Gobabeb Training and Research Internship Programme 2011
Project 1: Effects of Hartmann’s Mountain Zebra Dung on Soil Properties and Plant Growth at Zebra Pan, Namib-Naukluft Park –Bright Sanzila
Hartmann’s Mountain Zebras are dependent upon the mountainous transition zone between the Namib Desert and the inland plateau where they can find large fields to graze and periodic water resources. Since in 1998, the Langer Heinrich Uranium mine has been developing in this region. This mine may become a disturbance and impact the zebras’ native habitat and, thus, it is critical that we understand the zebras’ function in the desert ecosystem. This study observed how zebra dung impacts soil fertility, seed dispersal, and plant growth. In other studies, dung has been shown to provide critical nutrients, like nitrogen and phosphorous, which are required for plant growth. Soil samples beneath zebra dung and in no-dung (control) regions were analysed for pH, nitrate, organic matter, texture, and seed composition. The soil beneath the dung had significantly more nitrogen and organic matter than soil away from dung sites. The dung samples had high amounts of seed from a common annual grass (Stipagrostis ciliata), but little else. Additionally, a greenhouse experiment revealed that radish seeds grew higher when given a zebra dung manure treatment than seedlings watered with unfiltered tap water. These results suggest that zebra dung should in theory play a fertilizing function, but
field evidence is not available to show whether this happens in practice. Their role in seed dispersal appears to be limited, since the grass species that dominated the dung seedbank was widespread and normally rely on wind dispersal. The functional role of dung
– and thus zebras – in the Namib ecosystem is therefore not yet fully understood. Since dung usually plays an important role, the reasons for this (e.g. scarcity of conditions where dung, rare rainfall events and plant active growth phases overlap) should be further studied.
Project 2: Hypolithic Cyanobacteria (HLC): The effects of humidity on short-term recovery rate of Hypolithic Cyanobacteria – Elizabeth Lukas
Hypolithic Cyanobacteria (HLC) are microorganisms and primary producers that colonize transparent stones andare able to tolerate extremely arid conditions, like that of the Namib Desert. Beyond being well-adapted to desert conditions, these HLC provides several key ecosystem functions, including reduction of soil erosion, nitrogen fixation, contribution of organic carbon, and increased water infiltration. Unfortunately, HLC is very vulnerable to disturbances and may take decades to colonize after disruption; off-road driving, road construction, borrow pits, and uranium mines are all frequent and long lasting disturbances in arid soils. This study, building on a previous study on the same subject, looked at the recovery rate of HLC in areas that have been disturbed from 0.8 years to 61 years ago, analysed the effects of rehabilitation, and observed how moisture impacts HLC growth rates. A key aim was to increase the sample sizeof disturbed sites in the overall approach to understanding the nature of this impact.
The percent cover of HLC, as measured on stones sampled on linear transects, in disturbed areas was less than in undisturbed areas. Apparently, rehabilitation can assist HLC recovery rates as long as the areas are not disturbed after rehabilitation. Additionally, controlled water testing trials found no significant difference in HLC cover on dry and frequently watered quartz stones. On average, the Namib receives 23mm of rain annually but between June and July (2011) the Namib received 160mm; given the unpredictability of precipitation in the Namib, future studies should carry out longer-term moisture studies on HLC colonization. Overall, this study supports future rehabilitation efforts and provides baseline techniques for testing climatic variables on HLC colonization.
Project 3: The influence of termites on soil properties in three habitats in the central Namib Desert –Rosalia Iileka
Termites, social insects in the order Isoptera, can have a substantial impact on physical and biological soil properties; they have been shown to restore soil infiltration in otherwise compacted soils and concentrate nutrients for improved plant growth. In the Namib, Uranium mines are contributing to compacted soils and termites may be able to assist soil and vegetation restoration efforts. This study analysed the effect of the African Harvester Termite (Hodotermes mossambicus) on soil properties related to productivity and fertility. H. mossambicus is found in the drier savannahs
of Africa and the Namib Desert and constructs nests 1.4m below ground, on average. Soil samples near and away from termite mounds were taken from the rocky gravel plains, gravel plains, and riparian forests near the Kuiseb River. Soil property analyses revealed that soils near termite mounds have faster infiltration rates, organic matter content, nitrogen, and lower pH than soils away from termite mounds. There were no significant differences between the three different
site locations. These results suggest that termite activity could help restore compacted, nutrient-poor mining grounds. Now that we know the beneficial influence of termites in the Namib, further studies should characterise the distribution of H. mossambicus in the Namib Desert and determine whether there are specific barriers to colonisation of disturbed areas that could be mitigated.