Weatherdem's Weblog

Bridging climate science, citizens, and policy

Four-Corners Tree Die-Off Tied To Global Climate Change Drought


This post will cover a lot of ground.  I’m writing it having just read a PNAS paper from 2005 about a massive vegetation die-off event being tied to global climate change-type drought in the four-corner states.  I have been thinking that such a study should be done as I read and learned about the various pine beetle epidemics afflicting Western North America.  The paper, “Regional vegetation die-off in response to global-change-type drought”  contains the kind of information that is critical in piecing a number of different threads together to weave a coherent story.  The results contained within the paper, which can also be seen at this PNAS website,  provide a profound message about the impacts of climate change.  Such impacts have already occurred.  As I’ve written recently (here and here, for example), they are growing in number and intensity.  We ignore them at our (and the Earth’s) peril.

A series of big messages I got from this paper can be summed up as follows.  With human-forced climate change, warmer droughts are predicted to occur more often.  One such drought has already occurred (and could be continuing to occur) in the southwestern U.S.  That drought has had a profound impact on a large region’s worth of vegetation.  That impact came in two waves: the drought weakened the vegetation which then fell to the beetle epidemic.  The beetles were able to spread due to the warmth that characterized this drought.  With this and other region-wide die-offs, the potential for large changes in carbon stores is real we will face with their consequences.  As a result, carbon-related policies must be prepared to take such die-offs (and their after-effects)  into account.  The failure of region-wide ecosystems, a disaster on its own, would also present a real danger to our society.

The paper identifies regional-scale mortality of overstory trees.  Such events alter ecosystems and land surface properties for decades.  Greenhouse forcings are expected to amplify the periodic, cooler droughts found in previous climate regimes.  The drought that has occurred across the southwest since 2000 offers evidence about how those forcings manifest.  [On a short tangent, the widespread, severe drought in Australia provide additional evidence.]  This paper focused on a Piñon pine die-off.  Additional trees act as overstory species across the four states studied.  At this time, I’m not aware of similar studies detailing the greenhouse-forcing-drought-beetle-die-off relationship as it relates to those species.  It is something I will look for after writing this.

There is one figure in this paper that I want to draw particular attention to:

This figure shows annual average temperatures and precipitation values for all the stations included in the study.  The yellow-shaded vertical bands point out two regional-scale droughts – the first in the 1950s and the second in the early 2000s.  In particular, I want to draw attention to the rise in average annual temperatures from the mid-1990s to the mid-2000s (top panel): from ~10.7C to 12.3C.  Combined with the corresponding drop in precipitation from 380mm to ~250mm, this is what the authors have characterized as a global-change-type drought.  It contrasts with the 1950s drought by being statistically warmer to a significant level.  The bottom two panels also deserve some attention.  Two of the last four years in the study exhibited maximum average annual temperatures at the 90th percentile (panel c).  Three of the last four years in the study exhibited minimum average annual temperatures well above the 10th percentile (panel d).  That information isn’t available from the top panel

The reason I draw attention to the temperature rise in particular is the warning it provides about anticipated future warming across the region as the climate continues to respond to greenhouse forcing.  Under scenarios now considered likely with the “warming in the pipeline”, temperatures across this region are expected to rise another 2-10C.  As I wrote above, this paper demonstrates the impacts that warming has on dominant vegetation types: water stressing the plants and allowing bark beetle infestations to spread unabated.  With even more warming, what effects will ecosystems in the region experience?  I’ve written before about the bark beetle problem affecting the higher elevations of Colorado and other regions across the Rocky Mountains (see list below).  Those trees were impacted in a similar fashion that the Piñon trees were in this study.  How many additional species will be stressed to the point that they will also experience region-wide die-offs?  Under those same climate change scenarios, annual precipitation is expected to continue to decrease.  That decrease will be for all purposes permanent as far as humans are concerned.  Desert-level precipiation amounts are quite possible for hundreds of years.

Now look at the graph more closely.  We’ve seen the devastating effects just a small quantitative amount of warming has already had.  That’s one of the real dangers of climate change: ecosystems are quite used to the climate of the 20th century (in a larger sense, that of the past few thousand years).  There is no way of accurately foretelling how those ecosystems will respond to a significantly different climate, which we might already have entered into.  The die-offs I’ve seen and read about; the shifting climate and ecosystems zones I’ve seen evidence of tell me that the climate at the end of the 21st century could be quite different than the one of the 20th century.

Expanding on this a bit: at what stage would prairie grass die-off?  I can hear the denialist line about tree die-off and small animal die-off not being a big deal and not indicative of climate change.  The level of tree die-off discussed in this paper was unprecedented in scope: all ages, all sizes were affected.  Beyond that though, I wanted to come up with a scenario that would provide more visceral evidence of climate change impacts on human society.  If grass or hay or the like experienced a regional die-off due to an expanding, long-term warm drought, what would we do?  If cattle started dying by the millions due to water stress and epidemics, would more people take notice?  I have to think so.  I hope it doesn’t get to that level, but it might before we all aggressively look for greenhouse forcing solutions.

