East African Ecosystems Research Articles

Fire history and management as determinant of patch selection by foraging herbivores in western Serengeti, Tanzania

Although the use of fire as a management tool has increased during the past decades in East African savannas, there is insufficient knowledge about herbivores' utilization of areas with different fire history. We therefore examined large mammal herbivores' preference for patches that differed in fire history to test whether herbivores would non-randomly select patches according to availability. Our study area was the East African Serengeti ecosystem. Animals were recorded along transects at monthly intervals from May 2001 to April 2006, and data on the burnt and non-burnt areas along transects were extracted from existing fire maps. The prediction was tested using chi-square goodness-of-fit test, and selection ratio as a preference index for patch types. Our results show that African buffalo persistently occurred in non-burnt patches, whereas browsers (Giraffe and Kirk's dik-dik) and mixed feeders (Grant's gazelle and impala) were often seen in non-burnt patches but also used burnt patches. Grazer species (Thompson's gazelle, topi, wildebeest and Burchell's zebra) favoured patches burnt in the current year compared to non-burnt patches. For all species together, patches burnt repeatedly were least selected compared to those that were burnt only once in 3 years. The outcome of this study suggests that annual burning of the same patches is not optimal for biodiversity maintenance and ecosystem functioning.

Personal Perspectives on Commercial Versus Communal African Fire Paradigms When Using Fire to Manage Rangelands for Domestic Livestock and Wildlife in Southern and East African Ecosystems

Personal Perspectives on Commercial Versus Communal African Fire Paradigms When Using Fire to Manage Rangelands for Domestic Livestock and Wildlife in Southern and East African Ecosystems

Personal Perspectives on Commercial versus Communal African Fire Paradigms when Using Fire to Manage Rangelands for Domestic Livestock and Wildlife in Southern and East African Ecosystems

Africa is often referred to as the Fire Continent, and fire is recognised as a natural factor of the environment due to the prevalence of lightning storms and an ideal fire climate in the less arid regions with seasonal drought. On a global scale, the most extensive areas of tropical savanna, characterized by grassy under stories that become extremely flammable during the dry season, occur in Africa. The use of fire in Africa to manage vegetation for domestic livestock and indigenous wildlife is widely recognized by both commercial and communal land users. Research on the effects of fire has been conducted throughout the grassland and savanna areas since the early twentieth century, resulting in the development of effective and practical guidelines for prescribed burning for domestic livestock and wildlife management systems. Generally, the reasons for prescribed burning in Africa are similar for both commercial and communal land users, namely, to remove moribund and or unacceptable plant material and to control the encroachment of undesirable plants negatively affecting domestic livestock and wildlife. In addition, commercial operators use fire to manage wildlife conservation areas. Prescribed burning to control ticks is also widely used in communal communities but is generally not recognised in commercial livestock enterprises. However, research has shown that tick populations can be reduced using fire to alter the micro-habitat for these organisms. Until recently, commercial and communal land users held differing views on the appropriate season for prescribed burning, with the former igniting fires shortly after the first spring rains and the latter burning throughout the dry winter period. Subsequent research has shown that both seasons of burn have similar effects; the key requirement being that the grass sward is dormant at the time of burning to minimise the negative effects on the vegetation. A valuable tentative comparison has been made between fire management practices applied by commercial land users and communal land users, and provides an exciting opportunity for further and essential research to be conducted to gain greater insight into how communal African communities use fire. Based on extensive experience, my aim is to provide a personal perspective on the use of fire by commercial and communal land users for managing rangelands in southern and east African regions of the continent.

The potential of optical high resolution data for the assessment of leaf area index in East African rainforest ecosystems

Operational standard products of biophysical variables, such as leaf area index (LAI) derived from satellite observations (e.g. Moderate Resolution Imaging Spectroradiometer (MODIS), Medium Resolution Imaging Spectrometer (MERIS) or VEGETATION), serve the need for adequate input data for quantitative modelling of ecosystem dynamics on regional to global scales. For the validation of those products and for local applications, higher resolution LAI maps based on field and high spatial resolution satellite data are crucial. As validation sites in tropical rainforests are rare, a study was undertaken in a moist semi-deciduous tropical rainforest in East Africa. In situ LAI measurements were carried out with digital hemispherical photography on 30 test sites. Spectral vegetation indices (SVIs) and texture measures calculated from top-of-canopy Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Satellite Pour l'Observation de la Terre (SPOT)-4 High Resolution Visible and Infrared (HRVIR) reflectance data were compared with respect to their ability to predict effective LAI. Regression analyses showed that ASTER data were generally better suited, with simple ratio (SR) performing best for early and intermediate forest stages and texture measures (grey level co-occurrence matrix (GLCM) variance) derived from SWIR information rendering superior results in later forest stages. Finally, a high resolution LAI map could be constructed with an accuracy of 0.39.

