Interaction of Fire, Climate and Forest Structure in Northern Mexico

What determines when forest fires will occur? Why do some forests burn more than others? How do El Niño and other climatic factors influence forest fires? Do widespread climate events or local characteristics, such as fuel, topography and ignition events, have the greatest effect on fire occurrence? These are questions we are trying to answer in this study focused on fire, climate, and forest structure in the mountains of northern Mexico.

The project, funded by the National Science Foundation, will develop a new network of long fire and climate chronologies together with measurements of fuel dynamics in northern Mexico. We will incorporate a subset of unique relict sites where fire regimes and forest structures are least perturbed by human impacts over the nineteenth and twentieth centuries.

We will reconstruct fire regimes for the past ±300 years using fire-scarred trees, species composition, age distribution, landscape patterns of forest stands, and historical records. Climate variables of precipitation, drought, El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multi-decadal Oscillation (AMO) patterns will be assessed with existing and new tree-ring and instrumental data sets. Forest structure (trees, regeneration, woody and litter debris) will be measured on gridded plots.

These three long-term data sets will be applied to test the hypotheses that:

1. Historical fire occurrence was linked to broad regional climatic variability (e.g., ENSO, PDO, and AMO) and was synchronous at multiple scales in space and time
2. Fire frequency will plateau or decrease along the latitudinal gradient from the southwestern United States into northern Mexico, while elevation and topographic factors will exert strong influences on fire occurrence
3. Recent anthropogenic changes in fire regime affected forest fuels more strongly than climate shifts, but future climate change will have multiplicative effects on fire hazard and environmental consequences.

Images, left to right: pine understory, Peter Brown preparing to cut a sample, log with fire scars, Pete Fulé cutting a sample

Last updated: November 18, 2007