Local variation in seeds of ponderosa pine

Abstract

Variation in seed morphology among populations of ponderosa pine growing in south central Oregon was examined. A total of nine populations was sampled from a range of elevations within each of two distinct soil types: basalt residuals derived from Pliocene basalt flows and wind-deposited pumice originating from the eruption of Mt. Mazama 7600 years ago. Overall, an unusually diverse array of seed morphology was encountered. Slight but significant differences in seed shape and color were present between populations from the two soil types. Except for seed weight, no significant differences were found between populations within soils. Variation in seed weight was negatively correlated with seed source moisture as measured by elevation. For all traits studied, variance components for populations and soils were relatively minor, the within-population component accounting for a major portion of the total variation. Hypotheses are offered to explain the high levels of within-population diversity in seed traits as an adaptation to a spatially heterogeneous environment, as well as a defense against the foraging behavior of seed predators. Also, the possible adaptive significance of the observed variation in seed traits is discussed in relation to seedbed properties of the respective soils.