Testing a pyroclimatic hypothesis on the Mexico-United States border.

Area of Science:

• Ecology
• Environmental Science
• Forestry

Background:

• The pyroclimatic hypothesis posits a direct relationship between climatic indices and fire occurrence, enabling predictions of fire regimes.
• Cross-border comparisons in ecologically similar mountain ranges with differing cultural influences are valuable for disentangling climatic and non-climatic fire controls.

Purpose of the Study:

• To test the pyroclimatic hypothesis by comparing fire histories in Mexico and the United States.
• To evaluate the influence of climate versus land use on fire regimes in the Mesa de las Guacamayas and Chiricahua Mountains.

Main Methods:

• Developed a priori hypothetical models of fire occurrence.
• Compared these with empirical climate-based regression models using historical fire data.
• Analyzed fire history from northwestern Chihuahua, Mexico, and southeastern Arizona, USA.

Main Results:

• Fires were frequent in Mexico until the present, with some regime alteration.
• Fire was largely excluded in the Chiricahua Mountains after 1892.
• Empirical models better explained climate-fire variability than a priori models.
• Divergent climate-fire relationships were observed post-1892, indicating non-climatic influences.

Conclusions:

• Frequent fire regimes can cease due to non-climatic factors, such as land use changes (e.g., livestock grazing).
• Historical climate data can inform ecological reference conditions and future sustainability, but non-climatic factors must also be considered.
• Cross-border comparisons effectively reveal the interplay between climate and human impacts on fire regimes.