Impacts of Pastoralists on Woodlands in South Turkana, Kenya: Livestock‐ Mediated Tree Recruitment

Abstract

Since the turn of the century, African pastoralists have been held responsible for overuse of woody plants and for the degradation and desertification of many arid and semiarid lands. We analyzed the impacts of pastoral nomads and their livestock on the recruitment (establishment to first reproduction) of Acacia tortilis, a dominant tree in the dry woodlands of South Turkana, Kenya, where Acacia seedpods make up an important part of livestock diets. Seed density averaged over 85 times higher in bush‐fenced livestock corrals than in the surrounding environment. The survival and growth of 14 cohorts of trees ranging in age from 1 to 39 yr were investigated comparing tree stands originating inside livestock corrals with those originating outside. Corral soils contained nine times more C, three times more N, and six times more P than adjacent noncorral soils immediately following corral abandonment. Corral soils also retained more moisture than noncorral soils after rainfall. These soil conditions accelerated seedling emergence in corrals, and enhanced survival and growth of 1st‐yr seedlings. Survival of older trees in corral stands was not significantly different from those established outside corrals during this study. However, comparison of tree densities over time suggests that corral stands thin more rapidly than noncorral stands, probably because of crowding. The early survival and growth advantages of the corral environment appear to stabilize the reproductive patterns of A. tortilis in this arid ecosystem, where successful recruitment in noncorral sites may be restricted to the few years with high rainfall. Contrary to the conventional wisdom, pastoralists may be improving rangelands in South Turkana by enhancing recruitment reliability in this important tree species.

Impact of Sheep Bedding on Soil Nutrient Dynamics in the Centennial Mountains of Montana and Idaho

“…Augustine (2003) found that bomas that had recently been abandoned (1-5 years) had higher total soil N than the areas which had been abandoned for longer periods and therefore attributed the increased N to be from manure and urine inputs during the time the areas were actively used as bomas. Reid and Ellis (1995) reported that soils from abandoned bomas contained ninefold more total C and threefold more total N than adjacent control soils and that these elevated concentrations of C and N in bomas remained for up to 20 years following abandonment. This difference in total C and N accumulation in bomas is due to the fact that the majority of the areas surrounding bomas are nutrient poor and do not support much biomass production.…”

“…In East Africa, the study of Bbomas[ (enclosures for cattle protection), which are the equivalent of bedding areas, has shown that, following abandonment, bomas often support a unique plant community and potentially alter the spatial pattern of nutrient cycling within the ecosystem (Augustine, 2003). In Northern Kenya, old bomas contained sixfold to ninefold more soil nitrogen (N) and phosphorus (P) than surrounding habitats and supported thickets of regenerating Acacia tortilis (Reid and Ellis, 1995). In southern Kenya, abandoned bomas were dominated by a lawn of Cynodon nlemfuensis, with enriched concentrations of nutrients both in soils and grasses (Stelfox, 1986).…”

Rediscovery of Traditional Ecological Knowledge as Adaptive Management

“…In some cases, adjacent grazing areas are rotated in the same season as well (Niamir-Fuller 1998). Variations of this pattern, involving the rotation of herd animal enclosures, may result in landscape-level management in the long term through the production of islands of Acacia, a keystone species, by providing nutrient-rich microhabitats suitable for the growth of this tree species (Reid and Ellis 1995).…”

Long-term changes in Serengeti-Mara wildebeest and land cover: Pastoralism, population, or policies?

“…These land demands are controlled by biophysical and socio-economic factors, but also compete for limited space. The transition between forest͞ woodlands and grasslands is driven largely by edaphic factors and disturbances such as fires, heavy browsing by elephants, and natural succession (33)(34)(35)(36)(37), although many of these processes have underlying human drivers (38,39). Foremost among these is land conversion to agriculture (ref.…”