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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landscape and forest ecology. Insect outbreak severity and extent have been shown to be
influenced by landscape structure (Coulson et al. 1999; Radeloff et al. 2000; Cairns et al. 2008).
There is a long history of modeling MPB population dynamics (Berryman et al. 1984; Powell et
al. 1996; Logan et al. 1998; Heavilin and Powell 2008; Powell and Bentz 2009). However, we
still have little idea what triggers a stable, low density, endemic population to erupt to outbreak
levels which can become self-perpetuating through contagious spread between susceptible
stands. Once a population has exceeded the stand-level eruptive threshold, its capacity to
contribute to a landscape-scale outbreak will depend on the availability and the quality of
susceptible host trees in neighboring stands (Aukema et al. 2006; Safranyik and Carroll 2006).
As the resource gets depleted, the landscape structure at a larger scale becomes a critical factor.
2. Methodology
Our over-all objective is to develop a simple, flexible model which can accurately describe the
broad characteristics of the spread of MPB outbreaks in time and space over both lodgepole
pine and jackpine landscapes. Our goal is to provide a better understanding of the interactions
between landscape structure and the dynamics of mountain beetle populations, particularly
during the eruptive phase. We hope to identify how landscape properties interact with
population dynamics to enable MPB to erupt to outbreak levels and the different scales at which
these processes are interacting. The model will also provide a tool to assess the susceptibility of
current and future landscapes to mountain pine beetle outbreaks and benchmarks for forest
management plans and decision support systems.
2.1 Model development
This model can be thought of as comprising 3 interacting components. The site (sub)model
describes the ecological mechanisms that affect the probability that a low density MPB
population can escape from its limiting factors and erupt within both a lodgepole pine and a
jackpine stand. The landscape structure (sub)model describes how pine stands are distributed
over the landscape of concern both in terms of their presence and in terms of the ecological
factors which determine the characteristics of their susceptibility to MPB. The dispersal
(sub)model describes how the insects leaving one stand are dispersed over the landscape and
can thus contribute to triggering eruptions in neighboring or more distant stands.
At the forest stand level, the dynamics are controlled by the interaction between a host pine
species stand model and a mountain pine beetle population dynamics model. At the landscape
level, the dynamics of the system emerge from interactions between stands and local MPB
populations through insect dispersal. The dynamics of the system also depend on the initial
characteristics of the landscape (i.e. heterogeneity, patch size, connectivity) and the evolution of
its structure according to forest management and natural disturbance scenarios. Ultimately, the
simulation models will be implemented in CAPSIS, a simulation platform developed at the
Institut National de la Recherche Agronomique (France) to study the dynamics of forest
ecosystems.
3. Results and Discussion
This paper focuses on the development of the site (sub)model. Because previous research
(Carroll et al. 2004) showed that the stand-level dynamics of MPB populations can be well-
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.