Quantifying seed dispersal of Mountain Hemlock (Tsuga mertensiana) at alpine treelines: Kenai Peninsula, Alaska

As future climates are expected to change much more rapidly than in the past, it is important to understand the migration potential of species to predict what future ecosystems may look like. The alpine treeline in Alaska is one such system that has experienced rapid warming over the last 50 years along with a corresponding change in alpine treeline. In a tightly coupled vegetation-climate system, we would expect that the treeline should track climate relatively closely over periods as short as a decade. Unlike animals that can respond quickly to changing environmental conditions, plants are sessile and must respond inter-generationally. Therefore, the response of the treeline to changing climate must depend on the ability of seeds dispersing beyond the current treeline. Our research addresses this issue by: 1) quantifying mode of reproduction at treeline, 2) quantifying long distance dispersal using landscape genetics techniques. Analysis of genetic data will allow us to probabilistically identify parentage and dispersal distance and this information can be used to parameterize dynamic vegetation models, predictive models and to assess the influence of geographic features on genetic variation and geneflow.

This project represents a novel integration of genetics and geography to answer a pertinent set of questions that will allow us to have a deeper understanding of how treelines may migrate under altered climate conditions. Additionally, the importance of long distance dispersal and the relative abundance of clonal reproduction should be broadly transferrable to other treeline environments. Furthermore, the incorporation of genetic analyses into a spatial-ecology context will facilitate additional research of this kind in the future.

In addition to the general benefits of combining genetics and geography research, treeline research in particular will benefit from the knowledge gained here. The dispersal distances determined in this project can be used in future modeling studies to predict the form and rate of advance of the treeline under changing climate.