Ecological - Second Order
Fire & Wildlife
Whitebark pine (Pinus albicaulis) seeds are dispersed by Clark's Nutcracker (Nucifraga columbiana), a bird that makes caches under 2-3 cm of soil. Cached seeds may delay germination for one or more years in part because of underdeveloped embryos at the time of seed dispersal. Consequently, whitebark pine may show a soil seed bank strategy that is unique among pines (Pinaceae, Pinus). From 1990 to 1995 we studied natural whitebark pine regeneration following the 1988 Yellowstone fires to determine: (1) whether whitebark pine typically exhibits delayed seed germination and, if so, (2) how this affects patterns of regeneration over time, and (3) whether germination is the result of seed maturation or is stimulated by high levels of moisture availability. We established 275 permanent plots, each 20 m2 in area, divided between Henderson Mountain, Gallatin National Forest, Montana, and Mt. Washburn, Yellowstone National Park. In the Henderson Mountain study area, the ecological conditions or treatments included: dry, burned; moist, burned; dry, unburned; and moist, unburned. In the Mt. Washburn study area, the ecological treatments were dry, burned; moist, burned; and moist, moderately burned. Synchronous delayed seed germination occurred throughout both study areas. The greatest densities of new seedlings appeared in the summers of 1991 and 1993, but the greatest cone crops were produced in 1989 and 1991. Most germination followed two winters of seed dormancy. Regeneration densities were consistently highest on the Mt. Washburn moist treatments. High correlation between weighted means for new regeneration and March-plus-April precipitation, as well as the results of residual and multiple regression analyses, suggests that cone production two years prior and March-plus-April precipitation together account for the regeneration patterns in the Mt. Washburn study area. The role of precipitation requires further study. Delayed seed germination, producing a soil seed bank, may be an ecological strategy in whitebark pine that is the product of selection. Although underdeveloped embryos may be a consequence of both a short growing season and premature seed dispersal by nutcrackers, seed caching may further select for slow embryo maturation, as well as moisture resistant seed coats to reduce non-adaptive germination.