1. Landscape-soil interactions in the Chihuahuan desert Brian Murtaugh Meredith Albright Soils Geography November 6, 2007 Univ of Colorado, Boulder http://museum.utep.edu/chih/NHCD/images/desertview.jpg

2. 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

3. Desertification and Soil Jornada Basin New Mexico, USA

4. Site

5. Desertification

6. 5 Major Ecosystem Types Grasslands – Black grama – Playa Shrublands – Creosotebush – Honey mesquite – Tarbush

7. Grasslands Little bare soil Even soil dispersal Being overtaken

8. Black grama grasslands Sandy/gravely sites Deep loam CaCO 3 Relatively higher moisture content

9. Playa grasslands Low-lying Clayey soils Consistent texture Tobosa Burrograss

10. Shrublands Vegetation spread out Nutrient islands Slowly take over grasses

11. Creosotebush Locations vary Soils vary Little difference in soil moisture Produce compounds that influence other growth

12. Honey mesquite Deciduous shrubs Deep roots Most soil types

13. Tarbush shrublands Deciduous Clay-loam soils Might receive run-in water Use deeper water

14. Climate and Soil Soil profiles hold evidence of past Clay mineralogy Carbonates

15. Illuvial Tell age of horizon Grasses -> C 4 Shrubs -> C 3 C 4 dominates

16. Future Research Soil moisture content, texture, vegetation type Ecosystem dynamics

17. Takehome from Jornada Grasslands overrun by shrublands Carbonates tell history of region Low variance of soil types Soil moisture changes throughout site

18. Sevilleta National Wildlife Refuge 80 km south of Albuquerque Importance of site – Ecotones – Focus: Chihuahuan desert grassland to shrubland Google Earth http://sev.lternet.edu

19. 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/

20. 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

21. Soil Profile Grassland – Argillic horizon over a CaCO 3 horizon Shrubland – Patchy erosion of argillic horizon Under shrubs - relics Between shrubs –exposure of CaCO 3 Positive Feedback Inhibits grass establishment Grassland Shrubland (Kieft et al., 1998)

22. Nutrients Essential nutrients (N, K, organic C) – More highly concentrated under shrubs – Microbial microsites (greater moisture and OM) Positive feedback Increased nutrient cycling (Kieft et al., 1998)

23. 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)

24. 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

25. 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.

26. 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