A long-term grazing trial was started in 1977 at Armoedsvlakte Research Station, about 10km west of Vryburg, in Tarchonanthus veld of the Ghaap’s Plateau, which is a variation of the Kalahari Thornveld veld type. The main aim of this study was to use the extensive veld condition and animal production data set to investigate the effects and interactions of stocking rate, grazing system applied and seasonal rainfall on veld condition and cattle production. The grazing trial has changed three times since its inception resulting in three different phases. The main changes in veld condition during phase one (1977-1991) was due to density independent effects (e.g. seasonal rainfall) and not density dependent effects (e.g. stocking rate). A major change occurred in 1985 following a multiple year drought. The drought resulted in adverse changes in species composition, basal cover and residual biomass of all treatments. The system did not recover from the drought during phase one, despite well above mean seasonal rainfall for a number of years after the drought. During phase two (1992-1999) and phase three (2000 to present) completely different vegetation dynamics occurred than what was experienced during phase one. Density dependent effects (e.g. stocking rate) were more important in explaining variation in veld condition during these two phases. High stocking rates resulted in adverse changes in species composition, poor basal cover and a low residual biomass production. It is however important to note that seasonal rainfall did explain a significant additional amount of variation in veld condition. This suggests that a continuum of non-equilibrium and equilibrium vegetation dynamics occurred in these two phases. The residual biomass and seasonal rainfall model for phase one indicate completely different results for the gain per animal data. In the seasonal rainfall model, stocking rate does not have a significant effect on gain per animal, but seasonal rainfall and the interaction of stocking rate with seasonal rainfall explains most of the variation in gain per animal. This suggest a continuum of non-equilibrium and equilibrium dynamics and that animal production is more sensitive to seasonal rainfall than to stocking rate, although the significant interaction of stocking rate with seasonal rainfall suggest that the seasonal rainfall effect on animal production is dependant on stocking rate. The residual biomass model however indicates that stocking rate is more important than rainfall in explaining variation in the mass gains per animal. The stocking rate effect on gain per animal was significant and indicated that as stocking rate increased, that gain per animal decreases. Seasonal rainfall and the interaction of stocking rate with seasonal rainfall had no significant effect on gain per animal. The amount of variation explained by the seasonal rainfall model was larger than the residual biomass model and this indicates that rainfall explains more variation in gain per animal, than residual biomass does. This possibly indicates that non-equilibrium effects are stronger than the equilibrium effects, but it is important to notice that stocking rate had a significant effect in some cases. The gain per hectare models (seasonal rainfall and residual biomass) for phase one indicates that stocking rate has a significant effect on gain per hectare. Increasing stocking rates resulted in higher gain per hectare, which suggests that the turning point of the typical “Jones and Sandland model” has not been reached and this might be due to light stocking rates applied during the duration of phase one. The seasonal rainfall model however has significant effects of seasonal rainfall and interactions of stocking rate with seasonal rainfall on gain per hectare. This suggests that the effect of stocking rate is dependent on seasonal rainfall and that seasonal rainfall explain an additional amount of variation in gain per hectare. In general, it appreared that the optimal stocking rate for animal production was higher than those applied during the duration of the trial, but this is due to lower than planned actual stocking rates applied during all three phases of the trial. It is very difficult to determine a generic optimal stocking rate for different rainfall volumes and it is recommended that the actual stocking rate for different ecological zones be determined based on rainfall, biomass, species compos[i]tion, basal cover and available browse and not just on the provisional recommendations. The type of grazing system applied did not show any statistically significant effects on both gain per animal and gain per hectare for the animal production data during phase one. This result is interesting and contradictive to most of the scientific literature where some authors concluded from their studies that rotational grazing systems produce higher animal production than continuous grazing systems, whereas others researchers state that continuous grazing systems produce higher animal production than rotational grazing systems. In phase two both the residual biomass and seasonal rainfall models for phase two did not show any significant effects and interactions of stocking rate, seasonal rainfall level and/or residual biomass on both gain per animal and gain per hectare. Both the residual biomass and seasonal rainfall models for phase three did not show any significant effects and interactions of stocking rate, seasonal rainfall level and/or residual biomass on animal gains per animal. The seasonal rainfall model did not show any any significant effects and interactions of stocking rate, seasonal rainfall level and/or residual biomass on animal gains per hectare. However, the residual biomass model indicated that stocking rate had a significant effect on gain per hectare and the production closely followed the Jones and Sandland (1974) model as at low stocking rates, gain per hectare increases at a rapid rate, but as stocking rates increases to high stocking rates, the rate of increase in gain per hectare declines, until it eventually reaches a turning point, where after gain per hectare declines with increasing stocking rates. Stocking rate only had a significant effect on the condition score of cows during phase two and phase three, as high stocking rates resulted in poor animal condition in both phases. No significant effects and interactions of stocking rate and seasonal rainfall were indicated on calving percentage, weaning percentage, conception rates and percentage of desirable meat produced during phase two. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, [2011].

