04 Jan 2016: Interview

How Science Can Help to Halt
The Western Bark Beetle Plague

Entomologist Diana Six is focused on the beetle infestation that is wiping out conifer forests in western North America. In an interview with Yale Environment 360, she explains why the key to combating this climate-related scourge is deciphering the trees’ genetic ability to adapt.

by richard schiffman

For residents of the Rocky Mountain region of the United States and Canada, global warming is not an abstract concept. It is a reality they confront every day in the form of tens of millions of acres of pine and spruce trees that have died as a result of beetle infestations spawned by a hotter, drier climate.

Few people know as much about this forest plague as University of Montana entomologist Diana Six, who is working with colleagues to understand why the genetics of some individual trees enable them to survive even as whole forests around them are turning brown and perishing. Six says the infestations are now happening worldwide, with major outbreaks in Africa and Europe. But the worst impacts to date are in the North American West, where bark beetles are spreading quickly into new territories and attacking high-altitude tree species that were previously unaffected.

Diana Six

Diana Six
In an interview with Yale Environment 360, Six explains the root causes of the beetle infestations, discusses why U.S. Forest Service policies may be making the problem worse, and describes why the best hope for Western forests will come from the trees’ capacity to genetically adapt to a new climate regime. Science, she says, can help support this natural process of evolution by mapping genetic markers in trees that survive the insects, so forest managers can breed trees that are better able to cope with future beetle onslaughts. “The only way that we can help our forests in the long term is to strengthen their genetic abilities for adaptation,” says Six. “We have to consider some radical new ways of thinking.”

Yale Environment 360: What is the focus of your research?

Diana Six: Basically I look at the ecology and evolution of bark beetles. And now, of course, I look at how climate change is affecting them, because it’s impossible these days to work on bark beetles or anything else in the forest without looking at climate change.

e360: People who have not been to the Rockies lately may not grasp the extent of the tree die-off due to the bark beetle infestation. Could you paint a picture of what is going on there?

Six: It’s pretty amazing. There have been tens of millions of acres of trees killed. If you go north to British Columbia, a really big province, something like 80 percent of the trees are dead. You can get in a plane and fly for literally hours over dead forest. So this is massive. Beetle outbreaks are normal, they have been happening for thousands of years. But this one is estimated to be more than ten times bigger than any event we know of in the past. And there is no end in sight.

e360: What factors have contributed to the current outbreak?

Six: Drought stresses trees, and when trees are stressed, they don’t fight back as much, so it takes a lot fewer beetles to kill them. So you’ve got this perfect storm of more beetles because it’s warmer, and it takes a lot fewer beetles
Some areas have lost 90 percent of their trees within three years of the start of infestations.”
to kill the trees due to recent drought, and that triggers an outbreak.

Typically when you return to cooler, wetter conditions, these outbreaks would poop out. They didn’t just continue for years and years where they basically killed everything — the infestations would sort of self-contain. However, the problem now is we aren’t returning to cooler weather conditions. So over the past 25 years this beetle has just continued to advance: It just goes on and on until the beetles run out of trees.

e360: What surprises you the most about what you have been seeing?

Six: I think it is how quickly it has moved. In lodgepole pine, the beetle usually takes seven to ten years to work through an area. Now it is taking two or maybe three years. Because it is warmer, the beetle has been able to move up in elevation. That means it has gotten into white bark pine, a tree the beetle typically didn’t do much to before because it was too cold for it up there. Some areas that I have studied have lost 90 percent of these trees within three years of the start of infestations. The white bark pine is now recommended for listing as an endangered species.

e360: Are we talking about one insect species that is doing all the damage here?

Six: There are a lot of different pine beetles out there. In the Southwest, it is mainly the genus ips. A species in that genus, the pine engraver, is killing ponderosa, and a related species has wiped out big areas of piñon pines, some of which will probably never recover. With drought in some areas, spruce is becoming stressed, and the spruce beetle is blowing up — it is really active now in Colorado. With increasingly warmer and drier conditions predicted in the years to come, we can expect the Douglas fir beetle to become active. There are a number of other species that are waiting in the wings for their tree hosts to become more and more stressed and then they’ll start to kick into action.

e360: Insects in general are barometers of climate, aren’t they?

Mountain beetle damage

Dezene Huber/ Simon Fraser University via Flickr
An aerial view of the damage caused by the mountain pine beetle in British Columbia.
Six: That’s right. Insects are cold-blooded, they respond very rapidly to temperature. Colder weather dampens their reproductive rate, their feeding rate. On the other hand, everything speeds up with rising temperatures. So even with something like a degree or a degree-and-a-half of warming, you can double their reproduction and development rates, leading to rapid population explosions.

e360: We read a lot about the effect of climate change on polar bears but not so much about insects.

Six: And they are going to have one of the biggest impacts on our forests and our ecosystems planet-wide. You look at what mountain pine beetle is doing that is so far outside the norm. Smaller outbreaks in the past helped to regenerate the forest, which evolved in tandem with the beetle. But when you enhance a disturbance to this degree, you start to see not regeneration but destruction.

e360: Where are the beetles currently headed?

