Pining for fungi: red-cockaded woodpeckers and their fungal associates

Background/Question/Methods

Interactions between primary cavity excavators and the fungi that facilitate cavity excavation may be of critical importance to the maintenance of forest ecosystem function. These interactions have been considered in many systems. However, associations between primary excavators and fungi are generally drawn from visual observations of fungi and many key players of fungal communities are missed with this method. The interactions between endangered Red-cockaded Woodpeckers (Picoides borealis; RCW) and fungi are particularly interesting because these are the only birds that excavate through the sapwood and into the heartwood of living pine trees, a process that can take more than ten years to complete. Certain types of heartwood infecting fungi such as Porodaedalea pini can decrease cavity excavation time; the birds in turn may facilitate the dispersal and colonization of these fungi. Using molecular methods, we examined fungal communities in complete RCW cavities, incomplete RCW cavities (starts) and in non-cavity trees. To test if RCWs facilitate heartwood infection by the transmission of fungi during cavity excavation, we experimentally employed man-made woodpecker accessible and inaccessible cavity starts. In order to determine the effect RCWs have on fungal community composition, we tracked these communities through time. 

Results/Conclusions

Using a primer pair specific for Basidiomycete fungi, we found the rates of fungal presence in complete RCW cavities (n=36) to be 89% and 50% in incomplete RCW cavities (n=42). In trees with no RCW activity (control trees, n=60), the initial rate of fungal presence was 32%. Man-made starts were drilled into these trees and this rate increased to 50% after two years. Woodpecker accessibility did not affect the rate of fungal presence in man-made starts, but the community composition changed over time. Porodaedalea pini was the most common heartwood infecting fungus found in complete and incomplete RCW cavities. We identified twelve taxa of wood decay fungi within RCW cavities. We identified fourteen taxa of wood decay fungi within non-cavity trees. After two years, we identified twenty-one species of wood decay fungi in our man-made starts. There are many other fungi within these excavations, and even given the high diversity seen, the communities of fungi within complete and incomplete RCW cavities form tight groupings with each other. The communities of fungi within non-cavity trees do not resemble those found in RCW excavations.