Study Charts Climate Change’s Effects On Andes Forests, Finding Shifts, Diebacks

By on September 1, 2015

Researchers enjoy the sunrise at the Tres Cruces lookout in Manu National Park in the southern Peruvian Andes (Credit: Kenneth Feeley).

Even casual readers of climate change literature are familiar with some of the emblematic species that are suffering from it: polar bears, corals, sea birds and many types of fish. But not many people think of mountain trees. As Kenneth Feeley, associate professor of biology at Florida International University explains, there are many species being affected in the Andes mountains that deserve more attention.

Using paint, packing tape, calipers, rangefinders, wood samples and complex statistical equations to estimate the rates of growth, mortality and recruitment of Andes trees, Feeley and his collaborators have found that highland tree species are dying back from their former ranges while lowland trees are filling in the gaps.

Most studies of mountain trees focus on the large adults of the species, but Feeley’s most recent study also included young trees and shrubs, which has allowed him to distinguish between the effects of drought versus long-term global warming temperature changes.

As Feeley observes, “If there is a drought, you will see that legacy in the adult trees, but not in the young ones. If you see the same signs in the adult and the young trees, that indicates a much larger change in conditions over generations. That is what leads us to believe these are long-term, global warming changes.”

Kenneth Feeley demonstrates how to measure the size and growth rates of trees to science teachers from rural high schools in Madre de Dios, Peru. (Credit: Therany Gonzales)

Feeley says a general rule of the forest is that as the temperature increases, species should shift their ranges upward toward areas that used to be too cold for them. Some trees will start growing further up the mountains in colder areas while species that live in warmer conditions, in this case the lowland trees, will begin to spread upward into the range of the trees that prefer colder temperatures, altering the composition of the entire forest. This process is called thermophilization.

In the Andes, thermophilization could be caused by two different processes, Feeley explains. One would be an increase of lowland heat-loving trees. The other is a dieback of highland trees that prefer the cold. Feeley believes the second effect has been dominant.

To measure the effects of global warming on the trees, Feeley admits many of the techniques he and other researchers use are “fairly low tech.” They count, measure and identify trees using their advanced knowledge, plus measuring tapes and binoculars. They paint rings on trees to tell where the tree was measured and ensure that it is always measured in the same place in future censuses. Packing tape with a spring on it or calipers are used to measure tree growth.

Feeley’s team is hoping to move to using automatic data loggers and dendrometer bands instead, which can continually monitor changes in trees with micrometer-like precision and thereby show even small fluctuations in tree growth rates due to climate change, weather and water intake. A microprocessor would be embedded in the bands and allow growth data to be recorded continuously even in remote locations.

Currently, Feeley does all measurements from the ground. The team makes wood density measurements as well as determine wet or green volume and dry weight of wood samples, with one half of the weight assumed to be carbon a tree contains. The Carnegie Institute, which is helping in the work, is also developing a 3D map of the forest in which Feeley has performed his work. They are also considering using LiDAR, which can be deployed from the ground or an airplane.

Thousands of trees in forest plots throughout the tropical Andes are being monitored for growth using spring-loaded dendrometer bands (black bands) and are also being measured manually over periodic intervals for status and growth (red paint lines indicate the location of diameter measurement). (Credit: Kenneth Feeley).

“The reason that carbon measurement is so important is because it helps determine the dollar value on the carbon market for the area,” said Feeley. “People put a price on carbon; it’s a commodity which allows developing countries to be paid for not cutting down their trees. Getting an accurate carbon measurement is crucial for determining that value.”

The results contained many surprises for Feeley, chief of which was that they were able to see such large changes in Andean forests due to global warming in such a short time frame. Feeley says large changes occurred in only five years, and that he has seen these changes wherever he has gone in the forests of Colombia, Costa Rica and Peru.

“According to some of our estimates, the ranges of Amazonian and Andean tree species have shrunk by an average of more than 200 vertical meters over the past four decades – that’s really significant,” said Feeley.

Feeley has devoted time and energy to getting the word out that mountain species like highland trees are also suffering from the effects of climate change. He notes that it’s important to increase the public’s appreciation of the rapid changes that climate change is bringing to mountain forests in the Andes and around the world, and that these changes usually are not for the better.

“When climate change is brought up, people tend to think of glaciers and polar bears,” said Feeley. “But most people don’t think of rainforests. The tropics are also in trouble.”

Top image: Researchers enjoy the sunrise at the Tres Cruces lookout in Manu National Park in the southern Peruvian Andes (Credit: Kenneth Feeley).

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