Plants regenerate after fire by resprouting or via seed germination. We suggest that fire season can have important consequences on the post-fire regeneration rate of plants adopting these two different strategies, leading to changes in community composition. Specifically, we hypothesized that autumn fires will be more intense then spring fires, due to lower plant and soil water content, thus, creating new microsites for seed germination, i.e., favoring the seeder strategy. Resprouters, on the other hand, will regenerate faster following spring fires, which inflict lower damage on their tissues compared to autumn fires. We also hypothesized that autumn fires will reduce dominance levels to a greater extent than spring fires, while increasing the abundance of less prevalent species, resulting in higher community diversity. To test these hypotheses, we conducted a large scale field experiment in a typical Mediterranean woodland in Israel. The experimental system comprised of twelve 50×50 m plots, randomly assigned to one of the following fire treatments: (1) spring fire, (2) autumn fire, and (3) unburned control. Community composition surveys were held before and after the fires. In addition, during the first post-fire growing season, resprouting and germination rates were evaluated.
Results/Conclusions
Autumn fires were more intense than spring fires in terms of flame heights and above- and below-ground temperatures. Germination densities did not differ significantly between spring and autumn fires, but were significantly higher in burned than in unburned areas. Resprouting occurred only in the burned areas and it began immediately after the fires. Notably, although plants that experienced spring fire began resprouting three months before plants subjected to autumn fire, there was no significant differences in their total resprout stem volume. Indeed, the relative rate of change in total resprout stem volume tended to be higher in plants subjected to autumn fire, however, this pattern was significant only in Pistacia lentiscus, the most dominant resprouter in the study area. Autumn fires decreased dominance and increased the abundance of less prevalent species, resulting in higher community diversity compared to spring fires. Our findings illustrate that fire season influences community composition through its differential effects on different plant species.