The Indian Ocean dipole – the unsung driver of climatic variability in East Africa

AbstractA growing body of evidence suggests that an independent ocean circulation system in the Indian Ocean, the Indian Ocean dipole (IOD), is partly responsible for driving climate variability of the surrounding landmasses. The IOD had traditionally been viewed as an artefact of the El Niño–Southern Oscillation (ENSO) system although increasingly the evidence is amassing that it is separate and distinct phenomenon. We review the causes of the IOD, how it develops within the Indian Ocean, the relationships with ENSO, and the consequences for East African climate dynamics and associated impacts on ecosystems, in particular along the Eastern Arc Mountains of Kenya and Tanzania. We evaluate current research initiatives focussed on characterizing and constraining the IOD and examine how effective these will be in determining climate change impacts on East African ecosystems and how such predictive capacity can be used in developing policy.

Impact of ENSO on East African ecosystems: a multivariate analysis based on climate and remote sensing data

Abstract1 The El Niño‐Southern Oscillation (ENSO) is an important driver of inter‐annual variations in climate and ecosystem productivity in tropical regions. Most previous studies have analysed ENSO‐induced changes in climate based on a single variable, such as rainfall. Also, it is generally assumed that the ENSO impact in East Africa is geographically uniform.2 The objective of this study is to improve understanding of the impact of ENSO on East African ecosystems, by measuring teleconnections between an ENSO index and a number of ecosystem variables in a spatially explicit way and for different time lags. We analysed the spatial patterns of teleconnections in the region by combining time series of climate variables measured for meteorological stations with time series of a vegetation index and surface temperature data measured by remote sensing.3 Our results confirm the ENSO impact on the climatic and ecological variability in East Africa. However, the pattern of teleconnections is much more complex than generally assumed, both in terms of spatial distribution and impact on different ecosystem variables. Not all climate and land surface variables are teleconnected to ENSO in the same way, which leads to a complex impact of ENSO on the ecosystem. Moreover, the ENSO impact is highly differentiated in space, as the direction, magnitude and timing of this impact are controlled by the local climate system, the presence of large lakes, proximity to the coast and, possibly, local topography and land cover.

East African Ecosystems and Their Conservation

East African Ecosystems and Their Conservation

East African ecosystems and their conservation

PART I: ENVIRONMENTAL AND HUMAN HISTORY PART II: MARINE ECOSYSTEMS PART III: INLAND-WATER ECOSYSTEMS PART IV: GRASS, SHRUB, AND WOODLAND ECOSYSTEMS PART V: FOREST ECOSYSTEMS

Cyclical Changes in the Habitat and Climate of an East African Ecosystem

Ecological changes in an East African Game Reserve may be attributed to changes in climatic conditions and soil salinity. Tree damage from elephants and overgrazing by livestock are probably secondary factors.

A BIBLIOGRAPHY RELATING TO THE ECOLOGY AND ENERGETICS OF EAST AFRICAN LARGE MAMMALS

SummaryMany investigations have made contributions to an understanding of energy flow through large mammals in East African ecosystems. This paper lists references to such works and compiles them according to their application to various segments as they appear in an energy‐flow model. The first part indicates papers on pasture utilization, value of foodstuffs, animal numbers and distribution, population dynamics and secondary production. The second part assembles references dealing with individual animal species, stratifying them according to the subjects of ecology, food habits and nutrient utilization, population dynamics and growth.

The Distribution, Abundance and Status of Elephant in the Serengeti Region of Northern Tanzania

The importance of elephant (Loxodonta africana Blumenbach) in East African ecosystems stems from the animal's great size and its high mean ages of survival in most populations. These two factors enable the species to make relatively massive interventions (in terms of a diversion of energy flow) in an ecosystem, which may be of a long-term nature. These factors are also responsible for time lags of several years or decades in the response of an elephant population to self-induced environmental changes. In East African situations, where a rapidly expanding human population is maintained by an essentially subsistence economy, changes in land-use patterns are resulting in continuous contraction of habitat available to elephant, which serves also to cut off certain channels of response such as emigration and dispersion, at the same time as increasing the amplitude of response to levels ultimately threatening the population's survival. These aspects of the ecology of elephant in modern East Africa are responsible for much of the attention currently focused on the animal (Laws 1966, 1967a, b). This investigation was carried out against such a background, by means of systematic observations of elephant in the Serengeti region (between latitudes 1?S and 3?30'S, and longitudes 33?50'E and 36?00'E) of northern Tanzania from 1962 to 1965. Censuses were carried out in 1965, 1966 and 1967 under our direction, and the results have been incorporated into the general findings.