EFFECT OF FIRE ON TREE SPATIAL PATTERNS IN A TALLGRASS PRAIRIE LANDSCAPE

Spatial patterns of trees invading a tallgrass prairie in NE Kansas, USA were examined using a Geographical Information System. Without burning and with adequate moisture levels, the number of trees increased over a five year period by over 60%, while in an area burned annually the number of trees decreased. Under a variety of burning regimes Juniperus virginiana and Celtis occidentalis were significantly more uniform in their distribution pattern than Populus deltoides and Gleditsia triacanthos. In addition, three tree species (G. triacanthos, J. virginiana and U. americana) had a significant increase in the degree of aggregation with increasing tree height, while C. occidentalis showed no relationship between aggregation and tree height. There were significant associations between adult and juvenile trees at various scales, with bird dispersed J. virginiana having a higher critical distance (39 m) than wind-dispersed G. triacanthos and L. americana. The spatial pattern of tree species appears to be affected by the means of dispersion; trees with wind-dispersed seeds had clumped distributions, whereas most trees with bird-dispersed seeds were regular to random in their dispersion patterns. The spatial pattern of trees invading tallgrass prairie is a function of the burning regime, dispersal vectors, habitat availability and reproductive mode.