One additional question I have is what story does the post-2004 data tell?  I will look for additional, related studies to this one to fill out the scene.  It was somewhat surprising that this study was published in 2005 .  Nobody I’ve spoken to about the ponderosa pine die-off was aware of this paper – which is part of the reason I’m writing about it.  If anyone is aware of such a study, I’m all ears.  Otherwise, I’ll write something up on whatever I find.

Cross-posted at SquareState.

Here is a list of some of the bark beetle epidemic posts I’ve written:

Western Forests Could Become Carbon Source, Not Sink

2008 Pine Beetle Kill: 400,000 acres in CO

Healthy Forests/Vibrant Communities Act of 2009

Wilderness Society’s Aerial Investigation of CO Pine Beetle Kill

Beetle Killed Trees May Be Allowed to Burn

Battling the Mountain Pine Beetles

Catastrophic beetle kill in Colorado


4 thoughts on “Four-Corners Tree Die-Off Tied To Global Climate Change Drought

  1. Very good post. I blog about energy/climate issues all the time. This was one of my more recent posts.

  2. You have a very interesting blog, one of the best ones I’ve read. We could go on forever trying to determine the cause of global warming, but the truth is the impact is real and we need to collectively address the problem one backyard at a time. There is no silver bullet, but an imperfect attempt will be much better than the seemingly perfect position of doing nothing under the guise of preservation. Our globe is very interconnected and we have to try protecting our global assets.
    One of those assets is the conifer ecological system, which is the largest in the world and is under attack worldwide. The problem is we have more trees than ever before, on less space competing for even less nutrients due to the loss of healthy root zones environments potentially worldwide, and definitely in the US.
    I’m a big time tree hugger. I greatly appreciate what live pine trees in the woods give us, as evidenced by my website, and I also appreciate what dead pine trees give us in my dining room in the form of a parsons table. They are an asset that has to be managed by sustainable harvesting methods and healthy thinning.
    We no longer have anything that resembles any kind of sensible healthy forest management program. The end result is Mother Nature, who operates on a principle of “Survival of the Fittest”, is going to do what we humans won’t and if somehow it cost us our lives, as far a she’s concern, so be it.
    There are those who say, “Ah this is all just a course of nature,” which in some ways is true. The problem there is no protocol that I’m aware of in nature that enables nature to put out fires that would normally come through and create forest environment that has an age group of trees 25, some 50, some 75, some 100 years old. Due in large part to man’s interference, our biggest problem is most of our forest inventory is the same age and when this is killed off, the new growth is all going to be the same age and we will have a repeat of this same problem in another 100 years. Did you know that old a growth forest is far less efficient concerning carbon sequestering than new growth forests are? The problem right now is we are going to be without a very large portion of any forest for a while until it regenerates. I have trees on my property that are 3” to 4” in diameter, 15’ to 16’ tall and are 40 years old. That gives a window into regeneration time.
    So what are the answers? Here are some thoughts concerning possible solutions; Let the forest industry do their job. They will get it handled faster than any governmental program will. If it’s a break even to the general public after the expense of oversight of reasonable policies, so be it. They will get the forest regenerated faster than any other program. We do need to makes sure the penalties for non-compliance have teeth, not like what went on in the seventies.
    We need to have an on going forest educational policy that teaches children and their parents the value of this asset beyond them thinking it just looks pretty.
    We need to get across the concept that any piece of land can only support so many units of trees and some have to be cut to save the others. We have a serious problem that needs to be addressed one small bite at a time.
    Two things seem to be very puzzling to me; One how is it that we in the US can get so upset about the destruction of the rainforest and let this same thing happen in our own backyard, and two; Why is it that the general consensus is that this catastrophic problem is so big that it can’t be fixed, so we just throw our hands up and virtually walk away?
    Well there’s my two cents. Again, although we differ on some approaches to the solutions of this problem, I do commend your efforts. Good luck to you.

  3. Pingback: Wildfire Burn Areas Expected To Increase By Up To 175% By The 2050s « Weatherdem’s Weblog

  4. I am working on a project designed to increase the # of native trees growing in America. I’m a documentary filmmaker from Maui Hawaii. My wife and I are bringing communities together and planting native trees in all 50 states while documenting our adventure for a full length feature film. We have already planted trees in 25 states during the summer 2010. We are about to head out To plant native trees across the southern states. We will be visiting the 4 corners area. We are looking for locations to plant, trees that are native, and communities to bring together for a historic documented moment. We are also looking for experts to interview. Please share my website info with anyone who might be interested in working with us.



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