Effects of herbivory, fire, and tree harvesting on Acacia drepanolobium were studied using plant population dynamics as the philosophical basis of research. Specifically, growth rates, chrono-sequence of re-growth, biomass and charcoal yield, herbivory, flowering, seed production, germination, mortality and the ants of Acacia drepanolobium were studied in the black cotton ecosystem of Mpala Research Centre, Laikipia, Kenya, between September 1995 and December 2000. Acacia drepanolobium was the most abundant tree or shrub with densities ranging from 80% to 98% of all the overstorey species, but it was the least browsed of all the trees and shrubs in the black cotton ecosystem, ranging from a mean of 7.2% to 9% of the individuals browsed. The tree is inhabited by four Acacia ant species, Crematogaster mimosae, Crematogaster sjoestedti, Crematogaster nigriceps, and Tetraponera penzigi, which are believed to be obligate, and which probably play a role in the low browsing rates observed. Six herbivore treatments replicated three times (no herbivores - O; only cattle - C, all herbivores allowed - MWC {control}, mega-herbivores {elephants and giraffe} and wildlife {W} – MW only, wildlife – W - only {all wildlife except mega-herbivores} and wildlife and cattle only - WC) was the main experimental design used in understanding the dynamics of the tree species under influence of different herbivores. Mean annual height growth of A. drepanolobium trees was 24.9 cm yr-1, while the mean Relative Growth Rates ranged from 14.6 x 10 –3 cm cm-1 yr-1 to 18.7 x 10 –3 cm cm-1 yr-1. Growth rates were different among the herbivore treatments and between seasons. Shoots of the tree grew by a mean range of 6.8 cm to 9.1 cm, were similar among the treatments but differed among the seasons. Canopy volume increased over time although it fluctuated with seasons, suggesting an increase in bushiness of A. drepanolobium in the ecosystem. Trees occupied by different ant species showed differences in shoot density (number of new shoots per twig), being greater in Crematogaster nigriceps occupied trees compared with the other ant species. Swollen thorn (gall) density per unit of twig length was greatest in treatments with megaherbivores; these galls were significantly larger on trees occupied by the ant Crematogaster nigriceps. Treatments with herbivores were more spinescent than the total exclusion treatment. Spine lengths ranged from 0.8 to 2.4 cm, and recorded a progressive reduction of up to 36.36.7% in treatments without browsers suggesting a relaxation of induced defence in A. drepanolobium. Flowering in A. drepanolobium was low and staggered over the study period ranging from 0.8% to 2.0% of the trees with no differences among the treatments suggesting that the level of herbivory was not sufficient to influence reproduction of the tree in the experimental site. Consequently, seedling recruitment was very low within the experimental site. However, a nearby site recorded flowering of between 22.7% and 93.5%. Mean pod production, mean number of seeds per tree and mean weight of pods and seeds had a positive linear relationship with tree density (R2=0.77, 0.81 and 0.81 respectively). Trees occupied by Crematogaster mimosae were the most likely to flower (68%) compared with C. nigriceps (5.8%), again suggesting that ants had an effect on the tree’s reproduction. Mortality of A. drepanolobium trees averaged 0.9% to 4.2% over the study period, being significantly greater in treatments with mega-herbivores. Seedling survival ranged from 42% to 75%, being greatest in the cattle only treatment. Between 30% and 100% (mean 67.2%), of A. drepanolobium seeds were attacked by a bruchid beetle (Bruchus sp.). Seeds attacked by bruchid beetles had significantly lower germination rates. Similarly, seeds passed through a fire also recoded significantly low germination rates compared with normal seeds. Fire (3.4%) and bruchid beetles (20.7%) germination compared with (control) undamaged seeds (84%) play an important role in the population dynamics of A. drepanolobium. Fewer A. drepanolobium seeds (33%) were recovered from the surface compared with buried (72%) seeds after a fire, indicating seed loss from the effect of fire and predation. In the burn experiment, fire top-killed 16% of