Monday, August 6, 2018: 2:50 PM
346-347, New Orleans Ernest N. Morial Convention Center
Background/Question/Methods
In the late 19th century, Euro-American settlement and land-use changes triggered the collapse of frequent surface fire regimes across nearly every forested mountain range of the American West. By contrast, the Navajo Nation in northern Arizona and New Mexico was never settled by Euro-Americans and may therefore present a different history of human-fire interactions. The Diné have occupied the present-day Navajo Nation for centuries and are known to have acquired sheep and goats as early as the 1680s, with widespread pastoralism becoming more deeply rooted by the early 1800s. We evaluated the roles of climate and human influences through grazing on historical fire activity in Navajo forests by reconstructing multi-centennial fire regimes at 14 ponderosa pine-dominated tree-ring sites. Our reconstructions are compared to local tree-ring climate chronologies and to a wealth of archaeological and ethnographic data regarding historical Navajo settlement and land-use practices. We tested for changes in fire frequency and relative fire extent across distinct periods of Navajo history, and between areas of differing historical land-use intensity.
Results/Conclusions
Our Navajo fire history consists of 160 trees and 1,395 fire scars. Fire-climate relationships (1600-1832) indicate that wet conditions were important to grow sufficient grasses to burn during subsequent droughts. This evidence of fuel limitation on fire spread indicates the likely sensitivity of Navajo forests and fire regimes to the influences of livestock through fuel continuity. Similar to Savage and Swetnam (1990, Ecology), we found a significant early decline in fire activity (1820-1830) associated with rising Navajo pastoralism and increased livestock numbers. This early fire-regime decline was isolated to areas of seasonal grazing, concentrated where surface water was plentiful. The remaining sites within the 180,000 ha study area showed no changes in fire activity until decades later. By 1880, frequent surface fires were interrupted across all sites. This cross-scale disruption of fire regimes is associated with several socioecological factors, including the establishment of the Navajo reservation in 1868, US Government provisions of livestock in the 1870s, and access to the American economy through trading posts and the railroad in post-1881. Demand for Navajo wool products encouraged growth of herd sizes beyond historical subsistence levels, as transhumant practices became a deep-rooted part of Navajo culture and the legacy of the landscape.
In the late 19th century, Euro-American settlement and land-use changes triggered the collapse of frequent surface fire regimes across nearly every forested mountain range of the American West. By contrast, the Navajo Nation in northern Arizona and New Mexico was never settled by Euro-Americans and may therefore present a different history of human-fire interactions. The Diné have occupied the present-day Navajo Nation for centuries and are known to have acquired sheep and goats as early as the 1680s, with widespread pastoralism becoming more deeply rooted by the early 1800s. We evaluated the roles of climate and human influences through grazing on historical fire activity in Navajo forests by reconstructing multi-centennial fire regimes at 14 ponderosa pine-dominated tree-ring sites. Our reconstructions are compared to local tree-ring climate chronologies and to a wealth of archaeological and ethnographic data regarding historical Navajo settlement and land-use practices. We tested for changes in fire frequency and relative fire extent across distinct periods of Navajo history, and between areas of differing historical land-use intensity.
Results/Conclusions
Our Navajo fire history consists of 160 trees and 1,395 fire scars. Fire-climate relationships (1600-1832) indicate that wet conditions were important to grow sufficient grasses to burn during subsequent droughts. This evidence of fuel limitation on fire spread indicates the likely sensitivity of Navajo forests and fire regimes to the influences of livestock through fuel continuity. Similar to Savage and Swetnam (1990, Ecology), we found a significant early decline in fire activity (1820-1830) associated with rising Navajo pastoralism and increased livestock numbers. This early fire-regime decline was isolated to areas of seasonal grazing, concentrated where surface water was plentiful. The remaining sites within the 180,000 ha study area showed no changes in fire activity until decades later. By 1880, frequent surface fires were interrupted across all sites. This cross-scale disruption of fire regimes is associated with several socioecological factors, including the establishment of the Navajo reservation in 1868, US Government provisions of livestock in the 1870s, and access to the American economy through trading posts and the railroad in post-1881. Demand for Navajo wool products encouraged growth of herd sizes beyond historical subsistence levels, as transhumant practices became a deep-rooted part of Navajo culture and the legacy of the landscape.