Among the planet’s longest-living organisms—3,000+ years and growing—giant sequoias (Sequoiadendron giganteum) can seem pretty indestructible. They’re thought to be mostly disease, fire, and drought resistant thanks to their brilliant biology, but California’s years of severe drought have caused the browning of trees across the Sequoia and Kings Canyon National Parks.

Enter UC Berkeley forest ecologists Wendy Baxter and Anthony Ambrose. They mix science with adventure, climbing these incredible giants to collect foliage samples that can help determine the sequoias’ health and conservation needs. From bioGraphic.com:

Giant sequoias, like all trees, play a central role in the hydrologic cycle. Storms drop rain and snow, which giant sequoias can chug to the tune of 800 gallons per day—more than any other tree. As the trees draw water out of the ground, the air surrounding the leaves draws water through the trees and, eventually, back into the atmosphere. That process, called transpiration, creates tension within the tree’s water columns. The drier the atmosphere and the less groundwater available, the higher the tension. Under extreme drought conditions, when that tension grows too high, those columns of water can snap like a rubber band. Gas bubbles form, creating an embolism that prevents the flow of water up the trunk. If this happens enough, a tree will shed its leaves and can, eventually, die.

To measure water tension and other biological processes, climbers sample each tree twice a day, once under cool pre-dawn conditions when the tree is least stressed, and once under the heat of the midday sun. The scientists clip foliage from the lower and upper canopies, which allows them to assess conditions at different parts of the tree.

Read more about this awesome work at bioGraphic: Last Tree Standing.

Plus: An illuminating illustration of how giant sequoias overcome gravity by Jane Kim, who illustrated the Cornell Lab of Ornithology’s Wall of Birds.

Related videos: Why the Giant Sequoia Needs Fire to Grow and Magnificent Giant Tree: Sequoia in a Snowstorm.

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