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Land & Environmental

Down to Earth | ‘Keystone species’ vital

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By Catherine Zimmerman

My love of the land started very early, on a small farm in Miami County, Ohio.

My Dad, a third-generation vegetable farmer, was a very hands-on, learn-by-doing father. And because his passion and expertise were in growing stuff, he gave each of us six kids a patch of earth to plant whatever we wanted. So, at the age of 5, my infatuation with flowers and plants began. Dad taught me things like “feed the soil” — we used composted manure for fertilizer. In turn, the soil would feed the plants. “Be cautious about watering.” I was very prone to over watering! In other words, think about what the plant actually needs.

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The biggest lesson: “cherish the bees and insects,” because they are a major part of what makes the garden perform. It seems each year I garden, these early words of folk wisdom become more and more relevant.

Although he probably would not have uttered these words, Dad was talking about balance in the garden, the special interaction between species, soil, water and sun. Decades later we add to his observational thinking with good science.

We know so much more about what makes the garden grow, the ecosystem work. We also know that we are losing species. Extinction is a natural process, but to quote the International Union for Conservation of Nature, “The current species extinction rate is estimated to be between 1,000 and 10,000 times higher than the natural or ‘background’ rate.” For example, we have lost 30% of bird species, just since the ’70s. Scientists believe that this loss is due to dwindling biodiversity, creating an imbalance in ecosystems, destroying the ability of plant, animal and micro-organism communities to interact as a functional unit.

June is Pollinator Month and the best thing we can do to help pollinators and biodiversity is to plant native plants.

Why native plants? Native plants are defined as plants that grew naturally in the region before human settlement and have had many, many thousands of years to evolve with insect herbivores (insects that eat plants).

These plants are considered host plants because the butterfly seeks out the plant species it evolved with and lays her eggs. When the caterpillar hatches, it has a food source it can consume. These insects do not have an evolutionary history with plants from China or elsewhere, so they cannot eat those plants. In fact, they would not even know the leaves were food. It might as well be plastic! If we do not have native plants in our landscapes, those species, who have specialized on native plants, die out.

The iconic example is the monarch butterfly caterpillar, which can only eat milkweed. No milkweed, no monarchs. About 90% of our insects are specialists, so you can see why the alarm bells are going off.

Whereas native species are always better than non-native species in fueling food webs, not all native plants are equal. Keystone native species are superior because they support many more wildlife species. They do this by hosting greater numbers of butterflies, moths and skippers, and by providing nutritious berries, seeds, pollen and nectar.

Plant a keystone native oak tree, 500 species are hosted. Plant a native redbud, 24 species are hosted. It is clear we need to favor these keystone species when we plant our gardens, especially now. It is up to us.

Without these essential plants in every space we can plant, ecosystems will likely collapse. We really are at that tipping point.

In Yellow Springs, we have already started to try to reverse this trend by educating through our Wildlife Habitat Community initiative about the critical importance of native plants, reducing lawn, planting wildlife habitat and removing invasive species that threaten the existence of native plants.

The “Hosts with the Most” chart above shows the keystone species that make the greatest impact for biodiversity in your yard. For more info and to certify your property as a wildlife habitat, go to

If I could sit with my dad today and listen to his words of wisdom, I think his observational skills would be on point. Everything is connected. We would be well served to live by that basic belief.

*Catherine Zimmerman is an environmental filmmaker, sustainable landscape designer and current chair of the YS Environmental Commission.

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