Six: Right now the infestations are moving north. In the past, mountain pine beetles had only reached central British Columbia. It has moved in just four or five years all the way to the Yukon, due to warming temperatures that allow the beetle to live where it used to be too cold for them.

So many beetles were flying at one point that you could actually track their clouds on radar. There was one particular wind event that moved billions of them over the mountains and they became established on the eastern side of the Rockies in Canada, where they never existed before. They’ve adapted well to their new territory and have now moved clear across Alberta. I
So many beetles were flying at one point that you could actually track their clouds on radar.”
understand they are even in parts of Saskatchewan.

They have moved into Jack pine in the boreal forest, which extends clear across the continent and is such an important resource for carbon sequestration. Jack pine doesn’t have much of a defense against the insect, since it has not co-evolved with them. So projections are that it will make its way to the east and eventually enter our eastern pine forests in the U.S. Unlike some other beetle species, the mountain pine beetle is able to use most pines that it encounters. Pretty much every pine in its path is going to be susceptible.

e360: The U.S. Forest Service has been thinning forests as a response to this. Any evidence that this is helping with the beetle problem?

Six: The idea behind thinning is that if you have an over-dense forest where trees are so close together that they are competing for soil nutrients and water, if you thin that forest out, you will relieve that competition, the trees will become healthy, and that will strengthen their defenses against beetles. It was also thought that, if you thin forests, it disrupts the chemical communication of the beetles, which are the pheromones that they use to mass-attack trees. Neither of those ideas totally pans out.

Nobody has shown conclusively that pheromones get disrupted. Also, we know that thinned stands can go down as easily as un-thinned stands. In most of our forests, we have reached a situation where changes in temperature and drought have reached the point where thinning will no longer be effective. Under normal conditions it can help, perhaps. But the fact is we are just not there anymore. I visited one stand that had been thinned many years earlier as a demonstration of how thinning protects trees from bark beetles and enhances growth. Yet when the insects came through, that was the first stand to go down!

e360: So by trying to fix the problem, we sometimes only make it worse.

Six: As humans, we have this feeling that if something goes awry, we need to fix it, and that somehow we can. I don’t think that we necessarily always
You can’t force a forest to stay a certain way — eventually it will tip.”
know what needs to be done, or that when we do apply management that we are always actually doing the right thing. Sometimes we just need to realize that nature can sort itself out perhaps better than we can. So one of our biggest challenges as we approach our forests under the conditions of climate change is to recognize that things have shifted and that we have to consider some new approaches, some radical new ways of thinking.

e360: What new ways of thinking are you suggesting?

Six: Our past management practices do not incorporate genetics for the most part, and they certainly do not include adaptation. Typically, they focus on resistance, which is trying to force a forest to stay in a particular state. And that’s just not going to work — you can’t force a forest to stay a certain way. Eventually, it will tip.

Instead, we need to think about adaptation. When we talk about forests and natural ecosystems, adaptation comes down to the genetic potential of trees to deal with a new situation. So the only way that we can help our forests in the long term is to strengthen their genetic abilities for adaptation. We have to look at the way our practices either support or interfere with this capacity for adaptation.

e360: Are there human interventions involving genetics that can help trees survive?

Six: I think so. For the first time in history, we actually have the tools that would allow us to do this. If we go out in a forest and look at the trees of a given species, they may all look pretty much the same to us. But trees are actually some of the most genetically variable organisms on the planet. We are working on a project right now that is using genetics to detect trees that exhibit resistance to bark beetles and that have enhanced drought tolerance.

e360: Some trees are genetically predisposed to respond better than others?

Six: Absolutely. You see this massive devastation out there, and there are these single trees here and there that are doing just fine. If you look at their tree rings, they are growing much faster now under warmer, droughty conditions than they did when they first started to grow, say, 150 years ago. They don’t have a single beetle attack on them. So they are actually doing better under current conditions than they did in the past.

Those are the first trees that we are testing with our genetic methods, and we are comparing their genetics with that of the trees that were killed. We’re hoping that we can locate those genetic markers that will help us distinguish easily and cheaply which trees to cut and which to leave standing as part of forest management in the future.

e360: What do you see in the future? Is this outbreak just going to get worse and worse?


With Climate Change, Terrifying
New Normal for Western Firefighters

Climate Wildfires
In the last two decades, officials in Colorado have watched as massive, months-long wildfires have become a regular occurrence in their state. A Yale Environment 360 video goes onto the front lines with Colorado firefighters who describe what it’s like to continuously confront deadly blazes fueled by a hotter, drier climate.
Six: Well, obviously we need to do everything we can to limit greenhouse gases and slow this train down. But a lot of it is going to be totally unfixable, because we can’t turn the thermostat down, we can’t turn the sprinklers on. In the central northern Rockies, where I live, it has been predicted that we will lose 90 percent of the lodgepole pines, 80 percent of ponderosas, and 66 percent of spruce by 2060. And that is independent of the mountain pine beetle — that’s just due to the loss of suitable habitat that will support these species. These are big, big changes.

