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SUSTAINABLE ECOSYSTEMS AND
FOREST HEALTH
Session Summary
'Michael R. Wagner and Jill L. Wilson 1, Chairs
The symposium organizers challenged session chairs and
speakers to bring into focus. the widely professed idea of
management for sustainable ecPlogical systems. Our particular
symposium was challenged to address the intemctions between
forest health and sustainable ecosystems. This proved to be a
formidable task and readers are encouraged to judge for
themselves whether or not this task has been accomplished. Both
of the concepts" sustainable" and "health" remain without clear
deftnition and consequently there is no consensus on the
procedures needed to achieve "healthy sustainable ecosystems."
Much of this ambiguity arises because the root terms of health
and sustainability were developed in the context of forest
commodities and usually in the context of individual trees or
small stands. When these terms are applied to the much larger
watershed or landscape scale their meaning could be applied
more broadly, increasing what are already ambiguous concepts.
Wagner suggested other concerns with historical defInitions and
proposed some modillcations.
While precise defInitions may not have emerged, there was
considerable consensus regarding the need to focus on the role
insects and diseases play in basic ecological processes.
Schowalter suggested that insects and diseases may contribute
to maintenance or recovery of forest functional equilibrium
through pruning, thinning, nutrient cycling, etc. He further
maintains that these organisms may be instrumental in
maintaining ecosystems. Clancy likewise emphasized the role of
defoliating insects on forest biomass production, bioelemental
tmnsfer, and nutrient cycling. Clancy suggested research
approaches that might be used to address these issues for an
important western defoliator, the western spruce budworrn
(Choristoneura occidentalis). Various discussions and questions
throughout the session indicate that all speakers share the view
that insects and disease are essential elements of the ecosystem
and greater appreciation and research on this role is justifIed.
Hagle and Byler discussed how ecosystems respond to the
introduction of exotic organisms. They observed that
introductions greatly altered _some insect and disease regimes
but they did not obselVe the loss or addition of any ecological
function This novel view could change considerably how
impacts of insects and diseases are interpreted. This conclusion
contmsts somewhat to Wilson and Tkacz who suggest that
changes in incidence of insects and diseases may reflect changes
to the underlying structure and function of ecosystems.
Additional analysis, debate and discussion is needed to clarify
whether population outbreaks of insects and diseases are
indicators of unhealthy conditions or are healthy feedback
processes in ecosystems that function to restore forest
equilibrium. Under either of the above scenarios it is clearly
justifIed to examine long mnge trends in insects and diseases to
allow for interpretation of ovemll forest condition
Finally, Liebhold discussed the value of spatially explicit
models to assist in tmcking trends in insect populations.
Analytical approaches to address more landscape level effects
appear in place and will likely replace the historic modeling
approaches of systems models and process models. Spatially
explicit models are clearly the appropriate approach for
ecosystem level examination of the role of insects and
diseases.
As land management philosophies evolve from sustained
yield management through multiresource management toward
ecosystem management, the concepts of healthy forests and
sustainable ecosystems will change. All advocates of these
concepts need to recognize that consensus does not exist on the
meaning of these concepts nor on the likelihood of achieving
these objectives. Thoughtful managers, scientists, and the public
should continue to demand more clarity and specifIcity of these
ideas and encoumge continuing research to better understand
what is a healthy sustainable ecosystem.
1 Professor, School of Forestry, Northem Arizona University,
Flagstaff, AZ and Pest Management Specialist, USDA Forest
Service, State and Private Forestry, Flagstaff, AZ.
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