During this time of year, a lot of us are thinking about trees. For those who celebrate Christmas, a tree is usually the centerpiece for a family gathering around December 25. But that’s not the only time when we honor trees. Across the country, we commemorate trees on National Arbor Day, the first Friday in April; National Love a Tree Day, designated as May 16; National Tree Day, which is the first Sunday of August; and Look for an Evergreen Day, December 19th of each year. I’m sure I’m not the only who loves trees.
Of course, trees do a lot more for us than serve as the inspirers of holidays. They’re important to us as the producers of food crops, medicines and wood products. They also provide ecosystem services, a concept that allows researchers to quantify the benefits that nature contributes to people into monetary units. And surprisingly, perhaps, a new study suggests that trees provide greater economic value when they’re used to regulate air quality and climate than when they’re employed to supply products made from wood.
Trees regulate the climate by storing carbon, a greenhouse gas. But all the carbon sequestered in forests and trees worldwide could be thrown back into the atmosphere if large numbers of trees burn in forest fires. Trees can also stop scrubbing carbon dioxide from the air if they die due to drought or insect damage. Unfortunately, the likelihood of those threats impacting forests is increasing nationwide, making relying on forests to soak up carbon emissions a much riskier prospect.
However, a bright spot has been found in Pando, a massive aspen stand in south-central Utah that is the largest, most dense organism ever found. That clonal colony of trees seems to be taking three, disparate ecological paths based on how the segments are managed.
And it may point the way to protecting more of our trees.
More than $100 billion in supplied services
While the monetary value of the products that trees provide is relatively easy to quantify, the service value of 400 individual tree species and tree lineages growing in forests and plantations throughout the contiguous U.S. was not previously known.
To determine the value of the ecosystem services—such as filtering air pollutants—U.S. trees provide, researchers at the University of Minnesota and their colleagues recently calculated the economic contributions of these services for every U.S. tree species and lineage. They measured the net value of five, tree-related ecosystem services by calculating the value of benefits provided, minus the direct costs incurred to produce these services. The five, key ecosystem services included regulation of the climate from carbon storage, filtration of particulate matter from the air that harms human health, and provisioning services from the production of food crops, Christmas trees and wood products.
According to the authors of the study, which was published on April 5, 2022, in the open-access journal PLOS Sustainability and Transformation, the value of these five ecosystem services generated by trees totaled $114 billion annually. Carbon storage in tree biomass comprised 51 percent of the net annual value, while preventing human health damages via air-quality regulation contributed to 37 percent of the annual value. The remaining 12 percent of the net annual value came from provisioning services.
Trees in the oak and pine families were the most valuable, generating $22.3 billion and $25.4 billion in annual net benefits, respectively. The study had several limitations that likely contributed to an undervaluing of ecosystem services, since the researchers did not have access to data for many of them, such as erosion control, flood regulation and shade-related energy savings. Future studies may provide more accurate estimates of the monetary value of these benefits.
The fact that tree lineages have evolved to inhabit different ecological niches across the continent is important for sustaining the ecosystem services that we depend on for our life-support systems. These benefits from trees, however, are increasingly at risk. Climate change threatens nearly 90 percent of tree species, while pests and pathogens put 40 percent of the combined weight of all U.S. trees in jeopardy. And it appears that the species and lineages of greatest ecosystem service value are the most in danger due to climate change, increasing fire exposure, and pathogens and pests.
Increasing climate change considerations
Planting a tree, then, seems like it would be a good thing to do for the environment. But if large numbers of trees die due to drought, forest fires or insect damage, all the carbon stored in them could be thrown back into the atmosphere.
Sadly, the likelihood of those threats impacting forests is increasing nationwide, according to new research published in the journal Ecology Letters in May 2022, making relying on forests to soak up our carbon emissions a much riskier prospect. In fact, U.S. forests could look dramatically different by the end of the century. We’re likely to lose forests from some areas in the western United States, due to more severe and frequent disturbances and fires, but much of this depends on how quickly we tackle climate change.
For their study, the researchers modeled the risk of tree deaths from climate stress (drought and/or heat) fire and insect damage for forests throughout the United States, projecting how those risks might increase over the course of the 21st century.
