Tag: species dispersal

Nativism turns a blind eye to climate change

“Reflexive demonization of alien species ignores the beautiful but complex truth that nature fights to find a way—and for a planet navigating the pressures of climate change and overpopulation, that just might be our saving grace.” – Marianne Willburn, Garden Rant

Margaret Renkl writes an opinion column for the New York Times that I usually enjoy because she frequently writes about nature, often based on observations of wildlife in her own garden.  She lives in her childhood home in Nashville, Tennessee.  Much of her garden was planted with non-native plants and trees decades ago by her deceased mother.  Yet, in a recent column, Ms. Renkl blames non-native plants for a variety of crimes against nature. 

  • She suggests that non-native trees are blooming earlier than native trees, which she says has “skewed our experience of spring.”  She is apparently unaware that spring does indeed arrive earlier than it has in the past because of climate change.  Warmer weather arrives earlier, triggering the blooms of spring, not vice versa.  Both native and non-native plants are blooming earlier than they did in the past. 
  • She suggests that gardens planted with non-native plants are “blooming wastelands where the flowers feed nobody at all,” yet her columns are usually filled with the wildlife that lives in her own garden, with introduced plant species.
  • Although she does not use pesticides in her own garden, she believes that her neighbors’ non-native gardens require them to use pesticides that kill wildlife.  She says, “The typical suburban yard is actually worse than a wasteland. It’s a death trap.” She does not seem to know that most herbicide is used to kill non-native plants, not native plants nor does she seem to realize the contradiction in her indictment of gardening with non-native plants.  If there are more insects living in native gardens than non-native gardens, why would more pesticide be needed in non-native gardens?  If people could learn to love the clover, dandelions, and English daisies in their lawns as much as I do, they would use less “weed killers” on their lawns.

Ms. Renkl’s misperceptions about non-native plants seem to be based on a mistaken belief in their origins.  She says, “Ambulatory and omnivorous, human beings are a migratory species. That’s not true for the vast majority of plants.”  In fact, plants are just as mobile as animals, including humans.  Plants are carried by birds, animals, wind, ocean currents, etc.  They come and go as the climate changes, as it has many times in the past 500 million years that plants have existed on Earth.  Plants now considered non-native existed here in the distant past, in a different climate.  Here are a few examples of such dispersals; most occurred before humans even existed:

The ability to migrate is essential to the survival of plant and animal species.  As the climate changes, this survival strategy is quickly becoming even more important.  When we demand that plants be restricted to their historical “native” ranges, we doom them to extinction because when the climate changes, the vegetation must change.

Where did Ms. Renkl learn these myths?

Ms. Renkl’s cites Doug Tallamy’s Nature’s Best Hope as one of the sources of her mistaken beliefs.  Tallamy considers the existence of non-native plants the root of all evil in nature.  He calls them “ecological tumors.” He blames non-native plants for declining populations of both native plants and insects, and by extension to declining populations of birds that eat insects. 

In Nature’s Best Hope, Tallamy says, “…we must not use climate change as an excuse to do nothing.  Most species of plants and animals are far more resilient to climate variability than we give them credit for.  Besides, increasing the number and biomass of the plantings in our yards and public spaces is one of our most accessible and convenient tools to fight climate change.”  The problem with Tallamy’s dogma is that it inspires the public and land managers to eradicate established landscapes that are not native based on Tallamy’s claims that non-natives are “crowding out” native species and depriving wildlife of food. All native plant “restorations” begin by eradicating non-native plants, usually with herbicides that retard new growth.  In other words, the native plant ideology is causing the loss of vegetation and therefore the loss of stored carbon and the reduced capacity for carbon sequestration in the future.  The native plant ideology is not increasing biodiversity, nor is it “fighting climate change.”  It is more destructive than constructive. 

I’m not looking for “an excuse to do nothing.”  On the contrary, I believe every effort must be made to stop or at least slow down the inexorable advance of climate change.  The most basic effort we can make is to stop destroying functional vegetation, especially trees.  Then, there is a lengthy list of what we should be doing to reduce greenhouse gas emissions, which is another, equally important topic. 

