Potential causes of arrested succession in Kibale National Park, Uganda: growth and mortality of seedlings

Recent studies suggest that regeneration following large-scale disturbance in Kibale National Park, Uganda, is slow or possibly arrested. Here, data i s provided on the growth and mortality of seedlings in the forest understor y, treefall gaps, and in large gaps that suggest that this pattern of arres ted succession can be attributed partially to the fact that this East Afric an community lacks aggressive colonizing tree species. Growth and mortality rates were contrasted for seedlings of six tree species planted in the und erstory, small gaps, and large gaps for 36 months. Data suggest that specie s are adapted to gaps of particular sizes. For example, Uvariopsis congensi s grew faster in the understory than in small gaps, whereas Warburgia ugand ensis had the lowest mortality rate and highest growth rate in large gaps. Seedlings (n = 170) of 15 species were transplanted to assess the response of the tree community to large gap conditions. The limited survival of seed lings in large gaps relative to the understory suggests that only a small p roportion of the tree community in this forest regenerates best in gaps lar ger than those created by the collapse of a single tree. These findings dif fer from a number of studies conducted in other geographical regions, and s uggests that tree communities differ with respect to the proportion of tree species adapted to gaps of particular sizes. This may relate to variation among regions in their history of disturbance and thus frequency of gap for mation, size of gaps, and the duration of periods of release. Such variatio n could imply the existence of a corresponding pattern among tropical fores ts of differential vulnerability to human disturbance, which tends to creat e many large gaps.