Planting Giant Sequoias Sparks Controversy

Giant Sequoias are conifer trees, which can live for 3,000 years and grow to 300 feet tall and 30 feet wide at their base.  These towering trees grow naturally only on the western slopes of the Sierra Nevada mountains in California. Although they have evolved to be wildfire-resistant, they have suffered greatly in the wildfires of the last 6 years. The giant sequoias are very thick-barked which provides partial immunity to fire and even relies on fire for reproduction; however, scientists say the warming climate has made wildfires worse and deadlier for the trees.

from the USFS

Misguided forestry practices, which sought to suppress beneficial small and moderate fires allowed woodlands to become overly dense and ended up fueling the conflagration. Fire is essential to giant sequoias. Tree-ring records from giant sequoias show that frequent surface fires were the typical pattern of fire occurrence over the past 2,000 years. But this pattern changed after about 1860, when fire frequency declined sharply. During the century from the late 1800s until the late 1900s, fire was rare in many giant sequoia groves due to land use changes and many decades of fire suppression.

Giant sequoias have coexisted with fire for thousands of years. Their thick, spongy bark insulates most trees from heat injury, and the branches of large sequoias grow high enough to avoid the flames of most fires. Also, fire’s heat releases large numbers of seeds from cones, and seedlings take root in the open, sunny patches where fire clears away groundcover and kills smaller trees. But starting in 2015, higher-severity fires have killed large giant sequoias in much greater numbers than has ever been recorded.

Six fires, occurring between 2015 and 2021 killed many large sequoias in numerous groves across the Sierra Nevada. More than 85% of all giant sequoia grove acreage across the Sierra Nevada has burned in wildfires between 2015 and 2021, compared to only one quarter in the preceding century. The Forest Service believes we have reached a tipping point — lack of frequent fire for the past century in most groves, combined with the impacts of a warming climate — have made some wildfires much more deadly for the sequoias.

As part of a multi-year project to improve forest health through reforestation, Sequoia National Forest personnel worked closely with the national nonprofit American Forests to plant over 286,000 trees across 1,380 acres. This included over 14,000 giant sequoia seedlings. While new trees may regenerate on their own after a wildfire,  this cannot happen after high-severity burns when all the overstory trees are dead. In such cases, few, if any, green trees remain. Burned seeds on the forest floor are often unable to develop after experiencing such high temperatures. This is when planting becomes necessary to retain a forest landscape.

Also,  debris and fallen trees need to be cleared from the forest floor to allow seedlings to grow in bare soil, and clumps of burned trees that remain standing need t be removed from some areas. These burnt out trees are structurally weak and may fall soon, endangering the next generation of trees or the forest workers. According to the Forest Service, it is important to not wait too long to plant. If the landscape remains deforested, brush species that thrive in disturbed areas, will quickly carpet the forest, absorbing the moisture and space seedlings need to thrive. Many park land managers worry about vegetation type conversion, which follows high-severity fire and occurs when forested lands transition to shrublands. This can cause an ecosystem shift and is associated with a loss in biodiversity.

Now after two months of planting, a handful of conservation groups filed suit to stop the work last week. The groups contend that the reforestation project, which entails planting tens of thousands of sequoia seedlings on charred hillsides in Sequoia and Kings Canyon national parks, is inappropriate because the burned areas are designated “wilderness,” where human intervention is prohibited. Contrary to what park officials and the Forest Service say, the litigants assert that replanting trees is not needed for the groves to successfully regenerate.