High levels of tree mortality are occurring on forested lands in California due to drought and bark beetles.
 
Although the current drought is the primary catalyst, California’s forests are in sync with many other western forests with tree health in serious decline, often compromised by the existence of too many trees competing for limited resources, especially water.

Trees that appear healthy and green during periods of normal or above normal precipitation can become severely compromised and easy targets for bark beetles during periods of drought.

When, where, and the extent to which bark beetle related tree mortality occurs is influenced by forest stand conditions and weather patterns. A dramatic rise in the number of dead trees follows one to several years of inadequate moisture.

Stressed trees are suitable host material for bark beetles and their successful colonization results in more beetles and higher levels of tree mortality. The more severe and prolonged the drought, the greater the number of dead trees.

Tree losses are expected to continue to increase until precipitation levels return to normal or above normal for one to multiple years.

 

Many people get concerned that numerous standing dead trees contribute to the already ominous fire situation in many of our forests.

Typically, beetle-killed trees shed their needles within a few months of dying, so they don’t create as big a threat to fire spread as expected, however, high amounts dead trees do present a threat of spotting when a forest fire is burning around them.

Once trees fall, a fire could potentially burn longer and hotter, damaging soils and adversely affecting the site in the long-term.

Native bark beetles act as “agents of change” and play an important role in healthy, functioning forest ecosystems.

Bark beetles are small insects, about the size of a grain of rice, and brown to black in color. Their entire life is spent inside the tree except for a portion of time when beetles emerge to attack trees.

After attack, they emit a chemical (called a pheromone) that attracts other beetles. The beetles then mate and lay eggs in galleries or chambers they construct between the bark and the wood.

Adult beetles carry staining fungi which is introduced into the tree during feeding and gallery construction.

Tree mortality occurs from a combination of the fungi invading the water conducting tissue, and feeding and gallery construction by the adult beetles and larvae.

The primary bark and engraver beetle species of concern in California are in the genera Dendroctonus, Ips and Scolytus. Most of the current tree mortality has been caused by western pine beetle (Dendroctonus brevicomis), mountain pine beetle (Dendroctonus ponderosae) and Ips species.
 

Trees possess defense mechanisms that help them fend off attacks by bark beetles. When beetle populations are low and adequate moisture is available, trees have the advantage.

Healthy trees can produce enough resin (pitch) to overcome attacks by “pitching out” beetles that are attempting to bore in through the bark.

During drought or when trees are severely stressed by other factors (competition, diseases), they are not able to produce enough resin to defend against numerous attacks.
 

Many signs and symptoms of attack are similar regardless of the tree or beetle species.

External signs of beetle infestation are pitch tubes (combination of pitch, boring dust, frass) small holes in the bark, the presence of boring dust (produced by the beetle chewing) and/or frass (produced by the beetle feeding) and bark flaking by woodpeckers.

Pitch tubes resulting from successful attacks are typically reddish in color and vary in size depending on the beetle species. White or cream colored pitch tubes may be indicative of unsuccessful attacks.

Removing some bark will reveal adult and larval galleries, as well as dead or degraded inner bark. Galleries may or may not be packed with frass.

Trees with large amounts of dry boring dust in bark crevices and/or scattered around the base of the tree are likely dead or dying.

If a tree is infested with beetles, woodpeckers may chip off bark to feed on beetle larvae and pupae.

The first symptom of beetle-caused tree mortality is typically fading needles. Needles on successfully attacked trees begin fading and changing color over a period of several months.
 

There is nothing that can be done to save a tree once it is infested with bark beetles.

Improving tree growing conditions through selective tree removal (thinning) reduces inter-tree competition for limited water and nutrients. The best time to thin is during non-drought periods.

Know what tree species you have and identify individuals that are most susceptible to drought and bark beetles. Also identify trees for removal that may be hazardous to life or property.

Individual tree treatments such as preventive spraying with insecticides, the use of synthetic products that repel bark beetles, supplemental watering and prompt removal/disposal of infested trees may all be effective depending on the situation and the tree species at risk.

Avoid ineffective and unproven treatments. Treatments such as applying worm castings to the trunk, spraying insecticides into bark beetle entrance/exit holes or applying acephate via an encapsulated implant have no scientific support for being effective.

Do not leave cut green limbs, branches or wood in the vicinity of live trees. Some beetles are attracted to this material and doing so could result in more tree mortality.

Consult with a forest health specialist to determine the best treatments for your trees as there are several factors to consider and pros and cons to every treatment.
 

Tree mortality means trees have died. Trees dying is a normal occurrence in natural ecosystems. The difference now is that the extended drought has caused an abnormally high number—in the millions—of trees in California’s forests and wildland-urban interface areas to weaken and/or die. Weakened trees are more susceptible to attacks from bark beetles. Once a tree is successfully invaded by bark beetles, there is no recovery for the tree; it will die.
 

