Estimation of temporal variations in fire frequency from time-since-fire data
Date
2010-01-08T22:12:55Z
Authors
Reed, W.J.
Larsen, C.P.S.
Johnson, E.A.
MacDonald, G.M.
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Abstract
This paper introduces a method to estimate the fire frequency in a number of different temporal periods (epochs) and to assess whether these fire frequencies differ significantly. The method is applicable to time-since-fire maps, and unlike previous methods, includes the different hazards of burning to which a unit has been subject since its establishment. Maximum likelihood estimates of the fire frequencies are obtained, and likelihood ratio methods are used to obtain confidence intervals and to test the significance of postulated change points. The test is not strictly valid for change points suggested from exploratory data analysis and assumes that a change point to be tested is selected with prior reference to the data. The model used assumes that the hazard of burning does not depend on age or location, although it includes a contagion effect modelled by the inclusion of an overdispersion parameter, and the construction of a quasi log-likelihood function. The method is applied to published fire history data from the Kananaskis Valley. The results indicate that, as was to be expected, previous analyses have overestimated the fire frequency for the most recent epoch.
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Keywords
change point, disturbance, fire cycle, fire frequency, fire history, quasi-likelihood, maximum likelihood, overdisperion, contagion effect, technical reports (mathematics and statistics)