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

Area of Science:

• Ecology
• Botany
• Genetics

Background:

• Clark's Nutcracker (Nucifraga columbiana) is a key seed disperser for limber pine (Pinus flexilis) and whitebark pine (P. albicaulis).
• These pine species frequently exhibit a multi-trunk growth form at maturity.
• The seed caching behavior of Clark's Nutcrackers may influence the development of this multi-trunk architecture.

Purpose of the Study:

• To investigate the role of Clark's Nutcracker seed dispersal in determining the growth architecture of Pinus flexilis and P. albicaulis.
• To determine if multi-trunked pine trees originate from single seed caches containing multiple viable seeds.

Main Methods:

• Observation of Clark's Nutcracker seed caching behavior.
• Electrophoretic analysis of genetic variation within multi-trunked Pinus flexilis and P. albicaulis trees.
• Sampling of 2 to 4 gene loci to assess genetic distinctiveness of individual trunks.

Main Results:

• Twenty out of twenty-five sampled multi-trunk trees showed genetically distinct individuals comprising the trunks.
• This genetic diversity within multi-trunked trees strongly suggests multiple seedlings originating from single caches.

Conclusions:

• Clark's Nutcracker's seed caching strategy directly influences the multi-trunk growth form observed in Pinus flexilis and P. albicaulis.
• The study provides evidence that a single seed cache can result in the development of multiple, genetically distinct individuals forming a single apparent tree.