One of America’s preeminent re-searchers on tree mortality has a message for anyone who will listen.
He claims that nearly all coniferous forests in the American Southwest are at risk of being wiped out by the end of the century due to climate change and other factors. The good news is that there are things that can be done now with smart forestry management to reduce the impact.
Just like with human health, forests that are sick or in poor condition are more likely to suffer from pest outbreaks, wildfire, drought, heat waves or other natural disasters. But researchers don’t really know what causes tree mortality in many instances, and a group of scientists at the Los Alamos National Laboratory have studied the issue over the last few years to get a better picture of what really causes stressed trees to die.
The lead researcher on the project, Nathan McDowell, shares some of the insights from his research and talks about how the forest products industry plays a key role in shaping the future of America’s forests as well as the planet. The following Q&A is intended to spark a discussion that will help the timber industry understand the threats ahead.
Pallet Enterprise: What are real reasons that you think the trees are going to die in such large numbers in some regions of the country?
McDowell: We don’t think every tree in America is going to be dead in 50 years. But our projections are alarming, particularly in the Southwest. The big smoking gun is rising temperature. Precipitation always has and always will go up and down. And climate warming may influence that. The verdict is not clear on that.
What the verdict is clear on is that temperature will continue to go up a lot – a lot more than it already has. There really is no debate on that issue. And rising temperatures causes increased water loss from the foliage of the trees and the soil.
The impact is that for any given amount of precipitation, a future world will be a dryer world for plants. If an area of the world already gets a lot of rain, it could compensate.
Plants have holes in their leaves called stomata, which regulate water loss to avoid dehydration, and it allows carbon to come in. There is this balance all around the world that plants have to make. They want to gain carbon, but they don’t want to lose too much water. During dry periods, plants close the stomata, either fully or partially to avoid dehydration. But this comes at a cost. They have reduced ability to photosynthesize. In a future world due to higher rates of evaporation, plants will be forced to have greater stomatal closure for a given amount of precipitation.
Now this stomatal closure doesn’t prevent the plants from drying out if the drought is severe enough. In fact, we see a lot of evidence that it is the dehydration aspect that is really dominant in killing trees. But there could be a role for the loss of carbon, which is called carbon starvation. Loss of carbon can make plants more susceptible to insect attack.
Plants are a lot like us or other animals, which usually don’t die of outright starvation. Instead, the real cause of death is something else like a common cold, pneumonia or some other sickness. The same can be said for a lot of trees although not all of them. They are more vulnerable to the attack of insects and pathogens when they are in stressed conditions.
Evaporation will increase, but the exact way the trees die is something that varies from species to species or region to region. It does all come down to significant water loss or reduction in carbon supply.
Pallet Enterprise: Is your research applicable to deciduous trees, such as Appalachian hardwoods?
McDowell: We study coniferous trees because they are in our backyards. We care about all the other species. We do wish to study hardwoods in the future. It is still a bit speculative if hardwoods perform differently than what we have seen from coniferous trees, although evidence from western aspen trees suggest the similarities are much greater than the differences. But there are certain things that all plants have in common. Hardwoods have stomata and try to avoid hydraulic failure. They try to gain as much carbon as they can. And they are going to be exposed to higher temperatures.
There are reasons to believe that all plants and trees worldwide are going to be facing more extreme challenges in the future. There are some differences though between species. For example, some hardwoods can re-sprout. Some can lose their leaves in a drought, and they have enough carbon in reserve to regrow them next year when it is wetter. They are reasons to believe that hardwoods may be more resistant than conifers to worsening conditions.
On one hand, there is the negative potential of future hardwoods forests in terms of productivity without significant irrigation or really good management. But there are reasons to be more optimistic about hardwoods than conifers in the United States.
Pallet Enterprise: Is temperature increase really a forgone conclusion worldwide? Why?
McDowell: Over the long-term, temperatures are going to continue to increase over many decades if not centuries. Even if we stopped burning all fossil fuels today, the temperature is probably going to go up a minimum of 1 degree Celsius. And we have already gone up that amount since the pre-industrial period.
There are a number of reasons for this warming trend. A major reason is that CO2 has a long half-life in the atmosphere. Also, melting ice sheets cause the oceans to get warmer, which leads to atmospheric warming. It also has to do with deforestation in parts of the world that causes more warming, such as the Tropics. All these various effects are leading to general warming trends.
