Comparison of three devices for estimating fire temperatures in ecological studies

Questions: Are calorimeters and pyrometers accurate and reliable for describing fire parameters in large-scale ecological projects, and can data from them predict data derived from thermocouples? Do mechanical pre-treatments in Florida scrub areas alter fire properties? Location: Lake Wales Ridge, Florida, USA. Methods: We deployed thermocouples attached to digital dataloggers, copper and lacquer paint pyrometers and aluminium can calorimeters filled with water in four areas of undisturbed Florida scrub and sandhill vegetation and in adjoining areas pre-treated with logging, subcanopy felling or mowing. Individual dataloggers were positioned in areas spanning a range of vegetation structure; three calorimeters and three pyrometers were placed with each thermocouple. We also deployed individual calorimeter-pyrometer pairs. Sites were burned, after which we compared methods for characterizing fire, particularly the ability of pyrometers and calorimeters to predict values derived from thermocouples. Results: Pyrometers best predicted peak 1-minute mean temperatures and were least successful at estimating maximums. Calorimeters were associated with the number of minutes maximum temperatures exceeded 60 °C, but were damaged at high residence times and inconsistent at low temperatures. Both pyrometers and calorimeters detected site and treatment differences in fire intensities. These analyses and logistic considerations give pyrometers an edge over calorimeters in situations where dataloggers are impractical. Mechanical pre-treatments to fire altered fire parameters. Mowing reduced fire temperatures but had different effects on areas burned; this was related to the length of time elapsed between mowing and burning. Subcanopy felling increased both fire coverage and temperatures. Conclusion: Pyrometers outperformed calorimeters as a cheap method for describing relative temperature regimes that are a function of both temperature and residence time. Pyrometers were able to demonstrate how mechanical treatments applied prior to prescribed burning altered fire parameters. Pyrometers are a useful tool for investigating biological responses to fire at multiple scales and in heterogeneous vegetation.