The changing face of our forests - bark beetle and global warming

This is an article I wrote for the Four Corners Free Press out of Cortez, Colorado.  

It's the culmination of my day listening in on the "San Juan Bark Beetles and Watersheds Workshop" {which was organized by the Western Water Assessment and Mountain Studies Institute} plus discussions with some participants.

In particular, I thank Mike Blakeman from the Rio Grande National Forest.  Although Mike was a spectator, he has a scientific background and has a long standing familiarity with the developing scientific understanding.  He spent a good deal of time clarifying and offering further details, not all of which made it into this essay.  

Of course, any errors are mine alone and I will gladly fix any that are pointed out to me.  At the end of this essay I include links to authoritative information sources.

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Have you ever driven over Wolf Creek Pass, the one in southern Colorado straddling the Great Divide? At 10,857 ft. elevation, it's an example of America at its most magnificent; with high mountains and spruce forests stretching out in every direction.

Last summer I drove over Wolf Creek Pass for the first time in a couple years. My emotions went from amazed, to flabbergasted, then to the point of shock so great, I had to pull over in order to allow the magnitude of the destruction to soak in.  

In every direction mountainsides of mature trees are dead. Not patches of brown anymore, now its entire forests reduced to a few valiant but shrinking patches of green. That glorious forest - it's gone! No more walks under that beautiful green canopy. It seemed to me extra horrifying because we ourselves and our business/political leaders who steadfastly refuse to look past their/our own self-interests are at the root of this catastrophe. 

Given that background, when I heard that Durango was going to be host to a workshop for scientists and land managers called the: "San Juan Bark Beetles and Watersheds Workshop" - and the public was invited. I couldn't pass up their offer. I went to listen in and learn more about the topic. 

At "NO-VillageAtWolfCreek.blogspot.com" I have a speaker by speaker summation with links to the informative PowerPoint slide presentations, sponsored by the Western Water Assessment and Mountian Research Institute.  Since then, Mike Blakeman of the Rio Grande National Forest took the time to explain further details. 

Let me tell you, all of this stuff is fascinating and some surprising.   

For instance, mountain pine beetles co-evolved with and are hosts to a fungus species called "blue stain fungus." When these beetles lay their eggs, they leave behind some fungus that quickly multiplies; carpeting the nursery and then reaching in to attack the pine tree's resin defense system, thus protecting the developing beetle larva. 

Once the eggs are laid, the bark beetle has quite the complex life cycle. Take this mouth full: "Seasonality – appropriately timed phenology that is synchronized among individuals to facilitate a mass attack on host trees." 

Basically what it means is that bark beetles have an internal clock that regulates certain chemicals making them more, or less, susceptible to temperature extremes depending on seasonal timing. One lesson: it's the early autumn and late spring cold snaps that will kill large numbers of beetle larva. On the other hand, given the right temperature conditions the spruce beetle can half their reproduction time and produce twice as many beetles. 

Of the 600 some species of bark beetle, most go about their business unnoticed, while two species: the Mountain Pine Beetle and the Spruce Bark Beetle are doing most of the damage in the Rocky Mountains. 

Interestingly, drought stressed trees aren't that appetizing to beetles and it turns out that the greatest damage occurs after extended drought has ended and the weaken trees are rejuvenating themselves. At that point the trees once again provide nutrition to bark beetles, but they aren't strong enough to mount the defenses that would normally keep the beetles in check. 

The fire threat is more complex than I imagined, though once again, after an expert's explanation, it makes plenty of sense. After a mature forest dies, danger of the spectacular "crown fire" is highest during early stages of tree mortality while dead needles with their volatile oils are still clinging to branches. With time those oils evaporate and the needles and smaller branches fall to the ground, decreasing the crown fire danger. 

But that's not necessarily good news, because what follows is a buildup of fuels on the forest floor. This sets the stage for less dramatic slow moving ground fires which tend to cook the soil, leaving behind sterile soil and making forest regeneration much slower and difficult. 

The surprise lesson was how these massive beetle caused forest die-offs have been impacting watersheds and their downstream hydrology. The scientists admitted that quantifiable observations and large scale study areas are difficult to achieve and studies are still rather basic, but improving. Still, the valid studies that have been done to date indicate that beetle killed forests have resulted in minimal downstream impact on water volume or its quality. 

Scientists suggest the reason for this counter-intuitive finding is that bark beetles kill the mature trees and leave the undergrowth untouched. The understory of herbaceous plants and bushes and saplings then take advantage of all that extra available moisture and sunlight. It is reasoned that forest floor growth and nutrient cycles help compensate for the disappearance of living mature trees. 

Another lesson was that these various bark beetle species are endemic to their areas, meaning that they have evolved with the local forests and historic climate patterns. They have not invaded from other locations and their outbreaks have been triggered by local conditions. 

Why is this happening now? 

Ask that, and the scientists run for cover. They remind us that scientists deal in quantifiable facts and that this is an extremely complex situation with many interacting players - and that they simply don't know enough to speak with a high degree of certainty - which is how scientists prefer to keep it. But, we should remember uncertainty does not equal not knowing. 

Considering that our western forests have thrived despite millennia worth of cyclical droughts and bark beetle outbreaks, it's indisputable that something fundamental has changed. Among the culprits is climate related increasing drought conditions, ill-considered fire suppression practices, and "major windfall events" have all also been implicated in certain areas.  

However, looming over all of that is the reality of our warming planet and the cascading changes being observed. Most obviously, the number of freezing nights and extreme frost events has declined throughout mountains. This impact is even greater further north were the warming is more extreme than in our latitudes.  

Yet here's another obvious surprise: with ever-rising global temperatures there will come a point of diminishing returns and bark beetles themselves will begin to suffer from the heat... although that will be little comfort considering all the other cascading consequences of our self-created warming world.

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Rocky Mountian Bark Beetles

http://www.fs.usda.gov/barkbeetle

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Western Bark Beetles

http://www.fs.fed.us/research/invasive-species/insects/western-bark-beetle.php

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"San Juan Bark Beetles and Watersheds Workshop" was a cooperative effort between 
the Western Water Assessment (WWA), 
the Mountain Studies Institute (MSI), 
the San Juan Headwaters Forest Health Partnership, and 
the U.S. Forest Service 
for "exploring the water-related impacts of bark beetle infestations in the San Juans and the Rocky Mountain West."