Logs as refuges from fungal pathogens for seeds of eastern hemlock (Tsuga canadensis)

Abstract

The importance of fallen logs as recruitment sites for seedlings of some forest trees commonly is explained by the hospitable physical conditions such nurse logs provide. We used fungicide treatments to test whether logs also provide a refuge from pathogenic soil fungi for seeds of eastern hemlock (Tsuga canadensis). We tested two seedlots. For one seedlot, fungicide significantly improved survival of seeds in the soil, while seeds in logs were unaffected. This suggests that logs provide a refuge from pathogenic soil fungi. For the second seedlot, fungicide did not significantly improve survival either in logs or in soil, even though survival of control seeds was significantly lower in soil. This suggests that factors other than fungi must contribute to the success of seedlings on logs. Together, these results indicate that logs provide both physical and biotic benefits to seeds of eastern hemlock. When pathogens are important, logs provide enemy-free space; when risks from pathogens are low, logs still provide an improved physical environment.