National Cooperative Soil Survey Conference Ft. Collins, CO 28 June 2001

1. State and Transition Ecosystem Models - Application to Soil Survey and Dynamic Soil Properties Databases National Cooperative Soil Survey Conference Ft. Collins, CO 28 June 2001 Joel Brown NRCS Jornada Experimental Range Las Cruces, NM Arlene J. Tugel NRCS - Soil Quality Institute Jornada Experimental Range Las Cruces, NM

2. Part 1 THE APPLICATION OF NONEQUILIBRIUM SYSTEM DYNAMICS TO DESCRIBING SOIL/PLANT INTERACTIONS: SOME BASIC CONCEPTS Part 2 - Soil-Plant Interactions Part 3 - Soil Survey Applications Part 4 - Directions and Future Needs

3. ECOLOGICAL SYSTEM DYNAMICS competing paradigms CLEMENTS (1916) DYKSTERHIUS (1949, 1958) climatic climax endpoint change linear deterministic disturbance unimportant competition important VON BERTALANFFY 1968 HOLLING 1973 MAY 1977 WESTOBY et al 1989 multiple steady states change nonlinear disturbance important competition-less important thresholds

4. EQUILIBRIUM SYSTEM DYNAMICS CLEMENTS (1916) vegetation as a ‘superorganism’ determined by climate succession was predictable and had a predetermined outcome vegetation change was an autogenic process DYKESTERHIUS (1949, 1958) concept of functional edaphic units plant community/soil combination resulted in a unique (range) site established concept of ‘dynamic equilibrium’ described in terms of species dominance

5. LINEAR CHANGE IN ECOLOGICAL SYSTEMS Climax vegetation fire grazing climate Vegetation attribute Succession Competition time

6. NONEQUILIBRIUM SYSTEM DYNAMICS VON BERTALANFFY 1968 - GENERAL SYSTEMS THEORY HOLLING 1973-RESILIENCE AND STABILITY MAY 1977-THRESHOLDS AND BREAKPOINTS WESTOBY et al 1989-STATE AND TRANSITION thermodynamics-ecological systems as energy processors multiple steady states-structural dominance, function may change thresholds-point of entry into new domain hysteresis-lag times, failure to return to original configuration feedbacks-positive feedback accelerates change negative feedback suppresses change

7. STATES • STATE - a recognizable, resistant and resilient complex of two ecosystem components, the soil base and the vegetation structure • soil - developed through time from specific parent material, climate, landscape position and interaction with biota • - determine the site’s capability • - interaction between soil and vegetation determines functional status of site and inherent resistance to change Stringham, et al., 2001

8. STATES Vegetation attribute(S) time

9. TRANSITIONS • TRANSITION - the trajectory of a change • - change is precipitated by natural events or anthropogenic disturbances • - degrades the integrity beyond the point of self repair • THRESHOLD- boundary in space and time between two states • - irreversible for practical purposes Stringham, et al., 2001

10. TRANSITIONS thresholds Vegetation attribute(S) trajectory time

11. Graminoid-driven succession Shrub-driven succession Perennial grasses Short / low A = Tall / mid-grasses B = Mid / short grasses C = Short grass / annuals = Threshold D = Clusters and groves E = Woodland Herbaceous retrogression A B C Time or cultural energy increments required to drive system to new configuration CommunityComposition D E Woody plants Long / high Time high low low low low high Fire Frequency Modified from Archer, 1989 Grazing Pressure high Probability & rate of woody plant establishment

12. La Copita Research Area • Rio Grande plains of southern Texas • Semi-arid and subtropical • winter 14C; summer 28C • 29 in ppt. (720mm); May and Sept maxima

13. Potential Native Vegetation • Prosopis-Acacia-Andropogon-Setaria savanna(Kuchler, 1964) • Honey mesquite, acacia, little bluestem, foxtail

14. Current Vegetation • Subtropical thorn woodland (McLendon, 1991) (Prosopis glandulosa - honey mesquite with an understory of evergreen, winter-deciduous, and summer-deciduous shrubs) • savanna parklands in sandy loam uplands • closed-canopy woodlands in clay loam lowland drainages.

