Note: This was written in response to a piece in the Boston Globe on April 26th, 2023 titled "Got weeds? Read this before you whack them," which we felt was irresponsible in its lack of understanding about the importance of native plant species to ecological health, and promotion of non-native species. We submitted this to the Globe as a response, but it was rejected.
On a neighborhood walk on a warm May day, you may stop to admire the petals of a tulip or daffodil, a herald of spring for urban and suburban dwellers. Enjoy, but remember, the flower has no interest in you. It is spreading its beautiful colors only in the hopes of sending a message to insect pollinators - “Come! Share my pollen! Help me spread my genes!” And meanwhile, our native pollinators are on the same search for the pollen they need to raise their young. But when human environments are dominated by non-native plants, it is a missed connection. A love story with no happily ever after. A landscape dominated by non-native plants may appear to be thriving, but if you take a closer look, the insects that should form the foundation of the local food web will, for the most part, not be there. Plants and animals evolved together for millennia, creating tight collaborations that introduced species simply cannot partake in.
First, what are native plants? In New England, we can think of these as plants that were around before the arrival of European colonizers, that have a long evolutionary history with the land, animals, and indigenous peoples of our region. It is important to distinguish between “weedy” native plants (like Canada goldenrod) that may grow unchecked in a garden or disturbed setting but are kept in balance in natural ecosystems by herbivores and pathogens, and true invasive species, which are non-native plants that lack any natural checks and balances in their new environment so that even in intact, natural ecosystems they can outcompete native species and break that intricate web. The impact of invasive species can vary at the landscape level - some studies have shown that invasive species can increase productivity or carbon sequestration at certain scales. But at the local level, invasive plant species almost always reduce the native plants in a given habitat and drive local extinctions of native plants and the insects that depend on them for survival, including pollinators.
A meadow of native plants. Morse Kelley Pollinator Garden, Somerville, MA. Photo by Tori Antonino.
There are, of course, generalist pollinators out there; and when we see a non-native plant buzzing with honeybees (also an introduced species) or common eastern bumblebees (our local New England generalist bumble!), it is easy to be fooled into thinking that the plant is supporting a healthy pollinator community. But a pollinator community made up of only generalist species is not a healthy community - diversity is lacking. In New England, approximately 15% of our bee species are specialists, able to feed and raise their young on only select genera of predominantly native plants. Herbivorous insects are even more specialized, such as the caterpillars that grow into the butterflies we all love to watch in summer. Due to the specialized chemicals found in the leaves of plants, most herbivorous insects can only tolerate feeding on a select number of species. Our endangered monarch butterfly can only raise its young on milkweeds; without these specific native plants, the monarch will disappear, even though the adult butterflies may drink nectar from a wide range of plants. Specialist pollinators are often left behind in urban and agricultural settings without the native plants they need. When a pollinator does not have the plant it needs to survive, it dies.
And it’s not just insects that are impacted. The animals that eat those insects for their own survival suffer when there aren’t enough native plants. A 2018 study by University of Delaware researchers Desirée Narango and Doug Tallamy, and Peter Marra of the Smithsonian Migratory Bird Center, looked at the percentage of native plants in yards and the success of Carolina chickadees. They discovered that “if the yard has more than 70 percent native plant biomass, chickadees have a chance to reproduce and sustain their local population. As soon as the number of native drops under 70 percent, that probability of sustaining the species plummets to zero”.
Leafcutter bee on milkweed. Photo © Claire O'Neill, some rights reserved (CC-BY-NC)
Non-native plants aren’t bad or evil: they are misplaced, intentionally or accidentally, and can wreak havoc on the ecosystems they have entered. It is important to acknowledge that humans, in particular European colonizers, have had a more damaging effect on native ecosystems than any invasive plant ever could. While it can feel hypocritical to “blame” invasive plants for ecological problems that human colonization and globalization have caused, the removal of these plants is still necessary to restore landscapes to healthy conditions that can support biodiversity.
Even non-native plants that do not become invasive are not supporting the majority of the insects looking for food in that region. Dandelions do not provide the same nutritional value for emerging pollinators as pussy willow (14% to 40% protein, respectively), for example. We cannot rely on introduced species to support our pollinators in the way our native plants do. These introduced species take up valuable land that native plants could inhabit. They also hold the potential to become invasive. In their own ecosystems, where they are native plants, they work beautifully as part of the food web.
A good example is Phragmites australis, a species of reed on the USDA’s national invasive species list. In the US, where it has been for more than 300 years, it supports five insect species; in Europe, where it has evolved with the native beneficial insects for many thousands of years, it supports 170 species. This is why we need native plants. They are the foundation of a functional, healthy ecosystem. They provide food and shelter for the insects that feed the rest of the world, including humans.
Aster mining bee on New England aster Photo © Claire O'Neill, some rights reserved (CC-BY-NC)
We are in the midst of a biodiversity crisis that is intertwined with the climate crisis, both contributing to and affecting the other. But they are not the same thing. If we could snap our fingers and bring all carbon emissions back to pre-industrial levels but did not address the hallmark contributors of the biodiversity crisis - habitat loss, aggressive pesticide use, pollution, and invasive species - we still would be in serious trouble.
There are trade-offs, of course; effectively removing invasive plants can require hard labor and years of follow-up. Removing every non-native plant from a landscape is often impractical. But working towards a goal of at least 70% native plant species in urban habitats is obtainable and has been proven effective in supporting wildlife. Given limited time and resources, the responsible gardener can learn about which invasive plants are the worst offenders in their local area and focus on replacing those with native plants that best benefit at-risk specialist insects. We need to spread native plants wherever we can, make this an integral part of the curriculum from kindergarten through landscaping school, and work hard to keep non-native plants where they belong - in their own ecosystems where they will be part of an ancient, amazing web of life, an evolutionary love story that can continue into the next millennia.
Authors:
Renée Scott
Green & Open Somerville
NOFA/Mass Pollinator Network
Claire O’Neill
Green & Open Somerville
Earthwise Aware
Amy Mertl
Green & Open Somerville
Lesley University
Tori Antonino
Green & Open Somerville
Signers:
Frederica Gillespie
Native Plant Gardens of Southborough
Jean Devine
Devine Native Plantings, LLC
Biodiversity Builders (sm) Youth Education
Mystic Charles Pollinator Pathways Group
Amy Meltzer
MA Pollinator Network
Elders Climate Action Research Team and Natural Solutions Working group
Charlie Wyman
Lexington Living Landscapes
Alan Nogee
President, Friends of Cold Spring Park
Newton Community Pollinator Project
Sarah Wang
Mystic Charles Pollinator Pathways Group
Kim DeAndrade
Mystic Charles Pollinator Pathways
Mass Pollinator Network