Occurrence of Multi-genet Tree Clusters in "Wind-dispersed" Pines

Abstract

-Multi-genet tree clusters commonly occur in several species of bird-dispersed pine (Pinus spp.). In North America, this growth form results primarily from multiple seed germination in caches of Clark's nutcracker (Nucifraga columbiana). Growth forms with multiple trunks (tree clumps) occur reliably but at low frequencies in wind-dispersed pines. Because nutcrackers and seed-storing rodents are known to make multi-seed caches of winddispersed pine seeds, we tested the hypothesis that some of these tree clumps are in fact multi-genet tree clusters. Working in the Front Range of the Colorado Rocky Mountains, we collected foliage samples from 10 tree clumps each of ponderosa pine (Pinus ponderosa), bristlecone pine (Pinus aristata) and lodgepole pine (Pinus contorta) and genetically analyzed them by starch gel protein electrophoresis. We found that eight (80%) of the ponderosa pine tree clumps, two (20%) of the bristlecone pine clumps and four (40%) of the lodgepole pine clumps were multi-genet tree clusters. Based on growth from surveys in our sampling areas, we estimated that tree clusters occurred on 18% of our ponderosa pine sites, 8% of bristlecone pine sites and 5% of lodgepole pine sites. Thus, tree clusters also occur in wind-dispersed pines and may affect the population structure and mating patterns of these