Impacts of native versus domestic ungulates on biological communities in arid savanna
PhD by Johanna Reinhard (University of Potsdam)
Arid rangelands worldwide are adversely affected by high levels of human intervention and high climatic variability. In Southern African savannas, unsustainable and intensified lifestock management during the last decades often led to desertification with subsequent losses in ecosystem function and services.
I am investigating representative components of functional change in vegetation and the alteration in faunal community strucrture as a result of grazing/non-grazing. Furthermore, I would like to gain an holistic view on how species interact in a dryland community and how grazing of wildlife versus cattle grazing impacts the ecological communitiy. In order to understand underlying mechanisms of observed differences, I use a fully factorial ecological experiment via the establishment of herbivore exclusion sites.
Project under research group:
Vegetation ecology and nature conservation
Tenebrionidae biodiversity in Kuzikus wildlife reserve
Dawid Schimroszcyck (Museum and Institut of Zoology, Warsaw)
An investigation of the ecology and determination of tenebrionid fauna in Kuzikus and surrounding
Options for sustainable geo-biosphere feedback management in savanna systems under regional and global change (OPTIMASS)
Prof. Florian Jeltsch (University of Potsdam)
Savannas cover approximately 20% of the world’s land surface and 40% of Africa. Worldwide, they deliver almost 30% of the terrestrial net primary production and their carbon dynamics have a global impact. Savanna ecosystems are probably unparalleled in their dependence on the functioning of complex feedbacks between the geo- and biosphere, i.e. climatic conditions, atmospheric CO
levels, water availability, vegetation dynamics, soil-water dynamics and land use. Disrupting the regulating functions of these feedbacks may lead to irreversible, discontinuous transitions and a catastrophic change of the ecosystem. Since savannas contain a large and rapidly growing proportion of the world’s human population any disruption of these feedbacks thus risks the livelihood of millions of households depending on a sustainable provision of a variety of ecosystem services (e.g. water provision, forage production, tourism). This provision is under extreme threat due to climate and CO
changes as well as increasing land-use pressure.
Savannas of southern Africa are a hot spot of climate, land-use and socio-economic change and thus can function as a model-region for a broad range of savannas worldwide. Without a comprehensive concept for a sustainable adaptive management and use of this system under unprecedented conditions an aggravation of already existing poverty is to be expected.
This project therefore aims to develop robust solutions and innovative strategies for sustainable management and stabilisation of geo-biosphere-feedbacks in savannas across a broad range of climatic conditions and spatio-temporal scales. This goal will be achieved using a transdisciplinary approach based on thorough analyses of climate-water-vegetation-CO
and land use feedbacks under current and future conditions and their impact on ecosystem stability and key ecosystem services. The focal savanna region covers a range from arid to semi-arid to mesic savannas in Namibia. The analysis of the processes and conditions of the proposed broad range of savanna types with its diverging environmental conditions and management structures allows the project to develop tools and solutions to stabilise and restore geo-biosphere feedbacks and related ecosystem services that can be used as exemplary concepts for other regions worldwide.
Impacts of herbivory and fire on seedling establishment of a key bush encroacher (Acacia mellifera) in semi-arid African savanna rangelands – a new potential management tool to mitigate bush encroachment
MSc by Linda Böckenhof (University of Potsdam)
Bush encroachment, a consequence of unsustainable land use (i.e. overgrazing, altered fire regimes), is considered as a major form of land degradation that seriously threatens savannah biomes, which are of global economic, social and conservational importance. Fire management is a promising tool to mitigate bush encroachment, however farmers are often afraid to apply this option and even prevent natural fires. An alternative strategy may be the introduction of browsing wild antelopes that may feed on bush seedlings and saplings. However, the potential of browsing wild antelopes remains surprisingly unexplored. Thus, the role of browsing wild ungulates and their combined effects with a natural fire on seedling and sapling establishment of a main encroaching species, Acacia mellifera, were studied from Feb. to Apr. at a game farm and a cattle farm in a semi-arid Namibian savanna landscape. Browsing animal species and general animal abundances were identified by camera traps. Survival and growth of A. mellifera seedlings and saplings were studied at fenced (browser exclosure) vs. unfenced sites. Sapling performance across different environmental gradients (bush cover, waterhole distances, soil penetrability, animal densities) as well as at different microsites (grass vs. bare soil) and positions (under adult plant canopies vs. matrix) were analyzed. Additionally sapling survival and recovery rates four months after fire under high ungulate densities at the game farm and under low ungulate densities at the cattle farm were evaluated. Springboks were identified to successfully suppress seedling survival (27%) and sapling growth (93%). Sapling sizes were inversely proportionally linked to springbok densities reflecting their past and present spatial distributions. Grow conditions of saplings were better in tussocks since grass facilitation outperformed grass competition, and increased over the distance to adult shrubs as a consequence of various interfering distance-dependent competition and facilitation effects. Sapling performance across partly antagonistically operating environmental gradients was in sum favored at less encroached areas that consequently more urgently require careful management. Fire caused sapling mortality of more than 95% and the resprout ability was positively correlated to sapling size. Combined effects of fire and springbok browsing are most powerful where sapling establishment is favored by other facilitative environmental factors. Furthermore, springbok browsing can increase the destructive power of fire between fire intervals by suppressing compensational growth of resprouting saplings after fire and by hindering saplings to accumulate aboveground biomass and belowground energy reserves, which both reduces resprout abilities after the next fire. Thus the combined effects of fire and springbok browsing might have great potential to suppress the establishment of A. mellifera in semi-arid savanna landscapes.