A. drepanolobium trees but no tree or seedling was killed. On the other hand, fire significantly reduced the density of non-A. drepanolobium trees by between 50% and 100%, with none of them showing signs of coppicing after the fire unlike top-killed A. drepanolobium trees. Woody biomass from A. drepanolobium was strongly related to stem diameter (Y = 3.77x + 1.17, R2 = 0.96, P < 0.001). Mean charcoal production from earthen kilns was 2.83 Mg ha- 1. Height and stem diameter in coppicing stands increased at a mean rate of 28.6 cm yr-1 and 0.7 cm yr-1 respectively. Biomass in coppicing stands accumulated at a mean rate of 1.3 Mg ha-1 yr-1 in a 14-year period, yielding dry biomass of 18.26 Mg ha-1 useable wood that can produce a minimum of 3.0 Mg ha-1 of charcoal. This study shows that Acacia drepanolobium populations are affected by several factors including herbivory, fire and ants. The population dynamics of this tree shows that it can be harvested for sustainable charcoal yield over a 14-year cycle. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

The structure and composition of savanna vegetation is influenced by resource availability and disturbance. Grasses, a major component of savannas, influence this resource availability by competing directly with trees for light, water and soil nutrient resources. The direct causes of bush encroachment are not always apparent, but are commonly ascribed to overgrazing and consequent decreased grass competition. The interaction, both above and belowground, between tree and grass seedlings and the surrounding grass sward is dependant on many factors, such as soil depth, seedling species and sward composition. These factors, as well as the presence or absence of defoliation, in the form of grazing or fire dictate whether the system will remain in a transition state as savanna or move towards a stable woodland state. The major competitive effects experienced by the tree seedlings were dependant on grass species and nutrient level. A. nilotica was affected by aboveground competition while A. karroo was affected by belowground competition. E. capensis caused the greatest decrease in A. karroo plant biomass. Both E. capensis and H. hirta had large competitive effects on the aboveground biomass of A. nilotica, while S. africanus had the greatest effect on belowground biomass. Increasing nutrient availability resulted in an increase in the competitive effect exerted on A. karroo, while little to no change was seen in the competitive effect exerted on A. nilotica. Soil depth constrained plant size in both tree species. The intensity of belowground interactions on tree biomass was unaffected by soil depth, while aboveground competition had a significant effect on shallow soils. Belowground competition was also of greater importance than aboveground competition in dictating tree seedling height. Grass seedlings growing on all three soil depths differed in mean mass, with E. racemosa having the least mass and T. triandra having the greatest. Simulated grazing by cutting the surrounding sward resulted in biomass increases in all three grass species. Changes in savanna composition and structure are thus likely to be influenced by initial species composition and soil depth and soil nutrient composition. While grazing creates niches for grass seedling establishment, heavy grazing has been observed to increase grass seedling mortality. Encroachment is thus more likely to occur on intensively grazed shallow and deep soils than on medium depth soils. This highlights the importance of ensuring the grass sward remains vigorous by resting and monitoring stocking rates to ensure veld is not over-utilized. It is then possible to maintain some form of tree-grass coexistence at a level where available grazing is not compromised. