Presentation on theme: "Spatial Variation of Soil Characteristics with respect to Hill Slope Position and Vegetation Community Christopher Shepard REU Project Summer 2010."— Presentation transcript:
Spatial Variation of Soil Characteristics with respect to Hill Slope Position and Vegetation Community Christopher Shepard REU Project Summer 2010
Soil Formation Soil forms from the breakdown of parent rock material. Soil formation is affected by climate, topography, parent rock material, erosion rates, biotic community, and time.
Soil Creep and Mass Wasting Soil moves downslope under the influence of gravity and erosion. Soil can also be transported by wind. Soil movement can be greatly affected by vegetation community, climate, and hill slope position.
Slopes Slope aspect effects microclimate in desert environments (Monger and Bestelmeyer 2006) Vegetation composition changes as hill slope position changes (Bridge and Johnson 2000)
Research Questions Do soil characteristics change as hill slope position changes? Does soil creep behave as predicted in a semi-arid climate? And what effect does vegetation community have on soil creep? How does vegetation community and soil formation interact at different hill slope positions?
Research Location Sevilleta National Wildlife Refuge Los Piños Mountains 34 22'6.78"N 106 32'11.83"W
Cerro Montosa NPP Site 34 22’ 6.78"N 106 32’ 11.83"W Slope sequences followed transects previously setup by Esteban Muldavin Bedrock –schist –gneiss –vein Quartz –quartzite
Methods and Materials Hill Slope Soil Characteristics Vegetation Community
Hill Slopes Slope Sequences –5 different north and south facing slopes –4 soil pits dug on each slope –Total of 40 pits –Aspect of each slope was measured Crest Shoulder Backslope Footslope
Soil Characteristics Pits dug to bedrock Ped type, size, and grade % Gravel Consistence: Dry, Moist, Wet- Stickiness, and Wet- Plasticity Texture Color Carbonate development Depth
Vegetation Community Line Transects –40 transects completed –11 m transects –Parallel to slope position –Basal area and Canopy measured
Analysis Graphed as a function of hill slope position: –Soil depth –Soil Texture –Soil Color Compared soil depth and slope aspect to: –% Grass Basal area –% Canopy- Tree –% Canopy- Shrub –% Canopy- Grass
Soil Depth Along Slope Sequences
Soil Texture A horizons were primarily Sandy Loam and Loamy Sand. B horizons were primarily Silty Clay Loam, Clay Loam, and Sandy Clay Loam.
Soil Texture Along Hill Slope Position
Soil Color Along Hill Slope Position A horizon color Gray Brown 7.5 YR 5/3 - Found at all hill slope positions Light Yellow Brownish Gray 10 YR 7/2 and 8/2 - Found primarily at Crest and Shoulder B horizon color Gray Yellowish Orange 10 YR 4/3 Reddish Brown 5 YR 5/8 Gray Yellowish Brown 10 YR 6/3 Found at multiple hill slope positions
Discussion of Soil Characteristics Two different soil types –Both North- and South-facing slopes –Slope Sequences 2 and 4 –Slope Sequences 3 and 6 (and possibly 1) Fine soil material from wind (eolian) source –Leads to higher water holding capacity –Enables establishment by vegetation
Slope Sequences 2 and 4 Primarily A horizons Soil very thin Textures –Sandy Loam –Loamy Sandy Soil likely wind blown deposits
Slope Sequences 3 and 6 Both North- and South- facing slopes Soil very deep (>25 cm) –Well developed soil column –Thin A horizon –Thick B horizon –Strong CaCO 3 film and filament development Soil likely much older than soil on Slope sequences 2 and 4
Discussion of Soil Characteristics “Soil horizon development as determined by landform age…” (McAuliffe 1994). Different soil horizons and types –Landform same age over Los Piños –How are there such distinctly different soil types? 1.Change in climate 2.Change in depositional regime 3.Effect of grazing
Average % Grass Basal Area Along Hill Slope Position
Observed Trends between Vegetation Community and Soil The vegetation community may have an effect on the soil of both north and south facing slopes. % Grass Basal Area vs. Soil Depth –May lead to deeper soils on South-facing slopes –No correlation on North-facing slopes % Canopy of trees vs. Soil Depth –May lead to deeper soils on North-facing slopes –May lead to shallower soil on South-facing slopes % Grass Basal Area vs. Aspect –Grass prefer to live on shallower slopes
Conclusions Soil characteristics changed with respect to hill slope position Soil depth and aspect are likely linked to vegetation community Vegetation may have an effect on soil transport North and South facing slopes appear to behave differently, likely due to the differences in vegetation community, slope aspect, and microclimate.
Acknowledgements Les McFadden, Esteban Muldavin Jennifer Johnson Amaris Swann Summer REUs: Shayla Burnett, Harmony Lu, Rick Duran, Mitch Nakai, Cynthia Malone, Natasha Ribiero, Melissa Shaginoff, Antonio Nevarez, Amanda Labrado, Elida Iniguez Summer Interns: Brenda Nieto National Science Foundation
References McAuliffe RJ. (1994). Landscape Evolution, Soil Formation, and Ecological Patterns and Processes in Sonoran Desert Bajadas. Ecological Monographs, Vol. 64, No. 2: Monger HC and Bestelmeyer BT. (2006). The soil-geomorphic template and biotic change in arid and semi-arid ecosystems. Journal of Arid Environments. 65: Daniels RB and Hammer RD. Soil Geomorphology. Wiley (1992): New York. Bridge SRJ and Johnson EA. (2000). Principles of Terrain Organization and Vegetation Gradients. Journal of Vegetation Science, Vol. 11, No. 1: pp Francis CF. Plants on Desert Hillslopes. Edited by: Athol D. Abrahams and Anthony J. Parsons. Geomorphology of Desert Environments. Chapman and Hall (1994): London.