According to the U.S. Forest Service, tree mortality from bark beetles and drought has reached over 29 million trees, up from 3.3 million trees in 2014. Most tree mortality in California has occurred in the southern Sierra Nevada and the Central Coast. Researchers at the Carnegie Institution for Science have learned that approximately 58 million additional large trees are suffering from severe canopy water losses.
 

Ponderosa pine, Jeffrey pine, and pinyon pines are most impacted by bark beetles, but many trees have died just from lack of water in the current drought. Most other pine species, white fir and incense-cedar are also heavily impacted by the prolonged drought and by bark beetles. There is also an increase in tree mortality among oaks, although it is primarily attributed to drought, not bark beetles.
 

Beetles bore through tree bark and lay their eggs. Larvae feed on the tree’s living tissues, cutting off its natural process for transporting nutrients and water. One bark beetle infestation can create several thousand beetles and easily spread to neighboring trees.
 

Under normal conditions, bark beetles renew the forest by killing older trees and those weakened by disease, drought, smog or physical damage. When trees are weakened due to lack of water from prolonged drought, they are more susceptible to bark beetle attacks. Increasingly successful attacks cause the bark beetle population to explode.
 

Dead trees need to be removed. They are a fire hazard because they are fuel for wildfire to burn. Standing dead trees will rot, becoming unstable, and will eventually fall. Dead trees can fall on people, homes, buildings and infrastructure, such as power lines. The sooner a tree is removed the better. The more it rots, the more unstable it becomes. For larger trees located near houses and other infrastructure, foresters and arborists prefer to remove them in pieces. However, if the tree is too rotten, it is unsafe to climb and difficult to predict where it will fall.
 

On private property, it is the responsibility of the property owner to remove dead and dying trees. It is recommended that landowners consult with a licensed professional forester or arborist if they are unfamiliar with tree harvesting practices.
 

California’s Tree Mortality Task Force will be looking at resources and funding to help landowners, especially those located near evacuation routes, power lines, public roads and infrastructure. Currently, CAL OES is reviewing potential use of the California Disaster Assistance Act for Tree Mortality to local jurisdictions (counties, cities, and special districts) to help with the identification, removal, and storing of dead trees. Local jurisdictions must apply and show risk to public infrastructures.
 

The dead trees should be removed as soon as it is practicable to take them down. The longer the dead tree stands the higher the likelihood it could fall and hit your home, vehicle, or a neighbor’s property when it. Contact your homeowner’s insurance carrier to determine if your property is covered for this type of event, or if your tree lands on someone else’s property.

• FAQ's

Written James Hirby  ( Fact Checked by The Law Dictionary Staff ) 

Unless you live in an arid environment, your home region is likely to be home to a range of native tree species. If you own a single-family home that features a yard or fenced-in area, chances are good that you have at least one such tree on your property. Even if it's not a particularly tall or wide, you might be worried about its potential to cause significant damage to the structure of your home during a violent windstorm, snowstorm or other weather event. In fact, you might be thinking about forestalling this eventuality by trimming or removing it entirely.

Unfortunately, tree removal can quickly become ruinously expensive. Most homeowner's insurance companies advise their policyholders against attempting to cut down or trim large trees without the help of a professional tree removal service. If you need to take down an old tree that features a massive crown and twisted root structure, you might need to lay out as much as $5,000 to ensure that the job is done properly.

To make matters worse, your homeowner's insurance company won't pay to remove a hazardous tree from your property. Under the terms of most homeowner's insurance policies, homeowners are required to perform any maintenance work that's necessary to prevent significant damage to their homes. This provision is often sweeping. In fact, homeowner's insurance companies interpret it to cover routine maintenance tasks like storm-proofing windows as well as more complicated jobs like removing potentially dangerous trees.

It can also have serious real-world consequences. If your homeowner's insurance company can prove that you failed to perform certain types of maintenance work, it may try to associate this failure with certain subsequent damages to your home. If it can do so successfully, it may refuse to pay out on claims related to these damages. As such, it's important that you keep your home and property in excellent repair. Although this could be expensive in the short term, it's liable to pay off in the event that you file a claim. After all, repairing a potential problem is usually far cheaper than paying for the catastrophic damage that it's likely to cause.

If one of the trees on your property falls on your house, your homeowner's insurance company will try to prove that the tree was dead or dying. If it can do so, it will accuse you of failing to take the necessary steps to remove the tree and use this "fact" as justification for denying your claim. In order to prevent this outcome, you'll need to pay for the removal of the tree out of your own pocket.