Drought Takes Big Toll on Sierra Nevada Mountains

New Aerial Survey Identifies More Than 100 Million Dead Trees in California

The U.S. Department of Agriculture (USDA) recently announced the U.S. Forest Service has identified an additional 36 million dead trees across California since its last aerial survey in May 2016. This brings the total number of dead trees since 2010 to over 102 million on 7.7 million acres of California’s drought-stricken forests. In 2016 alone, 62 million trees have died, representing more than a 100 percent increase in dead trees across the state from 2015. Millions of additional trees are weakened and expected to die in the coming months and years.

With public safety as its most pressing concern, the U.S. Forest Service has committed significant resources to help impacted forests, including reprioritizing $43 million in California in fiscal year 2016 to conduct safety-focused restoration along roads, trails and recreation sites. However, limited resources and a changing climate hamper the Forest Service’s ability to address tree mortality in California. USDA Secretary of Agriculture Tom Vilsack and Forest Service officials are seriously hampered not only by short-term budgets passed by Congress, but also a broken budget for the Forest Service that sees an increasing amount of resources going to firefighting while less is invested in restoration and forest health, Vilsack said.

“These dead and dying trees continue to elevate the risk of wildfire, complicate our efforts to respond safely and effectively to fires when they do occur, and pose a host of threats to life and property across California,” Vilsack said. “USDA has made restoration work and the removal of excess fuels a top priority, but until Congress passes a permanent fix to the fire budget, we can’t break this cycle of diverting funds away from restoration work to fight the immediate threat of the large unpredictable fires caused by the fuel buildups themselves.”


dead trees sierra nevada california drought
Bark Beetles have contributed to tree die-off in the Sierra Nevada forest due to the drought in California

The majority of the 102 million dead trees are located in ten counties in the southern and central Sierra Nevada region. The Forest Service also identified increasing mortality in the northern part of the state, including Siskiyou, Modoc, Plumas and Lassen counties.

Five consecutive years of severe drought in California, a dramatic rise in bark beetle infestation and warmer temperatures are leading to these historic levels of tree die-off. As a result, in October 2015, Governor Jerry Brown declared a state of emergency on the unprecedented tree die-off and formed a Tree Mortality Task Force to help mobilize additional resources for the safe removal of dead and dying trees.

This year, California had a record-setting wildfire season, with the Blue Cut fire alone scorching over 30,000 acres and triggering the evacuation of 80,000 people. In the southeastern United States, wildfires have burned more than 120,000 acres this fall. The southeast region of the Forest Service is operating at the highest preparedness level, PL 5, reflecting the high level of physical resources and funding devoted to the region. Extreme drought conditions persist, and many areas have not seen rain for as many as 95 days.

Longer, hotter fire seasons where extreme fire behavior has become the new norm,] – as well as increased development in forested areas – is dramatically driving up the cost of fighting fires and squeezing funding for the very efforts that would protect watersheds and restore forests to make them more resilient to fire. Last year, fire management alone consumed 56 percent of the Forest Service’s budget and is expected to rise to 67 percent in by 2025.

As the situation in the southeast demonstrates, the problem of shrinking budget capacity is felt across the U.S., not only in the western states. The health of our forests and landscapes are at risk across the nation, and the tree mortality crisis could be better addressed if not for the increasing percentage of the Forest Service budget going to fight wildfire. “We must fund wildfire suppression like other natural disasters in the country,” Vilsack said.

Forest Service scientists expect elevated levels of tree mortality to continue during 2017 in dense forest stands; stands impacted by root diseases or other stress agents; and in areas with higher levels of bark beetle activity. Photos and video of the surveys are available on the Forest Service multimedia webpage.

Learn more about tree mortality and the work to restore our forests in California at the Forest Service’s web page by clicking here.

U.S. Department of Agriculture (USDA)

U.S. Forest Service

Native ecosystems blitzed by drought

Source: Alexandra Witze and Nature Magazine; Scientific American

Peter Moyle has seen a lot in five decades of roaming California’s streams and rivers and gathering data on the fish that live in them. But last month he saw something new: tributaries of the Navarro River, which rises in vineyards before snaking through a redwood forest to the Pacific, had dried up completely.

