Caterpillars and Keystones

Rose City Bluff Restoration volunteers with our Seed Project are currently fostering at least two plants for our fall planting that have been identified by the National Wildlife Federation (1) as host species plants: the vine maple (Acer circinatum) and the western crabapple (Malus fusca). These species host or feed some 200 beneficial caterpillars and pollinators. One of the largest trees on the Bluff is our huge Oregon white oak (Quercus garryana) next to the 62^nd Avenue stairs. The Oregon white oak is a commensal plant hosting as many as 400 beneficial insect species. The Bluff has over a dozen much smaller ones that we hope will be equally impressive someday.

Though Rose City Bluff Restoration would gladly tout the Bluff’s Oregon white oak and our Seed Project’s vine maple and crabapple as keystone plants, the term keystone species is controversial among biologists (2). A keystone species is one that has a disproportionately large effect on its natural environment relative to its abundance. Botanists identify plant species as keystones based on the number of insects such as caterpillars that they host or the number of native pollinator species the plant feeds. Almost sixty years after Washington zoologist and educator Bob Paine introduced the concept it is still a matter for debate among ecologists. Our massive Oregon white oak would likely qualify as a keystone in its natural environment, but it lives between a public park, a road, residential property, and a golf course. So, our oak has a different role to play on the Bluff. As beneficial as host species are, we especially enjoy our native plants for their beauty and educational value. They are simply great assets to our community.

(1) National Wildlife Federation. “Keystone Native Plants Marine West Coast Forests – Ecoregion 7.” https://www.nwf.org/-/media/Documents/PDFs/Garden-for-Wildlife/Keystone-Plants/NWF-GFW-keystone-plant-list-ecoregion-7-marine-west-coast-forest.ashx

(2) Ogden, Lesley. “Ecologists Struggle to Get a Grip on ‘Keystone Species’.” Quanta Magazine. April 24, 2024.https://www.quantamagazine.org/ecologists-struggle-to-get-a-grip-on-keystone-species-20240424