It all comes down to what scientists call "squealing," or "variance amplification near critical points," when a system moves back and forth between two states.
"A system may shift permanently to an altered state if an underlying slow change in conditions persists, moving it to a new situation," says Carpenter.
The way in which plants stop growing during a drought is an example. At a certain point, fields become deserts, and no amount of rain will bring vegetation back to life. Before this transition, plant life peters out, disappearing in patches until nothing but dry-as-bones land is left.
Okay the trees are squealing as loud as they can!
Here's another typical letter, but the links are fascinating and pertinent.
Dear Dr. Appleton, Dr. Harris, and Ms. Swanson,
I was sent this link to your report
which I read with intense interest. I could not find email addresses for all the authors, so if you get a chance to forward my message to Joel Koci, Kathy Sevebeck, and Dawn Alleman, I would appreciate that.
I live in New Jersey and for the past year have become more and more alarmed at the condition of vegetation here, as well and up and down the Eastern Seaboard where I have had occasion to visit.
The deterioration first of deciduous and then coniferous trees last fall has been followed by damage to shrubs and even annuals. This summer, completely dead trees of all ages and species have become commonplace. I am not a scientist but from reading up on the topic I have become convinced that the composition of the atmosphere is poisoning plants, and with a spectacularly alarming rapidity.
In your report where you describe the symptoms from the toxicity of ozone I have found precisely the description of what is readily observable in wild forests, planted landscapes, nurseries and even ponds.
I would like to tell you that I find a significant difference between your report and what is occurring, at least here in New Jersey.
The first regards your categories of trees most at risk and those with higher tolerence. I can assure you that here, every single species of tree is being visibly impacted with what looks to be irreversible decline. There are none whatsoever that are tolerant of whatever it is they are being exposed to. Some that are on the tolerant list, such as maples and ginko, are actually the most scorched and thin.
In your report you mention that peroxyacetyl nitrate (PAN) is more toxic to plants than ozone but less plentiful, and therefore less significant.
However I would be very grateful if you would consider this evidence - ozone has been around for decades and even worse in years past. It should have decreased this past year or so due to a slowdown in driving due to the economy and a cool wet summer. Yet, the damage to vegetation is exponentially worse, starting at the end of last summer and continuing this summer to the point where it is literally impossible to find a tree, shrub, vine or any plant whatsoever that doesn't display the symptoms you describe in your paper, in abundance.
I believe the explanation for this that best fits the facts is that the recently mandated addition of ethanol to gasoline, which creates acedaldehyde, the precursor to peroxyacetyl nitrate, could well amount to the primary agent.
I would like to direct you to this story, http://desdemonadespair.blogspot.com/2009/09/fall-colors-fade-in-us-west-as-aspen.html and note a couple of interesting things.
One is, that the bark beetle which is generally blamed for the death of aspens, is here depicted as not the only agent; drought and climate change are mentioned as causes for SAD, sudden aspen death. This echoes the sudden death I see here on the East Coast.
Two is, that you said in your report that ozone afflicted trees are more vulnerable to insect damage.
I wonder if perhaps pollution floating eastward from California freeways is piling up in the Rockies and is actually the underlying cause of bark beetle infestation (in addition of course to warmer winters) and SAD.
I started a blog on the topic of trees impacted by climate change if you care to visit, where I post links to published scientific research, and photos, muddled up with some personal more lighthearted events. witsendnj.blogspot.com
I hope you will consider the possibility that ethanol is wreaking havoc on trees, which are the foundation of life on earth, and other fauna. It is a horrific prospect but actually, if true, rather encouraging, because all we have to do is stop adding it to gasoline to halt such extreme botanical carnage. If it is ozone, it will take a much greater effort to shift quickly to completely clean energy in order to avoid ecosystem collapse and mass extinction.
There are other possible causitive agents - differences in the types of coal being burned, perhaps, or more prevalent UV radiation from the thinning of the stratospheric ozone layer - but I really hope someone with more expertise than I posses will take on this riddle and solve it.
Thank you so much for reading.