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Doctor of Philosophy / Department of Agronomy / Stephen J. Thien / Range and Training Land Assessment (RTLA) and Land Rehabilitation and Maintenance (LRAM) are key components of The United States Army's Integrated Training Area Management (ITAM) Program, which outlines its commitment to support the sustainable use of military training lands. The primary purpose of the RTLA Program is to provide information and recommendations regarding the condition of training lands to range managers for scheduling of training areas and monitoring the effectiveness of rehabilitation projects. The goal of the LRAM component of ITAM is to reduce the long-term impacts of training on installations through the implementation of improvements to vegetation cover and repairs to landscape damage in disturbed areas. Fort Riley Military Installation, located in the largest remaining expanse of tallgrass prairie in the Flint Hills of northeastern Kansas, is a major training reservation, with seventy percent of its 40,434 ha used for mechanized maneuvers. A randomized complete block design composed of M1A1 tank traffic in a figure-eight pattern during wet and dry soil conditions was established in each of two soil types, a silty clay loam and a silt loam, and recovery of physical, chemical, and biological indicator variables was monitored from 2005 through 2007. In a second study, the effectiveness of LRAM procedures, including leveling, mulching, and reseeding, was evaluated following wheeled vehicle disturbance. The goals of this study were to identify disturbance indicators appropriate for assessing soil quality and, based on the status of these indicators, develop a method for modeling the stage and rate of ecological degradation and potential response to remediation. Disturbance increased significantly during wet compared to dry soil conditions, for increased traffic intensity, and for curve compared to straight-a-way areas in both soil types. The greatest impacts were on above and below ground community structure, providing an effective bioindicator of ecosystem health for military training land managers. Remediation of wheeled vehicle disturbance with leveling and mulching, but not reseeding, increased total vegetation production. The tallgrass prairie typically is considered to be among the most resilient of military training lands, but resiliency is dependent upon soil type and training conditions, and may require longer periods of recovery than previously thought.

This study was conducted to determine livestock production, rangeland management and the mineral levels of soils, grass and cattle blood serum in two communal areas (Kwezana and Dikidikana). A total of 77 farmers from both Kwezana and Dikidikana were interviewed to determine farmers’ perceptions. Soil and grass sampling was done at three sites in each communal area. Soil and grass samples were analysed for N, Ca, Mg, K, P, Fe, Cu, Zn, Mn and Bo. Three, two and half year old Nguni heifers were randomly selected from each communal area and blood samples were collected for the analysis of Ca, Mg, K, Cu and Fe. Soil, grass and blood samples were all collected in two seasons (winter and summer). The results of the study revealed that feed availability was the major constraint in livestock production as indicated by 83 percent of thefarmers at Kwezana and 88 percent at Dikidikana. At both villages less than 20 percent practiced supplementation and grazing management. From both villages, 83 percent of the farmers did not know the forage species preferred by their cattle. The second study revealed significant seasonal variations in soil N in both study areas while forage N exhibited seasonal variations (P<0.05) only at Dikidikana. Spatial variation (P<0.05) in soil Mn was apparent in both seasons at Dikidikana and in summer at Kwezana. At Dikidikana forage P varied (P<0.05) both seasonally and spatially. In both study areas, there was a positive correlation (P<0.05) between soil and forage levels of Cu and Zn. The blood serum of animals from both study areas had higher (P<0.05) K and Na in winter than in summer. Farmers do not understand the composition of their rangelands but are concerned about cattle nutrition during winter. Indeed the mineral status of soils, forages and Nguni cattle blood serum tend to vary not only seasonally but also spatially. There is need therefore to assist the farmers to understand these changes in order to find ways of managing the rangelands in a way that will manipulate both seasonal and spatial variations in soil nutrients for the benefit of the grazing livestock. Further research is required to determine the digestibility of the forages and the amount of energy available from these forages for the grazing livestock.