15. Historical Record • Pre-settlement - light grazing and 10 yr fire frequency • Settlers reported grassland or open savanna in mid-1800’s (Inglis, 1964) • Livestock grazing since the late 1800’s • Absence of fire in 1900’s

16. Historical Record, cont’d • C3 trees and shrubs have displaced C4 grasses in last 100 years (radiocarbon analyses of SOC) (Boutton et al., 1998) • Mature trees were established over past 100 yr based on tree ring analysis (Boutton et al., 1998) • Aerial photo record of woody plant cover (Archer, etal., 1988) • 1941 - 10%; 1983 - 40%

17. 1976 1990 (5.26 ha) (6.52 ha) 1950 (3.59 ha) 1950 Woodland Groves Clusters Herbaceous Archer, et al., 2001

18. Vegetation CLUSTERS GROVE PIONEER CLUSTERS HERBACEOUS

19. Part 2 - Soil-Plant Interactions

20. Key Messages • Soil-plant interactions affect soil properties. • Disturbances affect soil properties. • Soil properties vary within and among states and affect capacity of the soil to function. • Changes in soil properties can be used to identify thresholds or serve as early warning indicators.

21. Sandy loam uplands Herbaceous or clusters Mesquite groves Clay loam lowlands Closed canopy woodlands Typic Argiustoll Typic Ustochrepts Pachic Argiustolls Soils on the Landscape 1950

22. Upland Site • Ecological Site: Sandy loam, 83C -Central Rio Grand Plain • Topography • Low relief, 1-3 percent slopes • Stability • Little erosion • No pedestals, rills, or gullies • No evidence of deposition in low lying areas Lowlands

23. Graminoid-driven succession Shrub-driven succession Perennial grasses Short / low A = Tall / mid-grasses B = Mid / short grasses C = Short grass / annuals = Threshold D = Clusters and groves E = Woodland Herbaceous retrogression A B C Time or cultural energy increments required to drive system to new configuration CommunityComposition D E Woody plants Long / high Time high low low low low high Fire Frequency Modified from Archer, 1989 Grazing Pressure high Probability & rate of woody plant establishment

24. Vegetation-Soil Dynamics - Grassland degradation Relict grasslands Mid- to tall-perennial grasses Potential production; 5000-6000 kg/ha • Current herbaceous vegetation • Short perennial grasses, annual forbs; • < 2700 kg/ha Onset of heavy grazing Redrawn from Hibbard, 1995 CENTURY model

25. Vegetation - Soil Dynamics Woody encroachment and heterogeneity CLUSTERS GROVE PIONEER CLUSTERS HERBACEOUS

26. Resource RedistributionIslands of fertility • Soil C and N pools increase (Viriginia, 1986) • N-fixing legume • Woody plants pump nutrients (and water) from deep soil horizons and beyond the canopy • Tall woody plants trap nutrient-rich dust • Woody plants attract birds, insects and mammals that enrich soil via defecation and burrowing

27. Graminoid-driven succession Shrub-driven succession Perennial grasses Short / low Herbaceous retrogression A = Tall / mid-grasses B = Mid / short grasses C = Short grass / annuals = Threshold A Time or cultural energy increments required to drive system to new configuration CommunityComposition Frequent fire Intense competition Woody plants Long / high Time high low low low low high Fire Frequency Grazing Pressure high Probability & rate of woody plant establishment

28. Graminoid-driven succession Shrub-driven succession Perennial grasses Short / low Herbaceous retrogression A = Tall / mid-grasses B = Mid / short grasses C = Short grass / annuals = Threshold B Time or cultural energy increments required to drive system to new configuration CommunityComposition Seedling establishment Loss of fine fuel Reduced fire frequency Woody plants Long / high Time high low low low low high Fire Frequency Grazing Pressure high Probability & rate of woody plant establishment

