Acacia-Commiphora bushlands and thickets
Acacia-Commiphora bushlands and thickets are unique ecosystems found in the dry, low-lying areas of East Africa, particularly in northern and northeastern Kenya, eastern Ethiopia, and Somalia. Characterized by tangled, spiny vegetation, this semi-arid habitat serves as a transitional zone between the East African savannas and the semi-deserts of the Horn of Africa. The dominant acacia and commiphora trees typically remain leafless for prolonged periods, conserving energy during extended dry spells. Following rainfall, the environment undergoes a rapid transformation, with a burst of greenery, flowers, and increased wildlife activity, making this a critical time for both animals and plants.
However, these ecosystems face significant challenges due to overgrazing by livestock, which threatens their delicate balance and can lead to soil degradation. Elephants, as keystone species, significantly influence the structure of these woodlands, but their increasing populations can also lead to damage of the vegetation. Moreover, the acacia-commiphora bushlands are experiencing pressures from climate change, population growth, and land use changes, including charcoal production. This complex interplay of natural and anthropogenic factors highlights the fragility and critical importance of these bushland ecosystems in sustaining both biodiversity and local communities.
Acacia-Commiphora bushlands and thickets
Category: Grassland, Tundra, and Human Biomes.
Geographic Location: Africa.
Summary: The acacia-commiphora landscape is dominated by thorny vegetation that transforms after rains; it is increasingly affected by drought and human changes.
The tangled, spiny, often leafless vegetation found in the dry, low-lying areas of east Africa is typical of the warm, semi-arid habitat known as the acacia-commiphora woodland and bush, which extends over much of northern and northeastern Kenya, parts of eastern Ethiopia, and through Somalia. This habitat is a transitional zone between two of east Africa's major ecological communities: the east African savannas and grasslands, and the dry lands and semi-deserts of the Horn of Africa.
A scarcity of water underpins the entire ecology of the acacia-commiphora woodland and bushland habitats. Therefore, extreme measures of survival are a feature of plant and animal communities in this area. The dominant acacia and commiphora trees, which give this woodland its name, form thickets with many other deciduous shrubs and trees that remain leafless for as much as nine months of the year, alongside succulents like Euphorbia spp. Only by shutting down in this way can the trees conserve enough energy to withstand the area's prolonged dry spells. As a result, these woodlands seem to be in a suspended state for long periods.
Transformation After Rainfall
A transformation occurs in the acacia-commiphora bushland after rains. The gray and seemingly lifeless trees suddenly burst into leaf, putting out buds that develop quickly into flowers so that pollination, seed production, and fruiting can all be accomplished rapidly.
Following rains, the acacia-commiphora bushland soon fills with flowers, creepers, and insect life. New grasses spring up from the red dust and from sandy patches in stonier, more open ground. From rhizomes and tubers, or from seeds that lay buried in the soil, herbs and other plants emerge. Wildflowers abound in this zone, quickly carpeting the ground and bush. The common species include Thunbergia, Ipomoea spp., Aloe spp., Boophone disticha, Craterostigma spp., and the labiates Ocimum and Orthosiphon.
This time is crucial for wildlife and livestock in this region, as food and water are briefly abundant. The typically dry streams and pans fill rapidly and turn into frantic sites of mating and breeding for insects including damselflies and mosquitoes, as well as large numbers of vocal frogs that are not typically associated with these dry zones. Some of these pans hold water for several months and become important reservoirs that keep thirsty animals watered well into the dry months.
At times of rain, leopard tortoises move about, making the most of the opportunity to lay their eggs in the rain-softened soil. Many other reptiles and invertebrates are also active and breeding at this time in the acacia-commiphora bushland.
Soon after the brief rains, the temporary pools, streams, and other water sources dry up. As another dry, dormant period begins, the elephants—a keystone species in the acacia-commiphora bushland—move to other areas where they know that they can find water. The commiphora trees lose their leaves and conduct photosynthesis through their peeling, papery bark, which has a layer of chlorophyll-bearing cells beneath it. Specialist tree-browsers, such as the reticulated giraffe and gerenuk, use their adaptive advantage of height to feed on vegetation.
Euphorbias and other succulent plants such as Sansevieria, which appear in low, spiky clumps, are among the few evergreen plants on view after the shutdown of acacia-commiphora leafy vegetation is complete. Dryland-adapted species of antelope like the lesser kudu and the tiny dik-dik are able to survive on these fleshy plants and on the occasional Boscia tree. Otherwise, the woodlands revert to a monotonous gray tangle of bare limbs for the rigors of another long dry season.
Effects of Livestock and Wildlife
In this land of extremes, overgrazing by livestock animals is a constant threat to the equilibrium of the acacia-commiphora bushland ecology. Overstocking and mismanagement can easily tilt the balance from a productive relationship to one that is damaging to both the environment and to the pastoralists, who, with their livestock herds, depend on the fragile resources the habitat provides. Overgrazing quickly results in capped ground—hard, impermeable soil that has little chance of reestablishing cover. Imbalances can become most obvious during long droughts, when livestock (mainly cattle) perish in large numbers.
Elephants also have an increasing effect on acacia-commiphora bushland vegetation. They leave many acacia trees stripped of their bark and push over commiphora trees. Because many of the areas previously open to elephants are unavailable today, their impact on the acacia-commiphora bushland is significant, creating large zones with dead or dying and damaged trees.
The acacia-commiphora woodlands depend for their stability on the extreme conditions that they embody at different times of the year. Abundant browsing and grazing after rain mitigates the effect of large herbivores by encouraging them to disperse widely through the landscape, allowing the acacia-commiphora bushland plenty of scope to propagate itself. When the vegetation shuts down in the absence of water, elephants and other large browsing herbivores leave the woodlands, sparing the trees and shrubs.
The acacia-commiphora bushland is an interesting habitat that is undergoing rapid changes due to the impact of climate change (extensive droughts), population growth, and increasing settlement, as well as large-scale conversion of areas for charcoal production.
Bibliography
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