Relationship between severity of trunk decay of Pinus koraiensis and soil properties around roots

The decay rate of standing Korean pine (Pinus koraiensis) in natural forests can be as high as 50% and is likely influenced by the soil properties and nutrient and water status of the site. To clarify the relationship between the severity of tree decay and soil properties in order to prevent decay in a natural mixed forest in the Xiaoxing’an Mountains, wood strength of standing trees was nondestructively assessed, and the severity of decay of extracted wood cores was quantified based on differences in mass between two decayed increment cores extracted at breast height and an intact increment core near the decayed ones. Soil samples from the critical root zone (non-rhizosphere) of each tree were analyzed for chemical properties and microbial composition. The abundance of chemical elements (especially total N and K) and the species richness of soil microbes increased as decay severity increased. Fungal number (FN) and actinomycetes number (AN) were related to decay severity (R2 = 0.504). Bacterial number (BN) was higher than FN or AN, but had a minor effect on tree decay. Path analysis showed BN might indirectly inhibit decay by affecting FN. Decay severity was not significantly correlated with either soil fungal or bacterial diversity. These results suggest that forest managers need to monitor levels of fungi and total N and total K levels to reduce the decay of Korean pine.