Spatial Patterns of Woody Plants and Tree‐Tree Interactions in an Indian Mesic Savanna

Aims Savannas are mixed tree‐grass systems maintained by complex interactions and feedbacks between bottom‐up (resources) and top‐down (e.g., fire and herbivory) forces. Much research in savannas has focused on understanding what enables tree‐grass coexistence. In contrast, tree‐tree interactions have received limited attention despite being equally important for determining savanna structure. Tree‐tree interactions can be facilitative, or competitive, with differential implications for woody cover and savanna structure. Further, these interactions can change across life stages of woody plants. In this study, we assessed patterns of tree spatial distributions to infer the nature of tree‐tree interactions (whether facilitative or competitive) across two life stages, saplings and adults, in an Indian savanna. Location Mesic savanna in southern India. Methods We assessed spatial patterns of trees using point pattern analysis and inferred the nature of tree‐tree interactions by examining neighbourhood effects, both conspecific and heterospecific, on plant survival and growth across the two life stages. Results We found that saplings were strongly aggregated while adult trees were randomly distributed. Despite being strongly aggregated, sapling growth and survival over 4 years were unaffected by neighbours (adults and saplings). Instead, initial size (basal area at first census) was the single best predictor of both sapling growth and survival. In contrast, adult neighbours negatively affected adult tree growth with effects being more pronounced for conspecific neighbours than heterospecifics. Other factors such as drought and fire, although important for sapling and adult performance, did not occur during our study period. Conclusion Our results suggest that tree‐tree interactions in this mesic savanna vary from neutral at the sapling stage to negative at the adult stage. Neighbourhood density influenced adult tree growth but not survival. Suppressive effects of neighbours on adult tree growth, although weak, suggest a potential role for competitive tree‐tree interactions in constraining tree cover in Indian mesic savannas.