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Distribution of Chihuahuan Desert and
Colorado Shortgrass Prairie Species
Controlled by Soil Moisture
Heterogeneity
In a Desert/grassland Ecotone at
Sevilleta National Wildlife Refuge
1
Charles A. Z. Buxbaum 2
Bouteloua gracilis (blue grama), B. eriopoda (black grama), and Larrea tridentata (creosote)
are the dominant plants of the McKenzie Flats area of the Sevilleta NWR in Central N.M. Much
recent research of the Sevilleta LTER has focused on discerning processes that regulate the
distribution of these species within a deserVgrassland ecotone. In this study, I examine the
hypothesis that landscape heterogeneity of soil depth and fine-textured fraction controls the
relative dominance of the three major species. The area is relatively flat, grading at a 2-3%
slope to the edge of a fault scarp. However, even the within the flattest parts of the landscape
there are abrupt and dramatic soil changes. These correspond to the presence of buried
channels that cut through a petrocalcic horizon that formed in a 500-100 ky old buried soil.
Cluster analysis of soil-moisture-related characteristics and Spearman rank correlation
analysis of soil data and dominance or codominance of the three species of interest shows the
following: B. gracilis, a Colorado Shortgrass Prairie species, dominates the buried
paleochannels, where the soil profile is deepest and clay accumulation is highest; B. eriopoda, a
Chihuahuan Desert grass, is most abundant where the buried petrocalcic horizon is within 40 to
60 em of the surface; and L. tridentata is the dominant species where the petrocalcic horizon is
exposed or near the surface. Understanding edaphic patterns in arid grasslands can help pr-edict
rates of desert expansion or retreat; and is a critical factor in grassland restoration.
This study illustrates the strong relationship between geomorphology, soils, and vegetation
patterns in arid environments. While grassland soils may appear homogeneous at the surface,
the climatic history of alternating wet and dry periods has caused alternating periods of soil
deposition and erosion. The vegetation patterns on the recent deposition AI soils of the Sevilleta
NWR grasslands follow the dissected pattern of a buried past landscape.
1
2
Abstract of a poster presented at the conference.
Dept. of Biology University of New Mexico, Albuquerque NM.
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