The White House recently released the National Climate Assessment which was prepared by a panel of scientists convened by the federal government. This report informed us that average temperature increase of only 2° Fahrenheit over the entire country in the past century has produced these changes in the environment:
- “Summers are longer and hotter, and extended periods of unusual heat last longer than any living American has ever experienced.”
- “Winters are generally shorter and warmer.”
- “Rain comes in heavier downpours.”
If greenhouse gas emissions continue to increase at the same pace, the report predicts an increase in average temperature of as much as 10 degrees by the end of the century. If an increase of only 2 degrees is capable of producing the extreme weather we are experiencing, it is difficult to imagine what we can expect if the temperature increases 10 degrees.
President Obama announced the report: “This is not some distant problem of the future. This is a problem that is affecting Americans right now. Whether it means increased flooding, greater vulnerability to drought, more severe wildfires—all these things are having an impact on Americans as we speak.”
The impact of climate change on plant life (1)
Henry David Thoreau recorded the arrival of spring at Walden Pond in Concord, Massachusetts in the 1850s. His data has been incorporated into the records of his successors, creating a continuous record across 160 years. Spring arrives in Concord, Massachusetts about three weeks earlier than it did in the 1850s. This pattern mirrors the changes occurring around the planet according to field studies and satellite images taken from space.
The response of plants to this change in seasons has varied, according to a study published recently by the Proceedings of the National Academy of Sciences. Some species of plants reach their flowering peak earlier in the year, while other species are extending their flowering into later in the fall.
Another study speculates that increased temperature isn’t the only factor influencing these changes in flowering patterns. Increased levels of carbon dioxide also may be affecting plants. Earlier snow melt may be another trigger for changes in timing of flowering. The availability of pollinators at the time of flowering is assumed to influence the long term survival of flowering plants. In other words, the affects of climate change on plants are complex and imperfectly understood.
The implications for gardeners who care about wildlife
The New York Times recently published an op-ed which offered an answer to this question: “How do we garden in a time of climate change?” There are probably many answers to that question, so we should understand the perspective of the author of the op-ed, James Barilla. He describes his background on his website: “… James Barilla held a variety of posts in wildlife research and management, crossing paths with wolves and mountain lions in remote wilderness and promoting “mini-beast” habitat in urban schoolyards. He first became intrigued by backyard wildlife while working in England for a land trust, where his job was to create wildlife habitat on the outskirts of a city.” He has a Master’s Degree in Environmental Science from University of Montana and a Ph.D. in English from UC Davis. He now teaches creative and environmental writing at University of South Carolina. He has written a book about gardening to support urban wildlife and articles published by Atlantic and National Geographic Magazine.
One of Mr. Barilla’s goals as a gardener is to provide habitat for wildlife. Million Trees is therefore very interested in his answer to the question, “How do we garden in a time of climate change?” because we are always responding to the perception of native plant advocates that the eradication of non-native plants will benefit wildlife. Mr. Barilla shares our view that, particularly at a time of a rapidly changing climate, it no longer makes sense to limit ourselves to native plants if we are to provide useful habitat to wildlife:
“In [the] microclimate [of our backyards], extreme gardening means making the yard hospitable for as many species as possible, without worrying so much about whether they originally belonged here or not. I used to think that tearing out turf and making room for native species like purple coneflower and switchgrass was the best thing I could do. But things aren’t that simple anymore. It doesn’t make sense to think in terms of native and nonnative when the local weather vacillates so abruptly. A resilient garden is a diverse garden.” (emphasis added)
Mr. Barilla also acknowledges the changing ranges of plants and animals in response to climate change and the need to accommodate those changes if species are to survive: “…species are disappearing across their native range but flourishing outside it…This phenomenon of species movement and adaptation is likely to become commonplace as the climate changes.”
Finally, Mr. Barilla appeals to us on moral grounds: “…we humans are responsible for the current changes. So we must also be responsible for helping other species survive them.” He uses the needs of the monarch butterfly as an example of a species that has been particularly hard hit by both climate change and the agricultural practices of humans. He urges gardeners to plant milkweed—the host plant of monarchs—in their yards.
Scientists in Ohio have concluded that episodes of extreme heat have reduced the population of native butterflies. Here in California, we can help monarchs by stopping the many projects that are destroying eucalyptus because monarchs use eucalyptus in several hundred locations along the coast of California as their overwintering roost.
