species heights have increased in the control and goat plots which are none fire treatments. However, it has also decreased remarkably in all fire inclusive plots and this indicated the role that the fire had played in reducing bush phytomass.
The density of woody plants almost remained unchanged in non-fire treatments (control and goat). Increase in the available browse on control treatment may be explained by the exclusion of goats while decrease in available browse in the goat plots could be attributed to utilization of acceptable species. Grazing had an impact in the reduction of growth of the woody species and their density even when acceptable species are highly dominant and available. In the observed results obtained in the Eastern Hardveld of Botswana at the Morale Pasture Research Station trial which suggested that where goats are used as a follow-up treatment to burning, species composition of the woody plants in the height class above 2 m remained constant while there were substantial changes within the lower height class particularly at a high stocking rate. This further suggests that goats had great influence on species not exceeding a height of 2 m.
The notable increase in bush phytomass in the winter fire treatment may be a result of the remarkably increase in woody plant density of species with reduced mean heights (seedlings) favoured by the growing season (spring-summer). The woody species responsible for the observed changes is the Acacia karroo, which seems to be highly favoured by fire to ensure germination of seeds while all other species suffer germination of seeds when fire was used. Increased heating duration at 150ºC resulted in the decline of seed viability of other Senegalia (Acacia) species by 4–12% while A. karroo maintained viability of 40–60%. Some A. karroo seeds survived even when exposed to temperatures of 200ºC and subsequently still germinated, which indicated that high temperatures are certainly a germination cue for this species.
Conclusions and recommendations
From the study, when goats are to be used in the Coastal Thornveld areas of the Eastern Cape as part of bush control strategy, it is recommended that they may be coupled with occasional use of fire during the mid-winter period where the effect of fire and browser is marked.
In the event that fire is used in the Coastal Thornveld as a bush control strategy in the absence of browser species it is recommended that, such fires be initiated during the dry summer periods which showed pronounced reductions in both bush phytomass and species mean heights, together with an insignificant increase in plant density. While herbage production won't be compromised in the process.
The results of the experiment have addressed the set objectives of the study in that grazing alone had insignificant impact in controlling regrowth of woody plants; even those species classified as acceptable and available to browsers. Use of browsers coupled with grazers is recommended to pastorals of these areas for profitable livestock ranching.
Acknowledgments
The authors acknowledge the management of Department of Agriculture at Dohne Agricultural Development Institute in funding the research project.
References
Aucamp AJ. 1976. The Role of the browser in the Bushveld of the Eastern Cape. Proceedings of the Grassland Society of Southern Africa 11: 135-138.
Balch JK, Brando PM, Nepstad DC, Coe MT, Silvėrio D, Massad TJ, Davidson EA, Lefebvre P, Oliveira-Santos C, Rochas W, Cury RTS, Parsons A, Carvalho K. 2015. The susceptibility of Southern eastern Amazon Forests to fire: Insights from a large-scale burn experiment. Bio Science 65: 893-905.
Burkepile DE, Burns CE, Tambling CJ, Amendola E, Buis GM, Govender N, Nelson V. Thompson DI, Zinn AD, Smith MD. 2013. Habitat selection by large herbivores
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Grassroots
August 2017
Vol. 17, No. 3
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