PS 19-263 - Impacts of seed predation on conifer trees at Mt. Rainier National Park

Abstract: Tree regeneration is critical to long-term forest responses to climate change, and thus, is an important process for ecologists and managers to understand. Interactions between trees and other species at these early life history stages are likely to be particularly important but have also been understudied. For example, warming in the next century will likely cause tree and seed predator distributions to shift to higher altitudes, but these range shifts may occur at different rates. If so, the introduction of new seeds and / or new seed predators could potentially alter tree regeneration in already established forest communities through the gain and loss of interactions. To help understand these interactions, we used seed predation experiments and camera traps to collect information about 1) seed predation rates; 2) mammalian seed predator preferences; and 3) how predation rates and preferences might change depending on the surrounding tree community. We focused on six coniferous species (Abies amabilis, Abies lasiocarpa, Chamaecyparis nootkatensis, Pseudotsuga menzeisii, Thuja plicata, and Tsuga heterophylla) at 3 different sites spanning a large elevation gradient (600-1500 meters) at Mount Rainier National Park, USA. At each location, we placed seeds from low-elevation and high-elevation species, separately and together, and monitored the disappearance of seeds (which we equated to predation). We also placed camera traps, allowing us to monitor animal activities and seed predator preferences and how these varied by site, species, and context. Overall, we found that deer mice (Peromyscus maniculatus) are the most common seed predator, regardless of elevation. However, a few less common seed predators were prevalent either at high (chipmunks – Tamia sp) or at low elevations (Voles – Microtus sp). Rates of seed predation were high enough that the majority of seeds dispersed in fall are likely to be predated within a month of dispersal. Tree species varied in seed predation rates, with additional site by species interactions. For example, the western red cedar (Thuja plicata) and the western hemlock (Tsuga heterophylla) were generally preferred over the subalpine fir (Abies lasiocarpa) at all sites, but rates of predation on these species were lower at high elevation sites. In all, we believe studying interactions between trees and their associated seed predators can help ecologists understand how forest communities and their mammalian occupants will be affected by climate change.