Anna C. Treydte

Herbaceous forage and selection patterns by ungulates across varying herbivore assemblages in a South African savanna

Herbivores generally have strong structural and compositional effects on vegetation, which in turn determines the plant forage species available. We investigated how selected large mammalian herbivore assemblages use and alter herbaceous vegetation structure and composition in a southern African savanna in and adjacent to the Kruger National Park, South Africa. We compared mixed and mono-specific herbivore assemblages of varying density and investigated similarities in vegetation patterns under wildlife and livestock herbivory. Grass species composition differed significantly, standing biomass and grass height were almost twice as high at sites of low density compared to high density mixed wildlife species. Selection of various grass species by herbivores was positively correlated with greenness, nutrient content and palatability. Nutrient-rich Urochloa mosambicensis Hack. and Panicum maximum Jacq. grasses were preferred forage species, which significantly differed in abundance across sites of varying grazing pressure. Green grasses growing beneath trees were grazed more frequently than dry grasses growing in the open. Our results indicate that grazing herbivores appear to base their grass species preferences on nutrient content cues and that a characteristic grass species abundance and herb layer structure can be matched with mammalian herbivory types.

Managing Semi-Arid Rangelands for Carbon Storage: Grazing and Woody Encroachment Effects on Soil Carbon and Nitrogen

High grazing intensity and wide-spread woody encroachment may strongly alter soil carbon (C) and nitrogen (N) pools. However, the direction and quantity of these changes have rarely been quantified in East African savanna ecosystem. As shifts in soil C and N pools might further potentially influence climate change mitigation, we quantified and compared soil organic carbon (SOC) and total soil nitrogen (TSN) content in enclosures and communal grazing lands across varying woody cover i.e. woody encroachment levels. Estimated mean SOC and TSN stocks at 0–40 cm depth varied across grazing regimes and among woody encroachment levels. The open grazing land at the heavily encroached site on sandy loam soil contained the least SOC (30 ± 2.1 Mg ha-1) and TSN (5 ± 0.57 Mg ha-1) while the enclosure at the least encroached site on sandy clay soil had the greatest mean SOC (81.0 ± 10.6 Mg ha-1) and TSN (9.2 ± 1.48 Mg ha-1). Soil OC and TSN did not differ with grazing exclusion at heavily encroached sites, but were twice as high inside enclosure compared to open grazing soils at low encroached sites. Mean SOC and TSN in soils of 0–20 cm depth were up to 120% higher than that of the 21–40 cm soil layer. Soil OC was positively related to TSN, cation exchange capacity (CEC), but negatively related to sand content. Our results show that soil OC and TSN stocks are affected by grazing, but the magnitude is largely influenced by woody encroachment and soil texture. We suggest that improving the herbaceous layer cover through a reduction in grazing and woody encroachment restriction are the key strategies for reducing SOC and TSN losses and, hence, for climate change mitigation in semi-arid rangelands.

To eradicate or not to eradicate? Recommendations on Prosopis juliflora management in Afar, Ethiopia, from an interdisciplinary perspective

As one of the most invasive species of arid and semi-arid areas of East Africa, Prosopis juliflora has become a major threat to livelihoods of the Afar pastoral people and to the fragile ecosystems they live in. This paper comprises results from a multidisciplinary study on the spread of P. juliflora as an invasive species in the Ethiopian Afar Region and provides suggestions on its management and control. The study investigated spread of P. juliflora, ecological aspects (shifts in vegetation biomass and soil properties) and socio-economic aspects (livelihood impacts, management activities and potential) of P. juliflora invasion. Ecological methods included conducting destructive harvesting on vegetation; soil analyses and a soil seed bank assessment as well as using allometric equations to estimate the biomass and carbon contents of P. juliflora. Socio-economic data was collected based a survey of 490 pastoral households including 213 from Amibara, 177 from Gewane and 100 from Awash Fentale. Stated and revealed preference methods (RPM) were used because impacts of P. juliflora are both tangible and intangible. The study found that wetlands (flood plains in the Awash Basin) are highly susceptible to Prosopis invasion relative to drylands. Clearing invaded land and continuously using it for crop farming would reduce the invasion. The study also found that the available nitrogen, phosphorus and organic carbon in the soil were high in highly invaded areas compared to less or non-invaded sites. However, the basal cover of native herbaceous vegetation and native tree diversity were found to be much reduced under high P. juliflora-invaded areas. Results from economic analyses also reveal that the benefits of the P. juliflora invasion in the Afar region are higher than the costs. However, some aspects such as increased risk of erosion, the impact of P. juliflora on the water table and long-term ecological changes were not examined, thus making the total economic valuation incomplete. Nonetheless, the study has captured most aspects of P. juliflora invasion in the Afar region and concludes that sustainable management and control of P. juliflora in the Afar region may be a better solution than eradication.

Carbon stocks and sequestration potential of dry forests under community management in Tigray, Ethiopia

IntroductionForests form a major component of the carbon (C) reserves in the world’s ecosystems. However, little is known on how management influences C stocks of woody vegetation, particularly in dry areas. We developed regression models for two dominant tree species to predict C stocks and quantified the potential of community managed forests as C sinks.MethodsPlots were randomly selected from community-managed natural forest, herbivore exclosures, and from communal grazing land. Tree and shrub biomass were estimated using a regression model on the most dominant woody species while herbaceous biomass was determined using destructive sampling.ResultsThe simplest model, based on only one single predictor variable, showed a good fit to the data for both species (Juniperus procera and Acacia abyssinica). Diameter at breast height (r2u2009>u20090.95) was a more reliable predictor than height (r2u2009>u20090.54), crown diameter (r2u2009>u20090.68) (pu2009<u20090.001). The C content of the total biomass for the managed natural forest and the exclosure were estimated as, 58.11 and 22.29xa0Mgxa0ha−1, respectively, while that for the grazing land was 7.76xa0Mgxa0ha−1, and the mean carbon content between the three land uses were significantly different (pu2009<u20090.05).ConclusionsWe conclude that forests managed by the community have a high potential for C sequestration and storage and their conservation should be promoted.

