In water limited forests with frequent fire, it is hypothesized that fire related ecosystem fluxes may exceed water related fluxes. Because conventional sawlog harvesting primarily removes nutrient poor wood from the ecosystem, it may not have the same importance as fire to nutrient cycling, even through it can have similar effects on forest composition and age structure. We developed NuCycling-Succession, a nutrient cycling extension for the LANDIS-II landscape model of forest dynamics, to examine the influence of fire and biomass harvesting regimes on nutrient cycling at multiple spatial scales in the Lake Tahoe Basin. NuCycling-Succession represents the continuum of decomposition and associated changes in chemistry using annual cohorts of leaf and fine root litter. This formulation may provide a more realistic representation of decomposition dynamics and their interactions with disturbances that affect the forest floor, like fire, than that in most nutrient cycling models. Considering the dominance of fire-related nutrient cycling dynamics under particular environmental conditions, forest management that incorporates fire may more effectively reduce the masses of nutrient pools and restore nutrient cycling dynamics to their pre-settlement conditions than management based on biomass harvesting.

Forest landscape disturbances are a global phenomenon. Simulation models are an important tool in understanding these broad scale processes and exploring their effects on forest ecosystems. This book contains a collection of insights from a group of ecologists who address a variety of processes: physical disturbances such as drought, wind, and fire; biological disturbances such as defoliating insects and bark beetles; anthropogenic influences; interactions among disturbances; effects of climate change on disturbances; and the recovery of forest landscapes from disturbances—all from a simulation modeling perspective. These discussions and examples offer a broad synopsis of the state of this rapidly evolving subject.

The Interior Northwest Landscape Analysis System (INLAS) links a number of resource, disturbance, and landscape simulations models to examine the interactions of vegetative succession, management, and disturbance with policy goals. The effects of natural disturbance like wildfire, herbivory, forest insects and diseases, as well as specific management actions are included. The outputs from simulations illustrate potential changes in aquatic conditions and terrestrial habitat, potential for wood utilization, and socioeconomic opportunities. The 14 chapters of this document outline the current state of knowledge in each of the areas covered by the INLAS project and describe the objectives and organization of the project. The project explores ways to integrate the effects of natural disturbances and management into planning and policy analyses; illustrate potential conflicts among current policies, natural distrubances, and management activities; and explore the policy, economics, and ecological constraints associated with the application of effective fuel treatments on midscale landscapes in the interior Northwest.

Forest thinning is a management strategy that is being implemented in coniferous forests in the Lake Tahoe Basin in institutional efforts to decrease fire severity, protect property, and restore pre-settlement structure and composition to those forests. Contemporary forests in the Lake Tahoe Basin are denser, less structurally heterogeneous, and have accumulated more fire fuels as compared to historic forest conditions. While forest thinning efforts might be expected to benefit the ecosystem as a whole by returning the forest to more historic states, mixed effects might be expected on individual species that have distinct habitat requirements. Some species of small mammals, important components of conifer communities, may benefit from more open forests, while others may be adversely affected. To determine salient ecological effects associated with forest- thinning activities in the Lake Tahoe Basin, we analyzed the responses of three representative species of sciurids (squirrels and chipmunks). We assessed: (1) the responses of the species to the changes in vegetation following forest thinning, (2) the responses of the same species to disturbances caused by actual entry and cutting during forest thinning, and (3) the differences in the responses of two population characteristics exhibited by the species--density and annual turnover of individuals. A priori we expected: (a) a deleterious forest -thinning effect on northern flying squirrels ( Glaucomys sabrinus ), due to their arboreal nature and apparent preference for old growth forests; (b) a relatively neutral forest-thinning effect on long-eared chipmunks (Tamias quadrimaculats ), because they are semi-arboreal and found in both open and moderately dense forests; (c) a beneficial forest-thinning effect on golden-mantled ground squirrels (Spermophilus lateralis ), since they are terrestrial and found in open forests and forest edges. To assess responses of the three representative species to forest-thinning practices, we conducted a mark-recapture study of small mammals and vegetation surveys over five years. We created linear mixed effects models and used them to determine the correlations between vegetation characteristics, treatment, and population parameters for each species. We used annual turnover of individuals of each species as a proxy measure for survival and emigration after forest-thinning. Higher annual turnover of individuals indicated lower survival and higher emigration rates. We assumed higher densities and lower annual turnover of individuals indicated more stable and persistent populations. We found that none of the representative species were affected by forest thinning over the five year-period of the study despite significant decreases in shrub cover, canopy cover, small tree densities, medium-sized tree densities, and snag densities. It is possible that there are delayed treatment effects; therefore, continued monitoring is necessary. To avoid possible problems with using population density exclusively to determine small mammal responses to forest thinning, future small mammal monitoring projects should focus on population dynamics measured over multiple years.