Causes of Decline of Inland Douglas-fir

By Thembi Borras

A reader from the Iron Peak area of Mendocino County asks why a number of good-size Douglas fir have died over the last five or so years?

Jack Marshall, Forest Pathologist at the California Department of Forestry and Fire Protection, corroborated the readers observations reporting an increase in the death of Douglas-fir in the vicinity of Willits north to Laytonville. However, the number of dead trees observed has been declining since its height in 2003. The flat-headed fir borer and the Douglas-fir engraver beetle are the likely mortality agents. The flat-headed fir borer can cause mortality in any sized Douglas-fir tree. The Douglas-fir engraver beetle can cause mortality in trees less than 10" in diameter. Weakened trees are most susceptible to intrusion by insects. Biologic pressures and environmental pressures can cause trees to become weak. Weak trees are destined to be outcompeted by their neighbors and relegated to a suppressed or intermediate crown position. Environmental pressures include drought, the effects of a disrupted fire cycle, soil compaction and increased exposure to the elements. Biologic pressures include disease agents. In this case, the Dermea canker causes dieback of limbs and tops which may invite the entrance of the Douglas-fir engraver beetle.

Another reader from the Blue Rock Creek area asks a series of related questions: Can the bark beetle that is killing the Douglas-fir be stopped? Should we let them continue since they are only taking out the "weak" trees? How should they be cut and removed without spreading the beetle?

Native pests will always be in the area, but you can be active in protecting the non-symptomatic population. The Douglas-fir engraver beetle, a bark beetle, and the flat-headed fir borer are native insects. Through early removal of the symptomatic tree, you can slow the population growth. Once cut, treat the slash by lopping and scattering, piling and burning or chipping. Debarking the logs is also effective in that the habitat where beetles breed and larvae feed is destroyed. If you cut an infected tree into firewood, tarping and sealing the piles of wood with clear plastic is an effective way to prevent the emergence of the beetle from the wood. Go to http://www.fire.ca.gov/ click on resource management, then pest management and finally Tree Notes #3 or go directly to http://ceres.ca.gov/foreststeward/pdf/treenote3.pdf for more information.

A portion of this production was gleaned from a conversation with Jack Marshall, Forest Pathologist at the California Department of Forestry and Fire Protection. If you have a local disease or insect question for Jack Marshall, he can be reached at Howard Forest in Willits at 707-459-7448.

The Relationship between Carbon Storage and Forest Disturbance

By Thembi Borras

Forests have tremendous potential to meter carbon dioxide emissions. Carbon is stored in forests until carbon is transferred back into the atmosphere through some sort of disturbance, such as forest loss, forest harvest or natural disturbance.

The scale of forest loss is more significant globally and nationally than it is regionally. Nonetheless forest loss is occurring regionally and has serious implications, 2% of existing forest and rangeland in the Klamath/ North Coast bioregion, which includes Mendocino County, will become, at a minimum, a rural residential neighborhood by the year 2040. If Mendocino County were considered individually, this figure would likely be higher given our proximity to the Bay Area. Statewide this figure is 10%. Part of the reason for this shift in land use is it can be more profitable to treat forestland as real estate than it can be to manage it. Shifting land use does not necessarily equate to forest loss but may lead to forest loss as it continues to do in Lake Arrowhead. In Lake Arrowhead, a Southern California forested neighborhood, bark beetle afflicted trees continue to be removed to reduce fire hazard and improve safety.

The amount of stored carbon is reduced at the time of harvest. When a tree is harvested, approximately 1/3 of the carbon is stored in the final product, for example, dimensional lumber and plywood. The remaining 2/3 is lost to the atmosphere, 1/3 of which is lost within 5 years, and the other 1/3 over time through decay. Stands at age 35 have 70 tons per acre of tree carbon. Stands at age 70 have more than double that, 194 tons per acre.

The amount of stored carbon is also reduced when harvest exceeds growth. Since the 1980's, growth in California has exceeded harvest. However, taken from 1996 data, nationally harvest exceeded growth.

Preventing forest loss, increasing forested area and forest management that increases forest age, increases growth relative to harvest, fosters a disease and fire resistant forest, has integrity, supports biodiversity and is economically sound can increase net carbon stores.

These strategies may be supported by performance based regulation, market incentives, land use laws, education, carbon credits, global fair trade laws and a functioning timber infrastructure.

A portion of this production was gleaned from The Changing California: Forest and Range 2003 Assessment for California from the California Department of Forestry and Fire Protection and Forest Carbon in the United States: Opportunities and Options for Private Lands a publication offered by The Pacific Forest Trust.