Quantifying the effects of burning on the diversity of arthropods in a fire-adapted longleaf pine (Pinus palustris) forest

Background/Question/Methods

 Fire is an important agent of disturbance in ecological communities, altering the structure and composition of the vegetative community and affecting overall ecosystem function. The longleaf pine (Pinus palustris) ecosystem is extremely fire dependent with a fire return interval of 3-5 years and supporting a diverse understory plant community. As arthropods are tightly associated with vegetative habitat, understanding the response of the insect community to burning is important for evaluating the resilience of the ecosystem to such disturbances. Investigating the changes in both the taxonomic and functional diversity gives greater resolution to the effect of burning on the overall arthropod community.

To quantify diversity, we erected a series of malaise traps to sample before, during, and four periods post-fire for one year. Sampling was done in conjunction with three separate fires conducted as part of regular management burning activities at Eglin Air Force Base in northwestern Florida. Specimens were organized by morphospecies and identified to family and assigned to a trophic guild. Abundance and richness of morphospecies were used to calculate Shannon (H’) and inverse-Simpson (1/D) diversity indices for community composition and fire stage comparisons.

Results/Conclusions

Sampling efforts resulted in a collection of 9,046 individuals comprised of 11 arthropod orders represented by 413 morphospecies (n) and four trophic guilds. Overall arthropod diversity decreased both during and immediately after fire and increased post burn. Hymenoptera (n=105), Diptera (n=119), and Lepidoptera (n=41) showed the greatest increase in diversity post fire. Orthoptera (n=26) were the only order to increase in diversity during the fire indicating a dispersal response to burning and subsequent decrease in diversity post burn suggesting delayed recolonization. Trophic guild analyses showed increased diversity of herbivores, detritivores, and parasitoids with a significant decrease in predator diversity over time since burn. Significant interactions are also seen between fire stage, order, and trophic guild, especially within the Diptera.

As the greatest increased taxonomic diversity was seen in three highly vagile orders, dispersal ability may give greater resilience to mobile taxa and give increased recolonization potential as the vegetative habitat returns post fire. Trophic diversity response indicates that bottom-up regulation is resulting in decreased predator diversity and latent recoveries in parasitoids and detritivores. Quantifying the diversity of the overall arthropod community allows for multiple comparisons in the responses of numerous taxa enhancing the understanding of ecosystem response to disturbance.