Fire mediated edge effects in bayhead tree islands

Abstract

Question: The role edges play in mediating the effects of disturbance is unclear. Bayhead tree islands, which experience above- and belowground fire, contain trees that recover from disturbance by seed (Pinus elliottii var. densa) and by sprouting (Gordonia lasianthus). How does distance-to-edge affect survival and post-fire response of trees with these contrasting life-history strategies? Location: Two bayhead tree islands at Archbold Biological Station, central Florida, North America. Methods: Stem diameter, depth of peat smoldering, char height, resprouting status, and location were recorded for all Pinus and Gordonia stems ≥8 cm. Distance to the edge of the tree island was quantified using GIS. Results: The focal species showed contrasting patterns of survival across the edge-to-interior gradient that reflected gradients of fire severity. Survival of Gordonia was lowest in the bayhead interior where peat smolder was deepest. Conversely, survival of Pinus was lowest near the edges where char heights were greatest. The distinct types of Gordonia resprouting (crown versus basal) also showed spatially contrasting patterns. Basal resprouting dominated near the edges and was positively influenced by char height, while crown resprouting was nearly constant across the edge-to-interior gradient and was negatively influenced by char height. Conclusions: The spatial patterns of tree survival and resprouting observed are likely due to gradients in intensity of peat smoldering and aboveground burning, coupled with differential susceptibility to these two types of fire. Despite the rarity of fire in wetland tree islands (compared to uplands) it may play an important role in structuring the spatial distribution of trees.