Sept. 1998
An Ecologist's viewpoint: Nonchemical Control of Noxious Species in Natural
Areas Is the Long-Term Solution.

     Noxious weeds are just the tip of the iceberg of current changes in
natural areas. The "noxious weed problem" is an economically visible
component of much larger shifts in plant species abundance due to human
impacts. This change, the very real transformation of our landscapes by
invasive plant species, is both a cause and effect of global change. The
extent to which new species are invading natural areas is the result of a)
climate change, b) changes in atmospheric chemical composition, including
but not limited to enhanced carbon dioxide concentrations and increased
inorganic nitrogen deposition, c) drastic changes in the natural
disturbance cycles (e.g., fire return intervals, grazing intensities and
frequencies, flood prevention, etc.), and d) the presence and abundance of
seeds of nonindigenous species capable of exploiting these changes.

     Grazed prairies in the Front Range of Colorado have experienced 150
years of fire suppression in a system that had a 7-20 year fire return
interval. We should therefore not expect fire-adapted species to maintain
their dominance under this regime. Atmospheric inorganic nitrogen
deposition is 3-10x higher than presettlement levels. This nitrogen
addition favors weedy species. Chronic and often intensive grazing by
cattle replaced infrequent grazing by bison. Cattle eat what they like
first, and therefore give a competitive advantage to less palatable
species. These factors in various combinations have transformed our
native prairies into "something else", and have given nonindigenous species
their opportunity to invade stressed ecosystems.

     Chemical control of invasive species in natural areas is seldom a viable
option due to the presence of native species that are also sensitive to
the chemicals. As one scientist described chemical use in a recent book
"Alien Invasions", "It's like hitting a nail with an anvil." Effective
nonchemical control procedures remain underutilized. Enhanced use of
biocontrols remains promising and appears sufficient for control of weeds
in some cases; however, under current management regimes, biocontrols,
alone, may be insufficient.

     The solution, of course, is to fix the ecosystem, not just focus on
killing weeds. Unfortunately, that's not what weed managers are paid to do,
and their bosses are not trained to see the bigger picture. Chemical or
nonchemical means of weed removal only fight symptoms. The solutions
require an important management decision. We either decide we will invest
the time, energy and resources to restore native species or we opt to
create a more desirable, nonindigenous plant community that is capable of
keeping the weeds under control. While most of us favor the former, the
realities of global change, as stated above, may preclude this option to all
but the wealthiest of private and public landowners. This fact further
emphasizes the need that must be placed on prevention of nonindigenous
species on our remaining "pristine" areas.

     Weed management in Open Space should therefore 1) put maximum
emphasis on excluding undesirable species from areas where they've yet to
establish, and 2) focus on containment and nonchemical control techniques
in heavily infested areas. Precluding the repeated use of chemicals is an
important safeguard of native biotic diversity. More enlightened use of
grazing and fire and certainly more emphasis on biotic control mechanisms
are warranted.

     Actions speak much louder than words. Boulder County officials have
been very helpful in providing management assistance on a 160 acre
nonchemical management area, but this area is only a tiny fraction of our
Open Space. We first need an articulated vision of what vegetation we wish
to have on these lands. We need to be open about the ecological and
economic costs of this decision. Then, based on that public vision, conduct
the appropriate land management activities. Weed management will then
compose an important but not stand-alone activity within these ecosystem
management programs.

(Tim Seastedt is a professor of EPO Biology at the University of Colorado,
Boulder, and is the head volunteer of the nonchemical controls of knapweed
effort located south of Superior.)