Climate Change and Fire Ecology of Valles Caldera - Preparing for the Future

Las Conchas Fire from State Route 4 in Valle Grande, June 27, 2011.

Courtesy of Jacquie Dewar

Human-caused climate warming and 20th-century forest management policies have led to dramatic changes in wildfire frequency and size, which in turn has impacted our forests’ ecosystem structure and functioning. Climate change drives wildfire frequency by raising temperatures, lowering relative humidity and increasing vapor pressure deficits, all of which contribute to lower forest fuel moisture, increased combustibility, and subsequent expansion of areas burned. Fire management policies over the last century, including the Forest Service’s “10 AM rule” (1935-1978) under which all forest fires were to be put out by 10 o’clock in the morning after ignition, allowed forest fuels to build up beyond historic levels.

Today, these massive fuel loads continue to feed extremely hot and fast-moving fires across large landscapes. Historically, forest fires burned unevenly and at varying intensities, leaving behind a mosaic of trees to supply seeds for natural forest regeneration; whereas, today’s fires burn ever-increasing areas with high-severity, stand-replacement outcomes. Recent examples in the Jemez Mountains include the Las Conchas (2011) and Thompson Ridge (2013) fires, both of which started with wind-blown trees hitting power lines on private land, but burned for weeks due to the difficulty in stopping the advancing flame fronts.

While policies for fire management have shifted away from “full suppression all the time,” climate warming continues to exacerbate fire behavior. Evidence for climate warming has been growing world-wide, and even our local weather stations corroborate the warming trend. Temperature data from the Village of Jemez Springs during 1914-2022 provide a nearly-exact match for climate model predictions. The Intergovernmental Panel on Climate Change (IPCC) predicted an increase of 1.8° F in northern New Mexico during the past 100 years, and our data show an increase of 1.82° F. We can anticipate a continued upward creep through the rest of the 21st century, although the rate of increase is still to be determined, dependent on human action to reduce atmospheric greenhouse gases.

Average annual temperatures in Jemez Springs, NM, during 1914-2022. Data from National Weather Service and National Park Service.

NPS/R. Parmenter

Given the climate warming record observed in Jemez Springs, are we seeing changes in forest fires here in the Jemez Mountains? Absolutely, yes, and the data tell the story. In the Jemez Mountains from 1909 to 2019 (111–year record), fire data from the US Forest Service and the National Park Service show an average of 68 forest fires per year (7,504 total fires!), of which 46/ year were caused by lightning, 17/year were ignited by humans, and 5/year were designated “cause unknown.” During the 20th century (1909-1999), the total area of forest burned each year averaged 1,179 acres (less than two square miles per year). Since that time (2000- 2019), the annual burned area has jumped in size to 17,720 acres (over 27 square miles per year), a 15-fold increase in just the last two decades! This has led to landscape-level changes in vegetation patterns, shifting large areas of the eastern flanks of the Jemez Mountains from mixed-conifer forest to a chaparral ecosystem dominated by Gambel oak and New Mexico locust.

So what can be done to preserve and manage our forests under future fire regimes? Valles Caldera National Preserve and the Santa Fe National Forest, the National Park Service and US Forest Service are working in tandem to thin the high-density forests to remove a century of fuel build-up, and reintroduce natural fire regimes to maintain the forest ecosystem. Historic fire regimes, based on tree-ring and fire scar studies going back centuries, indicate that much of the Jemez Mountains burned every 8 to 15 years, but these fires were low-intensity, slow-moving ground fires in the forest understory. Once the forest conditions are back within manageable limits, natural lightning strikes can ignite low-severity fires which fire managers can safely “let burn” to benefit the ecosystem. Forest management on the landscape scale is a high priority for virtually all land management agencies (local, state, and federal), as we all recognize the interconnectedness of our landscapes with respect to fire movements and behavior.

In addition to thinning trees and restoring natural fire cycles, our forest restoration work provides additional ecosystem benefits. Following thinning, trees experience reduced competition for soil water and nutrients, making them healthier and more resistant to insect attacks and fungal diseases. Restored forest habitats support healthy wildlife populations (e.g., elk, deer, turkey). Forests developing into old-growth status are an important means of carbon sequestration, extracting greenhouse gases from the atmosphere. Wider spacing of trees allows more snowfall to reach the ground and remain shaded from the sun, thereby reducing sublimation and increasing water availability during spring snowmelt. Finally, restored forest habitats provide beautiful outdoor settings for recreation, hunting, and fishing by both residents and visitors.

If we can restore our forests to improve fire management, increase water availability, and sustain ecosystem functioning, we have a chance to maintain our forest habitats through the coming decades in the face of climate warming. It’s important to remember that an individual ponderosa pine tree can live for 400 years, and assuming that humans can develop the social, political, and economic will to reverse climate warming in the next 50-100 years, the young pines that are alive today may live through this entire warming episode and come out the other side in reasonably good shape. Landscape forest restoration will take time – to borrow a line from the Chinese philosopher Lao Tzu, “Even the longest journey begins with a single step” – and we are taking those first steps today to provide the greatest chance for future forest survival in the Jemez Mountains.

History Grove, a stand of old-growth ponderosa pine trees on the northern edge of Valle Grande, Valles Caldera National Preserve.

NPS/Corey Lycopolus