By 2099, the models found, forest fire risks in the U.S. may increase by between four and 14 times, depending on different carbon emissions scenarios. The risks of climate stress-related tree deaths and insect mortality may roughly double over the same period. But in those same models, human actions to tackle climate change mattered enormously—dramatically reducing the severity of climate change lessened drought, fire and insect-driven forest die-offs.
In conclusion, say the scientists, climate change is going to supercharge these three big disturbances. Just in the past several years, we’ve had devastating fire seasons with increasing severity. Generally, the western U.S. is expected to be hit hardest by all three of these. And they’re interconnected: extremely dry and hot years, driven by climate change, tend to instigate lots of fires, insect outbreaks and tree mortality. But there’s opportunity here, too. Addressing climate change quickly can help keep our forests and landscapes healthy.
Proliferating Pando pieces
The ancient, gargantuan aspen stand dubbed Pando, located in south-central Utah, is more than 100 acres of quivering, genetically identical plant life; thought to be the largest living organism on Earth (based on its dry weight mass of 13 million pounds). What looks like a shimmering panorama of individual trees is, in reality, a group of genetically identical stems with an immense, shared root system.
Now, after a lifetime that may have stretched across millennia, the “trembling giant” is beginning to break up, according to new research published in the journal Conservation Science and Practice in September 2022.
Five years ago, a comprehensive evaluation of Pando showed that browsing deer (and, to a lesser degree, cattle) were harming the stand—limiting growth of new aspen suckers (clone shoots) and effectively putting an expiration date on the colossal plant. As older trees aged-out, new aspen sprouts couldn’t replace them because of the voracious animals. Pando was slowly dying.
In response to the threat, managers erected fencing around a section of the stand to keep grazing animals out, creating an experiment of sorts. A recent evaluation on the overall health of Pando showed that it seems to be taking three, disparate ecological paths based on how the segments are managed. Around 16 percent of the stand is adequately fenced to keep out browsing animals, allowing new aspen suckers to survive those first tender years to grow into new trees. But across more than a third of the stand, fencing had fallen into disrepair and was only lately reinforced. Past browsing still has adverse impacts in this section; old and dying trees still outnumbering the young.
In the areas that remain unfenced (approximately 50 percent of the stand), cattle and deer continue to consume the bulk of young sprouts. These hard-hit zones are now shifting ecologically in distinct ways. Mature aspen stems die without being replaced, opening the overstory and allowing more sunlight to consistently reach the forest floor, which alters plant composition. These unfenced areas are experiencing the most rapid aspen declines, while the other fenced areas are taking their own unique courses—in effect, breaking up this unique, historically uniform forest.
The solution to Pando’s survival, postulate the researchers, might not be more fencing. While unfenced areas are rapidly dying off, fencing alone is encouraging single-aged regeneration in a forest that has sustained itself over the centuries by varying growth. As a keystone species, aspen forests support high levels of biodiversity: from chickadees to thimbleberry. As aspen ecosystems flourish or diminish, myriad dependent species follow suit. Long-term failure of varying growth in aspen systems may have cascading effects on hundreds of species dependent on them.
Additionally, there are aesthetic and philosophical problems with a fencing strategy. If we try to save the organism with fences alone, we’ll find ourselves trying to create something like a zoo in the wild, say the researchers. Although the fencing strategy is well-intentioned, we’ll ultimately need to address the underlying problems of too many browsing deer and cattle on this landscape.
The lessons learned while protecting Pando will offer perspective on struggling aspen forests spanning the Earth’s northern hemisphere.
Added tree terms
A dendrophile is a person who loves trees. A tree hugger is someone who is regarded as annoying or foolish because of being too concerned about protecting trees, animals and other parts of the natural world from pollution and other threats. A nemophilist is someone who has a fondness or love for forests, woods or woodland scenery, or someone who often visits them; a “haunter” of the woods, so to speak.
I consider myself a member of all three groups. But I fervently hope that I remain the specter—and the trees themselves don’t become the ghosts.
Here’s to finding your true places and natural habitats,