Seed dispersal of wild peony (Paeonia brownii) in western Nevada

Background/Question/Methods

This research investigates the dispersal characteristics for wild peony (Paeonia brownii), an herbaceous perennial that produces large seeds and is found in Jeffrey pine forests at elevations between 1950-2000 m and in sagebrush scrub at elevations between 1550-1580 m in the mountain ranges of western Nevada.  Wild peony appears to follow a scatter-caching seed dispersal syndrome, but this has never been explored.  Scatter-caching is an unexpected dispersal mechanism for peony, considering that most rodent dispersed plants are large, woody trees and shrubs.

Results/Conclusions

Rodents removed seeds from under peony plants at an average removal rate of between 0.77% and 6.9% per day  These removal rates are significantly slower than those of Jeffrey pine seeds under similar circumstances.  Peony seeds radio-labeled with scandium-46 were tracked at 9 source plants at the Jeffrey pine forest site and recorded 102 caches with a mean dispersal distance of 5.9 ± 0.41 m, depth of 6.2 ± 0.83 mm, and 1.5 ± 0.11 seeds per cache.  Results indicate that yellow pine chipmunks, deer mice, and long-eared chipmunks are potential dispersers in Jeffrey pine forest habitat and Great Basin pocket mice, Panamint kangaroo rats, and deer mice are potential dispersers in sagebrush scrub habitat.  In 2009, the estimated mean number of days to cache detection for three cache types at the Jeffrey pine forest site was 13.9, 31.0, and 11.7 for peony, Jeffrey pine, and peony-Jeffrey pine mixed caches, respectively; there was no difference in cache detection at the sagebrush scrub site.  In 2010, cache pilfering rates were much slower and the estimated mean number of days to cache detection for three cache types at two sites was 124.5, 61.5, and 56.29 for peony, Jeffrey pine, and peony-Jeffrey pine mixed caches, respectively.  Jeffrey pine seeds were always removed if detected, but only 65% of peony caches that rodents excavated were removed from cache locations.  This indicates that peony seeds may be a low preference food item compared to Jeffrey pine seeds.  I propose that peony is expressing a novel dispersal strategy that allows them to exploit rodents for dispersal, but does not require them to follow the typical characteristics of rodent dispersed plants.  Rodents will preferentially cache more desirable seeds, but those seed caches will also be preferentially found and eaten.  Because peony plants are long-lived, even low rates of seed removal may be enough to maintain or increase their populations.