Diplodia (Diplodia pinea) is a geographically widespread fungal pathogen in the United States and impacts more than 20 pine tree species. Drought and intraspecific competition in pine stands have been implicated as predisposing factors for increased Diplodia shoot blight risk. The general objective of this study is to examine the interactive effects of climatic factors, biotic factors (intraspecific competition), and infection by Diplodia on the growth of pine forests (jack pine (Pinus banksiana) and red pine (Pinus resinosa)).
A total of 12 red pine and 12 jack pine stands were selected in Huron National Forest located in the northern lower peninsula region of Michigan. A dendrochronological approach was utilized to examine relationships between annual ring-width and past climate records in healthy and Diplodia infected pine stands across the two levels of initial stand density (low density (<988 trees per hectare) and high density (>1977 trees per hectare)).
Results/Conclusions
For either control or Diplodia affected forest stands, lower density stands had higher cumulative tree-level productivity compared to higher density sites. Temporal trends in average annual total aboveground biomass of red pine trees was generally greater in low density control sites and lowest in the high density Diplodia affected sites. Average annual total aboveground biomass of jack pine trees was also greatest in the low density control stands versus lower amounts for the high density control or Diplodia affected treatment groups.
For red pine, dendroclimatological analyses indicated that high density Diplodia affected stands were not significantly related to high temperature stress in summer while the other treatment types were sensitive. High density (control or Diplodia) sites were sensitive to summer moisture stress while the low density (control or Diplodia) treatment group was not sensitive to seasonal moisture stress. For jack pine, low density Diplodia stands were sensitive to cold spring temperatures which likely delayed the start of the growing season. The other treatment groups were not sensitive to seasonal temperature stress. Diplodia stands (low or high density) were sensitive to summer moisture stress. High spring moisture levels negatively impacted growth of jack pine within low density stands (control or Diplodia).