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

Summary Recent studies suggest that regeneration following large‐scale disturbance in Kibale National Park, Uganda, is slow or possibly arrested. Here, data is provided on the growth and mortality of seedlings in the forest understory, treefall gaps, and in large gaps that suggest that this pattern of arrested succession can be attributed partially to the fact that this East African community lacks aggressive colonizing tree species. Growth and mortality rates were contrasted for seedlings of six tree species planted in the understory, small gaps, and large gaps for 36 months. Data suggest that species are adapted to gaps of particular sizes. For example, Uvariopsis congensis grew faster in the understory than in small gaps, whereas Warburgia ugandensis 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 seedlings in large gaps relative to the understory suggests that only a small proportion of the tree community in this forest regenerates best in gaps larger than those created by the collapse of a single tree. These findings differ from a number of studies conducted in other geographical regions, and suggests 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 formation, size of gaps, and the duration of periods of release. Such variation could imply the existence of a corresponding pattern among tropical forests of differential vulnerability to human disturbance, which tends to create many large gaps. Résumé Des études récentes suggèrent que la régénération qui suit la perturbation importante qu’a connue le Parc National de Kibale, en Ouganda, est lente, voire me?me stoppée. On trouve ici les données sur la croissance et la mortalité des pousses dans les sous‐bois, dans les trous dus aux chutes d’arbres et dans les éclaircies plus grandes, qui suggèrent que ce schéma d’évolution immobilisée peut e?tre du?, en partie, au fait que cette communauté est‐africaine manque d’espèces d’arbres agressivement coloni?santes. On a comparé pendant 36 mois, les taux de croissance et de mortalité des jeunes pousses de six espèces d’arbres plantées dans les sous‐bois, les petits trous et les éclaircies plus grandes. Les données laissent entendre que chaq