Native plant advocates consider climate change irrelevant because they believe the existence of non-native plants is the sole culprit of all problems in the environment.  They see every environmental issue through the narrow lens of their dogma.  This comment on an article about the value of non-native plants by Marlene Condon published in [Chesapeake] Bay Journal is an example of such a misinterpretation of an environmental issue:

“English ivy is an evergreen, non-native, invasive groundcover that has demolished undisturbed natural areas…In salmon country that’s the difference between clean, cold streams and warmer streams filled with sediment.”

Eradicating ivy on stream banks is likely to produce more sediment because it will take some time for replacement vegetation to cover the ground, especially if herbicides are used to eradicate the ivy. Water is warmer in streams because of climate change and because there is less water due to water diversion and droughts. There are many other reasons for declining populations of salmon, particularly dams that prevent salmon from reaching their spawning grounds upstream.

Treat the cause, not the symptom

The native plant ideology ignores the underlying causes of changing ecosystems. Most changes are caused by the activities of humans, such as agriculture, development, water diversion, and pesticides.  Climate change is the underlying cause of some changes in nature and it will steadily become a more important factor.  Eradicating non-native plants will not reverse any of those changes nor will it prevent changes in the climate.    

  1. Alan de Queiroz, “The resurrection of oceanic dispersal in historical biogeography,” Trends in Ecology and Evolution, 20 No. 2, February 2005

Photo credit for featured photo: Garden Rant, Marianne Willburn

Climate change requires plants and animals move to survive

Our readers know that we consider climate change the most critical environmental issue of our time.  We also believe that the native plant ideology is antithetical to our concern about climate change for two reasons:

  • The changing climate requires that plants and animals move in order to survive. Therefore, the demand that historical ranges of native plants and animals be restored and maintained is both unrealistic and harmful.  It is unrealistic because the environment has changed in the past 250 years since the arrival of Europeans on the West Coast and it will continue to change.  Therefore, we cannot assume that the native plants that existed here in 1769 are still capable of surviving here.  It is harmful because animals can and do move as the climate changes.  Therefore, eradicating the plants they need for survival is harmful to them.
  • The eradication of non-native plants and trees is exacerbating climate change by releasing their stored carbon into the atmosphere, thereby contributing to the greenhouse gases that cause climate change. When prescribed burns are used to eradicate non-native plants or prevent natural succession the release of carbon into the atmosphere by the plants that are burned is immediate.  When large, mature trees are destroyed, the carbon they have stored as they grew is released into the atmosphere as the wood decays.  Furthermore, their ability to store carbon in the future is lost to us going forward.  Since carbon storage is directly proportional to biomass, whatever we plant in their place is incapable of storing as much carbon as the mature trees.

The umber skipper has adapted to Bermuda grass in lawns in the East Bay. Creative Commons
The umber skipper has adapted to Bermuda grass in lawns in the East Bay. Creative Commons

There is an important caveat that we must add to our first bullet point.  Changing location is not the only mechanism that can ensure species survival in a changing climate.  Many species are probably “pre-adapted” to the changed climate.  That is, they may be capable of surviving changes in the climate.  Secondly, species can adapt and/or evolve in response to changes in the environment, which is another mechanism that facilitates species survival.  We invite our readers to visit our post about the rapid evolution of finches in the Galopagos Islands in response to extreme weather conditions that caused selection events.

Today we will inform our readers of the scientific record regarding the need for plants and animals to move as the climate changes.  We will use the recently released fifth report of the Intergovernmental Panel on Climate Change as our source.

Intergovernmental Panel on Climate Change

First we will establish the credibility of the Intergovernmental Panel on Climate Change (IPCC).  The IPCC was formed in 1988 by the United Nations.  It is composed of thousands of scientists from all over the world, representing the 190 member nations of the UN.  The IPCC does not conduct original research.  Rather it compiles thousands of peer-reviewed scientific studies into reports that represent a consensus viewpoint of the global scientific community.  Typically, scientists from 120 countries participate in marathon sessions in which consensus must be reached before reports can be published.  The IPCC has published 5 reports since 1988, the most recent earlier in 2014.