Impacts of drought stress on perennial vegetation under different land use intensities - Assessing land use effects on plant functional traits in an African savanna
MSc by Julia Seidel (University of Potsdam)
Worldwide, savanna rangelands are subjected to an increase of woody plants, also known as bush- or shrub encroachment. This conversion has dramatic effects on the regional ecological and ecohydrological processes in these sensitive ecosystems, therefore being recognized as one of the most threatening forms of rangeland degradation. Unsustainable livestock grazing and poorly adapted game management have been identified to be the primary factors for this shift in vegetation. However, the feedbacks between herbivory, soil moisture and vegetation dynamics under variable climatic conditions seem to be poorly understood.
The current work is focused on the consequences of different land use intensities on the ecohydrological properties of the ecosystem in the African savanna. Therefore soil compaction, soil moisture and plant functional traits (e.g. plant water potential, regeneration potential, SLA, plant size) were conducted to assess the extent of drought stress on the perennial vegetation. Such a functional approach is a useful tool to improve the understanding of the complex responses of vegetation along a land use driven shrub cover gradient.
The results show that due to higher grazing activities soil compaction is increasing and thus leading to a reduction in soil moisture in the surface soil layers. The consequences in plant functional traits exhibit a contrasting trend for the life form types. Grasses show an increase in regeneration potential and SLA, whereas plant size tends to decrease with shrub cover. Shrub traits seem to react conversely to the bush encroachment.
Consequently the results indicate a striking relationship between vegetation and soil characteristics and clearly show that land use has a major influence on the ecohydrological feedbacks within the studied area. These findings provide a basic insight into the impact of land use consequences contributing towards an improved monitoring and management in semi-arid rangelands. To face future threats regarding accelerated climate change and increasing intensity of land use, further studies of plant functional traits and ecohydrological properties could provide important information, which may support the restoration of such degraded rangelands.
Feedbacks between Land Use and Plant Functional Traits of Herbaceous Vegetation in an African Savanna Rangeland
MSc by Claudia Hahn (University of Potsdam)
Until now the ecohydrological processes, the interplay between land use, soil and vegetation, remain unclear. It is not completely assessed to which extent shrub encroachment resulting from land use is affecting soil properties and further how the soil is influencing vegetation,although the impacts on economy and ecology are severe. That is why a systematic understanding of impact factors that structure vegetation communities of savannas is needed to guide future management options (Sankaran et al. 2005). Especially with the following questions a step towards an understanding of the ecohydrological feedback mechanisms in savannas shall be done:
1. Is land use aff ecting the plant community regarding the proportion of annual and perennial grasses?
2. Do soil properties (soil moisture and soil density) change with land use impact? To which extent does shrub cover alter the soil conditions?
3. Is it possible to use plant functional traits (morphological and physiological) to draw inferences about the state of shrub encroachment of a region? Which plant functional traits are most sensitive?
4. How do plant functional traits react to altered environmental conditions under increasing shrub encroachment? Do annual and perennial grasses show differences in their reaction?
Do Sociable Weavers
use punishment to maintain cooperative nest construction?
PhD by Gavin Leighton (University of Miami)
Although evolution by natural selection is often depicted as favoring ruthless, selfish behavior, cooperation is widespread in nature. Consequently, the evolution of cooperative behavior has become a central question in evolution and behavior. The present research examines the evolutionary stability of a particular form of avian cooperation, cooperative nest building. Communal nests represent a public goods dilemma: each individual benefits directly from the communal nest, but would benefit more if it could refrain from contributing to nest- building so long as others continued to maintain the nest. This research will investigate whether punishment behavior is used to stabilize the cooperative nest construction of sociable weavers in Namibia. This research on sociable weavers will provide results that will facilitate comparative analysis of behavior across multiple animal taxa; therefore, the research will provide information on the evolution of social behaviors and the stability of cooperative behaviors in wild populations. While most work on large-scale cooperative behavior has been performed in the eusocial hymenoptera and humans, little work has been performed in other systems. This work therefore represents a novel test of supposed behaviors that allow for the maintenance of public goods and therefore the stability animal societies.
Life history, breeding and rearing of the silk-poducing
Johanna Reinhard & Friedrich Reinhard (BRinK)
cocoons were recently discovered to be suitable for high quality silk extraction. Should there be demand of silk production, it is utterly important to investigate methods of rearing and breeding in order to safe guard the persistance of the species. BRinK studies life history of the insect and its breeding potential for sustainable silk production.
Near real-time ultrahigh-resolution imaging from unmanned aerial vehicles for sustainable land use management and biodiversity conservation in semi-arid savanna under regional and global change (SAVMAP)
Friedrich Reinhard (Kuzikus Wildlife Reserve)
Ant- Acacia symbiosis in Southern Africa
PhD by Heather Campbell (University of Reading)
The overall aim of this project is the study of ant-Acacia interactins in a Namibian Savanna ecosystem. In this symbiotic relationship ants receive food rewards and shelter within swollen thorns, whilst the Acacia is protected from herbivore damage by aggressive ant defenses. Although ant-plant interactions are widespreas in tropical forests, they are rarely found in savanna. The exceptions to this are the African Acacia species.
So far the only African
to have received detailed scientific attention is the
. The bulk of this information had been recorded at one field site in Laikipia, Kenya. The overall aim of conducting research at Kuzikus is to study ant-
interactions at a new location and on novel
. Thorn-dwelling ants provide antiherbivore defence for camelthorn trees,
, in Namibia. African Journal of Ecology.