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Fire Ecology, 2016
Volume 12, Issue 1

Patterns and Trends in Burned Area and Fire Severity from 1984 to 2010 in the Sierra De San Pedro Mártir, Baja California, Mexico
Authors: Hiram Rivera-Huerta, Hugh D. Safford, and Jay D. Miller
Pages: 52-72
DOI: 10.4996/fireecology.1201052

Yellow pine (Pinus spp. L.) and mixed conifer (YPMC) forests of California, USA (Alta California), have been negatively affected since Euro-American settlement by a century or more of logging, fire exclusion, and other human activities.  The YPMC forests in northwestern Mexico (northern Baja California) are found in the same climate zone as those of Alta California and support mostly the same dominant species, yet they are much less degraded, having suffered little logging and only 30 years of fire suppression.  As such, the Baja California forests are believed to more closely approximate pre-Euro-American settlement conditions, and they have been proposed as reference ecosystems for restoration and management of Alta California forests.  We studied fire severity trends in the Sierra de San Pedro Mártir National Park (SSPMNP), which supports the largest area of YPMC forest in Baja California, to determine whether fire severity is rising over the last three decades in the same manner that it is rising in the Sierra Nevada of Alta California.  We used LANDSAT data to identify 32 fires that burned 26 529 ha in the Sierra de San Pedro Mártir National Park in the period 1984 to 2010.  Of this, 1993 ha burned in YPMC forest types in 17 fires.  We found no temporal trends in forest burned area or in the proportion of high severity fire, but we did find that the mean size of high severity patches within fires is rising.  In the SSPMNP, the overall proportion of fire area burned at high severity averaged 3 % in both yellow pine and mixed conifer forests.  We found no significant autoregressive effects of year in any of our analyses, but the year with the most burned area occurred after drier-than-average periods.  In the SSPMNP data, there was no correlation between burned area and proportion of high severity fire; we interpreted this to mean that differences in fuels in SSPMNP were more important to fire behavior than weather conditions.  The SSPMNP continues to burn at very low severities, even after 30 years of effective suppression of lightning-ignited fires.  This is in stark contrast to similar forests in Alta California, which are experiencing fires of sizes and severities that fall far outside the historical range of variation.  Current fire severities in the SSPMNP are very similar to the levels of severity described for Alta California YPMC forests before Euro-American settlement.  Nonetheless, fire suppression policies in Mexican national parks in northern Baja California are causing increases in forest fuels and may be the cause of recent increases in high severity patch size.  Current wildfire trends in YPMC forests in Alta California should serve as a warning to Mexican managers that continued fire exclusion in the Baja California YPMC forests is a recipe for ecological disaster in these unique and important ecosystems.

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