No abstract

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 nonadaptive germination.

Earlier weaning has often been suggested as a cause for population growth after the evolution of food production. However, evidence for weaning-time reduction is largely circumstantial. Collagen stable nitrogen- and carbon-isotope ratios from juvenile and adult burials from four sites in eastern North America were measured to estimate weaning onsets and durations before and after the appearance of intensive food production. Two preagricultural Late Archaic sites (Indian Knoll and Carlston Annis) are compared with two highly agricultural Middle Mississippian sites (Angel and Tinsley Hill). Isotopic data and paleodemographic measures of birth rates provide no evidence for changes in weaning behavior or fertility with the development of food production in the prehistoric Lower Ohio Valley. Birth rates and weaning behavior appear to have been roughly the same at all four sites. These results indicate that models attributing population growth after the appearance of food production to earlier weaning are not universally applicable.

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 m 2 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 moistureresistant seed coats to reduce nonadaptive germination.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. INSTAAR, University of Colorado andThe Regents of the University of Colorado, a body corporate, contracting on behalf of the University of Colorado at Boulder for the benefit of INSTAAR are collaborating with JSTOR to digitize, preserve and extend access to Arctic and Alpine Research. AbstractTwo North American bird-dispersed pines, Pinus albicaulis and Pinus flexilis, were previously found to occur in three growth forms: single-trunk, single genet multi-trunk, and multi-genet tree cluster. The latter two forms are morphologically similar and distinguishable only by genetic analysis; they are together referred to as "tree clumps." In the Upper Engadine, Switzerland, we studied Pinus cembra to determine whether this pine species, which is dispersed by Nucifraga caryocatactes, also occurs in three growth forms. Examining the relative frequency of single-trunk trees and tree clumps, we surveyed P. cembra in three different forest areas and at elevations ranging from 1810 to 2300 m. Tree clumps occurred at 19 to 30% of the tree sites and up to 45% of the seedling sites. We sampled foliage from all trunks of 23 tree clumps (2 to 7 trunks per clump, 9 = 3.4, SD = 1.3) for analysis by starch gel protein electrophoresis at four gene loci: FE, PGI, PGM-1, and PGM-2. Sixteen of the 23 tree clumps (70%) contained more than one genet and thus were tree clusters. Extrapolation of this percentage suggests that tree clusters occupied from 13 to 21% of the P. cembra tree sites surveyed. A comparison of genotypes and degree of fusion between adjacent trunks in tree clumps confirmed that morphology is a poor indicator of growth form.