Thesis (M.Sc. Agriculture (Pasture Science)) -- University of Limpopo, 2021 / Savanna rangelands are ecosystems which are characterized by the co-existence of scattered trees and shrubs with a continuous grass layer. However, the grass and tree balance has been highly altered as a result of disturbances caused by bush encroachment. Encroaching woody species have been shown to decrease species richness and abundance of the seed bank and ground‐layer diversity. So far little is known on the effect of bush encroachment and soil depth on the soil seed bank diversity in savanna rangelands. The objectives of this mini-dissertation were to (1) determine the influence of soil depth on soil seed bank diversity in bush encroached savanna rangelands, and (2) determine the relationships between soil seed bank herbaceous vegetation and physicochemical properties in encroached rangeland. In order to address these objectives, a savanna rangeland was demarcated into two encroachment gradients spanning from open to encroached rangeland. Within each encroachment gradient, six plots of 10 m x 10 m were randomly selected, whereby soil sampling and herbaceous vegetation were carried out and determined. In each replicate plot per encroachment level, five soil samples were randomly collected at 0-10 and 10-20 cm depths. The number of seedlings of different species emerging from the soil samples was used as a measure of the number of viable seeds in the soil and the composition of the seed bank using the seedling emergence method. The total seed densities showed significant differences (P<0.05) in the 0-10 cm depth layer in the open rangeland and encroached rangeland. Bush encroachment significantly (P<0.05) decreased the seed density of perennial grasses, specifically in 0-10 cm depth layer. Further, species diversity increased with bush encroachment in the 10-20 cm depth layer. Menhinick’s richness index showed no significant difference in the open and encroached rangeland, while species evenness decreased in the 0-10 cm depth layer and increased at 10-20 cm depth.The study also revealed negative correlations between organic carbon, calcium, clay, silt and forbs while mean weight diameter (MWD), a measure of soil aggregate stability was positively correlated with forbs. The canonical correspondence analysis (CCA) showed that pH, phosphorus, potassium and calcium were positively correlated to Eragrostis curvula and magnesium was negatively correlated to Panicum maximum. In open rangeland, CCA revealed that clay content was negatively correlated with species evenness while xii magnesium was negatively correlated to the Shannon Weiner index. Further, silt content was positively correlated with species richness and evenness. In the encroached rangeland, the CCA showed a negative correlation between magnesium and the Shannon Weiner index. The Sørensen’s index between soil seed banks and aboveground vegetation was low with index values of 0.22 and 0.24 in open and encroached rangeland, respectively. / AgriSeta

Granivores are important components of sagebrush communities in western North America. These same regions are being altered by the invasion of the exotic annual Bromus tectorum (cheatgrass) that alters physical and biological dynamics in ways that appear to promote its persistence. This research directly relates to the restoration of B. tectorum-dominated systems in two inter-related ways. First, because these landscapes have large quantities of seeds applied during restoration, it is important to determine the major granivore communities in intact sagebrush communities and in nearby cheatgrass-dominated communities. Second, it is important to develop an understanding of patterns of seed harvest by granivores. In addition to the data chapters there are two review chapters; Chapter 1 highlights factors contributing to seed removal and Chapter 7 provides ecologically based techniques that could minimize the negative consequences of granivores during ecological restoration. Common groups of ants showed increased abundances; uncommon species and functional groups were generally negatively impacted by cheatgrass (Chapter 2). Conversely, rodents were negatively impacted by conversion to cheatgrass (Chapter 4). Ant seed removal was highly context-dependent (Chapter 3), depending on the background vegetation (large-scale among-patch effects), foraging distance from the nest mound (small-scale among-patch effects), and the presence of other seed species in mixture (within-patch effects). In addition, cheatgrass provided associational resistance to native seeds in mixture, meaning the presence of cheatgrass increased native seed survival. In Chapter 5 a novel statistical technique in the ecological sciences showed that rodents have marked preferences for some seeds over others and that more seeds were removed in sagebrush compared to cheatgrass-dominated sites, although associational effects among seed mixtures were not detected. In Chapter 6 we show that the amount of seed harvested depended on both intraspecific and interspecific seed density. B. tectorum seeds had associational susceptibility (increased harvest) in the presence of native seeds. Although the reciprocal effect may occur, we did not find statistical support for it. These sets of studies are not only of basic ecological interests, but are also important for developing management strategies for restoration of these degraded lands.

