1 research outputs found
Dendroecological testing of the pyroclimatic hypothesis in the central Great Basin, Nevada, USA
In the Great Basin region of western North America, records of past climate and wildfire variability are needed not only for fire use, but also for understanding the mechanisms behind the centuryâlong expansion of piñonâjuniper woodlands. The Mt. Irish area (Lincoln County, southâeastern Nevada) is a remote mountain ecosystem on the hydrographic boundary between the Great Basin and the Colorado River Basin. Nonâscarred ponderosa pines (Pinus ponderosa C. Lawson var. scopulorum Engelm.) and singleâneedle pinyons (Pinus monophylla Torr. & FrĂ©m.) were used to develop a treeâring reconstruction of drought (mean PDSI for MayâJuly from NV Climate Division 3) from 1396 to 2003. A hypothetical fire regime was obtained from the PDSI reconstruction and from explicitly assumed relationships between climate and wildfire occurrence. A census of fireâscarred trees was then sampled at the study area, and crossdated fireâscar records were used to generate the fire history, independently of the preâexisting pyroclimatic model. Out of 250 collected fireâscar wood sections, 197 could be crossdated (about 89% from ponderosa pines), covered the period from 1146 to 2006, and contained 485 fire scars, 390 of which could be dated to a single year. Numerical summaries were computed for the period 1550â2006, when recorder trees ranged from 16 to 169, using a total of 360 fire scars on 176 sections. Up to 1860, the time of EuroâAmerican settlement, fires that scarred at least two trees were very frequent (minimum fire interval: 1 year, mean: 4, median: 2, Weibull median: 3, maximum: 19), while fires that scarred at least 10% of the recorder trees were relatively rare (minimum fire interval: 40 years, mean: 66, median: 50, Weibull median: 63, maximum: 123). Fire frequency remained high during the 1780â1840 period, when fire was reduced or absent in other areas of the western United States. Both the âexpectedâ and the âobservedâ fire history showed lower fire frequency after EuroâAmerican settlement, which most likely displaced Native people and any deliberate use of fire, but did not introduce publicly organized suppression in the area. Therefore, less favorable climatic conditions, not postâsettlement fire management, were responsible for reduced wildfire occurrence in the modern era