The frequency, magnitude, and spatial distribution of heart rot in dominant temperate tree species in a forest dynamics plot

The composition, dynamics, and health of forest tree communities are governed by interactions with the abiotic and biotic environment. Fungi are critical biotic interactors that play an increasingly appreciated role in forest tree health, particularly with respect to mycorrhizal and pathogenic fungi. Heart rot fungi, while known to infect large fractions of the individuals in managed stands, have been considerably understudied in tree community ecology. Heart rot has been predicted to form hotspots in the forest due to crown or bole damage and/or soil moisture gradients, and is expected to vary across species due to life history differences. To address this knowledge gap, we quantified heart rot, the incidence, magnitude, and spatial distribution of heart rot in 328 individuals with diameters greater than or equal to 10 cm across the six most dominant tree species in a mixed broadleaf temperate forest dynamics plot. The results show that 71% of individuals display some degree of heart rot in this natural community. The incidence of heart rot does not significantly vary across species despite their life history strategy differences, but one species had significantly more heart rot in infected individuals. Lastly, heart rot was spatially clustered across species, but heart rot incidence and magnitude were not related to soil moisture, indicating the importance of crown and bole breakage, likely promoted by severe weather.

Summary: The present study conducted the first spatially explicit study of heart rot incidence and magnitude in a natural forest tree community. We demonstrate that over two-thirds of every large tree in the forest studied has some degree of heart rot, indicating their widespread, but underappreciated, role in tree communities. We demonstrate that heart rot is non-randomly distributed in this community and that spatial clustering of heart rot in forests is most likely due to hotspots of individual tree damage and not soil moisture.