High midsummer temperatures can cause heat and drought stress injury in first-year seedlings of Pinus ponderosa in pine/bunchgrass communities. On our Basalt Hill Field site on the University of Idaho Experimental Forest, we have demonstrated that significant interspecific competition occurs between pine seedlings and the established bunchgrasses (Agropyron spicatum). Competition from the bunchgrasses for soil water during the relatively hot and dry midsummer period reduced the amount of soil available for pine seedlings. Relatively high seedling mortality occurs because of direct heat stress resulting from midsummer soil surface temperatures than exceed 60°C and from the lack of water for transpirational cooling of the needles. The photograph shows a first-year pine seedling (center) between two established bunchgrasses.
Peter F. Kolb, Research Associate, Department of Forest Resources
Funded by McIntire-Stennis Research Grants Program, USDA.