- Rocky Mountain Research Station
- 240 West Prospect
- Fort Collins, CO 80526
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Home > Research Highlights > Landscape Fire Patterns
Causes and Consequences of Landscape Fire History Patterns
Problem
In the last decade wildfires have become larger and more intense, especially in the southwestern U.S. These fires have been fueled by the dense forest conditions that have resulted from a century of fire exclusion. Efforts to restore forests structure and surface fires have begun at some locations. However, given the extent of the problem (i.e., million of acres need to be treated) it is clear that restoration efforts need to be conducted over larger (landscape) areas. To implement restoration prescriptions at landscape levels, managers need to first know the fire history of that particular landscape including the frequency of different size fires, and how these historical fires were influenced by physical landscape properties like topography and vegetation. Up to now most fire history studies have been done over small (2-100 ha) areas, hence the need for landscape fire history studies that cover 300-3000 ha and can be used to develop precise landscape fire management plans and avoid one-size-fits-all prescriptions.
Methods
To investigate landscape fire history patterns we selected three distinct landscapes. In the Santa Catalina Mountains of southeastern Arizona we selected the Rose Canyon (1800 ha) and the Butterfly Peak (1100 ha) landscapes and in the Rincon Mountains we selected the Rincon Peak (300 ha) landscape. At each landscape we collected fire-scarred trees from 20 (2 ha) plots. These trees were used to determine the fire history of that particular plot and to reconstruct the relative extent of past fire events over the entire landscape, something that has been lacking from most fire history studies.
Results and Implications
In general, the results from this research suggest that landscape topography influenced the relative size of historical fires and thus fire intervals at individual locations. For example, by reconstructing the extent of fires between 1750 and 1900, we found large fires, that burned >75% of landscape, occurred every 12 years in Rose Canyon, but only once every 20 years in Butterfly Peak. Among individual plots, intervals between fires were longer (10-15 years) in the Butterfly Peak landscape that was dominated by mixed-conifer species generally on steep north-facing slopes. Conversely, fire intervals were shorter (6-10 years) among plots in the Rose Canyon landscape which was dominated by ponderosa pine on gentle south-facing slopes. The relationship between landscape topography and fire history patterns suggests that managers can use landscape topography to separate areas with different fire regimes and develop more precise restoration prescriptions.
Up to now researchers believed that most fires in Southwest forests were low severity, however the Rincon Peak fire history suggests that there were occasional severe fires that killed all trees. The Rincon Peak landscape consists of isolated pine forests surrounded by chaparral communities and rock outcrops. In this landscape we believe that fire corridors were often blocked by inflammable fuels (e.g., young stands of Manzanita) resulting in longer (up to 56 years) fire intervals and subsequent stand replacing fires. The Rincon Peak landscape fire history is also a valuable lesson to managers faced with managing a complex matrix of burned (non-flammable) and un-burned (flammable) fuels after recent fire events.
Current Uses
The results of this research are being used by managers to: (1) amend forest plan to allow lighting ignited fire to burn under certain conditions (2) develop long term (10 year) burn plans in the Rincon Mountains, and (3) asses the severity and extent of recent fires in a historical context. More information on this study can be found in: "Landscape fire history and age structure pattern in the sky islands of southeastern Arizona" Ph. D. Dissertation (2006), University of Arizona, Tucson AZ.
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Rocky Mountain Research Station
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