PORTLAND, Ore. –April 2, 2010. Countless
studies and reports exist describing how a landscape is impacted
after logging Douglas-fir:
What is the impact on the soil? Should one leave the debris in
place? Pile it? Burn it or haul it offsite in preparation for replanting
the area in the future?
However, few studies have examined this
hypothesis: Is it possible, that the debris remaining on the ground
after logging may actually
suppress competing vegetation resulting in a positive effect on
the survival of Douglas-fir seedlings?
At a variety of clearcut
sites, research forester Tim Harrington, noticed that plant invaders
were sparse when the debris was left
behind. He also began to reason that the method of dealing with
debris might indirectly affect the survival and growth of conifer
seedlings by way of its impact on vegetation that managers may
consider a nuisance.
Harrington and Virginia Tech professor, Stephen
Schoenholtz, conducted two studies to quantify the effects of
different levels of logging
debris on the productivity of Douglas-fir. These experiments compared
the effects of dispersing, piling, and removing logging debris
on the 5-year survival and growth of planted Douglas-fir seedlings
at logging sites near Matlock, Washington, and Molalla, Oregon.
I found that Scotch broom was the key woody competitor at the first
location,” Harrington says,“and blackberry was rampant
at the second.” Three treatments were tested at each site:
Only harvested logs were removed, leaving branches and treetops;
aboveground portions of entire trees were removed; or logs were
taken and branches and tops were piled at the site. “By the
second or third year of the research, the amount of terrain covered
by the key invasive (Scotch broom or blackberry) was much greater
where debris had been piled or removed,” Harrington explains,
adding that as broom cover at the Matlock site increased to 40
percent, Douglas-fir seedling survival decreased by 30 percent.
At the Molalla site, stem growth of the young trees decreased by
30 percent as blackberry cover increased to 80 percent. Dispersed
logging debris also suppressed development of other invasive plant
species, including oxeye daisy and velvet grass.
Some of the other
findings of the study include:
Debris decays, releases nutrients,
adds to soil productivity.
Mineral soil is exposed when debris
is piled or removed, allowing native plants to be squeezed out
while invasive plants grow rapidly.
Removal of debris also removes
a good source of carbon and nitrogen needed for forest productivity.
The problem is especially severe
on low-productivity sites having gravelly or sandy soils.
debris behind saves the cost of removal, but it may also increase
short-term fire risk.
The study, Effects of logging debris treatments
on five-year development of competing vegetation and planted
appears in the
recent issue of the Canadian Journal of Forest Research. The article
is coauthored by Harrington and Schoenholtz. Harrington is a research
forester at the Forest Service’s Pacific Northwest Research
Station, USDA Forest Service. He is based in Olympia, Washington.
Schoenholtz is a professor in the College of Natural Resources
at Virginia Tech, Blacksburg, Virginia.
Read about Harrington and
Schoenholtz’s study in the Canadian
Journal of Forest Research
more information please visit Science Findings: Toward More
Diverse Forests: Helping Trees Get Along in a New Organization,
The Pacific Northwest Research Station, USDA Forest Service,
is headquartered in Portland, Oregon. It has 11 laboratories
in Alaska, Oregon,