Significance of seed caching by rodents for key plants in natural resource management

Authors: Longland, William - Bill; Dimitri, Lindsay

Submitted to: Rangelands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2019
Publication Date: 12/19/2019
Citation: Longland, W.S., Dimitri, L.A. 2019. Significance of seed caching by rodents for key plants in natural resource management. Rangelands. 41(6):248-254. https://doi.org/10.1016/j.rala.2019.11.002.
DOI: https://doi.org/10.1016/j.rala.2019.11.002

Interpretive Summary: The production of new seedlings in many plant species occurs when seeds germinate and emerge as seedlings from shallowly-buried seed caches made by rodents. This type of food storage behavior is referred to as "scatter-hoarding." We review evidence from published literature of the importance of scatter-hoarding rodents for the propagation of some key plant species in the fields of range, wildlife, and forest management. The examples we review cover a variety of plant growth forms, including grasses, shrubs, and trees, as well as several different groups of rodents. In some of our examples, beneficial effects of scatter-hoarding rodents on plants are clearly in line with management goals, such as enhancing productivity of a native grass that provides important forage for livestock or of shrubs that provide essential forage for mule deer and other wildlife. Additionally, seedlings of many trees that are important sources of timber and nut production are attributable to scatter-hoarding by rodents. In other cases, seedlings produced from rodent caches may be problematic to natural resource management. For example, rodent scatter-hoarding can benefit certain tree species that are expanding and encroaching upon shrub and grass environments, thereby reducing their value as grazing lands. Because details of how seedlings are produced have not been studied in most plant species, effects of scatter-hoarding rodents are probably even more prevalent than the current literature would suggest.

Technical Abstract: For many plant species new seedlings become established from superficially-buried seed caches made by seed-eating rodents – the result of caching behavior known as “scatter-hoarding.” Scatter-hoarding rodents constitute the primary means of seed dispersal and seedling establishment for a diversity of plant forms, including grasses, shrubs, and trees. Here we review evidence of the importance of scatter-hoarding rodents for the propagation of some key plant species in the fields of range, wildlife, and forest management. Two examples of woody plant encroachment in range systems involve scatter-hoarding by rodents. Seed caches of various rodents, including deer mice, piñon mice, and pocket mice, facilitate establishment of juniper and piñon pine species in shrub-dominated rangelands. In the southern deserts, mesquite seedlings often establish from caches made by kangaroo rats. Kangaroo rats are also the main dispersers of Indian ricegrass seeds, and their scatter-hoarding activities are essential to seedling establishment of this native forage grass. Knowledge of the beneficial effect of kangaroo rat seed caching in this interaction has been applied in a management context to enhance seedling production of Indian ricegrass. Three examples are discussed in which scatter-hoarding rodents affect seedling production of key shrub species in the field of wildlife management. The vast majority of seedlings of antelope bitterbrush, which is often the most common constituent of winter diets for mule deer, originate from caches made by rodents. In montane systems chipmunks account for most bitterbrush seedlings, while at lower elevations this role is filled by species such as kangaroo rats, pocket mice, and deer mice. Although it has relatively low palatability for livestock, blackbrush can be a significant browse species for mule deer and desert bighorn sheep. Blackbrush seedling production is largely attributable to scatter-hoarding by kangaroo rats and related rodent species. Several species of manzanita and bearberry produce fruits that are important dietary items for game and non-game bird species as well as mammalian carnivores. Production of new seedlings for these shrubs is dependent on fire to stimulate germination, and the majority of seedling emergence following a fire is attributable to caches scatter-hoarded by chipmunks. Sugar pine, Jeffrey pine, and ponderosa pine – all economically important timber trees in the western U.S. – have winged seeds to facilitate dispersal by wind, but it is scatter-hoarding of the seeds by chipmunks following initial wind dispersal that accounts for the vast majority of seedling production. The importance of this plant-animal interaction is not unique to conifers, as numerous hardwood trees utilized for timber and/or nut production also owe most of their seedling emergence to scatter-hoarding rodents. Numerous oak species, hickories, pecans, walnuts, chestnuts, and almonds all provide examples. Most of the seedlings produced by these hardwood species are due to the seed caching activities of tree squirrels such as the eastern gray squirrel. Scatter-hoarding rodents are clearly central players in the productivity of many plant species, including numerous species that are key to natural resource management. Mechanisms of seed dispersal and seedling production have not been studied for a large proportion of plant species, so these interactions are probably more common than the current literature would suggest.