Introduction

Motivation and Scope

Changes in forest management and decades of fire suppression have resulted in drastically increased live and dead fuel loads in many western forests when compared to the time before the euroamerican settlement. When subject to ignition, these dense forests can propagate catastrophic fires over large areas. Due to the high fireline intensity, suppression is often difficult or impossible, and stand-replacing fires are often the consequence.

There are several ways to address the problem of high fuel loads. The null variant, i.e. waiting for nature to correct the problem with fires, is often judged unacceptable because of the disastrous extents these fires can reach. Prescribed or controlled burns that mimic the historic fire regime and aim at eliminating or reducing ground fuels are limited in their use due to pollution issues, risk of fires escaping and high cost per unit treated.

An alternative approach to reduce fuel loads is the mechanical modification or removal of flammable material. Modification aims at accelerating decomposition of fuels by increasing their surface-to-volume ratio and placing them close to the ground. A common way of fuel modification is mastication and subsequent redistribution in the stand. Modification is way of treating fuels that affects the fire risk in the short to medium time range.

Removal is a fuel treatment that immediately affects the fire risk within a stand and that can be used in virtually all conditions, since it does not result in air pollution or escaping fires. It is generally performed as a thinning that modifies the stand structure in a way that slows down or prevents propagation of fires. The product of the intervention are often large amounts of wood of various sizes, but often with a high ratio of biomass that is considered unmerchantable according to current timber market standards. The need to extract this material from the stand area in order to reduce fuel loads led to the search for new ways of utilizing biomass in the region where it is produced.

The present study examines the potential of using parts of the biomass for energetic purposes such as ethanol production or (co)generation of electricity in power plants. It does not address other fuel treatments than mechanical removal, and it does also not explicitly address other forest management aspects besides reduction of fire risk. The study is sponsored by the Department of Energy within the framework of the Bioenergy Feedstock Development Program hosted by Oak Ridge National Laboratory. Any conclusions drawn by third parties from the results presented here are not necessarily endorsed by the author or sponsor of the study.

Objectives

The study has three objectives

1. Examine silvicultural approaches that could be used to perform fuel treatments and evaluate their consequences for the long-term (100 years and more) stand structure development.
2. Provide a methodological framework for planning and simulating fuel treatments and evaluate and illustrate their effects based on currently available data and technologies.
3. Provide estimates for the long-term flow of biomass and wood products resulting from a potential implementation of the fuel treatment concepts developed.

The focus of the study is on developing a methodological framework for assessing the long-term supply of biomass for energy purposes under the assumption of a given forest management concept that includes fuel treatments such as presented below. Although some of the products and results of the study may be used to support decision-making, they are not to be considered decision criteria or as a planning methodology of their own. The issue of fuel treatments needs to be integrated into a broader policy of forest management, and typically, such a policy would have goals set on a strategic level. The framework developed within the study assumes that compliance with the following strategic goals is required (i.e. no silvicultural concept, technology etc. may be selected that jeopardizes one of these goals):

• Improving the disturbance resilience of the forest with regard to different impacts
• Maximize the productivity of the forest (non-timber products and services as well as timber products)
• Maximizing the adaptive potential of the forests in view of future changes in demands

It is important that this assumption is kept in mind when the fuel treatment prescriptions are developed. The management guidelines derived from these strategic goals may very well contradict other guidelines currently in place (e.g. for habitat protection), and it is a political process to sort out these differences.

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