An adult moose can stand up to 7 feet tall and weigh more than 1,000 pounds. They also eat at least 60lbs of food a day—including trees—and it turns out that their diet could have a surprising effect on the climate. Referencing a recent study in the Journal of Geophysical Research, the Washington Post reports that the largest member of the deer family impacts the way forests in high northern latitudes store carbon dioxide. Researchers in Norway assessed 11 years of data and found that whenever moose were grazing vegetation in deforested areas, their consumption of saplings that would normally replace trees cut for lumber reduced carbon storage in the area by as much as 60%. In a press release, ecologist and study co-author Gunnar Austrheim referred to moose as "an ecosystem engineer in the forest ecosystem" that has a strong impact on "everything from the species composition and nutrient availability in the forest."
On the other hand, though moose eating trees—they reportedly prefer to snack on birch, rowan, and willow—can change how forests grow and look, it can also affect forest reflectivity. That is, how the forest stays cool. It's a balance, according to research: In some places, moose eating trees can cause extra air pollution, almost half as much as human-made sources like cars and factories. Yet the clearing caused by moose can help the forest stay cooler, as more light reaches the forest floor, which helps to make up for some of the pollution. Moose, however, aren't the only large mammals affecting climate change. As PBS reported in March last year, cows expelling the methane naturally produced by their digestive process accounts for 14.5% of greenhouse gas emissions worldwide.
Large mammals eating trees and expelling gas may cause problems, but there are plenty of helpful creatures, too. One Earth lists five: sea otters, tapirs, whales, wolves, and surprisingly, the largest land-roving mammal on the planet, elephants. Otters eat sea urchin, which helps protect carbon dioxide-absorbing kelp forests, and tapirs' dietary habits help sustain rain forests. Whales have multiple beneficial effects, including absorbing an average 33 tons of carbon dioxide in their lifetime; wolves can bring balance back to an ecosystem over-grazed by elk; and elephants act as gardeners in the jungle, ultimately helping capture up to 9,000 tons of carbon in a single creature's lifetime. (Read more nature stories.)