Environmental factors influencing structure and distribution of east African green heart (Warburgia ugandensis Sprague) in Mt. Kenya Forest

Abstract

Effects from past climate, natural disturbances and human activities are significantly impacting negatively on current day processes in tropical indigenous trees forests. Most of the indigenous trees mostly hard woods have been logged by human activities. Warburgia ugandensis is a tree that is highly valued for its medicinal properties, timber, poles and fuel wood. Consequently, its population and distribution has been on the decline due to environmental and anthropogenic impacts. There is no documentation on how environmental factors affect distribution and population structure of W. ugandensis in Mt. Kenya forest and without which conservation strategies may be impossible. This study purposes to determine the present distribution and population structure of W. ugandensis in Mt. Kenya forests. Study area was stratified into four blocks based on potential natural vegetation: moist montane, moist intermediate, dry montane and dry intermediate natural vegetation types. Dry montane was the only vegetation type with W. ugandensis and therefore four forest blocks were selected for this study: Kangaita, Kahurura, Ontulili and Gathioro forests. Belt transects measuring 25 m wide and 500 m long were marked and subdivided into 20 sub-plots of 25 by 25 m from which four sub-plots were systematically selected for sampling. Rainfall data for all the sampled blocks were obtained from meteorological records while altitude data was obtained by use of geographical positioning system (GPS). Data was analyzed by SPSS 11.0 (2001) statistical software. There was a significant negative correlation between rainfall and the population structure of W. ugandensis. The species was concentrated in the drier parts of dry montane forests while none existed in the other three potential natural vegetation types.