How does a seed with no mobility of its own manage to travel long distances? With a little help from its friends, of course.
A new review by Pesendorfer et al. in The Condor highlights the unique relationship between large-seeded trees like oaks and pines, which depend on animal-facilitated dispersal (zoochory), and corvids, the ravens, crows, jays, magpies and nutcrackers of the world that often store seeds in spatially distributed caches (scatter-hoard). The review highlights the critical role that corvids play as ecosystem engineers by distributing seeds, as well as their potential to buffer the impacts of climate change by carrying seeds to newly available habitat.
Several examples demonstrate the beneficial role of corvids in both general plant ecology and habitat restoration. Acorns in Western and Central Europe are distributed by Eurasian Jays over long distances, and often into disturbed habitats where they grow well. Nutcrackers in both North America and Europe cache huge quantities of pine seeds. Both oaks and pines in temperate North America benefit from dispersal by several species of jays, making the birds a keystone species in the trees’ life history. Corvid seed dispersal has been critical in restoring multiple habitats, including oak woodlands in Western Europe, whitebark pine in the Rocky Mountains, and oak chapperel and pine woodlands in California’s Channel Island National Park.
The most critical function this mutualism may serve in the future is to allow seed-bearing tree species to better colonize landscapes that become newly available under the shifting conditions of climate change. This key benefit drives home the underlying message that in order to preserve this important function, corvids must stay connected between habitat patches and be able to freely disperse. Creating corridors and maintaining connectivity for these birds will be a necessary step in preserving the crucial ecosystem service they provide now and in the future.
Pesendorfer, M. B., T. S. Sillett, W. D. Koenig, and S. A. Morrison. 2016. Scatter-hoarding corvids as seed dispersers for oaks and pines: a review of a widely distributed mutualism and its utility to habitat restoration. The Condor 118: 215-237.