The influence of Holocene vegetation changes on topography and erosion rates: a case study at Walnut Gulch Experimental Watershed, Arizona
Quantifying how landscapes have responded and will respond to vegetation changes is an essential goal of geomorphology. The Walnut Gulch Experimental Watershed (WGEW) offers a unique opportunity to quantify the impact of vegetation changes on landscape evolution over geologic timescales. The WGEW is...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-06-01
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| Series: | Earth Surface Dynamics |
| Online Access: | http://www.earth-surf-dynam.net/4/471/2016/esurf-4-471-2016.pdf |
| Summary: | Quantifying how landscapes have responded and will respond
to vegetation changes is an essential goal of geomorphology. The Walnut Gulch Experimental Watershed (WGEW) offers a unique opportunity to quantify the
impact of vegetation changes on landscape evolution over geologic timescales. The WGEW is dominated by
grasslands at high elevations and shrublands at low elevations.
Paleovegetation data suggest that portions of WGEW higher than approximately
1430 m a.s.l. have been grasslands and/or woodlands throughout the late
Quaternary, while elevations lower than 1430 m a.s.l. changed from a
grassland/woodland to a shrubland ca. 2–4 ka. Elevations below 1430 m a.s.l.
have decadal timescale erosion rates approximately 10 times higher,
drainage densities approximately 3 times higher, and hillslope-scale
relief approximately 3 times lower than elevations above 1430 m. We
leverage the abundant geomorphic data collected at WGEW over the past
several decades to calibrate a mathematical model that predicts the
equilibrium drainage density in shrublands and grasslands/woodlands at WGEW.
We use this model to test the hypothesis that the difference in drainage
density between the shrublands and grassland/woodlands at WGEW is partly the
result of a late Holocene vegetation change in the lower elevations of WGEW,
using the upper elevations as a control. Model predictions for the increase
in drainage density associated with the shift from grasslands/woodlands to
shrublands are consistent with measured values. Using modern erosion rates
and the magnitude of relief reduction associated with the transition from
grasslands/woodlands to shrublands, we estimate the timing of the
grassland-to-shrubland transition in the lower elevations of WGEW to be
approximately 3 ka, i.e., broadly consistent with paleovegetation studies.
Our results provide support for the hypothesis that common vegetation
changes in semi-arid environments (e.g., from grassland to shrubland) can
change erosion rates by more than an order of magnitude, with important
consequences for landscape morphology. |
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| ISSN: | 2196-6311 2196-632X |