Forest-Management Modelling - Environmental Modelling: Finding Simplicity in Complexity - page 364

23

Forest-Management Modelling

Mark J. Twery 1 and Aaron R. Weiskittel 2
1 USDA Forest Service, South Burlington VT, USA
2 University of Maine, School of Forest Resources, Orono ME, USA

scale (stand versus individual tree) (see also Chapter 5),
reliance on data (empirical versus mechanistic) (see
also Chapter 7), representation of competitive processes
(distance-independent versus distance-dependent) (see
also Chapter 13), and degree of stochasticity (see also
Chapter 8). These differences have important implications
for how useful they are for forest management planning
process. Understanding these tradeoffs is important.
Forest-management activities range from the selec-
tive removal of certain individuals (thinning) to altering
soil nutrient availability (fertilization). Ascertaining the
long-term effects of these management activities is dif-
ficult because of the dynamic nature of trees and high
variability in the response of forests to management.
In addition, new questions on the effective manage-
ment of forests are emerging like the impacts of climate
change, broader ecosystem-management objectives, and
increased demands for forest-resource products. Thus,
models will continue to be an important component of
the forest-planning process.
The objective of this chapter is to explore various mod-
elling approaches used for forest management, provide
a brief description of some example models, explore the
ways that they have been used to aid the decision-making
process, and make suggestions for future improvements.

23.1 The issue

Forests are complex and dynamic ecosystems comprising
individual trees that can vary in both size and species.
In comparison to other organisms, trees are relatively
long lived (40-2000 years), quite plastic in terms of
their morphology and ecological niche, and adapted to
a wide variety of habitats, which can make predicting
their behaviour exceedingly difficult. Forests are widely
managed for a variety of objectives including biodiversity,
wildlife habitat, products, and recreation. Consequently,
forest managers need tools that can aid them during the
decision-making process.
Both conceptual and quantitative models are used in
forest management. Conceptual models are built from the
extensive scientific literature that describes forest response
to management (e.g. Moores et al ., 2007). Often concep-
tual models are difficult to apply because each forest is
unique due to its location and past management history.
In addition, one major objective of sustainable forest
management is the ability to compare multiple alter-
native management activities. Thus, quantitative models
are widely used because they can be used to update
and project forest inventories, compare alternative man-
agement regimes, estimate sustainable harvests, and test
important hypotheses regarding forest growth and devel-
opment (Vanclay, 1994). Quantitative models attempt
to represent forests with mathematical equations that
describe their behaviour over time.
Various quantitative models are used in forest man-
agement. These models differ in terms of their temporal
resolution (daily versus annual versus decadal), spatial

23.2 The approaches

The modelling approaches used in forest management
differ widely in their general frameworks as previously
described. One of the most significant distinctions is
the way that the models treat forest processes. Empirical