Eastern hemlock treees — NY Trees in Peril Eastern hemlock trees, Tsuga canadensis, killed by hemlock woolly adelgid (insects) in New York's Mohonk Preserve. © ©Jerry and Marcy Monkman/EcoPhotography

Out of Place

January 21, 2025

The balance of living things in an ecosystem develops slowly. When a non-native organism is introduced, change can happen quickly—and native species can be devastated, permanently altering the character of a landscape. That’s why The Nature Conservancy is marshaling science, stewardship and society to stem the toll of invasive species.

CT Trees in Peril Christopher Guzman and Nicole Pauloski prepares plant material for genome sequencing as part of the Tree Species in Peril project. © ©Jerry and Marcy Monkman/EcoPhotography

USING SCIENCE to fight the hemlock woolly adelgid

The hemlock woolly adelgid is an invasive aphid-like forest pest that is decimating native eastern hemlock trees, even in protected areas such as the most visited U.S. national park, the Great Smoky Mountains, in Tennessee and North Carolina. Yet, some individual trees are surviving. TNC, the U.S. Forest Service and other partners are racing to find those holdouts and study their defenses and DNA. Research is showing that breeding resistant specimens has the potential to help threatened trees, like hemlocks, endure. This approach is being used to protect forests from other problems, including emerald ash borers and Dutch elm disease. These combined efforts are essential in the era of climate change, as trees are monuments of carbon storage.

APPLYING STEWARDSHIP to halt eastern red cedar

Trees are the foundation of many ecosystems, but sometimes they don’t belong. That’s true for the Flint Hills of Kansas and Oklahoma, home to the largest expanse of tallgrass prairie in the world. Suppression of wildfires and the mounting effects of climate change are allowing woody shrubs and trees, including eastern red cedar, to proliferate. They are outcompeting native grasses and depleting water resources needed by wildlife, livestock and people. TNC is conducting research on our preserves in the area, supporting partner-led efforts and helping local landowners use prescribed fire to reduce the spread and impacts of this out-of-place vegetation. This suite of solutions improves the outlook for important species such as bison and helps maintain a landscape that holds deep cultural significance.

Kiwi A kiwi bird stands on the forest floor in New Zealand. © Ariboen/Shutterstock

LEVERAGING SOCIETY to root out stoats

Native birds that evolved over eons of geographic isolation are core to New Zealand’s identity. Locals refer to themselves as Kiwis in direct reference to the small, flightless birds with long beaks. But these birds face disastrous consequences from rats and stoats—predatory mammals in the same family as weasels—that humans brought to the island nation in recent centuries. An estimated 25 million native birds are killed in the country by introduced predators every year. The Kotahitanga mō te Taiao Alliance, a collaborative conservation initiative supported by TNC, aims to use the latest science and technology, alongside Indigenous knowledge, to control stoats and other pests on the nation’s upper South Island and to progress toward a vision of a predator-free region.

Watch Recording

Emerald ash borer — Emerald Ash Borer The emerald ash borer has killed tens of millions of ash trees so far and threatens to kill most of the 8.7 billion ash trees throughout North America. © Debbie Miller, USDA Forest Service

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Out of Place

USING SCIENCE to fight the hemlock woolly adelgid