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Predicting the Effects of Woody Encroachment on Mammal Communities, Grazing Biomass and Fire Frequency in African Savannas.

Smit IP, Prins HH - PLoS ONE (2015)

Bottom Line: Furthermore, although increased woody cover is associated with reduced livestock production, we found indigenous herbivore biomass (excluding elephants) remains unchanged between 20-65% woody cover.This is due to a significant reorganization in the herbivore assemblage composition, mostly as a result of meso-grazers being substituted by browsers at increasing woody cover.These effects will pose challenges and require adaptation of livelihoods and industries dependent on conditions currently prevailing.

View Article: PubMed Central - PubMed

Affiliation: Scientific Services, South African National Parks, Skukuza, South Africa; Centre for African Ecology, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Wits, South Africa.

ABSTRACT
With grasslands and savannas covering 20% of the world's land surface, accounting for 30-35% of worldwide Net Primary Productivity and supporting hundreds of millions of people, predicting changes in tree/grass systems is priority. Inappropriate land management and rising atmospheric CO2 levels result in increased woody cover in savannas. Although woody encroachment occurs world-wide, Africa's tourism and livestock grazing industries may be particularly vulnerable. Forecasts of responses of African wildlife and available grazing biomass to increases in woody cover are thus urgently needed. These predictions are hard to make due to non-linear responses and poorly understood feedback mechanisms between woody cover and other ecological responders, problems further amplified by the lack of long-term and large-scale datasets. We propose that a space-for-time analysis along an existing woody cover gradient overcomes some of these forecasting problems. Here we show, using an existing woody cover gradient (0-65%) across the Kruger National Park, South Africa, that increased woody cover is associated with (i) changed herbivore assemblage composition, (ii) reduced grass biomass, and (iii) reduced fire frequency. Furthermore, although increased woody cover is associated with reduced livestock production, we found indigenous herbivore biomass (excluding elephants) remains unchanged between 20-65% woody cover. This is due to a significant reorganization in the herbivore assemblage composition, mostly as a result of meso-grazers being substituted by browsers at increasing woody cover. Our results suggest that woody encroachment will have cascading consequences for Africa's grazing systems, fire regimes and iconic wildlife. These effects will pose challenges and require adaptation of livelihoods and industries dependent on conditions currently prevailing.

No MeSH data available.


Average body size of herbivores along a woody cover gradient.(basalts: solid circles; granites: open squares) (standard error bars included). Note how with increasing woody cover the average body size decrease, with negative slope coefficients (basalt: -2.94071 (p<0.0001; n = 3570); granite: -1.20524 (p<0.0001; n = 8682)).
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pone.0137857.g005: Average body size of herbivores along a woody cover gradient.(basalts: solid circles; granites: open squares) (standard error bars included). Note how with increasing woody cover the average body size decrease, with negative slope coefficients (basalt: -2.94071 (p<0.0001; n = 3570); granite: -1.20524 (p<0.0001; n = 8682)).

Mentions: When all species are combined the average Total Herbivore Biomass (THB) remains constant between 20–65% woody cover in both geological landscapes (THB: Fig 3 & Table 3). As species respond differently to the woody gradient, the Shannon Diversity Index decreases significantly (Fig 4), as does the average body size of herbivores (Fig 5).


Predicting the Effects of Woody Encroachment on Mammal Communities, Grazing Biomass and Fire Frequency in African Savannas.

Smit IP, Prins HH - PLoS ONE (2015)

Average body size of herbivores along a woody cover gradient.(basalts: solid circles; granites: open squares) (standard error bars included). Note how with increasing woody cover the average body size decrease, with negative slope coefficients (basalt: -2.94071 (p<0.0001; n = 3570); granite: -1.20524 (p<0.0001; n = 8682)).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4574768&req=5

pone.0137857.g005: Average body size of herbivores along a woody cover gradient.(basalts: solid circles; granites: open squares) (standard error bars included). Note how with increasing woody cover the average body size decrease, with negative slope coefficients (basalt: -2.94071 (p<0.0001; n = 3570); granite: -1.20524 (p<0.0001; n = 8682)).
Mentions: When all species are combined the average Total Herbivore Biomass (THB) remains constant between 20–65% woody cover in both geological landscapes (THB: Fig 3 & Table 3). As species respond differently to the woody gradient, the Shannon Diversity Index decreases significantly (Fig 4), as does the average body size of herbivores (Fig 5).

Bottom Line: Furthermore, although increased woody cover is associated with reduced livestock production, we found indigenous herbivore biomass (excluding elephants) remains unchanged between 20-65% woody cover.This is due to a significant reorganization in the herbivore assemblage composition, mostly as a result of meso-grazers being substituted by browsers at increasing woody cover.These effects will pose challenges and require adaptation of livelihoods and industries dependent on conditions currently prevailing.

View Article: PubMed Central - PubMed

Affiliation: Scientific Services, South African National Parks, Skukuza, South Africa; Centre for African Ecology, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Wits, South Africa.

ABSTRACT
With grasslands and savannas covering 20% of the world's land surface, accounting for 30-35% of worldwide Net Primary Productivity and supporting hundreds of millions of people, predicting changes in tree/grass systems is priority. Inappropriate land management and rising atmospheric CO2 levels result in increased woody cover in savannas. Although woody encroachment occurs world-wide, Africa's tourism and livestock grazing industries may be particularly vulnerable. Forecasts of responses of African wildlife and available grazing biomass to increases in woody cover are thus urgently needed. These predictions are hard to make due to non-linear responses and poorly understood feedback mechanisms between woody cover and other ecological responders, problems further amplified by the lack of long-term and large-scale datasets. We propose that a space-for-time analysis along an existing woody cover gradient overcomes some of these forecasting problems. Here we show, using an existing woody cover gradient (0-65%) across the Kruger National Park, South Africa, that increased woody cover is associated with (i) changed herbivore assemblage composition, (ii) reduced grass biomass, and (iii) reduced fire frequency. Furthermore, although increased woody cover is associated with reduced livestock production, we found indigenous herbivore biomass (excluding elephants) remains unchanged between 20-65% woody cover. This is due to a significant reorganization in the herbivore assemblage composition, mostly as a result of meso-grazers being substituted by browsers at increasing woody cover. Our results suggest that woody encroachment will have cascading consequences for Africa's grazing systems, fire regimes and iconic wildlife. These effects will pose challenges and require adaptation of livelihoods and industries dependent on conditions currently prevailing.

No MeSH data available.