In California’s Sierras and around the world, extreme drought and rising temperatures are killing trees and threatening the viability of forests. Some ecologists are saying that land managers now need to adopt radically new strategies.
The clearest way to the Universe is through a forest wilderness,” declared John Muir, whose belief in the necessity of untrammeled and enduring nature became the bedrock of contemporary conservation. No forests inspired Muir more than those blanketing the Sierra Nevada, “miles in height, and so gloriously colored and so radiant, it seemed not clothed in light but wholly composed of it, like the wall of some celestial city.”
Today, the forests of Muir’s “Range of Light” and their celebrated woody inhabitants are pitted against the 21st century’s version of the Four Horsemen of the Apocalypse — heat waves, extreme droughts, insect plagues, and massive wildfires — all linked to climate change. Some giant sequoias, the range’s most iconic conifers, suffered a sudden leaf dieback in 2014 as about half of their needles turned brown and fell to the ground. In Sequoia National Park, more than 70 percent of the big sugar pines and 50 percent of the large ponderosa pines growing in lower-elevation forests have been decimated by bark beetles. The U.S. Forest Service announced in November that an additional 36 million trees across California had died since its previous aerial survey just six months earlier, bringing the total number of dead trees since 2010 to more than 102 million.
The problem extends far beyond California. Writing in Science magazine in 2015, ecologists Constance Millar of the U.S. Forest Service and Nathan Stephenson of the U.S. Geological Survey concluded that extreme drought, exacerbated by rising temperatures and other megadisturbances, is pushing temperate forests in Europe, South America, and Australia, as well as the American Southwest “toward and over resilience thresholds,” with little prospect of returning to conditions of the recent past.
At a time when restoration of forests and other ecosystems is increasingly essential, the dominant paradigm of restoration science has been shaken to its core. Restoration ecologists, for whom returning lands to their state before the arrival of Europeans on the continent is still the basic, if rarely stated, goal, have been at loggerheads with so-called new ecologists, who challenge the primacy of native species in conservation thinking and champion the “novel ecosystems” of native and exotic species that increasingly dominate the planet.
But the controversy begs the questions: What do we do with declining forests in the Sierra Nevada and around the world? And how do we secure the future of the sequoia and other native species that have inhabited them for millennia?
To preserve the native biodiversity that could otherwise be lost, Millar, Stephenson, and other researchers have been encouraging federal land managers to employ a “toolbox” approach and hedge their bets with a combination of “resistance,” “resilience,” and “realignment” actions. Some resistance and resilience measures have been used by managers for years to reduce the massive fuel loads that have accumulated due to decades of fire suppression, and they are now being redirected toward helping forests withstand rapid climate change. One of the most important is forest thinning, a process in which small trees and brush are removed, either mechanically or through controlled burning. Thinning not only reduces a forest’s potential flammability but also its drought stress by decreasing competition for water and soil nutrients among the trees that remain. However, the need for such efforts is so vast, scientists note, that land managers must perform triage, deciding where in the landscape to ration their limited funds.
Read more at In the Sierras, New Approaches to Protecting Forests Under Stress