Fires are overlaid on the percent of summer precipitation (July, August, and September) based on 30-year normal annual values for the western United States (MTBS 2016; PRISM 2016).
Climate change and human population growth, as well as shifts in plant composition have all contributed to fire increase in the Western United States. Piñ
on and juniper are widely distributed land cover types throughout the west and are associated with many vegetation types, including invasive annual grasses that burn rapidly.
In spite of their prominence and visibility, fire dynamics within piñon and juniper land cover types, and the role that they might play in changing fire dynamics when they spread is poorly understood. These dynamics have not been investigated until now. This study examined the spatial and temporal patterns of fire in piñon and juniper land cover types throughout the Rocky Mountain region.
Researchers analyzed existing data from 1984 through 2013 to determine differences in total area burned, fire rotation, fire size and number, and length of fire season among different geographic scales within the Rocky Mountain regions. They analyzed at a regional level: Northern Intermountain, Southern Intermountain, Southern, and Central; then at ecoregions within each of the geographic regions; and finally in three types of piñon and juniper land cover within each geographic region and "level III" ecoregion.
Data came from the National Gap Analysis Program and the Monitoring Trends in Burn Severity (MTBS) Program.
The study looked at:
- How have fire regimes that include piñon and juniper changed over the past 30 years?
- How do the fire regimes vary geographically?
- Are piñon and juniper land cover types more or less likely to burn than adjacent land cover types within the same regions?
- Increases in the total area burned and decreases in fire rotations occurred in all four geographic regions for piñon and juniper land cover types during the 30-year period.
- Area burned over the 30 years (and annually), number of fires per year, and larger fire size all followed the same geographic trend: Northern Intermountain > Southern Intermountain > Southern Rocky Mountain > Central Rocky Mountain.
- Fire rotations (measure of expected fire frequency) for piñon and juniper land cover types were generally within historical ranges for the regions.
- Percentage of the study area that burned in piñon and juniper land cover types was higher than in non-piñon and juniper land cover types in both the Southern Intermountain and Central Rocky Mountain geographic regions.
- The increases in fire, due to global change factors and – in the northern and southern intermountain regions – increases in rapidly burning invasive annual grasses, may be increasing vulnerability of piñon and juniper ecosystems.
- The magnitude of the effects of increased fire activity varied across the four geographic regions because of factors such as invasive annual grasses, bark beetles, and climate change.