Holocene Fire, Climate and Erosion in the Jemez Mountains, New Mexico: Natural and Anthropogenic Controls
Abstract
Ponderosa pine and mixed-conifer forests in the Jemez Mountains have been ravaged by extensive severe fires in the last two decades, which burned almost 1000 km2, roughly 30% of this middle-elevation range. Tree-ring fire history reconstructions indicate that a low-severity fire regime characterized the ca. 400 years before Euroamerican settlement, and that fuel buildup from fire suppression and land-use impacts contributed to increased fire severity in recent years. In order to better understand natural variability, climatic influences, and erosional effects of wildfire activity since ~5000 cal yr BP, we identified and 14C-dated fire-related alluvial deposits in the 2002 Lakes Fire area in the southwestern Jemez Mountains. These deposits indicate that most late Holocene fire-related erosional events were relatively minor, consistent with the low-severity burns that dominate the tree-ring record, but larger debris flows also occurred, suggesting at least small areas of high-severity fire. Although changes in postfire sedimentation are not so clearly related to millennial-scale Holocene climatic changes as in the Northern Rocky Mountains, peaks in fire-event probability correspond with severe regional multidecadal droughts ca. 1800 and 375 cal yr BP. Local microclimatic controls on vegetation, soils, and post-fire sedimentation are also evident. Relatively dense mixed-conifer stands including Douglas-fir typify moister north-facing basins, where soils are apparently thicker and more permeable than on southerly aspects. Alluvial fans of these basins are dominated by fire-related deposits (77% of measured stratigraphic thickness), thus we interpret that little erosion occurs in the absence of wildfires. Holocene fire-related events from north slopes are also of somewhat lower frequency, and possibly of higher severity. In contrast, in ponderosa pine-dominated south-facing basins, fire-related deposits make up only 39% of measured fan deposits. On drier south aspects, thin soils, large areas of steep exposed bedrock, and sparser vegetation allow greater runoff and sediment in the absence of fire, making for a lesser relative importance of fire in erosion. The lack of exposed and dated deposits older than 5000 cal yr BP, even where fan feeder channels were incised to bedrock in debris-flow and flood events after the 2002 Lakes Fire, indicates that most stored alluvium was scoured from these channels in the middle Holocene, possibly from more severe fires and postfire erosion. It also suggests that erosional response after the Lakes Fire was at least locally greater than at any time in the last 5000 yr, possibly from the combined influence of fire suppression and recent warming and severe drought. However, expansion of this small study area would allow a clearer view of fire-climate-erosional linkages in the Jemez Mountains, and the degree to which modern climatic warming and anthropogenic impacts have heightened severe fire activity.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMGC24A..05M
- Keywords:
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- 0429 BIOGEOSCIENCES Climate dynamics;
- 1625 GLOBAL CHANGE Geomorphology and weathering