Vent d'Autan

The Sierra San Pedro Mártir (SSPM) is a mountain range in the northern portion of the Baja California peninsula in Mexico. The forest on the SSPM appears simple, dominated by Pinus jeffreyi and other conifers. Its understory is mostly sparse, with ample space between the large, thick-barked pines. Being used to find dense vegetation in natural landscapes, I was curious to understand the processes that keep this forest spacious and healthy. Surprisingly, the thing that keeps this forest functioning is something normally thought of as detrimental — fire. In the SSPM fire suppression threatens the forest and regional ecological cycles. 

As in other parts of Mexico, Baja California sits on a transition zone where vegetations of different origins meet. But unlike the rest of Mexico, where summer rains are the norm, parts of Baja California present a Mediterranean climate, characterized by winter precipitation and mostly dry summers. “In California’s Mediterranean climate, decomposition of organic matter proceeds slowly because temperatures are too low for microbial activity when moisture is available in winter. Thus, fuel tends to accumulate because the vegetation itself produces more organic matter than is decomposed” (Minnich & Vizcaíno, 2002). 

The accumulation of fuel under such environmental conditions has led to the emergence of fire as the main recycler of matter in this ecosystem. “The SSPM is unique within the California floristic province in that its forests are still influenced by lighting-ignited fires…” (Stephens, 2004). “Almost any afternoon during summer there are a few smokes that can be seen in the distance” (Minnich & Vizcaíno, 2002). “Summers are dry except for afternoon thunderstorms of the North American monsoon” (Minnich et al., 2000). The influence of the North American Monsoon System on the Mediterranean Climate of the SSPM is also evident on the location of most fire scars within the annual growth mark on tree core samples, which correspond to late spring and middle summer (Stephens et al. 2003 & 2010). 

For understanding the SSPM and reconstructing fire histories, some researchers have preferred dendrochronology while others have used aerial photography. I believe both approaches provide useful insights. In a dendrochronology study, spatially larger fires were found to occur on particularly dry years and were commonly “preceded by significantly higher precipitation 1 year before the fire” (Stephens et al., 2003). 

A study utilizing repeat aerial photography found strong evidence that the natural fire regime in the SSPM consists “of relatively high intensity surface fires that denude surface litter, shrubs, saplings, and pole-size stems.” And after a local intense fire, “the thicket matures, [and] subsequent low intensity fires selectively thin it into an old-growth, low density patch” (Minnich et al., 2000). While the specifics of this explanation are debatable, there is no question on the essential role wildfires play in maintaining this forest healthy and resilient. 

It has been recognized that the SSPM, “offers a unique opportunity to assess the influence of fire suppression” (Savage, 2000). This is because “Limited fire suppression began in the mid-1970s” (Stephens, 2003), in contrast to the extensive fire control implemented in forests north of the Mexico-U.S. border.  

In other western North America forests “fire exclusion caused tree infilling… resulting in substantially denser forests with continuous layered canopies… high surface fuel loads and fuel ladders connecting surface to crown fuels” (Prichard et al., 2021). This is why fire suppression has been called the ‘firefighting trap’ as it “contributes to ongoing fuel accumulation and landscape-level fuel continuity, which then precludes suppression under extreme fire weather, and results in more severe and usually larger fires” (Moreira et al., 2020). 

North of the international border, “Fire policy failed to recognize that in this Mediterranean type climate… periodic fire was necessary for the maintenance of plant communities” (Minnich & Vizcaíno, 2002). As recently cited, “’The seven largest fires by acreage in California history all occurred within the last six years,’ said Carroll Wills, senior communication advisor at California Professional Firefighters. ‘On that basis alone, you can quantify the degree to which recent conditions have contributed to the fire problem’” (Kim, 2023). 

The policies in place might see a success preventing fires, but ecologists are sure this is a misunderstanding of natural cycles. “‘Success’… measured as reduced area of land burned in any given year… [will] be failure in the long term, as EWEs [extreme wildfire events] are merely postponed” (Moreira et al., 2020). But unfortunately, sound policies can take a while to be adopted. “Despite calls to restore fire as a cultural and ecological process… the dominant approach to wildfire management continues to be aggressive suppression” (Prichard et al., 2021). 