Pseudoroegneria spicata and Elymus wawawaiensis are two native perennial bunchgrasses of North America's Intermountain West. Frequent drought, past overgrazing practices, subsequent weed invasions, and increased wildfire frequency have combined to severely degrade natural landscapes in the region, leading to a decline in the abundance of native vegetation. Being formerly widespread throughout the region, P. spicata is a favorite for restoration purposes in the Intermountain West. Elymus wawawaiensis, which occupies a more restricted distribution in the Intermountain West, is often used as a restoration surrogate for P. spicata. However, since most restoration sites are outside the native range of E. wawawaiensis and as the use of native plant material may be more desirable than a surrogate, the use of E. wawawaiensis as a restoration plant material has been somewhat controversial. The main goal of my research was to identify plant materials of these species with superior seedling growth, drought tolerance, and defoliation tolerance, traits that may contribute to enhanced ecological function in restored rangeland plant communities. I conducted a growth-chamber study to evaluate morphological and growth-related traits of germinating seedlings of these two species. My study suggested that, while the two bunchgrasses are similar in many ways, they display fundamentally different strategies at the very-young seedling stage. While P. spicata exhibited greater shoot and root biomass to enhance establishment, E. wawawaiensis displayed high specific leaf area (SLA) and specific root length (SRL), two traits commonly associated with faster growth. According to the eco-physiology literature, plants with greater stress tolerance display lesser growth potential. However, my greenhouse study showed that E. wawawaiensis was relatively more drought tolerant than P. spicata, despite higher expression of growth-related traits, e.g., SLA and SRL. While the two species displayed similar water use efficiency when water was abundant, E. wawawaiensis was also more efficient in its water use when drought stress was imposed. In a field study, I found E. wawawaiensis to be twice as defoliation tolerant as P. spicata. This study showed that P. spicata is typically more productive in the absence of defoliation, but E. wawawaiensis was more productive after defoliation due to its superior ability to recover and hence is a better candidate for rangelands that will be grazed. Hence, my study showed that E. wawawaiensis, despite being regarded as a surrogate for P. spicata, exhibits superior seedling establishment, drought tolerance, and defoliation tolerance. Therefore, E. wawawaiensis has advantages as a restoration species for the Intermountain West.

No description available.

In my thesis, I examined impacts of nesting and floral resources on ground-nesting bee assemblages at nine ranch sites with differing grazing histories. Because ecological disturbances can strongly affect the availability of foraging and nesting resources over time, I also examined the impacts of grazing history on nesting and floral resources for ground-nesting bees. I sampled bee assemblages, a comprehensive array of vegetation and soil measures, and floral abundance and richness. I used these data to determine (1) the importance of different nesting habitat resources and livestock grazing history for ground-nesting bees and (2) how livestock grazing history influenced the availability of nesting and floral resources. I found that sites with sandier soils had greater abundance and richness of ground-nesting bees, and sites with less compacted soils had greater bee abundance. Contrary to many other studies, the availability of bare ground was not important for ground-nesting bee abundance or richness. Grazing history did not affect any measures of nesting or floral habitat, and had negligible effects on ground-nesting bee abundance, richness, and community composition. My results suggest that the availability of sandier or less compacted soils may be limiting for ground-nesting bee abundance or richness, especially in areas with predominately clay soil types. In this context, the availability of such nesting resources may be more limiting than floral resource availability. More research is necessary to tease apart the effects of different nesting and floral resources for bees, and how different grassland management types affect bees through those resources. My findings highlight the importance of considering nesting habitat resources in bee conservation and restoration efforts.