Publisher Summary This chapter reviews the rates at which Coarse Woody Debris (CWD) is added and removed from ecosystems, the biomass found in streams and forests, and many functions that CWD serves. CWD is an important component of temperate stream and forest ecosystems and is added to the ecosystem by numerous mechanisms, including wind, fire, insect attack, pathogens, competition, and geomorphic processes. Many factors control the rate at which CWD decomposes, including temperature, moisture, the internal gas composition of CWD, substrate quality, the size of the CWD, and the types of organisms involved. The mass of CWD in an ecosystem ideally represents the balance between addition and loss. In reality, slow decomposition rates and erratic variations in input of CWD cause the CWD mass to deviate markedly from steady-state projections. Many differences correspond to forest type, with deciduous-dominated systems having generally lower biomass than conifer-dominated systems. Stream size also influences CWD mass in lotic ecosystems, while successional stage dramatically influences CWD mass in boat aquatic and terrestrial settings. This chapter reviews many of these functions and concludes that CWD is an important functional component of stream and forest ecosystems. Better scientific understanding of these functions and the natural factors influencing CWD dynamics should lead to more enlightened management practices.

Ecology of Coarse Woody Debris in Temperate Ecosystems

Increased forest fire activity across the western continental United States (US) in recent decades has likely been enabled by a number of factors, including the legacy of fire suppression and human settlement, natural climate variability, and human-caused climate change. We use modeled climate projections to estimate the contribution of anthropogenic climate change to observed increases in eight fuel aridity metrics and forest fire area across the western United States. Anthropogenic increases in temperature and vapor pressure deficit significantly enhanced fuel aridity across western US forests over the past several decades and, during 2000–2015, contributed to 75% more forested area experiencing high (>1 σ) fire-season fuel aridity and an average of nine additional days per year of high fire potential. Anthropogenic climate change accounted for ∼55% of observed increases in fuel aridity from 1979 to 2015 across western US forests, highlighting both anthropogenic climate change and natural climate variability as important contributors to increased wildfire potential in recent decades. We estimate that human-caused climate change contributed to an additional 4.2 million ha of forest fire area during 1984–2015, nearly doubling the forest fire area expected in its absence. Natural climate variability will continue to alternate between modulating and compounding anthropogenic increases in fuel aridity, but anthropogenic climate change has emerged as a driver of increased forest fire activity and should continue to do so while fuels are not limiting.

https://www.pnas.org/content/pnas/113/42/11770.full.pdf

Impact of anthropogenic climate change on wildfire across western US forests

Several recent papers have suggested replacing the terminology of fire intensity and fire severity. Part of the problem with fire intensity is that it is sometimes used incorrectly to describe fire effects, when in fact it is justifiably restricted to measures of energy output. Increasingly, the term has created confusion because some authors have restricted its usage to a single measure of energy output referred to as fireline intensity. This metric is most useful in understanding fire behavior in forests, but is too narrow to fully capture the multitude of ways fire energy affects ecosystems. Fire intensity represents the energy released during various phases of a fire, and different metrics such as reaction intensity, fireline intensity, temperature, heating duration and radiant energy are useful for different purposes. Fire severity, and the related term burn severity, have created considerable confusion because of recent changes in their usage. Some authors have justified this by contending that fire severity is defined broadly as ecosystem impacts from fire and thus is open to individual interpretation. However, empirical studies have defined fire severity operationally as the loss of or change in organic matter aboveground and belowground, although the precise metric varies with management needs. Confusion arises because fire or burn severity is sometimes defined so that it also includes ecosystem responses. Ecosystem responses include soil erosion, vegetation regeneration, restoration of community structure, faunal recolonization, and a plethora of related response variables. Although some ecosystem responses are correlated with measures of fire or burn severity, many important ecosystem processes have either not been demonstrated to be predicted by severity indices or have been shown in some vegetation types to be unrelated to severity. This is a critical issue because fire or burn severity are readily measurable parameters, both on the ground and with remote sensing, yet ecosystem responses are of most interest to resource managers.

/pdf/fire-intensity-fire-severity-and-burn-severity-a-brief-3f34ow4qed.pdf

Fire intensity, fire severity and burn severity: a brief review and suggested usage

/pdf/farsite-fire-area-simulator-model-development-and-evaluation-2fmdhe0wmn.pdf

FARSITE : Fire Area Simulator : model development and evaluation

https://www.fs.fed.us/psw/publications/skinner/psw_2005_skinner(agee)001.pdf

Basic principles of forest fuel reduction treatments

Development and structure of the Canadian Forest Fire Weather Index System

Some theory and observations are presented on the factors governing the start and spread of crown fire in conifer forests. Crown fires are classified in three ways according to the degree of depend...

Conditions for the start and spread of crown fire

The expected age-class structure of a forest dependent on random periodic fire for disturbance and renewal is derived and presented. It is simply the negative exponential distribution, well known i...

Age-class distribution and the forest fire cycle

Forest fire danger rating research in Canada was initiated by the federal government in 1925. Five different fire danger rating systems have been developed since that time, each with increasing universal applicability across Canada. The approach has been to build on previous danger rating systems in an evolutionary fashion and to use field experiments and empirical analysis extensively. The current system, the Canadian Forest Fire Danger Rating System (CFFDRS), has been under development by Forestry Canada since 1968. The first major subsystem of the CFFDRS, the Canadian Forest Fire Weather Index (FWI) System, provides numerical ratings of relative fire potential based solely on weather observations, and has been in use throughout Canada since 1970. The second major subsystem, the Canadian Forest Fire Behavior Prediction (FBP) System, accounts for variability in fire behavior among fuel types (predicting rate of spread, fuel consumption, and frontal fire intensity), was issued in interim form in 1984 with...

/pdf/canadian-forest-fire-danger-rating-system-an-overview-2sef8v5kx4.pdf

Canadian Forest Fire Danger Rating System: An Overview

This study investigates the impact of postulated greenhouse warming on the severity of the forest fire season in Canada. Using CO2 levels that are double those of the present (2 × CO2), simulation ...

C. E. Van Wagner

Papers

Development and structure of the Canadian Forest Fire Weather Index System

Conditions for the start and spread of crown fire

Age-class distribution and the forest fire cycle

Canadian Forest Fire Danger Rating System: An Overview

Climate change and wildfire in Canada