29. Graminoid-driven succession Shrub-driven succession Perennial grasses Short / low Herbaceous retrogression A = Tall / mid-grasses B = Mid / short grasses C = Short grass / annuals = Threshold C Time or cultural energy increments required to drive system to new configuration CommunityComposition • Shrub-altered environment • nutrient enrichment • wind blown soil is trapped • attracts animals/seed vectors Woody plants Long / high Time high low low Fire Frequency low low high Grazing Pressure high Probability & rate of woody plant establishment

30. Graminoid-driven succession Shrub-driven succession Perennial grasses Short / low Herbaceous retrogression = Threshold D = Clusters and groves E = Woodland D Time or cultural energy increments required to drive system to new configuration CommunityComposition Infrequent fire Nutrient enrichment Woody plants Long / high Time high low low low low high Fire Frequency Grazing Pressure high Probability & rate of woody plant establishment

31. Graminoid-driven succession Shrub-driven succession Perennial grasses Short / low = Threshold D = Clusters and groves E = Woodland Herbaceous retrogression Time or cultural energy increments required to drive system to new configuration CommunityComposition Woodland dominance Catastrophic or no fire Woody plants Long / high E Time high low low low low high Fire Frequency Grazing Pressure high Probability & rate of woody plant establishment

32. La Copita - Probable Future • Decreased grazing and increased fire are not likely to prompt a decrease in woody plants, although further expansion of woody plants may be curtailed • With heavy grazing and no fire, woody cover will continue to increase in herbaceous clearings

33. Soil Properties

34. 2.2 1.4 0.84 Carbon and Nitrogen 0 - 10 cm Percent (Hibbard, et al., in press)

35. S&T Model for Sandy Loam 83C B D E C A Plant community is determined by grazing, fire, climate and edaphic variability Plant community is determined by rainfall, fire, woody plant management and edaphic variability

36. Part 3 - Applications to Soil Survey

37. Why are dynamic soil properties important? • The capacity of soils to function depends on both: • inherent soil features and • dynamic soil properties that are susceptible to change in response to management, natural disturbances or climate change.

38. Function, Resistance and Resilience • Resistance:the capacity of soil to continue to function through a disturbance (resist change) • Resilience:the capacity to recover functional and structural integrity following a disturbance (rate and level of recovery) (Seybold, etal, 1999)

39. Soil Function, Resistance and Resilience Compaction disturbance Soil with high resistance Soil function (% of capacity) Low resistance and high resilience Low resistance and low resilience Time (years) (Seybold, etal, 1999)

40. Recovery and Remediation • The soils’ ability to recover may be limited by changes in its capacity to function. • In extreme cases, such as the loss of topsoil, restoration to original plant community may not be possible.

41. Why should we document dynamic soil properties for S&T models? • Provide greater accuracy for dynamic soil properties that affect the capacity of the soil to function (interpretations). • Hydrologic group • Useful for prediction of soil resistance, soil resilience, vegetation changes, and effects of disturbances or climate change. • C - sequestration • Provide reference “values” for rangeland inventories and planning • Management goals; early warning indicators

42. What kind of data storage framework is needed? A framework of Ecological Sites and S&T models can encompass soil properties that differ as a result of disturbances,type of managementand type of land use. This type of framework will enhance our ability to organize information related to soil-plant as well as soil-management interactions that affect soil properties and plant communities over time and at multiple scales. Reference or benchmark soils and eventually all soil map units used as rangeland will have a soil property database entry for states and thresholds of the STM.

43. Ecological Site Database Framework S&T model Runge fine sandy loam Herbaceous Herbaceous, pioneer clusters Clusters,Groves

44. What’s next? • Identify measurable soil properties that reflect ecological processes and the functional capacity of rangelands • Use S&T models to select sites for sampling • Use S&T models as a framework to organize data and to show relationships among plants, management, dynamic soil properties, and inherent soil properties.

45. What’s next? - cont’d • Evaluate the feasibility of incorporating land uses other than rangeland into a database framework based on S&T Models. • Identify research needs

46. Part 4 - Directions and future needs

47. DIRECTIONS Use modeling technologies to complete databasesUse observations to determine critical relationships and regionsSubstitute space for time

48. FUTURE NEEDS Models are representations of what we knowObservations are likely to create the impression of linear changeConstruct critical experiments to determine important events, actions