But these models assume that the forest is genetically homogenous, that everything is the same. And they are not. I suspect that there is a lot more genetic variability out there that will allow for more adaptation and greater persistence than we currently anticipate.

e360: You are suggesting that evolution will kick in and help to a degree?

Six: If we let it. If we don’t go out and replant with stock that may not be genetically correct, if we don’t thin or cut down trees that may have been selected by beetles or drought to survive. We have to get smart about how we are treating our forest if we’re going to help nature’s process of adaptation to proceed.

POSTED ON 04 Jan 2016 IN Biodiversity Climate Forests Forests Science & Technology Science & Technology Asia North America 


I don't understand why they don't log the trees that have been infected and use the wood to build homes or furniture or something. Seems like such a waste of wood to me. I live in BC and have seen the devastation the beetle has caused. I'm so glad you scientists are trying to solve the problem. THANK YOU.
Posted by Thomas on 04 Jan 2016

I was told it was because of a stain that develops,
rendering it undesirable.
Posted by Walt on 15 Jan 2016

Trees have been dying prematurely EVERYWHERE
around the earth, and the major underlying reason is
that they are weakened from absorbing pollution.
Bark beetles started killing trees in the 1950's in Los
Angeles, due to the severe pollution there, and they
are also right now killing pines in the southeast US,
where is has been wetter, not drier, due to climate

Furthermore, it's not just bark beetles, every sort of
pathogen has become epidemic on every species of
tree, for the exact same reason. In fighting off the
damage from ozone, they lose the ability to fend off
insects, disease, and fungus.

Posted by Gail Zawacki on 18 Jan 2016

I liked the article. I think it is particularly
important that we look out in the future, and
attempt to answer the difficult questions about
what our forests may look like given the effects
of climate change. Currently we spend way too
much time looking backwards and trying to re-
create what the forests was like before modern
man had any influence on them.
While the beetle infestation problem and its
devastating effect on our forest is extreme. I
believe we have a much more urgent problem
with the potential for more large catastrophic
high intensity wildfires. The drought conditions
and the beetle kills have just compounded the
problem with the extreme amounts of fuel on
the ground, and standing in our National Forests
(15 times what would be normal). Unless we do
some things quickly (selective forest thinning by
logging, mastication, prescribed/controlled
burning of excess fuels), we will have many
more large super high intensity wildfires that will
not only destroy the forest and the species
which inhabit it for decades, but possibly
forever. These fires are so hot they not only kill
everything but bake the earth, so that trees will
not naturally regenerate.
Many of our National Forests are unhealthy
because of a century of mismanagement, they
have been allowed to become 10 times as dense
as would a normal healthy forest. This has
contributed to stressing the trees and facilitating
the beetle infestation, but more importantly
provided the extreme level of fuels for these
huge catastrophic fires.
While we stop and take a macro look at what
the forest ecology might be in the future, we
also have to stop using well-meaning laws like
the Endangered Species Act to try to manage
our forest one species at a time. This continues
to have a devastating effect on other species
and the overall forest ecology.
Proper forest management requires that we
take a macro look at how we attempt to conduct
forest restoration and that we consider all
species plant, animal and man, as we proceed
to answer the difficult questions about what our
forests should look like in the future.
Unfortunately, this very complex issue has no
easy answer, but we must proceed to minimize
the immediate danger from these catastrophic
wildfires before there is no forest left to save.
Posted by Stan Harger on 09 Feb 2016

I think the term for it is: "A day late and a dollar short". The researchers are fiddling while Rome burns.
Posted by Francis M. Miller on 15 Feb 2016

Better understanding the genetic bases of forest
change is a great project.

Better information can lead to better management
choices - and it seems that generally less is more.
Human interventions in natural systems are often
shortsighted because we have a strong bias toward
doing things that immediately benefit our
industries. I wonder what else we are missing in
the longer-term picture of forests under changing
climate conditions.

If these findings are correct, then the commonly
advocated salvage logging of live trees in beetle-
killed stands would take out exactly the individual
trees needed for the forest to rebound. Not a good
idea for forest ecosystems or forest-dependent

Even logging the dead trees is not without
ecological impact, e.g. ground disturbance and loss
of biomass, but market conditions are the real
reason it has not been done on a huge scale.
Bluestain fungus in beetle-killed wood is desirable
as a niche product for trim and furniture, but
there's not enough demand to dent the supply.
Finally, standing dead wood is only valuable for a
couple years at most, so loads of it is not
marketable and not worth hauling.

I'm not dead set against any logging, but I do
think the knee-jerk "fix it with a saw and a
skidder" reaction just gets us deeper in the hole.
Posted by David Morris on 18 Feb 2016


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Richard Schiffman is a New York-based environmental journalist, poet, and author of two biographies. His work has appeared in the The Guardian, The Washington Post, The Christian Science Monitor, and on National Public Radio, among other outlets.



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