How the climate has changed and how it will continue to change

The IPCC compiled several different sources of data to report how the climate has changed from 1900 to the present.  Then they modeled the multitude of variables that influence climate to predict different trajectories for the climate going forward to 2100.  The many variables that influence climate interact in complex ways that are not entirely predictable.  There is therefore some uncertainty in those predictions, as there is in any prediction of the future.  Therefore, future temperature is depicted by the following graph as “bands” of probability.  The bands become wider as the graph depicts further into the future, as we would expect; that is, the distant future is less predictable than the near future.

Observed and projected temperature change, IPCC 2014
Observed and projected temperature change, IPCC 2014

Here’s what we learn from this graph:

  • The graph reports that the average global temperature has increased by 1° Celsius (1.8° Fahrenheit) from 1900 to the present.  Graphs depicting the more distant past indicate that the climate began to warm around the time of the industrial revolution, about 1850.  Therefore the total increase in temperature is greater than that depicted by this graph.  However, the rate of increase has accelerated greatly in the past 50 years.
  • The upper range of projected temperature increases on the graph is labeled RCP8.5 (Representative Concentration Pathway 8.5). That pathway is based on the assumption that present levels of greenhouse gas emissions will continue to increase at the same rate as they have in the recent past.  The mean prediction of that pathway is a global temperature increase from the present to the end of the century of 3.7° Celsius (4.6° Fahrenheit).
  • The lower range of the projected temperature increases on the graph is labeled RCP2.6 (Representative Concentration Pathway 2.6). The mean prediction of that pathway is a temperature increase to the end of the century of 1° Celsius (1.8° Fahrenheit).  That pathway is based on the assumption that greenhouse gas emissions are radically reduced, beginning immediately, as represented by the following graph from The Guardian.  This graph also depicts two intermediate emission scenarios between the present trajectory(RCP 8.5) and the maximum predicted reductions in emissions (RCP 2.6)

Projected energy use
Projected energy use

Movements needed for survival in a changing climate

The world has done little to reduce greenhouse gas emissions and America has done even less.  According to a recent Gallup Poll, only 39% of Americans are “concerned believers” in climate change.  Another 36% of Americans believe the climate is changing, but don’t believe it will affect them.  Twenty-five percent (25%) of Americans do not believe the climate is changing.  Therefore, for the time being, it seems extremely unlikely that our polarized politics in America will be capable of responding effectively to the grim reality of climate change.  Within that context, we inform you of the final graph from the IPCC report about the need for plants and animals to move from their present ranges in response to climate change and their variable ability to do so.

Adaptation to Climate Change. IPCC
Adaptation to Climate Change. IPCC

On the vertical axis, the graph depicts the ability of plants and animals to move, measured in kilometers per decade.  The horizontal lines depict the need of plants and animals to move in response to various scenarios of climate change as we described earlier.  The bars depict the ability of plants and animals to move and the height of each bar informs us of the variable ability of plants and animals to move.  Trees are the least able to move, unless we have the wisdom to plant them outside their native ranges—at higher latitudes or elevations–where they are more likely to survive in the future. 

For example, if we radically reduce greenhouse gas emissions immediately (RCP2.6), most species of trees and plants will be sustainable at their present latitudes and elevations.  But if greenhouse gas emissions continue on their current trajectory (RCP8.5), most species of trees and plants will not be capable of moving far enough, fast enough to survive as the climate warms.  Although trees and plants are capable of moving only very slowly, most animals are capable of moving more rapidly.  Will they have the plants they need to survive in their new ranges?

 Putting our heads in the sand

Surely there aren’t many native plant advocates in the San Francisco Bay Area who don’t believe in the reality of climate change.  The Gallup Poll reports that most people who don’t believe in climate change are Republicans and in the San Francisco Bay Area Republicans are a small minority.  And so we ask native plant advocates this question:  How do you reconcile the reality of climate change with your demand that native plants be restored and maintained where they existed 250 years ago in a very different climate?