Seed dispersal by nutcrackers causes multi-trunk growth form in pines.

We present a unique example of a seed disperser determining the basic growth architecture of two species of plants. Clark's Nutcracker (Nucifraga columbiana) is the primary disperser for Pinus flexilis and P. albicaulis, caching clusters of seeds in the process. Both pine species often occur in a multi-trunk growth form at maturity. Electrophoretic analysis based on 2 to 4 gene loci revealed that two or more trunks were genetically distinct individuals in twenty of the twenty-five multi-trunk trees sampled. This supports the hypothesis that several mature individuals can arise from single caches.