Drought, Tree Mortality, Insects and Diseases Donald R. Owen California Department of Forestry and Fire Protection
Survival of Fire-Injured Conifers in California Donald R. Owen, 1 Daniel R. Cluck, 2 and Sheri L. Smith 3 1 Entomologist, CAL FIRE, 6105 Airport Rd., Redding, CA 96022 2 Entomologist and 3 Regional 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 four generations 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. attacks various pine species 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 windthrown material. Subsequent generations can attack standing trees.
Pine Engraver, Ips spp. 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
Fir engraver, Scolytus ventralis attacks true firs, e.g. white and red firs A key agent of tree mortality on dry fir sites Stands most vulnerable where mean annual precipitation <25 East Shore Lake Tahoe 1995 During drought, mortality can exceed 60% of the trees in a stand Outbreaks that develop during drought collapse quickly when drought ends
Wood Borers the most important with respect to forest and tree health are in the Families Buprestidae, Cerambycidae, and Siricidae ovipositor
Flatheaded fir borer Phaenops drummondi 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 watering Preventative 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