Mexican woods offer a look at California forests’ past

August 24, 2005

by UC Division of Agriculture & Natural Resources

A largely unmanaged forest in Mexico holds lessons for improving the health of California wildlands, according to UC Berkeley fire science professor Scott Stephens.

His twice yearly research expeditions to the unspoiled Sierra de San Pedro Martir have convinced him that the forest management plans in California should be revised to improve the ecosystem’s resilience to insects, diseases, drought and catastrophic fires.

For seven years, Stephens has studied the Jeffrey Pine-mixed conifer forests in the mountainous national park of Baja California, named after the Christian martyr St. Peter. The mountain range is connected to the Laguna and San Jacinto Mountains of southwest California. The flora and fauna are similar to Southern California and eastern Sierra Nevada forests. The greatest difference is the time of the forests’ fire seasons. The majority of fires occur in summer in the Mexican forests, but fires are more common in California forests in the late summer and fall.

“When you are over there, with all the familiar shrubs and soils and trees, sometimes you have to remind yourself you’re in Mexico,” Stephens said.

A large portion of the 100,000-acre Mexican forest has never been harvested and has survived through centuries of natural fire cycles, making it a living example of what many California forests would be without the exploitive logging practices of earlier generations, fragmentation by development and disruption of natural fire cycles.

Fires burned naturally in Sierra San Pedro Martir

Until 1970, there was no fire suppression at all in the Sierra de San Pedro Martir. Today, only eight people are assigned to put out blazes by going in when smoke is spotted and cutting a line around the fire. In contrast, most California forest fires are managed aggressively with armies of firefighters, sophisticated equipment, helicopters and air tankers.

Vacation homes, developed camp grounds, lavish lodges, museums and shopping centers are not to be found in Mexico’s Martir. In California, many mountain areas have become populous tourist destinations. Twelve thousand people live in the vicinity of Big Bear Lake, where a local Web site,, claims there are more Mexican restaurants per capita than in the average Baja peninsula city. The population at Mammoth Lakes, on the eastern side of the Sierra Nevada Mountain Range, is nearly 8,000 year round. The average cabin in Lake Arrowhead, known locally as the Alps of Southern California, costs more than $200,000.

Another influence on current California forest ecosystem is historical timber harvesting practices. Some 125 years ago, California and Nevada pioneers began logging the eastern Sierra Nevada and the San Jacinto, San Bernardino and Laguna mountains for mining and development.

“In the late 19th century, most of the trees in the eastern Sierra Nevada were used to support silver mining,” Stephens said. “The logging that took place before early Californians understood sustainable timber harvest practices created huge disturbances in the forest ecosystems that still affect those forests today.”

Differences are profound

The differences Stephens and his staff have seen in the never-touched and frequently burned Mexican forests compared to California’s fire-suppressed and highly developed forests, Stephens said, are striking.

For example, in the early 2000s, following a few years of drought, the Southern California mountain landscape was dominated by dead trees, which had succumbed to native bark beetle attacks. The Mexican mountains experienced the same drought, but many more trees were able to survive the bark beetle onslaught. Further, in 2003, a 10,000-acre wildfire took place in the Mexican range.

“We’ve been working in that wildfire area,” Stephens said. “Even though the trees were incredibly stressed by drought, less than 4 percent of the over story trees are dying. At the end of the drought in California, even without the fire, many more trees were dead. Martir has resiliency that we don’t see anywhere in California.”

Stephens attributes the resiliency to the Mexican forest’s diversity. When Stephens and his staff surveyed the forest, they were able to calculate average numbers of dead snags, old-growth trees, saplings and downed wood on the forest floor over large areas, but individual plots reflect this average only 10 percent to 15 percent of the time.

“That means in 85 percent of the area, there is tremendous variation in the forest makeup,” Stephens said. “But what we’re doing in the United States is actively managing forests for average conditions and what we’re getting is a giant carpet of trees. When all the forest areas are the same, fires, disease and insects can more easily move through entire stands.”

Diversity breeds resilience

The effects of relatively frequent, lower intensity fire found in the Martir are variable and patchy forests. When later threats encounter patches and spaces, the forests have a greater ability to survive.

Based on his research in Mexico, Stephens said he believes the approach taken in the United States in forest management must be changed. He suggests greater forest diversity can be achieved by giving greater latitude to “on the ground” forest managers, allowing them to be creative rather than strictly adhering to per-acre management plans.

“They can go in and try some things to break up the homogeneity,” Stephens said.

Stephens’ forest studies are funded in large part by the UC Agricultural Experiment Station, an organization of researchers on the Riverside, Davis and Berkeley campuses affiliated with the UC Division of Agriculture and Natural Resources. Stephens’ next trip to the forests of Sierra de San Pedro Martir is scheduled for October.