Walia Special Edition on the Bale Mountains (2011) - Zoologische ...

Characteristics and Origins of Glades in the Harenna Forest, Ethiopia
Giovanni Chiodi 1 and Michelle Pinard 1 *
1 Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, UK
*Email: m.a.pinard@abdn.ac.uk
Abstract
Soil, vegetation and historical land use were investigated in nine glades (peri-forest grasslands)
in the Harenna forest, Ethiopia. The aims of the study were to characterize the glades in terms of
soil properties, vegetation and land use, and to investigate their origins, with particular reference
to possible anthropogenic versus natural origin. Three glades and three adjacent forest sites were
studied at each of three altitudes (2300 m, 1850 m, 1750 m) along a soil toposequence. Relative
to adjacent forest soils, soils in glades were distinct with lower pH, total exchangeable bases and
base saturation. Permanent grazing was associated with lower plant species richness and higher
monocot biomass than seasonal grazing; dicot species richness in glades increased with altitude.
Leaching, promoted by local topographic and drainage conditions, and waterlogging are suggested
as potentially important to the formation of the glades, though some glades have characteristics
consistent with an anthropogenic origin. The glades are important for both permanent and temporary
settlers in the Harenna as grazing for livestock; their high social and conservation values could be
compromised by intensive grazing and local expansion of agricultural land.
Introduction
The Harenna forest of Bale Mountains National Park is unusual for many reasons. It extends across
a large altitudinal gradient, thus includes elfin, Erica forest, as well as tall rain forest and subtropical
savanna. Scattered within the forest, but concentrated in the western region, are areas of land that
are dominated by herbaceous vegetation. These distinct patches of grasslands, or forest glades,
represent an important component of the Harenna, in that provide a grazing resource for native
herbivores and local livestock, hunting grounds for predators such as lion, leopard and hyena, and
habitat for endemic species such as the Bale shrew (Yalden 1988).
Despite their ecological and social importance in Bale, little is known of their origins.
Backeus (1992) provides a general review of literature related to peri-forest grasslands, and defined
them as areas dominated by non-arboreal vegetation that occur within forested regions. Both
anthropogenic and natural factors can play a role in their origins, acting independently or together.
In the region, burning and forest conversion to agricultural and grazing land are potentially important
anthropogenic factors. Natural factors such as geomorphology and soil nutrient status could also be
important, as could flooding by oligotrophic waters (Chauvel et al. 1996; Backeus 1993).
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 131