The Summer Shade of Trees Could Save Species

Candice Gaukel Andrews September 3, 2019 0
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The shade from trees instantly cools us down on hot summer days. Trees are nature’s sunscreen: sitting under one provides the equivalent of a sun protection factor (SPF) of 10.

We still have three weeks until the end of a long and brutally hot summer. At times, it seems the only respite we can get outside during our picnics, state fair visits, outdoor music festivals and cabin-by-the-lake stays is to find some shade, most often under a tree.

But we’re not the only creatures who find relief in the shadows in our rapidly warming climate. For other beings, shade not only provides a temporary salve from the sun, but it could actually mean the difference between survival as a species and going extinct.

In fact, a recent study suggests that by using a new formula, ecologists may be able to predict which species are able to come to their own “behavioral rescue” by seeking shade during the world’s increasing number of superhot days.

A predictive framework for estimating how a species’ behavior might mitigate the ill effects of rising temperatures was first tested on the southern rock agama lizard, a species native to South Africa. ©Bernard DUPONT, flickr

Considering shade-seekers

In a paper published in May 2019 in the science journal Global Change Biology, researchers at Rice University in Houston, Texas, noted that in the past a number of high-profile studies focused on the impact of temperature on the overall health of many animals but ignored behavior in making predictions about the possible impacts of climate change. To address that issue, they examined both the habitats and behavior of 39 species.

Formerly, to control for external factors, almost all such research was performed in a laboratory, where temperatures could be increased while all other factors remained constant. The experiments often showed that the overall health, or fitness, of individuals falls off as temperatures increase, especially in insects and other ectothermic animals whose bodies can’t self-regulate temperature.

However, these sorts of laboratory tests don’t allow for animal behavior in the wild during hot spells, such as seeking shade. So, to examine the consequences of such a behavior across a wide range of wildlife, the scientists created a mathematical framework that accounts for variability in microclimates in species’ habitats to estimate the cost-benefit trade-off an individual faces when expending energy to seek shade. For example, if getting to a shady spot requires an enormous outlay of the animal’s energy, it could be impractical.

The framework was first verified on tests with the southern rock agama, a lizard native to South Africa, and was later applied to a database of 38 insect species from Africa, Asia, Australia, Europe and North America.

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In summer, deer often seek shade midday. Fawns are especially suited for forest respites: their back fur is mottled with white spots, mimicking shafts of light through the trees and thus camouflaging them.

Using Intergovernmental Panel on Climate Change temperature projections for the year 2050, the researchers found that 19 of the insects they tested were likely to be negatively impacted by warming temperatures. They further found that behavior would likely mitigate the ill effects of warming for 17 of those 19 species, including six that were predicted to experience behavioral rescue, a situation where behavioral adaptation keeps the species from going extinct. In fact, warmer temperatures, in conjunction with behavioral adaptation, were predicted to increase fitness for 10 species.

In addition to looking at the direct effects of behavior and temperature on any one species, though, it will be important for ecologists to consider how rising temperatures will affect a species’ predators, competitors and food resources, including prey.

And, behavior will only go so far. If an animal lives where there is no shade or other means to cool off, it’s obviously not an option.

This chart shows the climate mitigation potential of 20 natural pathways. By far, the biggest solution for holding warming below a rise of 2 degrees Celsius above preindustrial levels (the goal of the Paris Climate Agreement) is to have more trees. ©“Natural Climate Solutions,” PNAS

Calculating tree cost-effectiveness

In all this life-and-death forecasting, the shade of trees seems to be a huge component. It’s said that to combat climate change, every country on Earth could stop the burning of oil completely. Or, they could simply pay attention to the way they manage their land.

In a recent, groundbreaking study published in the Proceedings of the National Academy of Sciences and led by scientists from The Nature Conservancy—along with 15 other institutions worldwide, including the Brazilian government and Cornell University—researchers quantified the potential impact of 20 land-based actions that could be taken to ease human impacts on the Earth’s environment. If implemented, those actions could lead to more than a third of the greenhouse gas emission reductions needed to keep global warming under the target of the Paris Climate Agreement by 2030.

The biggest solution: plant more trees.

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Wetlands, such as this one in Wisconsin, hold the most carbon per acre. Preserving them could secure more than 600 million tons of carbon emissions a year by 2030.

Trees are a cost-effective answer, absorbing carbon dioxide from the atmosphere as they grow. The three largest options for increasing the number—and size—of trees worldwide are listed as reforestation, avoidance of forest loss and better forestry practices.

According to the study, increasing tree counts and size alone could remove 7 billion tons of carbon dioxide annually by 2030, the same as taking 1.5 billion gasoline-burning cars off the planet’s roads.

In Canada, for example, which boasts 28 percent of the world’s boreal forests, this alternative could be particularly effective. Unfortunately, addressing land stewardship involves a lot of competing interests. Just on the conservationist side, there are multiple stakeholders: environmental groups, indigenous people and government agencies hoping to hit environmental protection targets.

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Trees cast a long shadow in our lives: they clean our air and drinking water, provide cooling and reduce the effects of climate change. For other creatures, they stand between them and extinction.

Agriculture was also listed as a key player in land-based climate solutions to global warming. Agricultural land covers 11 percent of the globe. A change in farming tactics, including a more thoughtful application of chemical fertilizers, could improve crop yields while reducing harmful nitrous oxide emissions.

Other actions address the preservation of wetlands, which the study says make up significantly lower portions of the Earth than forests and agriculture but hold the most carbon per acre. Peatlands, in particular, were estimated to hold one-quarter of the carbon stored by the world’s soil. Avoiding the draining and conversion of them—mostly for palm-oil cultivation—could secure the equivalent of a store of 678 million tons of carbon emissions a year by 2030—comparable to removing 145 million cars from the streets.

This summer, while you, your family and your friends sit under the shade of a tree to get out of the hot sun for a minute or two, remember to scooch over just a bit. The dimness that provides you with a brief moment of relief may just save a fellow creature from extinction—forever.

Here’s to finding your true places and natural habitats,

Candy

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