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Trees Are Migrating West to Escape Climate Change

Climate
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By Marlene Cimons

An individual tree has roots and, of course, it doesn't move. But trees, as a species, do move over time. They migrate in response to environmental challenges, especially climate change. Surprisingly, they don't all go to the Poles, where it is cooler. As it turns out, more of them head west, where it is getting wetter.


Sure, some species, such as evergreens, are heading to the Poles to escape the heat. But others, like certain oaks and maple, are going west in search of rain. For the most part, "tree migrations are moisture related," said Songlin Fei, associate professor at Purdue's University's department of forestry and natural resources, who has studied this phenomenon in recent years. "Precipitation has a stronger near-term impact on species shift than temperature."

Both trends are a consequence of climate change, which is producing more heat and heavier rainfall, fueling deforestation. This is worrisome, as forests soak up carbon from the atmosphere, and recent evidence suggests that soil is exhaling carbon dioxide faster than trees can take in. The migration of trees may help preserve individual species, but also threatens to destabilize forest ecosystems.

An oak tree. Pixabay

Fei analyzed the movement of 86 tree species from across the Eastern United States between 1980 and 2015 using using field data from obtained from the U.S. Forest Service. He found that 73 percent of tree species shifted to the west, while 62 percent moved poleward.

"The majority of the species move westward are broadleaf species that can better handle flood and drought, and have a large seed mass, which improves the seedling's ability to survive," he said. "One example of westward shift species is Scarlet Oak. Miss Scarlett 'gone with the wind,' but Scarlet Oak is 'gone with the rain.'"

A Scarlet Oak.Katja Schulz

Researchers compared the distribution of trees in 1980 and 2015, calculating the distance and direction of the trees' movement. During the more than three decades covered by the study, the mean annual temperature in the eastern United States, where they collected the data, rose around 0.3 degrees F on average, Fei said. The northern areas of that region saw among the largest temperature increases, he added. Precipitation patterns in the regions also changed during those years, as increasing heat spurred in widespread droughts, another reason for trees to gravitate toward the rain, he said.

The scientists' initial findings appeared in a study published in the journal Science Advances last year. Fei and his team currently are working to update the earlier results, hoping to publish their new findings soon. The researchers have concluded that changes in rainfall and temperature have put "the resilience and sustainability of various forest ecosystems across eastern United States in question," Fei said.

Changes in temperature and precipitation between the recent past (1951–1980) and the study period (1981–2014) across the eastern United States.Science Advances

To be clear, the study focused only on the eastern half the country, meaning tree species didn't move to, for example, California, Oregon or Washington. In fact, the transition was gradual. "Species, on average, moved about 10 miles per decade, or about one county during the study period," Fei said.

The trees have picked up on the trends driven by climate change, moving from regions getting less rainfall than in the past to those that are getting more. Even though the Southeast still gets more rainfall than the Midwest, it's been receiving less in recent years than its historical average, Fei said. At the same time, rainfall has been increasing in the Midwest. "Reduction of moisture in the Southeast and increase of moisture in the Midwest is one of the major reasons caused the shift of species," he said.

Fei said it helped that the team could use real-world data for its analysis, and that they did not need to rely on traditional computer modeling. "It is not future predictions," he said. "Empirical data reveals the impact of climate change is happening on the ground now. It's in action."

Reposted with permission from our media associate Nexus Media.

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Farms with just one or a handful of different crops encourage fewer species of pollinating and pest-controlling insects to linger, ultimately winnowing away crop yields, according to a new study.

Up to half of the detrimental impacts of the "landscape simplification" that monocropping entails come as a result of a diminished mix of ecosystem service-providing insects, a team of scientists reported Oct. 16 in the journal Science Advances.

Monocrop palm oil plantation Honduras.

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"Our study shows that biodiversity is essential to ensure the provision of ecosystem services and to maintain a high and stable agricultural production," Matteo Dainese, the study's lead author and a biologist at Eurac Research in Bolzano, Italy, said in a statement.

It stands to reason that, with declines in the sheer numbers of insects that ferry pollen from plant to plant and keep crop-eating pests under control, these services will wane as well. But until now, it hasn't been clear how monocultures affect the number and mix of these species or how crop yields might change as a result.

Aiming to solve these questions, Dainese and his colleagues pulled together data from 89 studies cutting across a variety of landscapes, from the tropics of Asia and Africa to the higher latitudes of northern Europe. They tabulated the number of pollinating and pest-controlling insects at these sites — both the absolute number of individuals and the number of species — along with an assessment of the ecosystem services the insects provided.

In almost all of the studies they looked at, the team found that a more diverse pool of these species translated into more pollination and greater pest control. They also showed that simplified landscapes supported fewer species of service-providing insects, which ultimately led to lower crop yields.

The researchers also looked at a third measure of the makeup of insect populations — what they called "evenness." In natural ecosystems, a handful of dominant species with many more individuals typically live alongside a higher number of rarer species. The team found as landscapes became less diverse, dominant species numbers dwindled and rare species gained ground. This resulting, more equitable mix led to less pollination (though it didn't end up affecting pest control).

"Our study provides strong empirical support for the potential benefits of new pathways to sustainable agriculture that aim to reconcile the protection of biodiversity and the production of food for increasing human populations," Ingolf Steffan-Dewenter, one of the study's authors and an animal ecologist at the University of Würzburg in Germany, said in the statement.

The scientists figure that the richness of pollinator species explains around a third of the harmful impacts of less diverse landscapes, while the richness of pest-controlling species accounts for about half of the same measure. In their view, the results of their research point to the need to protect biodiversity on and around crops in an uncertain future.

"Under future conditions with ongoing global change and more frequent extreme climate events, the value of farmland biodiversity ensuring resilience against environmental disturbances will become even more important," Steffan-Dewenter said.

Reposted with permission from our media associate Mongabay.

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