Pallet Enterprise: What are things that the forest products industry can do to improve the health of forests and help alleviate concerns caused by global warming?
McDowell: The forest management sector has the greatest opportunity to really help mitigate climate change. And that is because through the management of large tracts of land the earth can absorb more carbon. People talk about different geoengineering ideas. Those things are drops in the bucket compared to what the earth’s forests do. These forests suck up 30% of our fossil fuel emissions every year.
The forests are one of our greatest assets in terms of mitigating climate change. This calls for wise management that maximizes the uptake and storage of carbon. In the West, the region historically has had a lot of ground fires. Those helped to clean out and improve forest density. But today, we have way overgrown forests. So when we have a wildfire or insect outbreak, the results are massive forest loss, which causes a whole lot of carbon to go into the atmosphere.
When trees are dead, they don’t take trees out of the atmosphere. So they are not doing their service. And they decompose, so they actually put out more CO2. Now harvesting trees and turning them into lumber or wood products is a way to store carbon. Harvesting when done wisely is a good thing to do.
Pallet Enterprise: Wise management, you are talking about improved forest density. Are there certain species that are more drought tolerant?
McDowell: We should be trying to plant and grow trees thinking about a future warmer climate. I haven’t studied that specifically. But we should be thinking about growing more drought tolerant species or taking species from lower elevations and planting them in higher elevations. Every region is different, but they are all going to get warmer.
Local foresters, university professors and extension specialists certainly will know about your local environment and tree species. They may or may not be experts on tree mortality and climate change. But they certainly can help you discover what trees are more drought tolerant in your system.
Pallet Enterprise: What can the industry do? It seems like properly used wood products can be part of the answer here?
McDowell: Absolutely, managing our forests for yield, income, wildlife, aesthetics, tourism and carbon storage can become part of the larger equation. We have to make it worthwhile for the private landowners. There is movement in the direction in there being dollar value to carbon storage.
Pallet Enterprise: What big questions is your future research looking to answer?
McDowell: We are focused on three big things. We are continuing our research and looking at the effects of climate change in the Tropics. It is a much more complex question down there due to the high diversity of trees.
Secondly, we are looking at the consequences that matter to humans. For example, our projections suggest that river flows in the Colorado River basin are going to go down due to climate warming and disturbance in the forests. And that matters for energy production and irrigation in the Southwest.
The third big focus is trying to look for the good news. Climate warming models currently suggest that the Boreal forests should grow better. Measurements don’t support that. There are lots of stresses being observed in Canada and Alaska. But the models say they should grow better because the increased temperatures are a good thing for them. Also, elevated CO2 levels are a good thing because plants like CO2. With a changing climate, we need to be asking, ‘Where are the opportunities where can we grow trees better in the future than we did in the past?’
Pallet Enterprise: Your research has suggested that there will be major tree mortality in the next 50-100 years in some forests in the United States. Some models suggest 100% mortality. Have those projections been overblown?
McDowell: We predicted enormous tree mortality in the Southwest and throughout the Temperate zone of the world for conifers. And I stand by the word “enormous” because we think there is going to be a huge change in these conifer-dominated forests. Will every tree die? Our models are the best in the world, but they aren’t good enough to tell us if exactly every tree will die. Even in a forest ravaged by wildlife, there are islands of trees that survive. Our models suggest that 100% of trees in certain regions will die. But even if our models kill off too many trees, an 80% tree mortality rate is still a significant problem. One thing you have to remember is that our models are based only on drought induced mortality not wildfire, which makes them conservative.
We do strongly believe that forests are going to look very different in the future.
Pallet Enterprise: How does your research in the Southwest translate to the pine populations in the Southeast?
McDowell: That’s a great question because the South is the timber bread basket for the United States right now. I think the Southeast has the opportunity to do really wise management because it is private land. Those people can focus on managing the right species to help mitigate warming temperatures and droughts. We don’t know what is going to happen to overall rainfall in the South. But even in areas where rainfall goes up, droughts will occur. And when those droughts do occur, it will be warmer. So there are significant risks in the Southeast. But there is also significant opportunity.
Pallet Enterprise: What is the big takeaway from your research that the forest products industry needs to be aware of?
McDowell: The forest products industry is facing significant risk from warming temperatures, but they also arguably have the greatest opportunity to deal with it and to do something useful to impact climate change. They are an extremely valuable member of the community to make a difference.