How dynamics and drivers of land use/land cover change impact elephant conservation and agricultural livelihood development in Rombo, Tanzania

ABSTRACT Land use/land cover (LULC) change affects the provision of ecosystem services for humans and habitat for wildlife. Hence, it is crucial to monitor LULC particularly adjacent to protected areas. In this study, we measured LULC change in Rombo, Tanzania, an area with high-potential agro-ecological zones that is dominated by human–elephant conflicts (HECs). We used remote sensing and geographical information system techniques, questionnaires and village meetings to assess spatio-temporal patterns of the LULC changes in the study area. Using Landsat imagery, digital elevation model (DEM) and ground truthing, we classified and monitored changes in LULC from the years 1987 to 2015. We found that within Rombo, settlements were increasing, while agricultural and agroforestry lands were decreasing and respondents’ perceptions varied along the altitudinal gradient. Patterns of HEC and LULC were observed to change along the gradient and the later threatened the agricultural land and ecological integrity for elephant habitat, leading to high tension and competition between elephants and people. This research offers baseline information for land use planning to balance wildlife conservation with livelihood development in Rombo and highlights that managing the impacts of LULC changes on HEC and elephant habitat loss is a matter of urgency.

Balancing African Elephant Conservation with Human Well-Being in Rombo Area, Tanzania

The critical assessment of the nature and extent of human-elephant conflict (HEC) and its impact on conservation efforts are essential if we are to meet the challenges related to extinction of local population, as well as loss biodiversity. Conservationists need detailed information on HEC in areas where these challenges prevail to improve intervention in the face of limited funds/resources. We assessed the status of HEC at Rombo area over the last six years. Data based on household surveys, focus group discussions, spatiotemporal analysis of site observations, and reported incidents of damage within the last six years were mapped. Out of all HEC cases analyzed, the most were crop damage which took place at night and the damage was severe between May and July, when cereal crops were mature. In upland areas of Rombo, HEC hotspots were observed inside the protected forest plantation where local people cultivated their annual crops. Cold spots concentrated in upland areas outside the protected forest plantation dominated by settlement and agroforestry less preferred by elephants. In lowland areas, HEC hotspots were observed in village lands close to the PAs, within settlement and farmland dominated by seasonal crops. This suggests that HEC management efforts such as establishment of buffer zones should be directed around the areas adjacent to PAs and prevention should focus on cultivation of the alternative crops and farming systems that are less preferred by elephants. Our study highlights the importance of using a combination of data collection techniques to pinpoint fine-scale HEC hotspots in a highly conflict-prone location of Tanzania.

Effects of clipping and irrigation on carbon storage in grasses: implications for CO2 emission mitigation in rangelands

ABSTRACT Understanding how individual grasses respond to herbivory and rainfall has been hampered by the difficulty of quantifying above- and belowground carbon (C) storage in grasses. Particularly by restoring degraded rangelands through reseeding, their C storage potential can be greatly enhanced. The responses of reseeded grasses to the effects of herbivory and precipitation were assessed to evaluate the potential of individual grasses for C storage as a technique for climate change mitigation. Clipping experiments were conducted on mature grass tufts of two native grass species, Chloris gayana and Cenchrus ciliaris, in the semi-arid Borana rangelands, Ethiopia. Further, above- and belowground C storage of young grasses of the same species in pot and field plot trials was experimentally quantified under simulated grazing and variable rainfall. The results showed that aboveground C was significantly 4 times lower in the clipped compared to unclipped mature grasses. In contrast, 3 times higher C was found in young reseeded grasses that were clipped compared to unclipped ones. Clipping and irrigation in combination significantly influenced belowground C in young grasses, with reduced irrigation overriding clipping effects. The paper concludes that moderate grazing should be encouraged to enhance CO2 uptake, consequently contributing to climate change mitigation in rangelands.

A nature-based approach for managing the invasive weed species Gutenbergia cordifolia for sustainable rangeland management

BackgroundThe invasive weed species Gutenbergia cordifolia has been observed to suppress native plants and to dominate more than half of the entire crater floor (250xa0km2) in the Ngorongoro Conservation Area (NCA). As this species has been found to be toxic to ruminants it might strongly impact animal populations in this ecologically diverse ecosystem. Hence, a nature-based approach is urgently needed to manage its spread. We tested two Desmodium spp extracts applied to G. cordifolia and assessed the latter’s germination rate, height, fresh weight and leaf total chlorophyll content after 30xa0days in both laboratory and screen house experiments.ResultsSeedling germination rate was halved by Desmodium uncinatum leaf extract (DuL), particularly under higher concentrations (≥75xa0%) rather than lower concentrations (≤62.5xa0%). Likewise, in both laboratory and screen house experiments, germination rate under DuL treatments declined with increasing concentrations. Seedling height, fresh weight and leaf total chlorophyll content (Chl) were also most strongly affected by DuL treatments rather than D. uncinatum root extract, Desmodium intortum leaf extract or D. intortum root extract treatments. Generally, seedlings treated with higher DuL concentrations were half as tall, had one-third the weight and half the leaf Chl content compared to those treated with lower concentrations.ConclusionOur study shows a novel technique that can be applied where G. cordifolia may be driving native flora and fauna to local extinction. Our data further suggest that this innovative approach is both ecologically safe and effective and that D. uncinatum can be sustainably used to manage invasive plants, and thus, to improve rangeland productivity.