Elizabeth Reinhardt¹, Robert Keane¹, Joe Scott

 ¹USDA Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory

INTRODUCTION

This study will develop, evaluate, and compare methods or approaches to measure crown fuels and incorporate the crown fuel information into landscape-scale land use and planning processes. In particular, we will develop and test techniques for canopy fuel data collection using a wide variety of methods that will eventually be implemented into fire management. First, we will destructively sample all canopy biomass by crown fuel components using standard biomass sampling techniques harvesting trees at four cutting entries. Prior to each cut, we will estimate several crown fuel characteristics using five indirect methods (LAI-2000, CID-PCA, Ceptometer, Spherical Densiometer, Hemispherical Photography). We will also conduct a standard timber inventory on the sampled stand so that we can develop and verify a consistent method for inventorying canopy fuels that can be used across agency boundaries. The inventory method will allow managers to more accurately assess the effects of fuel treatments on canopy fuel characteristics and expected fire behavior. We will also establish a consistent procedure for canopy fuel characterization. Products of this research will be of direct and immediate benefit to wildland managers in federal agencies for mapping fuels, assessing hazard and risk, designing hazard mitigation treatments, and simulating fire behavior and effects. A consistent method of characterizing canopy fuels is particularly important in landscape-level planning projects that cross administrative or ecological boundaries.

GOALS and OBJECTIVES

• Develop and test alternate indirect methods (timber inventory and LAI measurement) of quantifying canopy fuels against direct measurement (destructive sampling)
• Document the vertical, horizontal, and size-class distribution of canopy fuels for several sample stands
• Document the effects of several levels of treatment on canopy fuels
• Develop a canopy fuels photo guide to help wildland managers "develop and eye" for canopy fuels
• Create a computer program so that fire managers and silviculturists can calculate important crown fuel characteristics to evaluate impacts of potential treatments on canopy fuels

STUDY PLAN

Introduction

Crown fire is now a chief concern among many forest managers in the western US and Canada because they have increased in frequency, intensity and size in many areas (Mutch et al. 1993, Arno and Brown 1988). Compared to surface fires, crown fires are responsible for many more burned acres, more smoke per acre, greater and longer lasting ecological damage (i.e. higher severity), greater threats to firefighter and public safety and increased risk of property and structure loss. Research over the last two decades has identified four canopy characteristics that significantly affect the incidence of crowning. The crown base height (height of the bottom of the live crown from the ground surface), crown bulk density (mass per unit volume of combustible crown biomass, including foliage, twigs and branches), stand height (average height of the dominant tree strata in a stand) and canopy closure (percent vertically projected canopy cover in the stand). A number of fire models and computer-based fire modeling systems require estimates of these canopy fuel characteristics to accurately simulate crown fires.
The goal of this research is a comprehensive description of crown fuel characteristics for fire management. This study is a two-pronged effort to measure the crown fuel characteristics germane to fire modeling using the (1) simple and easy measurements of standard forest inventory measurement techniques and (2) leaf area measurement equipment.

Methods

We measured canopy fuels exhaustively on a single fixed-radius plot at each of five study sites in the Interior West, each in a different conifer forest type. Each branch on each tree was measured and weighed, and a subset of branches were sorted by size class and ovendried. We conducted the sampling in stages, beginning with the smallest diameter trees in each plot and working toward the larger diameter trees. Before sampling and after 25, 50 and 75 percent of the basal area was removed we photographed the stand (using both stereo and hemispherical photography), and used several optical sensors to estimate gap fraction and leaf area index. This method provided estimates of canopy fuel characteristics as if the stand had received thinning from below treatments of increasing intensity.

A stereo-photoguide (Scott and Reinhardt,2005) allows managers to estimate canopy fuels visually. Methods have also been published (Keane and others, 2005, Reinhardt and others, 2006) to estimate canopy fuels from optical data and from stand data.

Results and Application: This study has developed methods used to map canopy fuels, model crown fire occurrence and behavior, and evaluate effectiveness of fuel treatments designed to reduce crown fire hazard. The methods have been used in LANDFIRE (a national interagency fuel mapping project), FFE-FVS (the Fire and Fuels Extension to the Forest Vegetation Simulator), and site-specific as well as regional analyses of crown fuel hazard and fuel treatment strategies.

Sampling in Stages

To expand the range of canopy conditions for this study, we removed a fixed amount of basal area from the stand in three separate cuts to provide estimates of four different stand structures or closures. We will remove approximately 25 percent of the basal area in three harvest entries to vary crown density and distribution conditions. The first cut will bring the stand to 75 percent basal area, then the second to 50 percent, then 25 percent. The last 25 percent basal area will be left on the stump. This cutting technique will provide us with four crown fuel conditions (100%, 75%, 50%, 25%).

Percent of Original Basal Area

Coconino National Forest 7 mi NW of Flagstaff, AZ

100% 75% 50% 25%

Digital hemispherical photographs Lolo National Forest 40 mi W of Missoula, MT

100% 75% 50% 25%