Landscapes Forest and Global Change - ESA - Escola Superior ...

R.A Fleming et al. 2010. Forest management and climate, through landscape structure, affect the potential for insect outbreak
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described in the context of stand density management diagrams (Farnden 1996), it was decided
to use this approach to model the host pine stands.
Stand density management diagrams (SDMD) are graphical representations of stand
development that illustrate the interactions between stocking and other stand parameters such as
mean diameter, top height, and volume. In a modeling context, when many stands have to be
“grown” simultaneously, SDMDs present the advantage of eliminating the need to perform
complex mathematical analyses often used in individual tree, distance-dependent growth and
yield models. This SDMD approach also provides needed flexibility and transparency in
preparation for modeling MPB spread into landscapes dominated by a different pine species for
which there has been no prior experience.
The site (sub)model describes the key ecological mechanisms affecting the growth of MPB
populations within even-aged stands of lodgepole pine in the context of SDMDs. This growth is
non-linear: at low densities, tree defences, competitors, and lack of suitable habitat severely
restrict MPB populations. But as stands age, the trees become more susceptible to mass attack in
which upwards of a 1000 MPBs will aggregate to overwhelm the defences of an individual tree.
Besides age, other stand properties, particularly tree density, also affect a stand’s ability to resist
a mass attack. Stands are most susceptible beyond 80 years of age, but by at least 160 years the
phloem in their trees has become too thin for a mass-attacking MPB population to successfully
reproduce itself.
In this presentation, we describe the site (sub)model and show how it can be used to
infer a variety of different possible patterns of spread for MPB outbreaks. We also show
that the local stand dynamics can be crucial determinants of the larger landscape
patterns that emerge when landscape structure and dispersal dynamics are also
considered.
References
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