Some ecological side-effects of chemical and physical bush clearing in a southern African rangeland ecosystem

An examination of the potential efficacy of high‐intensity fires for reversing woody encroachment in savannas

Managing biodiversity in the Anthropocene: discussing the Nature Futures Framework as a tool for adaptive decision-making for nature under climate change

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