Native plant advocates are putting their heads in the sand
We (and thousands of people with whom we have collaborated in the past 15 years) have made every effort to inform native plant advocates that they are mistaken in their assumption that native plants provide habitat superior to non-native plants. We have provided them with the many empirical studies that prove otherwise, including one cited by Mr. Barilla in his op-ed: “One study in Davis, California, found that 29 of 32 native butterflies in that city breed on nonnative plants. Thirteen of these butterfly species have no native host plants in the city; they persist there because nonnative plants support them.” This study by Professor Arthur Shapiro and his graduate student was published over 10 years ago. (1) It is only one of 5 local studies that report similar findings for every taxon of wildlife: benthic microorganisms, insects, amphibians, reptiles, birds, mammals.
There are similar studies elsewhere in the country and around the world that also find equal numbers of insects in native and non-native vegetation. The British Royal Horticultural Society is conducting a 4-year study of insect use of plants. Their preliminary findings are that insects are equally likely to use native and non-native plants. Even Doug Tallamy was unable to find evidence to support his mistaken assumption that more insects use native plants than non-native plants.
Yet, native plant advocates refuse to consider the damage they are doing to both the environment and wildlife that is struggling to survive the destruction of their habitat. They demand the destruction of thousands of healthy trees, storing millions of tons of carbon dioxide that is released into the atmosphere when the trees are destroyed, thereby contributing to climate change. They demand that herbicides be used to eradicate non-native vegetation and kill the roots of the trees that are destroyed to prevent them from resprouting.
Here are a few specific examples of native plant advocates– and the environmental organizations that support them– refusing to consider the damage being done to the environment and wildlife:
- Neighbors of Mount Davidson in San Francisco have been trying for several years to discuss plans of the Natural Areas Program to destroy 1,600 trees on Mount Davidson with the Bay Area Chapter of the Sierra Club, which supports those plans. The Chapter Sierra Club leadership has repeatedly refused to even discuss the issue with the neighbors who are members of the Sierra Club. The final response came from the Sierra Club Executive Director, Michael Brune who supports the refusal of Chapter leadership to discuss the issue with Club members.
- The Sierra Club recently announced in its newsletter, The Yodeler, that it has asked the East Bay Regional Park District to destroy 100% of all eucalyptus trees on over 1,200 acres of park land. East Bay Regional Park District has estimated the average density of the eucalyptus forest on their properties at 650 trees per acre, which means that the Sierra Club is demanding that over 780,000 trees be destroyed in the East Bay.
- The Sierra Club recently announced that it has asked UC San Francisco to implement its original plan to destroy over 30,000 trees on Mount Sutro in San Francisco. In making this request, they claim that such destruction will benefit native plants, although the original plan did not propose to plant any native plants. (These plans are presently on hold, although UCSF is now in the process of destroying about 180 trees they consider hazardous, in the height of nesting season.)
- San Francisco’s Department of the Environment has submitted an application for funding to create a Biodiversity and Ecology Master Plan which proposes to treat all open space in San Francisco as “natural areas” using the Natural Areas Program as its model. The Natural Areas Program is presently restricted to 1,100 acres of city-managed park land. If implemented, this plan could eradicate non-native plants on all city-owned open space as well as private backyards.
The changing climate requires that we reconsider the commitment to native plants in historic ranges because they are probably no longer adapted to those ranges. They must move if they are to survive and we must accommodate that movement if we want them to survive. Likewise, we must reconsider everything we are doing to contribute to climate change, including our use of fossil fuels and deforestation.
If you are a member of the Sierra Club, please tell them your opinion of their recent demands to destroy more trees in San Francisco and the East Bay than is presently planned by the owners of those properties. Also, urge them to listen to the concerns of their members regarding the plans for tree removals by San Francisco’s Natural Areas Program. Their address is: San Francisco Bay Chapter Sierra Club, 2530 San Pablo Ave. Suite I, Berkeley, CA 94702-2000
If you live in San Francisco and don’t want all open space in the city to be treated as native plant museums, please write to Polly Escovedo (who is considering the grant application to create a Biodiversity and Ecology Master Plan) by May 14, 2014: firstname.lastname@example.org
(1) This section is from: Carl Zimmer, “Springing Forward, and Its Consequences,” New York Times, April 23, 2014
(2) SD Graves and AM Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110 (2003) 413-433