Living with Biodiversity
By Dr. Douglas Tallamy (for Biodiversity Day, May 22, 2022)
In case you haven’t heard, life on earth is in trouble. This is why I am asking you to get on the Homegrown National Park® MAP. Each and every one of us has the power to regenerate biodiversity and we don’t have the luxury of time to do it.
Distressing statistics about declining biodiversity are being reported so fast now that they are running into each other. North America has lost 3 billion breeding birds in the last 50 years; earth has lost 50% of its insects with continuing declines being reported nearly everywhere; and the UN predicts 1 million species will go extinct in the next 20 years. Not only are we in the midst of the 6th great extinction event the earth has suffered, but massive defaunation of species not yet extinct is rampant. We hear much about the climate crisis, and rightly so, but what most people fail to appreciate is that our disregard for the well-being of biodiversity is as grave a threat to humans as climate change is, because it is healthy, productive ecosystems, not Best Buy or Costco, that support us.
To put it bluntly, we are destroying the natural world that we cannot live without. It’s not that we purposefully have nature in our sights. Rather, we simply refuse to share our spaces with the natural world. We have clung to the notion that humans and nature cannot coexist as if it were true (it’s not). And so, as our population has expanded, we have exiled nature more and more to parks and preserves that are too small, too few in number, and too isolated to sustain it. The grim statistics above are a stark reminder that our protected lands (just 12% of the U.S.) are not sufficient to sustain the amount of nature our ever-growing populations require.
Fortunately, there is a solution to this existential crisis. We can save nature by learning to live with it. We must now practice conservation not only within parks and preserves, but also outside of them, where we live, work, shop, farm, and play: that is, in built, human-dominated landscapes. There are four roles every landscape must play if we are to forge a sustainable relationship with the natural world that supports us. First and foremost, we must landscape with plants that support local food webs, for it is the transfer of energy from plants to animals that enables the animals that run our ecosystems to exist. Second, all landscapes must pull CO2 from the atmosphere and store the carbon first in plant tissues and then long-term in the soil at that site. All landscapes must also help manage the local watershed. No one has the ethical right nor ecological permission to design a landscape that degrades the watershed in which it lies. Finally, all landscapes must nourish a complex community of native pollinators by supplying the pollen and nectar they require to successfully reproduce.
Built landscapes don’t do these things naturally; they must be designed specifically with ecological function in mind. Because we have created landscapes primarily for our aesthetic pleasure ever since we started designing landscapes, built landscapes often fail to accomplish at least one of these ecological goals, and, sadly, many landscapes fail to accomplish any of them. If there is one central tenet of ecological landscaping, it is this: Plant Choice Matters. Plants differ wildly in their ability to deliver ecosystem services, so we must carefully choose from among hundreds of options to select the plants that are best at enabling particular ecological functions. Turf grass, for example, is the worst choice for supporting pollinators and the local food web, for sequestering carbon, and for managing the watershed. And yet we have blanketed an area larger than New England with lawns. If we want to create landscapes that permit wildlife such as birds to reproduce, we must choose plants that host caterpillars, because caterpillars dominate nestling diets in the vast majority of North American bird species.
This is not simply a matter of favoring native plants over non-natives, although that is a good start. Combined, non-native crepe myrtles, Callery pear, burning bush, Forsythia, and Japanese barberry host fewer than five caterpillars species and always in very low numbers. But even native plants differ hugely in their ability to host caterpillars. Oak species in the Mid-Atlantic states, for example, host 557 species of caterpillars, while tulip poplar hosts only 21, and yellowwood and Virginia sweetspire host none at all.
Not only do we need to become comfortable with landscapes that support many species of caterpillars, but we need landscapes that support great numbers of those caterpillars; it takes nearly 10,000 caterpillars to bring a single clutch of most birds’ nestlings to the point of independence. Imagine the number of caterpillars required to support healthy populations of robins, catbirds, chickadees, titmice, cardinals, blue jays, chipping sparrows, and Carolina wrens! These are common birds that we expect to be in our yards yet cannot be there without many thousands of caterpillars to support them.
Ecological landscaping based on proper plant choice can provide those caterpillars but wide-scale acceptance of landscaping to meet the needs of our fellow earthlings requires a shift in the mindset of landowners everywhere. Our culture has successfully vilified nearly all insects from time immemorial. After all, if our plants are decorations, we certainly don’t want insects marring otherwise perfect leaves by munching or sucking them. Understandable, if plants were just decorations. But they are far more than that. They are the first trophic level that supplies food for all animal life on terrestrial earth. A plant without some holes chewed in some leaves is an ecological freeloader, one that is taking up valuable space without contributing its share of the energy it has captured from the sun to the local food web. A few such plants will not cause ecological collapse, but landscaping with unproductive decorations wherever we go, does.
Rather than demanding beautiful but ecologically dead landscapes, let’s seek trophic balance in our landscapes, which will include native plants, the insects that eat them, and the many natural enemies that keep those insects in check. We do not have to abandon aesthetics as a goal, but it should no longer be the only goal. We can create landscapes that host thousands of caterpillars and dozens of bird species without ugly defoliation, because those birds will eat hundreds of caterpillars every day, as will the dozens of species of predatory and parasitic insects and spiders that will be attracted to such landscapes. We will not have too many rabbits, groundhogs, or voles mowing down our gardens if we provide habitat for foxes, hawks, and owls in our neighborhoods. We can throw away the toxic pesticides with which we have permeated our living spaces, and we can fire Mosquito Joe because natural enemies will keep most pests at low densities. But we must learn to tolerate some imperfection. We should not imagine our landscapes as static postcard scenes to be mowed and clipped and raked into compliance each week, but rather as integral parts of a dynamic, living planet.
Every one of us is responsible for earth stewardship because everyone requires the life support such stewardship sustains. Transitioning to landscapes that nurture the life we all need—landscapes that enhance local ecosystems rather than degrade them—is a challenging departure from past practices, but it is also exciting and rewarding, and our only viable path forward. And this transition is the central mission of Homegrown National Park. Please help us spread this important message to your friends and neighbors who have never heard it before and please ask them to get ON THE HNP MAP . Thank you for your interest and support.
— Doug Tallamy