Estimates of fuel loadings in forest and rangeland ecosystems of the United States are critical for accurately predicting fire behavior and effects of alternative fuel and ecosystem restoration treatments.

Accurately measuring surface fuel loadings in the field is difficult because it requires a complex integration of several sampling methods designed for implementation at disparate scales. This study created a new fuel sampling method, called the photoload sampling technique, to quickly and accurately estimate loadings for six surface fuel components using downward-looking and oblique photographs depicting sequences of graduated fuel loadings by fuel component. The six components are the four size classes of downed dead woody (1 hour, 10 hour, 100 hour, 1000 hr), shrub, and herbaceous fuels. This technique involves visually comparing fuel conditions observed in the field with photoload sequences to estimate fuel loadings. Photoload sequences are a series of downward-looking and close-up oblique photographs depicting a sequence of graduated fuel loadings of synthetic fuelbeds for each of the six fuel components. This report presents a sampling protocol that uses the developed photoload sequences to estimate fuel loading in the field. The set of photoload sequences were developed for common fuel components of the northern Rocky Mountains of Montana, USA. A companion publication details the methods used to create the photoload sequences and presents a comprehensive evaluation of the technique using 29 participants across five sites in western Montana.

PRINCIPAL INVESTIGATOR

Robert E. Keane, Deputy Program Manager, Fire, Fuel, and Smoke Science (FFS); Research Ecologist; Director, Fire Modeling Institute (FMI)

Staff

Laurie Dickinson, Wayne Lynholm, Courtney Couch, Curtis Johnson, Daniel Covington, Kathy Gray

GOALS AND OBJECTIVES

This study had four distinct objectives that were linked together to ultimately deliver a method of estimating surface fuels using the photoload technique. These objectives were:

• Develop methods for producing photoload sequences (downward-looking photographs of synthetic fuelbeds depicting graduated loadings).
• Develop a set of photoload sequences for use in the northern Rocky Mountains for estimating fuel loadings of six major fuel components using photos of synthetic fuelbeds.
• Evaluate this technique by comparing estimates from a number of people with conditions actually measured on the ground.
• Develop a sampling protocol for estimating fuel loadings using the photoload sequences.

The photoload sampling procedure was designed to allow the user to sample fuels at a point, plot, and stand level so that the variability of fuel components can be captured at the appropriate spatial scale. The photoload sampling technique was also designed for fire managers and researchers to monitor and inventory fuels and the evaluators in this study reflect that audience (these protocols are also detailed in the companion report). And last, the photoload fuel loadings estimated from the field evaluation are compared to actual fuel loadings measured on the ground to provide an estimate of precision and accuracy of the photoload sampling method 

METHODS AND RESULTS

In summary, development of the photoload sequences involved 1) collecting the fuels to be photographed in the field and bringing them back to the laboratory to measure dry weights and densities, 2) constructing the fuelbeds in sequential series of increasing fuel loads for each component, 3) photographing these fuels on a stage in a studio, and 4) importing the digital photographs into software to create the photoload sequences. We evaluated the photoload technique on five sites on the Ninemile District of the Lolo National Forest in western Montana, USA selected to represent common stand types and fuel conditions in the northern Rocky Mountains. We also completed another study that compared five fuel sampling techniques that used these same sites. We used a set of nested plots to test the photoload sampling technique and also to collect actual loadings to evaluate the accuracy and consistency of the photoload method.

In general, visual estimates made using the photoload technique were reasonably accurate for most fuel components, especially when the experience of the sampler was high. Accuracy was highest when the fuel loadings were the lightest, probably because relative differences in observed and estimated values tended to be smaller when loadings were low. Most participants tended to underestimate loadings for nearly all fuel components except the fine fuels of 1 hour and herbaceous vegetation, and these underestimations got larger as the fuel loadings increased. Moreover, the variability of the estimations increased with fuel loading. This could have definitely been improved by a more intensive and improved training session. We believe the estimations would have been more accurate if we had previously measured actual fuel loadings on some demonstration microplots and used these demonstration microplots to calibrate the evaluator’s estimations. We also believe that the training should have involved an expert accompanying the novice to evaluate at least 10-15 microplots to ensure that the novice’s estimates have included all appropriate adjustments. Overall, the photoload sampling technique appears to be a viable means of estimating fuel loading for input into fire behavior and effects modeling. It performs quite well under many fuel conditions and the accuracy and precision of the estimates appears to improve with sampling experience. It appears to be a useful means of estimating fuel loadings of common surface fuel components. Users may tend to underestimate actual fuel loadings with the photoload sampling technique, but this can be corrected with abundant calibration exercises and extensive field experience.

FUNDING ORGANIZATIONS

This work was entirely supported by the Rocky Mountain Research Station Fire Fuels and Smoke Science Program.

PUBLICATIONS

Keane, R. E., and L. J. Dickinson. 2007. The Photoload sampling technique: estimating surface fuel loadings using downward looking photographs. General Technical Report RMRS-GTR-190, USDA Forest Service Rocky Mountain Research Station.

Keane, R. E., and L. J. Dickinson. 2007. Development and evaluation of the photoload sampling technique. Research Paper RMRS-RP-61CD, USDA Forest Service Rocky Mountain Research Station.

Sikkink, P., and R. E. Keane. 2008. A comparison of five sampling techniques to estimate surface fuel loading in montane forests. International Journal of Wildland Fire. 17:363-379.

Sikkink, P., R. E. Keane, and D. C. Lutes. 2009[in press]. A user's guide to fuel loading models. General Technical Report RMRS-GTR-XX, USDA Forest Service Rocky Mountain Research Station, Fort Collins, CO, USA.

Holley, Violet J.; Keane, Robert E. 2010. A visual training tool for the Photoload sampling technique. Gen. Tech. Rep. RMRS-GTR-242. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 235 p.