Thu, Jun

The Climate Ready Tree Myth


CLIMATE WATCH - For decades, humanity has been warned about the perils of the coming climate crisis caused by human activity. 

Societies and cultures have had different reactions to this, but until recently, most of what humanity has done falls somewhere between denial and good intentions backed by insufficient action.  Though we are far from a place where human beings have made a firm commitment to address climate change, we are seeing more action in recent years than ever before.  The change is less the result of a new enlightenment than it is a reaction to ever more severe environmental catastrophes happening as the predicted consequences of climate change begin to come to fruition.  One of the latest of these reactions in Southern California comes in the form of encouragement to plant so-called “Climate Ready Trees” which are generally exotic, non-native trees from desert ecosystems around the world.

In most cases, human culture mainly proves effective dealing with things in a reactionary fashion.  There are penalties to this kind of approach.  Commercial air travel offers an example.  Many of the safety innovations on airplanes today are the result of improvements made after analyzing fatal plane crashes.  In some cases these solutions were considered prior to disasters but were dismissed as costly and unnecessary.  With respect to climate change, our collective airplane is the planet where we live, and we don’t have the luxury of crashing the earth in order to redesign a better earth in another iteration.

We know the causes of climate change, but some of the solutions bandied about focus on mitigating the damage we are causing to the planet in lieu of addressing the causes of the problem.  Rather than eliminating the use of plastic from most products and packaging, our solutions focus on costly and inefficient ways to capture and reprocess plastic that are only modestly successful at best and impractical at worst.  Rather than having frank discussions about population and how humans are now using most of the arable earth to raise food for just one species—ourselves—we focus on manipulating nature to constantly increase the amount of food we can produce, despite evermore deadly consequences to the very ecosystems that gave rise to us.

You need look no farther than Los Angeles City parkways to understand that for about the last 150 years, the people living here have replaced our thriving native ecosystem with an almost entirely non-native, sterile urban forest.  Our streets are filled with water-hungry exotic turf grass and monocultures of trees planted in rows in order to appeal to an outdated human desire for the artificial aesthetic of uniformity.  This has created a Los Angeles where less than 3% of our street trees are now native, and the non-native trees we have used to replace them consume on average six times the water of our drought adapted native trees.

In Los Angeles County, 70% of residential water use goes to support landscaping of exotic water-hungry lawns, tropical plants, and non-native trees.  Many of the trees planted in Los Angeles in particular were put into the ground during massive upticks in the population of our city in the first half of the twentieth century.  Tens of thousands of these trees will be reaching the end of their lifespan in the next few decades.  Climate change has made our urban forest canopy more important than ever to offset the heat island effect, create shade for our citizens, and mitigate the impact of extreme weather events.  Therein, we are going to need to replace a lot of trees.

This brings me to a growing movement within a well-intentioned subset of the Southern California horticultural community with respect to the trees we plant in our urban forests.  It’s getting hotter.  There’s less water to go around.  Applying the reactionary iterative methodology to this situation, some have concluded that the solution is to plant trees from deserts in Mexico, China, and Australia that require the absolute least amount of water in order to survive.  As with most simplistic ideas, this sounds reasonable upon first look.  It seems logical that these “Climate Ready Trees” from far-flung deserts can be integrated into our urban canopy and will future-proof Los Angeles against higher temperatures and less precipitation.  That’s the argument in a proverbial desert nutshell.  But the human history of tinkering with nature because we think we know better is a long story of unintended consequences and disastrous results.

By filling our city with non-native exotic landscaping, we’ve lost 90% of our regionally local butterflies, songbirds, and other pollinators at a time when we most need them to preserve biodiversity that is under a climate crisis assault on multiple levels.  Replacing water-slurping non-native trees with water-sipping non-native desert trees only exacerbates our biodiversity problems.  Instead, these desert trees will, like the swamp and tropical trees before them, become islands of ecosystem sterility in Los Angeles for another century because these tree species are not part of the local web of life.  Right now it is more crucial than ever that we create an urban forest that is a biodiversity lifeboat for habitat.  Because of myriad reasons including climate change, human mischief, and encroachment into habitat, the fire season in California has gone from a three-month annual phenomenon a generation ago to a year-round spectacle today.  Though fire cycles are a natural part of life in our native ecosystems, the volume and frequency of fires today exceed what the natural system can absorb.  A thriving native urban forest can serve as refuge for flora and fauna while maintaining genetic diversity.  No non-native tree can do that.

Most importantly, the non-native trees that are the darlings of current discussion fail at the one thing they are thought to do best—prepare us for climate changes.  The La Brea Tar Pits offers detailed insight into long scale history in Los Angeles County.  Southern California has some of the greatest annual precipitation fluctuation on the planet.  This has made our non-riparian plants among the most drought adapted in the world.  Research at the tar pits has established that our local native plants have endured significant climate change since the Pleistocene epoch.  In the last 50,000 years, LA County has experienced significant periods of ice age cooling, severe warming with drought, and large fluctuations in carbon dioxide levels that are extreme by today’s standards.  These changes led to the disappearance of many megafauna.  Yet, the fossil record provides ample evidence of many of the local native plants and trees we have today, adapting to these changes.  What do Coast Live Oak, Southern California Black Walnut, Toyon, Valley Oak, Scrub Oak, Manzanita, and every other locally native plant have in common?  All of them proved more adaptable to severe climate change than Mastodons, Columbian Mammoths, Saber-Toothed Cats, and Giant Sloths.  Adaptability is hard-wired into the DNA of our natives.  Keep in mind that even the most extreme climate models show a future Los Angeles where very heavy extended rain events will still happen, even if they are less frequent.  Imported species of desert trees are not adapted to that.  The problems of climate change are very real and very serious, but the human focus needs to be on addressing the human-driven causes of climate change, not retro-engineering nature to live within the world we continue to damage.  We created this mess, and we are responsible for preserving the local biodiversity that is our heritage and the only path to true sustainability where humans exist as part of a healthy ecosystem.  Every time we plant another native landscaping plant or native tree, we are creating an opportunity for our natural flora and fauna to survive and evolve together with the changing planet.  Only human hubris would conclude we know better than millions of years of evolution and should import plants from other regions to adapt to climate change.


(Charles Miller is a Climate Reality Project ambassador with two decades in environmental advocacy.  A LEED Green Associate and certified native plant landscaper, his training includes a sustainability education from UCLA.  He created the advocacy organization, LA Native, which promotes biodiversity through native landscaping on behalf of over 30 stakeholder groups.)