LONG-TERM GLADES IN ACACIA BUSHLAND AND THEIR EDGE EFFECTS IN LAIKIPIA, KENYA

Throughout the Laikipia ecosystem in Kenya, isolated glades occur with in acacia bushland and woodland communities. These glades are at least several decades old. They are reported to be old settlement sites of traditional pastoralists no longer present, and their size, location, and orientation are consistent with the settlement sites of related pa storalists studied elsewhere. The purpose of this study was to documen t the effects of these glades at the local and landscape levels. Worki ng in central Laikipia, we documented differences in vegetation, anima l use, and soils at four of these glades, and at increasing distances from glade edges. Four ''glade specialists'' dominated the plant commu nities within glades, and were very rare outside of glades. Pennisetum stramineum, one of six glade edge species, formed a ring of dense tal l grass around most glade edges. The transition to acacia bushland at the glade edges was not always abrupt (depending on the trait consider ed), resulting in edge effects that differed in depth and sharpness. E dge depth, defined as the distance required to attain two-thirds of ba ckground levels for a trait, ranged from 0 to 200 m. Understory plant species richness and diversity were lowest inside glades, and graduall y increased with distance from glades. However, because glades support ed species not found elsewhere, the presence of glades increased overa ll species diversity. The density of wild and domestic large mammal du ng was up to 10 times greater inside the glades, and declined with dis tance from glade edges. Similarly, soil nitrogen, potassium, carbon, c alcium, and sodium were greatest inside glades. Soil phosphorus, magne sium, and manganese were not elevated inside glades or within 100 m of glades, but instead were much more abundant in background samples. Th ese glades may be maintained by high densities of large mammals, eithe r through herbivory or through changes in soil chemistry. Glades may b e attractive to mammals because of the high quality of food there, or as part of an anti-predator strategy. The result is a relatively perma nent community mosaic that increases ecosystem heterogeneity and resou rce use by domestic and wild animals. The spatial nature of this heter ogeneity differs among species, depending on their distributions relat ive to the glades.