Plant Adaptation to Global Warming

Essays, Stories, Adventures, Dreams

Chronicles of a Footloose Forester

By Dick Pellek


Plant Adaptation to Global Warming


The debate about climate change is not going away anytime soon.  For whatever reasons, there are plenty of climate change deniers holding firm in their beliefs.  Some offer mild objections because they can and do cite temperature anomalies. Others, especially those who have vested commercial interests in maintaining the pretense that the climate is not changing, at least not changing beyond the historical boundaries of natural climate fluctuations, hope that opinion continues to trump facts.  Some corporations and fossil-fuel industries put considerable effort into protecting the status quo as regards how we as a world society deal with perceived climate changes.  And when elected leaders who have broad access to the bully pulpit come right out and declare that global warming is a hoax, they carry many of their loyal supporters with them.  Unquestioning supporters may think that if the President of the United States declares that global warming is a hoax that was invented by the Chinese to weaken the American economy by encouraging us in a fruitless effort to do something about it, that makes future planning and mitigation efforts more difficult.
This chronicle choses to address the climate issue as one of global warming, rather than one of climate change.  During the truncated evolution of the debate about climate, the trend line in temperature change has been one of warming.  Although the term “global warming” is not as readily accepted among reluctant observers who might otherwise and begrudgingly acknowledge the fact of climate change, the trend lines on graphs show a pattern of warming for the past 200 years or so.  We are talking about changes over time and on a worldwide basis, not about the ups and down in daily and local weather patterns.  Nevertheless, there will always be people who rely on their opinions as somehow superseding the recorded facts.   For too long, the myth that opinion trumps facts has prevailed.  Another myth that perception is everything is also false, but is sometimes overpowering.  

Climate changes have, however; altered the institutional recommendations of many scientists who study the adaptations of both plants and animals with regard to their preferred habitats.  Perhaps the oldest tracking system in popular use refers to the cold hardiness maps issued by the USDA in 1960 and periodically updated.  An update is currently being prepared and will show a 2018 publication date.


2012 version of plant hardiness zone map




Another standard reference map, one by the non-profit, non-political Arbor Day Foundation, also dates back decades and has been updated in response to climate change.  Their interest for the past 50+ years has been to inform gardeners and horticulturists about the hardiness of plants within the arbitrary boundaries of temperature regimes in the continental United States.  By definition, hardiness of plants describes their ability to survive adverse growing conditions. It is usually limited to discussions of climatic adversity. Thus, a plant's ability to tolerate cold, heat, drought, flooding, or wind are typically considered measurements of hardiness.  Hardiness of plants is defined by their native extent's geographic location: longitude, latitude, and elevation. Inasmuch as there are real differences in annual temperature regimes throughout the United States, the meteorological and climatological sciences have long ago categorized the climates themselves and ascribed approximate boundary lines on maps to help orient us.

For many horticulturists, the Arbor Day Foundation map of cold hardiness zones in the continental United States is a standard reference.  Although its publication date is 2002, there were previous hardiness zone maps using the same criteria and also published by the Arbor Day Foundation.  Changes in the maps from 1990 to present day circumstances put geospatial and interactive markers on changes in the boundaries themselves.



The map above is popular because it is easy to understand. There have also been updates over time to show changes in hardiness zones as a result of global warming.

In 2002 the USDA initiated a project with the American Horticultural Society to update the 1990 map. A year later the AHS released a draft of the update which showed that many of the hardiness zones had moved northward reflecting a general warming trend. The USDA, after a brief review, decided to reject the draft and gave little justification for its decision. Its terse dismissal raised the possibility that it was a political decision - the USDA was concerned that the AHS Draft gave support to global warming proponents and decided to suppress the project to avoid controversy and not embarrass the Bush Administration. Ten years later the USDA released the 2012 Hardiness Zone Map which added two new climate zones and showed a general warming trend across the country. The USDA, however, noted that, "Changes in zones are not reliable evidence of whether there has been global warming." It seems obvious that the issue of climate change became a political football that has been tossed around ever since.
Whether the casual reader is a climate change denier or a believer in climate changes that are trending more specifically toward an ever-warming planet, we as a society should at least recognize that there is a considerable body of scientific knowledge that should inform our opinions.  Using recommended plant hardiness zone maps facilitates our judgement calls when it comes to choosing which plants are best adapted to various latitudes and elevation.

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