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Climate Changed

Scientists on the ground in the world’s forests are witnessing big changes as trees adapt (or not) to the world’s new climate

Forests are one of the most important ways our planet regulates its climate. It’s simple: Trees remove carbon from the atmosphere and store it. Older forests tend to store more carbon than younger ones, and a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire midsized tree. Understanding the world’s forest systems is an essential factor in building a picture of our planet’s health. Forest ecologists can do this by walking through the forests they study and gathering data on each and every tree. One of those forest-walkers is Kristina Anderson-Teixeira, leader of the Ecosystems and Climate Initiative for Smithsonian’s Forest Global Earth Observatory (ForestGEO), which monitors more than 6 million trees around the world.

How Scientists Study Forests

Gathering data on the health of a forest is a surprisingly monumental task. ForestGEO monitors 65 forests in 28 countries; the 6 million–plus trees within those forests represent about 10,000 different species, with size of each forest-monitoring plot in the network varying from 50 to 100 acres. In each of those plots, a scientist has physically interacted with every single tree.

“It’s something that requires a lot of work, as well as forestry and botany skills,” Anderson-Teixeira says. “In each of these plots, every tree greater than one centimeter diameter — the size of your finger — has been mapped out on a grid and identified, measured, given a permanent tag, and revisited typically every five years.”

Researchers gather data on the traits of the tree. For example, to understand how successfully the trees are performing photosynthesis and responding to drought, they consider these questions: How are the leaves doing? What is the size and thickness of the leaves? What is the nutrient and nitrogen content of the leaves? At what level of dryness do they start wilting? What is the size of the water vessels within the wood? (Wider vessels are more susceptible to drought.)

The researchers note which trees have died, their growth rates, and the abundance of each species. They will also estimate, based on the tree’s size, how much it weighs — about half the dry weight of a tree’s wood represents the amount of carbon it holds. That data, combined with a series of other measurements, will help tell researchers which species of tree is better at surviving the current climate conditions, along with how much carbon the entire forest is holding onto, the rate at which carbon and water vapor are being exchanged in the atmosphere, and the overall health of the forest.

ForestGEO started out as a grassroots coalition of scientists who were curious about forest health. Today, it’s the only network of research forests that has standardized these protocols across all the different types of forests on a global scale. “This puts us in a unique position to do comparisons. We’re looking at larger plots and smaller tree sizes than is typical of most forest plots. It’s really very powerful in terms of data and the types of questions we can ask,” Anderson-Teixeira says.

They’re learning about patterns of failing health that are now starting to emerge in forests around the world. They’ve discovered that the trees are experiencing drought, wildfires, melting permafrost, disease, and insect infestation, which are all either products of climate change or factors that are worsened by it. But they’ve also seen that some tree species and some forests are more resilient to these changes than others.

Big Trees and Big Drought

One of the biggest and most pervasive consequences of climate change worldwide is drought. As the climate warms and the amount of precipitation doesn’t change, drought is more likely. These droughts don’t happen everywhere, but where they do occur, they can be much more severe than in the past. What ForestGEO has helped discover is that it’s the bigger, older trees—the ones that hold the most carbon—that have a tendency to suffer more when their local ecosystem dries up.

That’s because lifting water up to great heights is much more of a challenge. The canopies of big trees also reach higher, so they are exposed to higher leaf temperatures from the sun, higher wind speeds, and lower humidity. Smaller trees have the benefit of being protected by the big trees around them.

In Panama, where the network has been studying the forest (in Barro Colorado Island, Cocoli, and Sherman) since about 1981, the trees stretch from a dry area on the Pacific Ocean to a wet area in the Caribbean. That climate gradient is enough to show a variation in how large trees can handle drought. It turns out there is a big difference in the tree’s traits depending on what side of the isthmus they live on. On the Pacific side, many of the larger trees drop all their leaves during the dry seasons, whereas this is uncommon on the wetter, Caribbean site. Those larger trees also suffer more during drought: “That had a big impact on the carbon balance of the forest,” Anderson-Teixeira says.

More Fires, Less Forest

As the climate warms and drought becomes more severe, the wildfires that sweep certain areas of the world also become more damaging. In fact, the ForestGEO plot at Yosemite, in the Sierra Nevada, burned in the massive Rim Fire of 2013, which spread rapidly because of drought. This region traditionally experiences fire during the warmer months of the year, and fire is very important to the health of many forests around the world. But drought conditions and warmer temperatures due to climate change are throwing their natural systems of fire off balance.

