Understory Diversity Affects Monodominance of Anogeissus leiocarpa

Abstract

The persistence of monodominant communities in tropical ecosystems, known for their high diversity, has challenged tropical ecologists. Species diversity could influence the persistence of monodominance by limiting the competitive edge of the monodominant species particularly in the forest understory. However, the role of stand diversity or demographic structure in maintaining monodominance particularly in early life stage in forest understory remains elusive. We studied Anogeissus leiocarpa in monodominant stands in West Africa. We used generalised linear mixed effect models to test the effect of stand species diversity on stem density and dominance of A. leiocarpa in the understory and how this effect changes from the stand centre to the edge. Anogeissus leiocarpa density and dominance decreased from the stand centre to the periphery. Anogeissus leiocarpa dominance in the understory was below 50% on average, suggesting that monodominance emerges during the transition from the understory to the canopy. Increase in community diversity had negative effects on A. leiocarpa seedlings density perhaps due to increased diversity in competition mechanisms. Contrary to our expectation for a pioneer species, A. leiocarpa lacked vigorous recruitment and did not exhibit the expected negative exponential population structure. The diameter- and height-based size class distributions were not correlated across populations, indicating that using the population structure as an ecological diagnostic tool could lead to suboptimal conservation decisions.