Landscape-soil interactions in the Chihuahuan desert

Brian MurtaughMeredith Albright

Soils GeographyNovember 6, 2007

Univ of Colorado, Boulder

http://museum.utep.edu/chih/NHCD/images/desertview.jpg

Introduction• Located in Chihuahuan Desert• 60 km apart• Sevilleta

– 250 mm annual precipitation– Moisture deficit most of the year– Low 1.6° C– High 25.1° C

• Jornada– 250 mm annual precipitation– Low 5° C– High 25° C

SEV

Desertification and SoilJornada Basin

New Mexico, USA

SiteSite

Desertification

5 Major Ecosystem Types

• Grasslands– Black grama – Playa

• Shrublands– Creosotebush– Honey mesquite– Tarbush

Grasslands• Little bare soil• Even soil dispersal • Being overtaken

Black grama grasslands

• Sandy/gravely sites• Deep loam• CaCO3

• Relatively higher moisture content

Playa grasslands

• Low-lying • Clayey soils• Consistent

texture

Tobosa Burrograss

Shrublands• Vegetation spread out• Nutrient islands• Slowly take over grasses

Creosotebush

• Locations vary• Soils vary• Little difference in

soil moisture• Produce compounds

that influence other growth

Honey mesquite

• Deciduous shrubs• Deep roots• Most soil types

Tarbush shrublands

• Deciduous• Clay-loam soils• Might receive run-in

water• Use deeper water

Climate and Soil

• Soil profiles hold evidence of past• Clay mineralogy• Carbonates

Carbonates

• Illuvial• Tell age of horizon• Grasses -> C4

• Shrubs -> C3

• C4 dominates

Future Research

• Soil moisture content, texture, vegetation type

• Ecosystem dynamics

Takehome from Jornada

• Grasslands overrun by shrublands• Carbonates tell history of region• Low variance of soil types• Soil moisture changes throughout site

Sevilleta National Wildlife Refuge

• 80 km south of Albuquerque• Importance of site

– Ecotones– Focus: Chihuahuan desert grassland

to shrubland

Google Earthhttp://sev.lternet.edu

• Invasion of creosotebush (Larrea tridentata) into grasslands– Potential causes: climate change, increased

rodent activity, altered fire frequency, land-use changes, shift in groundwater levels

– Changes in species composition– Changes in surface soil

How do soils change with the transition from grasslands to shrublands?– Soil profile– Texture– Nutrients

Creosotebush

Grama-dominated grassland

http://sev.lternet.edu/

http://sev.lternet.edu/

Distribution of Vegetation

• Grassland to shrubland– Decreased biomass– Decreased soil coverage

• Affects soil characteristics– Soil profile– Texture– Nutrient levels

(Cross and Schlesinger, 1999)

Grassland

Shrubland

Soil Profile

• Grassland – Argillic horizon over a CaCO3

horizon• Shrubland

– Patchy erosion of argillic horizon

• Under shrubs - relics• Between shrubs –exposure of

CaCO3

• Positive Feedback

Inhibits grass establishment

Grassland

Shrubland

(Kieft et al., 1998)

Nutrients

• Essential nutrients (N, K, organic C)– More highly concentrated

under shrubs– Microbial microsites

(greater moisture and OM)

• Positive feedbackIncreased

nutrient cycling

(Kieft et al., 1998)

Texture• Soil Texture

– Grassland• uniform texture • 83% sand, 8% silt, 9% clay

– Shrubland • Heterogeneous • 64% sand , 26% silt, 10% clay

• Consequences– Under shrubs

• Higher water holding capacity• Increased CEC

• Positive feedback

Deposition of fine particles

(Kieft et al., 1998)

Conclusions• Positive feedback towards shrublands

– Patchy distribution of fine-textured soils– Loss of the argillic layer between shrubs– Patchy distribution of essential nutrients

• Shrubland encroachment is widespread– Creation of islands of fertility in Sevilleta and Jornada

• Characteristic soil qualities under grasses vs. shrublands in both sites

http://www.nsf.gov/news/mmg/media/images/eco4_f.jpg

References - Sevilleta• Kieft, T.L., C.S. White, S.R. Loftin, R. Aguilar, J.A. Craig, D.A. Skaar. 1998. Temporal Dynamics

in soil carbon and nitrogen resources at a grassland-shrubland ecotone. Ecology 79(2): 671-683.

• Cross, A.F., W.H. Schlesinger. 1999. Plant regulation of soil nutrient distribution in the northern Chihuahuan Desert. Plant Ecology 145: 11-25.

• White, C.S., D.I. Moore, J.A. Craig. 2004. Regional-scale drought increases potential soil fertility in semi-arid grasslands. Biology and Fertility of Soils 40: 73-78.

• Schlesinger, W.H., J.A. Raikes, A.E. Hartley, A.F. Cross. 1996. On the spatial pattern of soil nutrients in desert ecosystems. Ecology 77: 364-374.

• Kurc, S.A., E.E. Small. 2007. Soil moisture variations and ecosystem-scale fluxes of water and carbon in semiarid grassland and shrubland. Water resources research 43: 1-13.

• Long Term Ecological Research, Sevilleta. http://sev.lternet.edu/• Brady, N.C., R.R. Weil. The Nature and Properties of Soils. Pearson Prentice Hall, 2008.• Buxbaum, C.A.Z., K. Vanderbuilt. 2007. Soil Heterogeneity and the distribution of desert and

steppe plant species across a desert-grassland ecotone. Journal of Arid Environment 69: 617-632.

References - Jornada• Havstad, Kris M., L.F. Huenneke, William H. Schlesinger (Eds.), Debra P.C.

Peters, Robert P. Gibbens, Structure and Function of a Chihuahuan Desert Ecosystem: The Jornada Basin Long-Term Ecological Research Site,Oxford

University Press 2006