Parallel A: Fire Ecology

 
Tick borne diseases such as heart water and babesiosis (red water) cause significant mortalities and economic losses to domestic livestock and game farmers in South Africa. The potential for reducing the incidence of ticks through prescribed burning was successfully achieved in the Ngorongoro Crater in Tanzania in 2003. However, the effects of burning on tick populations are complex because fires can affect both ticks and their host species. Based on the results from Ngorongoro Crater, the Research and Development Section of Working on Fire International initiated a research trial in 2015 in the Lowveld south of Nelspruit, Mpumalanga. Verification of the positive impact of prescribed burning to reduce or control tick populations will strengthen the basis for using prescribed burning as an effective veld management practice in African grasslands and savannas. However, fire cannot be seen as a stand-alone tool to reduce or control tick populations as it will require using appropriate fire regimes comprising type and intensity of fire and season and frequency of burning together with grazing management and animal stocking rates to reduce and/or control the density of tick populations. The main hypothesis being tested in this long-term project is that tick populations increase in abundance when the grass sward becomes moribund and exceeds a grass fuel load of 4000 kg/ha resulting in a favourable micro-climate involving higher air temperatures and humidity’s. The first site for the research project is on the De Kaap Valley Conservancy, Nelspruit, Mpumalanga. At this initial stage the tick surveys are being restricted to open thornveld that include various aspect profiles. Twenty one vegetation surveys were conducted using an adapted point centred quartered method on 200m x 80m plots. The standing herbaceous biomass was estimated with a disc pasture meter using the generally accepted calibration for African grassland and savannas viz. (y = -3019 + 2260 √x, where y = mean grass fuel load (kg/ha) and x = mean disc height (cm)). Tick population densities pre- and post burn were recorded and monitored using an established flannel drag sampling technique used by the Onderstepoort Veterinary Institute. Drags were conducted on 33 sites, 100m x 1m in size, of which three were control sites. Initial cool burns (< 1000 kW/m) were applied to remove moribund grass material and establish time zero. Expected project duration will be a minimum of 60 months. The preliminary results presented pertain to the tick species identified on the site, as well as the relative numbers of each tick development phase on a species basis. The number of tick species identified on the research site was twelve, with the dominant species being Rhipicephalus appendiculatus and Rhipicephalus decoloratus. The former is known to be the vector for Theileria parva, the causative organism of East Coast fever in cattle as well as Rickettsia in humans.

In African savannas, fluctuations in rainfall, nutrients, herbivory and fire plays a major role in sustaining these complex and dynamic systems. Simultaneously, soils play a vital role in supporting healthy and functioning ecosystems. Besides providing a medium for plant growth, soils play a major role in ecosystem functioning through nutrient cycling and water filtration through the system, thus when soils are degraded important ecosystem services are affected. Numerous studies from various locations around the world deduced that fire can play a major role and effect soil properties. Even though fire is regarded as a key driver in savanna systems, there is a lack in current understanding on the impacts of long-term fire management on soil properties.
The Experimental Burn Plots (EBPs) in Kruger National Park is a long-term fire/ herbivory experiment which was initiated in the 1950’s. This experiment offered a unique opportunity to determine the impact of long-term fire treatments on soil water retention capacity, soil total carbon, total nitrogen and soil compaction. Results suggest that at water contents of < 5%, the No Burn plots where fires have been excluded for more than six decades, have a higher water retention capacity and retain water more efficiently than regularly burnt soils. This was measured on both coarse-grained granite-derived soils as well as finely-textured basaltic soils. When water retention capacities are compared across geologies, the finely-textured basaltic soils retained water more efficiently than the granitic soils. The ability of a soil to retain moisture is affected by soil properties such as soil texture and soil organic matter content. With regards to soil total carbon, results suggest that fire exclusion results in significantly higher total carbon in basaltic soils only (p < 0.001), and not granitic soils. Similarly, total nitrogen is significantly higher on the No Burn plots on the basaltic soils (p < 0.001) than the granitic soils. Overall, basaltic soils contain roughly double the total carbon and total nitrogen content than that of granitic soils. This relationship may be explained by the increase in biomass and clay content on the basaltic soils as opposed to the granitic soils.
With regards to soil compaction, results suggest that frequent annual burning increases to soil compaction (p< 0.05). This may be attributed to veldfires denuding an area of vegetation and exposing the soil surface to environmental elements and processes such as raindrop impact and splash. Vegetation cover is important for protecting the soil surface and affects the fate of raindrops. Furthermore, the presence of herbivores enhances soil compaction due to trampling (p < 0.05). Herbivores tend to concentrate on recently burnt areas due to improved post-fire grazing as well as enhanced visibility against predators. Depending on the degree of soil surface compaction and the soil type, soil compaction may lead to decreased infiltration rates, increased runoff production and increased erosion rates. These results are particularly important for land-use management where veld burning is used as a management tool for controlling vegetation structure and composition, combatting bush encroachment and improving grazing quality for livestock and game.

Acceptability of plant material to herbivores is influenced by among other factors; nutrients, plant secondary metabolites and growth stage of the plants. However, the effect of these factors on Seriphium plumosum L. acceptability to livestock is still not clearly understood, despite its importance in managing its encroachment in grassland communities. The study used 2 x 2 x 2 factorial analysis of variance to investigate the effect of season (wet and dry), fire (fire and no fire), slope position (top and bottom) and their interaction on Seriphium plumosum forage quality. We tested the hypothesis that S. plumosum forage quality varies temporally, spatially and in fire and no fire treated S. plumosum edible materials. Seriphium plumosum edible material was collected during the wet and dry season from fire and no fire treated areas at both top and bottom slopes before analysed for forage quality; nutrients (protein (CP) content, neutral detergent fibre (NDF)), and plant secondary metabolites (total phenolics (TP) and condensed tannins (CT)). Season had a significant effect on S. plumosum forage quality (CT, CP, NDF, TP and CT). Fire had a significant effect on S. plumosum CP content. Interestingly, Slope position did not have any significant effect on S. plumosum forage quality. Interaction of season x fire had a significant effect on NDF and CP (P < 0.05). Seriphium plumosum had significantly higher CP and CT in the wet season (6.69 % ± 0.20 (SE)) and (1.56 mg/gDw ± 0.13) than in the dry season (5.22 % ± 0.13) and (1 mg/gDw ± 0.03), respectively. Neutral detergent fibre and TP was significantly higher (58.01 % ± 0.41) and (14.44 mg/gDw ± 1.03) in the dry season than in the wet season (53.17 % ± 0.34) and (11.08 mg/gDw ± 1.07), respectively. Crude protein was significantly higher in burned (6. 31 % ± 0.22) than in unburned S. plumosum edible material (5.60 % ± 0.15). Seriphium plumosum CP was significantly higher in wet season x burned (7.34 % ± 0.31) than wet season x unburned (6.08 % ± 0.20) material and dry season x burned (5.34 % ± 0.18) and unburned (5.09 % ± 0.18) material, which were similar. Neutral detergent fibre was similar in dry season x burned (58.31% ± 0.54) and dry season x unburned (57.69 % ± 0.62) material and significantly higher than similar wet season x burned (52.43 % ± 0.45) and wet season x unburned (53.88 % ± 0.47) material. This study suggests opportunities for integrating fire, browsers and supplements in the control of encroacher S. plumosum, especially during the wet season because of its high CP and CT content.