“They looked in July like they normally look in September or October, at the end of the dry season,” says Moyle, a fish biologist at the University of California, Davis.

Blame the drought. The Navarro and its hard-pressed inhabitants are just one example of stresses facing a parched state. From the towering Sierra Nevada mountains — where the snowpack this May was only 18% of the average — to the broad Sacramento–San Joaquin river delta, the record-setting drought is reshaping California’s ecosystems.

It is also giving researchers a glimpse of the future. California has always had an extreme hydrological cycle, with parching droughts interrupted by drenching Pacific storms (see ‘Extreme hydrology’). But scientists say that the current drought — now in its third year — holds lessons for what to expect 50 years from now.

“The west has always gone through this, but we’ll be going through it at perhaps a more rapid cycle,” says Mark Schwartz, a plant ecologist and director of the John Muir Institute of the Environment at the University of California, Davis. He and others are discussing the drought’s ecological consequences at the annual meeting of the Ecological Society of America, which runs from August 10 to 15 in Sacramento, California. He says that the state’s plant and animal species are at risk in part because California ecosystems are already highly modified and vulnerable to a variety of stresses.

Many of the state’s 129 species of native inland fish, including several types of salmon, are listed by federal or state agencies under various levels of endangerment. “We’re starting from a pretty low spot,” says Moyle. He hopes to use the current drought to explore where native fish have the best chances of surviving.

That could be in dammed streams such as Putah Creek near the Davis campus, where water flow can be controlled to optimize native fish survival. Another focus might be on spring-fed streams such as those that flow down from volcanic terrain in northernmost California and can survive drought much longer than snow-fed streams.

In the late 1970s, Moyle discovered that native fish in the Monterey Bay watershed recolonized their streams relatively quickly after a two-year drought. But today’s streams face greater ecological pressures, such as more dams and more non-native species competing for habitat.

Other challenges arise in the delta where the Sacramento and San Joaquin rivers meet, north-east of San Francisco. An invasive saltwater clam (Potamocorbula amurensis) has taken advantage of warming river waters and moved several kilometres upriver, says Janet Thompson, an aquatic ecologist with the US Geological Survey (USGS) in Menlo Park, California.

Potamocorbula out-competes a freshwater clam (Corbicula fluminea), and accumulates about four times as much of the element selenium from agricultural run-off and refineries as its freshwater cousin does. When endangered sturgeon feed on Potamocorbula, the fish consume much more selenium than is optimal. “That’s the biggest shift that we’ve seen that’s of environmental concern,” says Thompson. “These are the kinds of things that can have a lasting effect on a predator species.”

Teasing out the drought’s effects on terrestrial animals is tougher. Researchers have documented drops in various California bird populations this year, such as mallard ducks (Anas platyrynchos) and tricolor blackbirds (Agelaius tricolor). But many other factors — especially habitat loss — also come into play, so it becomes hard to isolate the effects of drought.

The drought’s effects on larger animals such as bears are also uncertain. Anecdotal reports suggest that more bears than usual are showing up closer to people this year, says Jason Holley, a wildlife biologist at the California Department of Fish and Wildlife in Rancho Cordova. Within the space of six weeks this spring, four black bears appeared along the Sacramento River corridor, much farther out of the mountains than normal. “Those sorts of calls definitely pique your interest,” says Holley, who thinks that dry conditions in the mountains might be pushing bears closer to populated areas.

The longest-lasting effect could be on California’s forests, including its iconic giant sequoias. The drought has handed forest ecologists an unplanned experiment, says Phillip van Mantgem, a forestry expert at the USGS in Arcata, California, who is speaking at the Sacramento meeting.

Researchers are gathering data to examine whether thinning of plots in the forest, in part to reduce fire risk, might help trees do better under drought. Tests may also help to reveal the main mechanisms by which drought kills different tree species, whether by interrupting the flow of water within the tree or by starving it. “I’m really curious to see how this turns out,” van Mantgem says.

There should be plenty of time to gather data. Climatologists expect an El Niño weather pattern to form in the Pacific this year, which usually brings more rain and snow to parts of California (see Nature 508, 20–21; 2014). But the pending El Niño looks to be weaker than first expected, and may not have much, if any, influence on ending the drought. Chances are that the state will remain dry well into 2015.