Patterns and Trends in Burned Area and Fire Severity from 1984 to 2010 in the Sierra de San Pedro Mártir, Baja California, Mexico

Hiram Rivera-Huerta,Hugh D Safford,Jay D Miller

doi:10.4996/fireecology.1201052

Abstract

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 Martir 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 Martir 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.

Highlights

Studies of semi-arid forests in western North America show that, before the arrival of Europeans, fire was a common and important ecological process
Within the perimeter of the Sierra de San Pedro Mártir National Park, we identified 32 fires that burned an area of 26 529 ha in the period from1984 to 2010
All of the fires we identified started outside the park or in chaparral or herbaceous vegetation in the park’s lower southern region, and most entered yellow pine and mixed conifer (YPMC) forest areas under relatively severe fire weather conditions

Summary

Introduction

Studies of semi-arid forests in western North America show that, before the arrival of Europeans, fire was a common and important ecological process. Lawson], Jeffrey pine [P. jeffreyi Balf.]) and mixtures of these with other tree species burned on average every decade or two, with fires dominated by low severity effects (Agee 1993, Stephens et al 2003, Van de Water and Safford 2011). After they settled in California, USA, Euro-Americans began to extinguish light fires whenever and wherever possible, as it was thought that such fires damaged the forest and timber resources. Fire suppression practices in California were originally held as an example for other countries to follow (Stephens and Ruth 2005), but since the ecological consequences of the practice have begun to manifest themselves in more extensive and more severe forest fires, among other ecological problems (Miller et al 2009b, Miller and Safford 2012)

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