By Thembi Borras
In a workshop I recently attended on biointensive farming, I was challenged to harvest vegetables as a byproduct of growing soil. With the exception of the ocean and the atmosphere, soil is the medium in which everything we consume grows. Trees depend on the 25% or more of their biomass found in the soil, which physically functions to store water, circulate air and water and support tree roots.
Despite the importance of soil, soil loss, soil compaction and organic matter loss continue to diminish soil productivity in forests. Forest site productivity, which is the capacity of the land to grow trees, is, in part, a function of soil productivity. Forest site productivity can be measured in annual production in bf/acre/year and is an important standard used by foresters to plan, describe and compare forestlands. As forest site productivity declines so does annual production rates and the length of time between harvests may become longer.
In New Zealand, a 20 percent drop in site productivity was revealed after 1" of topsoil was removed. In my own experience I have walked areas in Central Mendocino County that obviously suffer from topsoil loss and compaction, the magnitude of which being frequently connected to the extent of the legacy skid trail network and drainage associated with it as evidenced by the light colored subsoil, stunted trees and gullies.
Soil loss reduces the supply of nutrients and water. Soil compaction retards root growth and the circulation of air and water. And, organic matter loss accelerates erosion and may decrease water retention, structure, porosity, and resistance to compaction. These conditions are not easily reversed given the amount of time it takes for easily crumbled, humus and nutrient enriched topsoil to develop. In the context of agriculture, it takes 500 years to build 1" of topsoil which is significantly longer than the time that it is taking to lose 1" of topsoil, only 28 years in some cases.
For the most part, we have inherited the soil productivity we use to prosper today. To insure that future generations are able to flourish we must reverse the depletion trend and begin to accumulate soil wealth. In the context of forestry, practices exist to minimize the loss of soil productivity, however there are no economically viable practices to restore soil, soil structure and organic matter once it has been lost. My challenge and that of future generations will not be growing trees, agricultural crops or raising cattle but will be growing the soil on which they depend.
A portion of this production was gleaned from Sustaining Site Productivity on Forestlands; A User's Guide to Good Soil Management published by the University of California and the Proceedings from the Soil, Food and People Conference held in 2000 at UC Davis.
Showing posts with label soil compaction. Show all posts
Showing posts with label soil compaction. Show all posts
June 25, 2006
January 29, 2006
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.
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.
Subscribe to:
Posts (Atom)
