Net primary production (NPP) is a key component of ecosystem function, with fine roots commonly accounting for over half of NPP. Insect larvae of Scarabaeidae and Elateridae are widespread and often dominant (biomass) fine root herbivores, but their effect on fine root mortality is poorly quantified. When fire is excluded from the longleaf pine-wiregrass ecosystem, hardwoods and shrubs encroach, surface organic matter accumulates, and wiregrass coverage decreases. We asked how these changes in system structure influence the abundance of root feeding insects (RFIs). Because RFIs are known pests of cool-season grasses, we predicted that fire would have a positive effect on RFI abundance by way of maintaining wiregrass dominance in the understory. Plots were established in each of six stands: three treated with prescribed fire on a two-year cycle, and three treated by approximately ten years of burn exclusion. In each plot, soil samples were collected and sieved to estimate insect abundance, and the percentage of plot area that was bare ground or covered by wiregrass, woody plants, or other forbs was estimated.
Results/Conclusions
Contrary to our prediction, RFI abundance was consistently lower in the fire maintained stands (χ2=7.7, d.f.=2, p=0.02). Scarabaeidae abundance was negatively related to fire management (p=0.0029) and to the amount of bare ground and wiregrass in the understory. The interaction between bare ground and wiregrass was significant (p=0.0031); the negative impacts of each factor were enhanced when the other factor was high. Elateridae abundance was negatively related to fire management and to the amount of bare ground in the understory, with the interaction significant (p=0.026 fire excluded, p=0.0079 fire maintained). The strong relationship between bare ground and abundance is probably due to the influence of surface organic matter on soil moisture, which is of known importance to RFIs. These results suggest that fire may have significant implications for fine root herbivory in fire-maintained woodlands.