The premonition that “Large and catastrophic fires may result if fire suppression is instituted” (Minnich et al. 1997), has been pointed out for decades in discussions about how to best manage the SSPM (Stephens et al., 2003; Safford, in Harper et al., 2021). “Continued disregard for the long-term implications of strict fire exclusion and mounting forest fuels in the SSPMNP [Sierra San Pedro Mártir National Park] will likely result in large areas of forest loss in the future” (Rivera-Huerta et al., 2016). 

But while the exact solutions still seem unclear, there are promising approaches to conserving these forests more effectively. Prichard et al. (2021) maintain that “an intentional merging of Indigenous and western knowledge is needed to guide future forest conditions and restore active fire regimes to wNA [western North America] forests.” 

As well as reducing damage, a more sympathetic approach to fire management could save money. Minnich et al. (1997) point that in the SSPM “an unmanaged fire regime will result in forests and chaparral that require much less funding to manage,” adding that fire control should be exclusively implemented in areas adjacent to resources such as the astronomical observatory. 

The resources that are currently allocated to combat wildfires could be used to further investigate these unique mountains of Mexico. Wildland firefighters would no longer have to be fighting in vain, and their time, skills and knowledge of the land could be applied to projects that help better understand and conserve this outstanding ecosystem. 

The SSPM is where most rainfall and infiltration take place in the state of Baja California, playing a key role in replenishing the aquifers on which the state’s economy depends (CONANP, 2006). The SSPM is also home to many endemic species that would be irreversibly disturbed if massive fires become the new regime in the SSPM. There is a better way of conserving the SSPM and all of the benefits it provides. 

References

CONANP (2006). Programa de Conservación y Manejo Parque Nacional Sierra de San Pedro Mártir. México.

Delgadillo, J. (2022). La flora y vegetación mediterránea de México [Youtube video]. Sociedad Botánica Méxicana. https://www.youtube.com/watch?v=ZjZ7MzIdt3M

Kim, M. (2023). Illuminating Wildfire Risk. Optics & Photonics News. https://www.optica-opn.org/home/articles/volume_34/september_2023/features/illuminating_wildfire_risk/

Minnich, R. A., Barbour, M. G., Burk, J. H., & Sosa‐Ramirez, J. (2000). Californian mixed‐conifer forests under unmanaged fire regimes in the Sierra San Pedro Mártir, Baja California, Mexico. Journal of Biogeography, 27(1), 105-129.

Minnich, R. A., & Franco-Vizcaíno, E. (2002). Divergence in Californian vegetation and fire regimes induced by differences in fire management across the US-Mexico boundary. Both sides of the border: Transboundary environmental management issues facing Mexico and the United States, 385-402.

Minnich, R. A., Franco-Vizcaíno, E., Sosa-Ramírez, J., Burk, J. H., Barry, W. J., Barbour, M. G., & de la Cueva-Salcedo, H. (1997). A land above: protecting Baja California’s Sierra San Pedro Mártir within a biosphere reserve. Journal of the Southwest, 613-695.

Moreira, F., Ascoli, D., Safford, H., Adams, M. A., Moreno, J. M., Pereira, J. M., … & Fernandes, P. M. (2020). Wildfire management in Mediterranean-type regions: paradigm change needed. Environmental Research Letters, 15(1), 011001.

Prichard, S. J., Hessburg, P. F., Hagmann, R. K., Povak, N. A., Dobrowski, S. Z., Hurteau, M. D., … & Khatri‐Chhetri, P. (2021). Adapting western North American forests to climate change and wildfires: 10 common questions. Ecological Applications, 31(8), e02433.

Rivera-Huerta, H., Safford, H. D., & Miller, J. D. (2016). Patterns and trends in burned area and fire severity from 1984 to 2010 in the Sierra de San Pedro Mártir, Baja California, Mexico. Fire Ecology, 12(1), 52-72.

Safford, H. (2021). Forest Fires & Conservation [Youtube video]. Conservation Careers. https://youtu.be/-MXbRgoFcBA?si=8IQw8k4-G9tFtIZo

Savage, M. (2000). Fire Suppression and Drought Induced Mortality. 2nd Interface Between Ecology and Land Development in California, 97.

Cover image: Sierra San Pedro Mártir and Devils Peak, Southern Baja California, Mexico. Image: Jaime Sanchez Diaz (jsanchezd) / Wikimedia Commons.

Spanish Translation by Patrick Gibson