Study plots were established to determine the effects of various environmental factors on ponderosa pine seed germination and initial seedling establishment and growth. A series of soil surface treatments were performed on plots in two locations: within or under the influence of overstory pine trees and in openings away from the pine influence. Seed germination was significantly greater in the opening plots. The overstory canopy and forest floor restricted the amounts of precipitation, light, and heat reaching the soil and probably decreased germination. Cutworms, birds, and small mammals caused the greatest seedling mortality. The largest seedlings occurred in the fire-treated plots. This was attributed to an increased nutrient supply and reduction of competition. Open-grown seedlings were larger than those growing under the overstory canopy. Amount of sunlight, degree of competition, and susceptibility to injury because of location appeared to be the major factors contributing to the seedling size differences. Because of abnormally high precipitation during the growing season, results may not be typical of average growing seasons.
United States Department of Agriculture, Forest Service, "Influence of Some Environmental Factors on Initial Establishment and Growth of Ponderosa Pine Seedlings" (1979). Forestry. Paper 26.