2012 Relative Abundance of Rodents in WBP Communities & Rodent Predation and Dispersal of Seed

Project: Relative abundance of rodents in whitebark pine communities and rodent predation and dispersal of whitebark pine seed.

Agency/Forest or Park/District: Cascades Range, WA

Project coordinator: Teresa Lorenz

Contact: Teresa Lorenz, graduate student, University of Idaho, Moscow, ID, 83844. lore5748@vandals.uidaho.edu, 509-731-5226

Cooperators

Dr. Kerri Vierling (graduate advisor), University of Idaho

Dr. Marty Raphael (project advisor), Pacific Northwest Research Station

Jodie Canfield (project advisor), Gallatin National Forest (for the Montana study sites only)

Source of funding /amount

FHP: $8,280

Supplemental funding: $23,600 from University of Idaho and FS

Dates of restoration efforts

2012

Objectives

This project has three major objectives: (1) determine the composition of the rodent community in whitebark pine stands, (2) measure vegetation and whitebark pine health in these same stands to link rodent abundance with habitat features, and (3) conduct a seed dispersal experiment to assess the proportions of whitebark pine seeds that granivorous rodents consume versus disperse.

Acres/ha treated

N/A

Methods

We conducted this study from 2010 through 2012. We measured rodent relative abundance using standard small mammal live trapping methods. Within each study site, we randomly placed two 40 x 40 m small mammal trap grids. Each grid consisted of 25 traps set 10 m apart. We conducted small mammal trapping at each grid once during autumn (August, September or October) in 2011 and 2012. Traps were set for 5 day intervals and baited with sunflower seed (treated to prevent germination). All small mammals except shrews were identified to species, ear-tagged, and immediately released. For the purposes of this project, we considered the number of individuals captured as an estimate of relative abundance, and the number of species captured as an estimate of species richness. To determine factors associated with small mammal abundance, we also conducted vegetation surveys at five plots within each small mammal trapping grid for a total of 80 vegetation plots surveyed. We also conducted cone counts on 10 mature, canopy-level whitebark pine trees at each study site.

We used two methods to examine how rodents obtain or handle whitebark pine seeds at our sites. First, to examine the extent to which rodents pilfer seeds from nutcracker caches, we attempted to mimic Clark’s nutcracker caching behavior by caching 186 whitebark pine seeds at random sites within four of our study sites. Caches contained 3 seeds each (approximate average size of nutcracker seed cache) and were buried within 3 cm of the soil surface (approximate average depth of nutcracker seed caches). We buried a penny within 2 cm of the cache site to enable us to relocate caches using a portable metal detector. We wore gloves when handling seeds and pennies to minimize human odors that may cue rodents to caches. We returned to these cache sites 10 to 12 months after placement, located the penny with a metal detector and then systematically sifted through the soil to locate seeds and seed hulls. For each site we noted the number of seeds remaining and number of seed hulls (indicates seeds were consumed by rodents at the cache site).

Secondly, were interested in determining whether rodents will collect seed from the ground surface, and what proportions of such seeds rodents would consume versus disperse. At each of 16 plots at 4 study sites, we presented rodents with 30 seeds that had been coated in florescent powder. We presented the seeds to rodents in small piles (approximately 5 cm x 5 cm), intended to mimic the number of seeds on average within whitebark pine cones. We returned to these plots 2 to 5 nights later, checked whether the piles had been visited by rodents, and then used UV light to follow the trail of fluorescent powder to seed caches and larders. At each cache site we recorded cache depth, number of seeds per cache, distance from origin (location where we had deposited the seeds), and direction from origin. For larders, which were difficult or impossible to access, we estimated the number of seeds placed in larders by subtracting the total number of seeds not accounted for in caches or consumed at that site.

Planting? If so, source of seedlings? Resistance?

Outcome

Overall, rodent abundance fluctuated considerably among whitebark pine stands in our study, and rodent abundance appeared driven more by shrub, grass, and CWD cover than by cone density in whitebark pine. Our results also suggest that rodents have the potential to act as effective seed dispersers in whitebark pine stands, at least during primary seed dispersal. In our study, most seeds obtained by rodents either through caches or seed piles were not consumed, but were taken to cache sites by rodents. Future research is needed to monitor the final fates of such seed caches, since rodents rarely leave seeds in one cache site for long periods of time. Additionally, comparative studies are needed of nutcracker versus rodent seed dispersal in areas with high versus low whitebark pine mortality in order to shed light on whether rodent seed dispersal can play a beneficial role in whitebark pine restoration.

Monitoring since completion of the project

Dates: none

Plans for future monitoring? none planned

Will outcome meet goals?

Yes, we addressed all of our study objectives in this project.

Future actions/follow up?

none planned

Miscellaneous comments

none