When climate change first became a hot topic (pardon the pun) about 10 years ago, it was consistently described as “global warming.” When scientists observed the effect that global warming was having on plants and animals in California, they reported that the ranges of native plants and animals were moving to higher elevations and northern latitudes in search of cooler temperatures.
A study published in Nature magazine in December 2009 found that plants and animals must move as much as 6 miles every year from now to the end of the century to find the conditions they occupy now. When the plants move, the animals that depend on them must adapt or move with them to survive. Professor Art Shapiro (UC Davis) has been studying California butterflies for over 35 years. He reported (1) that native butterflies are moving to higher elevations, where temperatures are lower, but that ultimately, “There is nowhere else to go, except heaven.”
More recently we have experienced extreme weather that cannot be adequately described as “global warming.” We have seen epic storms that have resulted in unprecedented flooding, while other places have experienced prolonged drought. We are as likely to have an extremely cold winter as we are to have an extremely hot summer. So the phrase “global warming” has evolved into the more accurate description: “climate change.” Aside from our anecdotal observations of these extreme weather events, science is beginning to catch up to provide an analytical understanding of our observations. The story of climate change is now much more complex and the challenges it presents have become correspondingly more difficult and unpredictable.
Changes in Precipitation
Although places like Pakistan, Australia and some states in the US have recently experienced more rain and flooding than history has recorded, scientists have been reluctant to attribute this to climate change until very recently. Computer modeling of nearly 50 years of weather data has finally enabled scientists to confirm that these increases in precipitation are the result of “…the effects of greenhouse gases released by human activities like the burning of fossil fuels.” (2)
And, like increases in temperature, changes in precipitation also result in the movement of plants and animals to “find” the conditions to which they are adapted. Scientists have recently challenged previous assumptions about the movement of plants and animals to higher elevations. They now report (3) that in some places in California in which precipitation has increased, plants have responded by “moving” to lower elevations. Scientists acknowledge that the affect on the animal populations in their historic ranges is unpredictable because insects, for example, are more sensitive to changes in temperature and may not be able to move downhill with the plants they presently depend upon.
Changes in Fog Patterns
Fog is another weather event that is important in California, particularly along the coast, where the warm air from the interior meets the cold air from the ocean. The result of this confluence of cold and warm air is fog, particularly during the summer when the difference in temperatures is greatest.
The redwood is our native tree that is closely associated with the foggy coastal conditions in California. The redwood requires the fog drip to irrigate it during the dry California summer and its range is limited to sheltered areas because it does not tolerate wind. The range of the redwood in California is therefore limited to a few hundred miles along the coast. Its narrow range makes it particularly vulnerable to climate change.
In Muir Woods, for example, higher temperatures have reduced coastal fog by 30% in the past century. Scientists expect this loss of summer fog drip to result in a significant loss of water to the trees and they predict that it will affect the survival of the redwoods in the long-run.(4)
Implications of climate change for native plants?
Clearly, we still have much to learn about climate change:
- Which weather events are indicators of long-range trends?
- Climate change is apparently not just one trend, such as increased temperatures. It is probably many different types of weather events, such as increases or decreases in snow and rainfall, hurricanes and typhoons, fog and wind. Obviously, we don’t yet have the complete picture of what or where long-range changes have occurred or which are likely in the future.
- We know little about the affect that climate change will have on the natural world. How will plants and animals respond to climate change? Which plants and animals will survive and, if so, where will they survive?
We marvel at the confidence that the local native plant advocates have in their agenda. How did they select the pre-European landscape of the late 18th century to replicate? What makes them think that plants and animals that lived here 250 years ago are still sustainable here, let alone that they will be sustainable in the future?
These are rhetorical questions, which we will presume to answer for our readers: Native plant advocates may compensate for radically changed environmental conditions by using intensive gardening methods. The use of herbicides, irrigation systems, prescribed burns, constant weeding, soil amendments, fences and boardwalks, etc., may artificially mimic the conditions of 250 years ago. However, the result is a native plant garden that is neither natural nor more biodiverse than what can be achieved with less effort, with less toxicity and fewer scarce resources. While we can see the value of a native plant garden to preserve our horticultural heritage, we find it more difficult to justify the large-scale efforts that we currently find in all of our public lands. Is it realistic to garden all of our public lands in perpetuity?
(1) Arthur Shapiro (UC Davis), Contra Costa Times, 1/19/10
(2) “Heavy Rains Linked to Humans,” NY Times, 2/16/11 http://www.nytimes.com/2011/02/17/science/earth/17extreme.html?_r=1&scp=1&sq=heavy%20rains%20linked%20to%20humans&st=cse
(3) “Mountain plant communities moving down despite climate change, study finds,” Los Angeles Times, 1/24/11
(4) “Fog burned off by climate change threatens to stunt Muir Wood’s majestic redwood,” Marin Independent Journal, 2/5/11 http://www.marinij.com/marinnews/ci_17297751?IADID=Search-www.marinij.com-www.marinij.com