As described by Douglas W. Tallamy, a well-known environmental author and educator, keystone plants are unique components of local food webs that are essential to the participation of most living organisms within those food webs, either directly or indirectly.

A sustainable local food web requires a minimal number of keystone plants, or the diversity and abundance of insectivores, such as birds and bats, who rely on caterpillars and moths for food, will deteriorate, and the local food web will collapse.

Many native plant species are keystone plants due to their crucial role in maintaining the viability of local food webs as providers of food resources that support caterpillars that, in turn, are needed by birds to thrive and reproduce.

There are two types of keystone plant species: host plants that feed caterpillars of butterflies and moths, and host plants for native specialist bees that feed on pollen only from specific plants.

Keystone plants are identified based on areas of similar climate, geology and soils known as an ecoregion. Pennsylvania is within the Eastern Temperate Forest (ETF) Ecoregion.

The National Wildlife Federation has an extensive list of keystone plants and the number of caterpillars and bees they support. The list of keystone plants for the ETF Ecoregion is found at www.nwf.org.

https://www.nwf.org/-/media/Documents/PDFs/Garden-for-Wildlife/Keystone-Plants/NWF-GFW-keystone-plant-list-ecoregion-8-eastern-temperate-forests.ashx

Butler County gardeners may be surprised to learn they already grow keystone plants in their landscapes! Some widespread native plants are listed for the ETF Ecoregion; following are examples of trees, shrubs, and perennials.

Two examples of keystone trees are the oaks (Quercus spp.) and cherries (Prunus spp.). Compared to other tree species, white oak (Quercus alba) supports the most caterpillars (436 species). Black cherry (Prunus serotina) supports 340 species of caterpillars.

Blueberries are noteworthy keystone shrubs. The northern highbush blueberry (Vaccinium corymbosum) and lowbush blueberry (Vaccinium pallidum) support 217 species of caterpillars. Shrubs in the willow genus (Salix spp.), specifically black willow (Salix nigra), support 289 species of caterpillars and 14 species of bees.

Many perennials familiar to Butler County gardeners are identified as keystone plants.

In late spring and early summer, lanceleaf coreopsis (Coreopsis lanceolata) supports seven species of caterpillars and 22 species of bees. Summer blooming keystone perennials such as evening primrose, a biennial plant (Oenothera biennis), hosts 19 species of caterpillars, while black-eyed Susan (Rudbeckia hirta) and green-headed coneflower (Rudbeckia laciniata) sustain 20 caterpillar and 29 bee species. In late summer and early fall, woodland sunflower (Helianthus divaricatus) supports 66 caterpillar and 50 bee species.

Fall blooming perennials, such as stiff goldenrod (Oligoneuron rigidum), hosts 104 species of caterpillars and 42 species of bees. Close behind the goldenrods in support of 100 species of caterpillars and 33 species of bees are the blue wood aster (Symphyotrichum cordifolium) and smooth aster (Symphyotrichum laeve).

As summer wanes, take stock of your landscape and count the number of keystone plants gracing your gardens. End-of-season sales at nurseries and greenhouses may lead you to introduce new species of these important plants into your local ecosystem.

To learn more about keystone plants, visit Penn State Extension’s online resources, such as soft landings, or caring for caterpillars through their life cycles using keystone trees, at https://extension.psu.edu/programs/master-gardener/counties/monroe/news/soft-landings-crucial-habitat-for-pollinators

https://extension.psu.edu/programs/master-gardener/counties/monroe/news/soft-landings-crucial-habitat-for-pollinators

and choosing native plants at https://extension.psu.edu/pennsylvania-native-plants-for-the-perennial-garden.

https://extension.psu.edu/pennsylvania-native-plants-for-the-perennial-garden

.

The National Wildlife Federation www.nwf.org offers extensive resources for native and keystone plant usage.

If you have questions about keystone or native plants, call the Garden Hotline of Penn State Extension Master Gardeners in Butler County at 724-287 4761, ext. 7, or email them at butlermg@psu.edu.

Lisa Marie Bernardo and Mary Alice Koeneke are Penn State Extension Master Gardeners of Butler County.