This story was originally published on Yale Environment 360. It is part of the Climate Desk collaboration.
The famous Sequoia National Parks groves, which are 300-foot tall, sit high above California's San Joaquin Valley, on the Sierra Nevada's western side. They are now under threat like never before. Wildfires have destroyed large swathes of forest and now insects are threatening to kill sequoias.
These majestic trees, and the forest ecosystem in which they live, are also under threat. Due to the smog from the San Joaquin Valley and urban areas, the ozone levels in Sequoia, and Kings Canyon are among the highest in America. Sometimes, the smog levels in this area are as high or higher than those in Los Angeles.
It is well-known that ozone at ground level (or tropospheric) can cause damage to trees and other plants. This happens by altering a variety of biological processes at cellular level. Research has shown that high levels of ozone can negatively impact the growth, vitality, water balance, flowering, and defense abilities of plants.
Researchers have recently focused their attention on how the harmful effects of ozone can affect entire ecosystems. They can impact biodiversity and harm insects, wildlife, and soil.
These knock-on effects include making plants less nutritious, decreasing the scent trails that pollinators use to find their target, changing the timing and location of leaf fall, altering the forest floor and the microbes and other organisms that dwell there, as well as reducing the harvests of staple foods like wheat and corn. Scientists predict that these negative impacts will worsen as the planet heats. Ground-level ozone levels rise with rising temperatures.
Because the effects of ozone on the Sierras and other places are hard to study and have not been well-funded, it is difficult to fully understand their impacts. It can be difficult for scientists to distinguish ozone's effects from other stressors like drought or warmer temperatures. Many of the changes caused by ozone could not be detected for many years or even decades.