Similar changes are occurring in the Klamath region of Oregon, where Anderson-Teixeira’s lab has studied the effects of climate on forest regeneration following severe fires (as part a separate research project not affiliated with ForestGEO). Normally, this area gets a mix of small fires that take out most of the understory (plant life that grows at the foot of trees in a forest), while leaving the big trees unharmed, and the occasional big fire that kills all types of trees. Once these fires sweep, however, the forest regenerates and comes back healthier than it was before. But this is no longer always the case. Says Anderson-Teixeira: “With climate change, we’ve now changed fire regimes. Many places are experiencing larger and more severe fires.”

When the ecosystem attempts to regenerate in a warmer climate after these large and persistent fires, it faces the challenges of less moisture, higher temperatures, and, unfortunately, more fire. “That establishment phase is difficult for trees. They need a window of opportunity for the seedlings to get established, get deep roots to withstand drought, and get bigger than the shrubs that burn easily,” Anderson-Teixeira says. As the Western region faces more regular and more severe burns, it may overcome the capacity of some parts of the landscape to regenerate. In some places, the forest regenerates more slowly, but the next fire is coming sooner than ever before.

Losing Ground, Literally

Trees in the Arctic are facing a unique set of challenges. At Scotty Creek in Northern Canada, melting permafrost is toppling trees. In this region, trees have limited area to grow, and the ground between frozen areas of permafrost is mostly bog, where trees can’t grow because their roots become waterlogged. But as the climate warms, the ground is literally melting out from under them.

Trees are therefore losing the area in which they can grow and shifting closer the edge of a permafrost plateau, which causes stress. In addition to teetering on the edge, sometimes “they’ll fall over, lose their rooting,” Anderson-Teixeira says. And thanks to the strange nature of melting and refreezing in these regions, the availability of water is changing. Which means that the trees in permafrost regions that don’t fall down are somehow facing a combination of drought and becoming waterlogged.

Invaders from Near and Far

In Virginia, Anderson-Teixeira’s home state, the forest that she monitors is under attack by beetles—specifically, emerald ash borers. An invasive species, originally from Asia, they were likely brought into the area on plants imported by local nurseries. Nearby, at another ForestGEO site called the Harvard forest, trees are being attacked by the hemlock wooly adelgid (related to aphids), also an invasive species native to Asia and brought to the United States by nurseries.

The destruction of trees by insects such as these is additionally increased by climate change. “It often speeds up the metabolism of the pests. So with warmer temperatures, they can reproduce faster,” says Anderson-Teixeira. “Some are normally killed off by the cold, so if you don’t get hard freezes in the winter, they’re more likely to survive.” And it’s not just happening in Virginia and Massachusetts. Driven by a combination of drought stressing the trees and warmer temperatures helping the beetles, native bark beetles are decimating forests along the entire West Coast.

Not All News Is Bad News

Perhaps some good news is that ForestGEO’s monitoring isn’t only revealing the death and destruction of trees. In Panama, when drought destroys certain trees, it opens up the undergrowth to light, and the other trees tend to grow much faster. “Drought can cause light-limited forests to be more productive, and increased carbon dioxide concentrations in the air can allow trees to use water more efficiently,” Anderson-Teixeira says. That means there are signs that some forests are resilient and have the chance to adapt to the changing climate.

“If we can conserve healthy, diverse forests and keep them otherwise intact, they’re going to be much more resilient to climate change. There’s some space to adapt,” Anderson-Teixeira says. “Forests are incredibly valuable for climate protection. There’s a lot of potential to help mitigate climate change through reforestation.”

Plus, there’s a lot the average person can do to help assist with this type of research and support forests around the world. The first is to support — through funding and/or volunteering — science and conservation initiatives focused on understanding, preserving, and protecting local, national, and international forests. The second, says Anderson-Teixeira, is to practice conscious consumerism. Many products on the market are derived from farms that require deforestation to produce the mass quantities we consume globally. For example, palm oil and beef wreak havoc on healthy forests. Even simply building a road through an existing forest can be damaging to its overall health.

It’s also important to fight climate change in general by reducing your personal emissions and supporting broader social initiatives, like the Paris Climate Agreement. You can check if your city or state supports these emission-reducing measures at, and encourage your local leaders to get on board if they aren’t already.

“We have to be smart about how we manage our forests,” Anderson-Teixeira says. If we care for them correctly, they will give us a healthy planet in return.

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