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Thursday, April 6, 2006

Guest View: Thin Trees the Right Way

By April Fletcher

    Before the beetle infestation became epidemic, in the March 2001 version of my "Beginners Guide to Forest Thinning on Private Lands," I warned about the dangers of cutting trees at certain times of year:
    "If you have to thin in late winter, spring or early summer, you may invite insect infestations that can kill the trees you want to keep. To avoid that you will need to remove the living branches you cut, and cover all cut firewood with plastic securely in a sunny spot where the heat of the sun can bake the logs and kill insects. Use clear plastic, and seal the bottom tightly to create a 'greenhouse.' It's better to make several smaller stacks than one larger one, and pile logs tightly. Don't pile cut wood or chips near the base of trees. They will invite insects to your healthy trees. I recommend you trim living branches off of trees any time from August through December, since cuts may also attract insects."
    I first learned about bark beetles when working on the population dynamics of Dendroctonus brevicomis, a ponderosa pine bark beetle, at UC Berkeley in 1971. I was working for Don Dahlsten, a prominent forest entomologist who was also editor of Environment Magazine at the time. I later completed my bachelor's degree from UCB in conservation of natural resources.
    While I have been a strong supporter of forest thinning, I have frequently warned Ciudad SWCD, State Forestry staff and landowners that thinning at the wrong time of year would draw beetles.
    Beetle facts are as follows:
   

Each species of bark beetle has evolved to attack a particular kind of tree;
   

Stressed trees draw beetles that are in the vicinity.
   

When live branches are cut from trees in spring and early summer in normal years, the cut surface will tend to draw beetles— and may result in loss of those trees that have been trimmed;
   

Wood and branches cut in late winter, spring and early summer in normal years will rapidly draw beetles that will attack trees nearby;
   

Trees can become stressed when thinning results in a significant change of exposure;
   

Drought adds stress to a dense forest;
   

Forests can be thinned safely in late summer, fall and through February in normal years, and after the first frost until the end of January in drought years;
   

There is no safe way to thin trees when beetle populations are epidemic and flying.
    When the County Commissioners recently turned down a resolution to fund an emergency green waste collection program, intended to encourage forest thinning, they probably did many homeowners a favor. Residents do need to pressure the Commissioners for green waste days— but in late fall after the beetles have sequestered for the winter.
    This is not the time to be thinning. Thinning should be initiated only when beetle threats are minimal: late summer in years when we have good monsoons beginning in July, and after the first frost in dryer years when beetle populations are high.
    Although beetle populations dropped with the heavy rainfall in September and October, current and projected drought conditions threaten a rapid population increase. By now the larvae of beetles that survived have completed their development and emerged and are flying. By the second emergence (around late May or June), populations are likely to be high again.
    We have had very little precipitation since mid-October. Even recent snow has amounted to insignificant moisture. Adding stresses by thinning to trees already drought-stressed may be all that is needed to "tip the scales" and draw beetles.
    While I am a very strong advocate of thinning, and I realize some homeowners may need to remove trees from immediately around their houses for fire protection, thinning that leads to more beetle infestations and dead trees with dry, brown needles on them, could just as likely temporarily increase fire danger as reduce it— until the needles drop.
    It is truly unfortunate that many people don't see the need to thin around their homes until they panic in the spring as fire danger increases. If trees must be removed from around a home now for fire protection, all logs should be "solarized" with plastic sealed entirely around the bottom— well away from other trees— the same day they are cut. The stump should be cut low enough to cover it with dirt, and branches should be hauled off promptly to the transfer station rather than chipped. Lower, living branches should not be trimmed until late fall unless grasses or needle buildup at the base would be sufficient to carry a fire.
    Anyone thinning this late in the winter should count on losing additional trees unless they have remaining trees sprayed professionally with 2 percent carbaryl. (Forget those alternative "natural" pesticides— they don't work very well.) Remaining trees should be monitored closely, and at the first sign of beetle infestation— small pitch blobs or sawdust-lined holes in the trunk— cut down, and removed entirely right after cutting. A professional should confirm suspect trees before they are cut. Waiting until trees begin to sicken (needles lighten) gives the beetles a chance to emerge and fly to other trees nearby.
    Copies of my 2006 revision of "A Beginners Guide to Forest Thinning on Private Lands" are available free at the Sandia Ranger Station or the Western Store in Tijeras, for those who want further explanation of the points I've made here, or for those who want to know where to begin in thinning their property.
    April Fletcher, B.S., M.S., is an environmental biologist and an East Mountains resident.