Drought, Tree Mortality, Insects and Diseases

Donald R. OwenCalifornia Department of Forestry and Fire Protection

Survival of Fire-Injured Conifers in CaliforniaDonald R. Owen,1 Daniel R. Cluck,2 and Sheri L. Smith3

1Entomologist, CAL FIRE, 6105 Airport Rd., Redding, CA 960222Entomologist and 3Regional Entomologist, USDA Forest Service,

Forest Health Protection, 2550 Riverside Dr., Susanville, CA 96130

Trees under moisture stress exhibit a variety of impacts

• Premature loss of foliage

Trees under moisture stress exhibit a variety of impacts

• Premature loss of foliage• Decreased growth

Trees under moisture stress exhibit a variety of impacts

• Premature loss of foliage• Decreased growth• Crown dieback. Insects and diseases both may contribute

Phomopsis canker

Trees under moisture stress exhibit a variety of impacts

• The most severely stressed trees may be killed, usually by insects. Bark beetles are the most common mortality agents for conifers. Some wood borer species also are important.

Trees under moisture stress exhibit a variety of impacts

• Premature loss of foliage• Decreased growth• Crown dieback. Insects and diseases both may contribute to

dieback• The most severely stressed trees may be killed, usually by insects.

Bark beetles are the most common mortality agents for conifers. Some wood borer species also are important.

Preexisting stressors, such as root disease, mistletoe, and over crowding compound the stress.

In addition to moisture stress, high temperatures and unusual rainfall patterns have been significant issues during the current drought.

2014• Precipitation averaged 63% of normal. The current drought is distinguished by

calendar year 2013, which was the driest on record for California. While the drought has severely impacted all of California, minor relief was seen in the Sacramento River drainage, which received above normal precipitation during February and March of 2014. Areas to the south remained drier than normal during this time.

• Calendar year 2014 ranks as CA’s hottest (now being surpassed by 2015). Daily highs in Redding equaled or exceeded 100°F 52 times during the year; 20 of those days were in July.

2015 • Precipitation averaged 74% of normal. Spring was dry, with the majority of

precipitation occurring from October 2014 to February 2015. An important aspect of the precipitation was the lack of snow accumulation in mountain areas. Statewide, snowpack on April 1, 2015 was only 5% of average.

• Calendar year 2015 thus far ranks as California’s hottest on record, with mean monthly temperatures reaching record or near record highs during January, February, March, and June.

Current and Future Conditions

• All tree species and areas of the state, to some degree, are impacted by the drought. The extent and broad impact of the current drought distinguish it from other recent drought episodes.

• Pine species are experiencing the most mortality statewide, especially in the southern half of California. True fir mortality, mostly white fir, becomes more prominent as you go north, especially on drier eastside sites and in northeastern California. Aggressive bark beetle species are a significant contributor to this mortality. Additionally, significant numbers of live oaks are dying in portions of southern California.

• Trees on drier sites may be growing near the lower limit of precipitation needed to support growth and defense against pests. During drought, trees in these situations have the highest mortality rates. In Trinity County, Douglas-fir on drier sites are being killed by insects.

• Current year tree mortality is approaching 30 million (all species) statewide

• After several years of high reproductive success, large bark beetle populations will continue to kill trees in significant numbers even after the drought ends. In the aftermath of the 1976-77 drought, tree mortality did not decline significantly until 1979.

Western pine beetle, Dendroctonus brevicomis

(tree killer) attacks Coulter and ponderosa pines

Two generations per year in northern part of range; three and sometimes fourgenerations in southern portion

Western pine beetle• Outbreaks often develop during drought. • Trees are typically killed in groups• Endemic populations attack diseased, damaged, or otherwise stressed trees.

Pine Engravers, Ips spp.

Numerous species of Ips in California

Ips species in California produce at least two and sometimes six generations per year

First adult flights can occur in March with a second generation flying 6 weeks later

The preferred host for the first generation is slash or windthrownmaterial. Subsequent generations can attack standing trees.

attacks various pine species

Pine engravers commonly kill smaller trees or the tops of larger trees

Pine engravers can become important mortality agents during drought

Outbreaks are usually of limited duration

Pine Engraver, Ips spp.

A key agent of tree mortality on dry fir sites

During drought, mortality can exceed 60% of the trees in a stand

Outbreaks that develop during drought collapse quickly when drought ends

Stands most vulnerable where mean annual precipitation <25”

East Shore Lake Tahoe 1995

Fir engraver, Scolytus ventralisattacks true firs, e.g. white and red firs

Wood Borers

the most important with respect to forest and tree health are

in the Families

Buprestidae, Cerambycidae,and Siricidae

ovipositor

Flatheaded fir borer

Phaenopsdrummondi

in Douglas-fir

M. californica in Jeffrey pine

• Insect most often responsible for Douglas-fir

mortality on drier sites

• Feeds principally in the cambial region producing

tunnels tightly packed with fine boring dust

• Principally colonizes the main stem; often attacks in

conjunction with bark beetle species that attack tops

and limbs

• One year life cycle

Bark Beetle Management

Long-term vs

Short-term solutions

Fell, Peel, and Burn

Long-term

Thin to reduce competition

Avoid injuring trees during logging, construction, etc.

Avoid practices or activities that promote disease

Plant trees adapted to the area – use an appropriate seed

source

Thinning to Reduce Competition Avoid thinning during drought (if possible)

Choose leave trees well-suited to the site

Remove high risk trees

Consider potential interactions with diseases

e.g. dwarf mistletoe, root disease

with blackstain concern, avoid thinning during the spring /

early summer

Short-term

Beetle-infested trees cannot be saved

Fertilizers will not save trees

Remove infested trees if feasible Winter is a good time to do this

Tree removal must be accomplished before beetle emergence

(easier said than done)

Trying to eliminate beetles by other methods is possible, but equally problematic (burn, bury, chip, tarp, etc.)

During drought: Manage slash – timing / lop and scatter For high value trees, consider

Deep wateringPreventative pesticide treatment of uninfested trees

Pesticides registered for use against bark beetles• Carbaryl

• Synthetic Pyrethroids

• Emamectin Benzoate

• Vebenone

Resources

CAL FIRE Contacts for Assistance and Advice

• Don Owen (530) 224-2494 don.owen@fire.ca.gov

• Chris Lee (707) 726-1254 christopher.lee@fire.ca.g

• Tom Smith (916) 599-6882 tom.smith@fire.ca.gov

• Kim Corella (805) 550-8583 kim.corella@fire.ca.gov

TREE NOTES (CAL FIRE)

Forest Insect and Disease Leaflets (USFS)

Current Drought Situation prepareforbarkbeetle

USFS Region 5 Forest Health