Neighbourhood analysis in the savanna palm Borassus aethiopum:: interplay of intraspecific competition and soil patchiness

A previous study of the spatial patterns of Borassus aethiopum (a humid savanna palm tree) led to the following predictions: H I. Trees and termite mounds positively influence all developmental stages; H2. There is intense competition between B. aethiopum juveniles; H3. Juvenile and seedling survival and growth rates are higher away from mother plants; H4. Mound positive effect overwhelms the effect of intraspecific competition for very young B. aethiopum individuals, the reverse applies to older, non-reproductive individuals. To test for these hypotheses the potential positive and negative neighbourhood effects were analysed. Progression of seedlings into the juvenile stage and juvenile growth were analysed through logistic regression models including the effects of four neighbourhood indices designed to model the respective influence of B. aethiopum juveniles and adults, trees and termite mounds. Statistical results explain the observed spatial pattern and reveal two main neighbourhood effects that influence both B. aethiopum juveniles and seedlings: a positive effect of mounds due to the fact that they constitute nutrient-rich soil patches, and a negative effect of juveniles due to intraspecific competition. Seedlings would be mostly affected by the mound positive effect, whereas juveniles would be mostly affected by competition.