title: Spatial vegetation patterns and neighborhood competition among woody plants in an East African savanna.
abstract: The majority of research on savanna vegetation dynamics has focused on the coexistence of woody and herbaceous vegetation. Interactions among woody plants in savannas are relatively poorly understood. We present data from a 10-yr longitudinal study of spatially explicit growth patterns of woody vegetation in an East African savanna following exclusion of large herbivores and in the absence of fire. We examined plant spatial patterns and quantified the degree of competition among woody individuals. Woody plants in this semiarid savanna exhibit strongly clumped spatial distributions at scales of 1-5 m. However, analysis of woody plant growth rates relative to their conspecific and heterospecific neighbors revealed evidence for strong competitive interactions at neighborhood scales of up to 5 m for most woody plant species. Thus, woody plants were aggregated in clumps despite significantly decreased growth rates in close proximity to neighbors, indicating that the spatial distribution of woody plants in this region depends on dispersal and establishment processes rather than on competitive, density-dependent mortality. However, our documentation of suppressive effects of woody plants on neighbors also suggests a potentially important role for tree-tree competition in controlling vegetation structure and indicates that the balanced-competition hypothesis may contribute to well-known patterns in maximum tree cover across rainfall gradients in Africa.
authors.affiliation: Natural Resource Ecology Laboratory and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, Colorado, 80523, USA.|Arcadis, Denver, Colorado, 80246, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Dohn
authors.affiliation: Rangeland Resources Research Unit, USDA Agricultural Research Service, Fort Collins, Colorado, 80526, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Augustine
authors.affiliation: Geospatial Sciences Center of Excellence, South Dakota State University, Brookings, South Dakota, 57006, USA.
authors.forename: Niall P
authors.initials: NP
authors.lastname: Hanan
authors.affiliation: National Centre for Biological Sciences, Tata Institute of Fundamental Research, GKVK Campus, Bellary Road, Bangalore, 560065, India.
authors.forename: Jayashree
authors.initials: J
authors.lastname: Ratnam
authors.affiliation: National Centre for Biological Sciences, Tata Institute of Fundamental Research, GKVK Campus, Bellary Road, Bangalore, 560065, India.|School of Biology, University of Leeds, Leeds, LS2 9JT, United Kingdom.
authors.forename: Mahesh
authors.initials: M
authors.lastname: Sankaran
mesh_terms: D000349:Africa; D017753:Ecosystem; D065948:Grassland; D008137:Longitudinal Studies; D014197:Trees
keywords: 
  Acacia
  ; aggregation; pair correlation function; patchiness; pattern formation; semiarid savanna; spatial ecology; woody plant interactions