Science speaks: Seeing a lake for the trees (Opinion)
Lake Tahoe’s cold, clear water provides an oasis in a dry landscape. Fed by the Lake, the lower Truckee River supports flourishing communities and ecosystems along its length and through to its final destination at Pyramid Lake. While a remarkable set of conservation efforts protect Lake Tahoe from urban runoff and pollutants, the majority of the Lake’s water originates in the forested creek, stream, and river drainages that surround it, and these forests are changing.
Since the end of the last ice age, high elevation forests have covered the Tahoe Basin and helped keep the Lake clear and cold. The Washoe People used small, frequent fires to remove brush and dense clusters of young trees for centuries. Their fire management resulted in more fire-resistant forests with more old-growth trees and fewer small trees, shrubs, and forest floor vegetation. Then, European-American settlers clearcut the Tahoe Basin in the 1800s. As the forests regrew, settlers suppressed wildfire to protect the growing number of people and buildings in the Basin.
A century of growth without burning resulted in the forest we see today. It is denser, younger, and more prone to explosively intense fires than it was before the 1800s. Forest managers recognize the forests’ precarious state, and they are racing to restore it using techniques like small tree removal and prescribed burns to reduce the fuels that feed destructive wildfires. Fortunately, widespread forest management can not only improve fire resilience, but also protect the snowpack and stream flows that people and ecosystems rely on.
Forests dominate the land area of the Tahoe Basin and influence nearly every stage of water’s journey, from its arrival as snowfall to when it flows into the Lake. Trees capture falling snow in their branches, slowing accumulation on the ground. Tree canopies shade and protect the snowpack from melting, while their sun-warmed trunks can accelerate melting. Although canopy shade additionally reduces water loss from soils and smaller plants, during drought years trees can use up to half of the precipitation that falls over the Basin. Trees also protect water quality by holding soils in place, preventing runoff that clouds Tahoe’s waters, and promote soil development. In a nutshell, trees exert a wide-ranging influence on a healthy path for water to reach the Lake.
As those who spend time across the Basin know, Tahoe’s forests are diverse. There is variation in the tree size and spacing, the slope of the terrain, and the unseen soils, rocks, and groundwater below the surface. This diversity means that managing a forest to maintain snowpack and stream flows might, by necessity, look different from one location to another. Some places may simply be better fits for forest restoration investments than others.
Forest management is one of the few ways we can directly influence the quantity and quality of water supplies that benefit the Lake and downstream communities. The massive and destructive Caldor Fire – whose flames left once-green hillsides black and baren – demonstrated the negative impacts of catastrophic vegetation loss, as rain and melting snow eroded soils and flushed sediment and nutrients into the Lake.
On the other side of the coin, increased forest restoration has the potential to reduce the risk of wildfire, increase snow accumulation and water supplies, improve biodiversity, and increase resilience to drought. The Lake Tahoe West Restoration Partnership (bit.ly/laketahoewest) and Tahoe Central Sierra Initiative (bit.ly/tahoe-csi) are exploring potential benefits of forest management for snowpacks and biodiversity at a landscape-scale to help determine where and how to use limited resources to restore the forest.
Ensuring the success of landscape-scale environmental investments in the Tahoe Basin demand that resource managers and the public have the best information available. Science, including the contributions of the Tahoe Science Advisory Council, will be a critical part of creating and sharing the knowledge that supports water management in Tahoe’s uncertain future climate.
Aidan Manning is a Ph.D. student in the graduate program in hydrologic sciences and Adrian Harpold is an associate professor in the Department of Natural Resources and Environmental Science at University of Nevada, Reno. Dr. Harpold has been a member of the Tahoe Science Advisory Council since 2019. Learn more about the council’s work at tahoesciencecouncil.org.
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