Introduction

In 2003, 5 general areas were identified as concerns to healthy forests in the United States—wildfires, non-native invasive insects and pathogens, invasive plant species, outbreaks of native insects, and changing ecological processes (USDA-FS 2003). Eastern forests in the United States have been subject to unprecedented threat due to invasion by forest pests (Brockerhoff and others 2006, Liebhold and others 1995, Lovett and others 2006) that threaten extinction of host species, engineer fragmented landscapes, and add to fuel loads, which increase risk of wildland fires. Disturbances exert a strong influence on forest structure, composition, and diversity (Connell 1978, Huston 1994, White 1979). However, different types of disturbance have different consequences for vegetation. Surface fires, for example, primarily kill small trees and spare the larger individuals (Abrams 2003, Frelich 2002), often slowing the rate of successional replacement. Canopy disturbances such as insect outbreaks primarily damage larger trees and may accelerate the process of succession (Abrams and Scott 1989, Frelich 2002, Lafon and Kutac 2003, Veblen and others 1989).

Stohlgran and Schnase (2006) suggest that risk analysis techniques, including simulation modeling, that are often used in the assessment of health risks and other hazards, are not only applicable to invasive species, but are needed. Forest managers have been increasingly integrating stand-level forecasting tools, such as the Forest Vegetation Simulator (FVS), in the forest decision-making process (Dixon 2002). More recently, landscape models that operate at a scale of 100s to 1000s of km² have begun to be evaluated for use in forest management, (e.g., Shifley and others 2000).

LANDIS (Mladenoff and He 1999) is a simulation modeling environment developed to predict forest landscape change over time. It is a spatially explicit landscape-scale ecological simulation model that incorporates both natural (fire, wind, and biological disturbance) and anthropogenic disturbance (harvesting). LANDIS has been adapted for use in a variety of forest management applications. Examples of applications relevant to this study include He and others (2002b) (forest harvesting and fire disturbance), Akcakaya (2001) (risk assessment and landscape habitat models), Shifley and others (2000), Mehtaa and others (2004) (landscape change and management practices), and Gustafson and others (2000) (forest succession and harvesting).

Landscape models offer the unique ability to assess forest process and pattern over broad spatial and temporal scales. Forest managers increasingly need to implement management strategies that incorporate forest sustainability, ecological restoration, wildlife habitat viability, recreational opportunities, and scenic value. Many of these concerns involve broad spatial and temporal scales. The objective of this study is to demonstrate the effectiveness of using LANDIS for forest threat assessment and restoration. To illustrate this, we examine one non-native invasive insect, hemlock woolly adelgid (HWA) (Aldelges tsugae Annand (Homoptera: Adelgidae)) and one indigenous invasive insect, southern pine beetle (SPB) (Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae)). Both insects currently threaten tree species within the Southern Appalachian Mountains of Eastern North America. In this analysis, we present initial results from our work with LANDIS 4.0 and present a framework for using LANDIS II, which will help evaluate the potential impacts of existing and future multiple interacting forest threats in eastern forests.