UNDERSTANDING THE INFLUENCE OF LANDSCAPE STRUCTURE ON FIRE HISTORY

INIGUEZ, J. (1,2), SWETNAM, T. (1), BAISAN, C. (1)

(1) Laboratory of Tree Ring Research, (2) Rocky Mountain Research Station, Flagstaff Lab.

It is widely understood that dry climatic years cause large fires. However, during other non-drought periods other factors are important in determining fire extent. The objective of this research was to study the influence of landscape structure and time since last fire on historic fires. The study was conducted in the Santa Catalina Mountains of southeastern Arizona where fire histories were reconstructed and compared between relatively heterogeneous and homogenous landscapes defined by biotic (vegetation) and abiotic (topography) factors. A total of 40 1-hactare fire history plots were stratified by aspect classes in the two study areas. The results show slight differences in mean fire interval (MFI) between aspect or slope classes. At the landscape level, fires recorded by two or more plots occurred every 5-6 years on each of the two landscapes. However, the MFI for larger fires (scarring >50% of the recording plots) was 20 years in the heterogeneous landscape and 10 years in the homogenous landscape. Similarly when fires occurred, they were typically smaller in the heterogeneous landscape scarring an average of 32% of recording plots whereas in the homogenous landscape the average fire scarred 45% of plots. At the stand level, the MFI for plots within the heterogeneous landscape tended to be longer and more skewed by longer intervals than in the homogenous landscape. Results also show that within the homogenous landscape the length of the fire interval was important, explaining half of the variability in fire size.