Masters Theses

Date of Award

8-2014

Degree Type

Thesis

Degree Name

Master of Science

Major

Geography

Major Professor

Henri D. Grissino-Mayer

Committee Members

Sally P. Horn, Yingkui Li

Abstract

In recent years, crown fires have raged through mixed-conifer forests in the American Southwest that historically experienced frequent, low-severity wildfires. Land management agencies now wish to restore wildfires to their historical range of variability, but this requires information on fire regimes before Euro-American disturbance took place. We characterized the historical fire regime of a high elevation, mixed-conifer forest in the Magdalena Mountains, New Mexico. This research evaluated the different climate drivers, represented by the Palmer Drought Severity Index (PDSI), the El Niño-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO), that influence the occurrence of wildfire. To characterize the fire regime we developed fire frequency statistics and evaluated the seasonality of wildfire events across the period of 1630 to 1890. To test short-term (interannual) variations in climate and their influence on wildfire occurrence we relied on Superposed Epoch Analysis (SEA). To test the relationship between wildfire events and long-term climate oscillations (decadal to multidecadal), we used Bivariate Event Analysis (BEA). BEA was used to test whether fire events and climate events operate synchronously, asynchronously, or independently of each other. We found that fire frequency ranged from 7 to 8 years from 1630 to 1890, and fires primarily occurred in the early portion of the growing season (late spring to early summer). Fires ceased after 1890 with only two recorded fire events in 1906 and 1953. Based on SEA of PDSI, ENSO, and PDO, conditions 2 to 3 years before a fire event were wetter than average, while in the year prior to, and in the year of a fire event, conditions were drier than average. BEA revealed an asynchronous relationship with extreme wildfire years and El Niño events, while all other relationships between wildfire events and positive and negative phases of ENSO, PDO, and AMO were independent. We conclude that interannual climate variability is the main driver of the frequent, low-severity wildfire regime in the mixed-conifer forests of the Magdalena Mountains, while long-term (multidecadal) climate trends do not appear to influence the occurrence of wildfires.

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