Comparison of different methods for the in situ measurement of forest litter moisture content

Abstract

Abstract. Dead fine fuel (e.g., litter) moisture content is an important parameter for both forest fire and ecological applications as it is related to ignitability, fire behavior and soil respiration. Real-time availability of this value would thus be a great benefit to fire risk management and prevention. However, the comprehensive literature review in this paper shows that there is no easy-to-use method for automated measurements available. This study investigates the applicability of four different sensor types (permittivity and electrical resistance measuring principles) for this measurement. Comparisons were made to manual gravimetric reference measurements carried out almost daily for one fire season and overall agreement was good (highly significant correlations with 0.792 < = r < = 0.947, p < 0.001). Standard deviations within sensor types were linearly correlated to daily sensor mean values; however, above a certain threshold they became irregular, which may be linked to exceedance of the working ranges. Thus, measurements with irregular standard deviations were considered unusable and relationships between gravimetric and automatic measurements of all individual sensors were compared only for useable periods. A large drift in these relationships became obvious from drought to drought period. This drift may be related to installation effects or settling and decomposition of the litter layer throughout the fire season. Because of the drift and the in situ calibration necessary, it cannot be recommended to use the methods presented here for monitoring purposes and thus operational hazard management. However, they may be interesting for scientific studies when some manual fuel moisture measurements are made anyway. Additionally, a number of potential methodological improvements are suggested.

Preliminary results of statistical analysis focused on the dependence between forest litter moisture and relative air humidity

“…The research in this field is more oriented to finding the methods to automate the process of its measurement (Schunk et al 2016), or to model the fine fuel (also forest litter) moisture (Viney 1991;Schaap et al 1997;Ogee, Brunet 2002).…”

A New Passive Microwave Tool for Operational Forest Fires Detection: A Case Study of Siberia in 2019

“…Finder detects spatial pixels with very severe fire hazards stored in holder's memory. The decision maker analyzes the input data from the holder and resolves the origin of these pixels from the signal (abnormal) or from the noise (background) [43,44]. As a result, an SDMP block based on this data makes a final decision about the pixel state.…”

Corrigendum to: Estimation of surface dead fine fuel moisture using automated fuel moisture sticks across a range of forests worldwide

“…Alternatively, the Speedy Moisture Meter (Dexter and Williams 1976) or Wiltronics T-H Fine Fuel Moisture Meter (Chatto and Tolhurst 1997) can be used to obtain instantaneous measurements in any location but also require manual measurement. Soil moisture sensors have been trialled to continuously and automatically measure surface dead FFMC, but with mixed success (Condera et al 2012;Wilson et al 2014;Nyman et al 2015;Schunk et al 2016). This approach is under experimentation and cannot currently be used in operational fire management.…”