Seminars

1. Seminars • EECB seminar Thurs 4:00 PM OSN 120. Dr. Larry Stevens, Grand Canyon Wildlands Council. “Biogeography of the Grand Canyon, and Colorado River Management”.

2. Reading • Textbook Chapter 12 and 13 • Sparrow, A., M. Friedel, and D. Tongway. 2003. Degradation and recovery processes in arid grazing lands of central Australia part 3: implications at landscape scale. Journal of Arid environments 55: 349-360.

3. Outline • Case study: identifying communities and relating to environmental conditions • Student case studies • Productivity – plants and ecosystems • GPP, NPP, and Efficiency • Global and environmental patterns of NPP • Production in forest VS rangeland • Factors influencing productivity – fire, herbivory, nutrient pulses, etc. • Climate change, CO2 accumulation, and carbon sequestration

4. Identification and interpretation of community patterns • Using classification (TWINSPAN) to identify wet meadow communities • Relate community classification to environmental (hydrologic and geomorphic) variables • Interpret impact of stream incision on vegetation communities

5. Humboldt-Toiyabe National ForestCentral NevadaSan Juan Creek Reese River Birch Creek

6. Reach-scale vegetation patterns Below-fan: Intermediate valley characteristics Woody riparian, mesic & dry meadows Above-fan: Broad valley bottom Wet meadows At-fan: Narrow valley bottom Woody riparian and upland vegetation

7. Objectives – Hydrologic Component • Determine the dominant vegetation types & their species associations within Kingston Meadow • Examine relationship of vegetation types to the current hydrologic regime within Kingston Meadow • Evaluate any changes in vegetation associated with a different hydrologic regime following meadow restoration activities

8. Sampling Scheme • Determine the composition, ground cover, and biomass of the vegetation associated with each piezometer or nested well across a hydrologic gradient within the meadow • 14 cross-valley transects (10 with piezometers/wells; 4 more to adequately sample vegetation) • 55 sampling points (45 nested piezometers + 10 additional sampling points) • 110 sample plots (2 subsamples per sampling point)

9. Terrace Height TWINSPAN From unpublished data and Henderson, 2001 Stream cross-sections

10. Meadow GroundwaterCharacteristics Meadow Type From Linnerooth & Chambers, 2000

11. Vegetation Types- Hydrology Plots

15. Current System Dynamics • Climate changes that occurred over 2000 years ago are still influencing system dynamics • Recent incision began at the end of the Little Ice Age about 290 years ago • The rate and magnitude has undoubtedly been increased by human disturbance

16. Stream Incision: Causes • Overgrazing in riparian zone and upland areas within the watershed • Roads (crossings, captures) • Sediment “starvation” due to long-term climate effects

17. Stream Incision: Causes Barrett Canyon Corral Canyon

18. Stream Incision: Causes • Overgrazing in riparian zone and upland areas within the watershed • Roads (crossings, captures) • Sediment “starvation” due to long-term climate effects

19. Stream Incision: Consequences • Lowers water table in the riparian zone (threshold event) • Stream flow becomes isolated from former floodplain • Development of inset terraces • Invasion of more-xeric species • Narrowing of riparian zone and loss of riparian habitat

20. Barley Cr. (Monitor Range) San Juan Cr.

21. Cottonwood Creek 1998 1994

22. Gaining Systems Non-Incised Meadow Ground Surface Water Table Surface Incising Meadow Ground Surface Water Table Surface Losing Systems Ground Surface Water Table Surface

23. Your turn… • List management issues/projects you know of in range and forest ecosystems. • Which of the ecological processes or interactions we have discussed so far do you need to understand? • Can you make predictions or recommendations based on your understanding of the ecological systems?

24. Productivity • Energy captured by autotrophs. • GPP=total solar radiation fixed into chemical energy via photosynthesis • NPP=GPP-respiration • Textbook Figure 12.1 = energy pathways at primary trophic level. Solar energy is reflected, emitted, assimilated, respired, consumed by herbivores, turned into detritus, or stored in standing crop/biomass.

25. Efficiency • Proportion of energy converted into plant material. Three components: • Exploitation efficiency = ability to intercept light. GPP/solar radiation X 100%. Affected by LAI, leaf orientation, latitude, topographic location. • Assimilation efficiency = ability to convert absorbed light into photosynthate. GPP/absorbed radiation X 100%. Affected by CO2 absorption, temperature, light and water availability. • Net production efficiency = capacity to convert photosynthate into growth/reproduction rather than respiration. NPP/GPPX 100%. Depends on temperature and amount of non-photosynthetic biomass supported.

26. Net Primary Production • Difficult to measure accurately on large scale because requires measures of photosynthetic and respiration rates. • Usually use changes in biomass over time NPP = (wt+1- wt) +D + H Where (wt+1- wt) is change in biomass over time D= biomass lost to decomposition H= biomass lost to herbivores

28. Net Primary Production • Can also use allometric means: changes in plant size; use regression to assess. • Allometry provides measure of root production (mini-rhizotron images) • Global scale • Models based on climate, precipitation, evapotranspiration • Also – remote sensing data

30. Carbon balance • NPP-decomposition/loss to herbivores • Essentially change in standing crop over time • Important in assessing impact of vegetation on CO2 emissions under Kyoto Protocol etc.

31. Relationship of biomass to productivity • BAR = biomass accumulation ratio • Ratio of dry weight biomass to annual NPP. • Higher for plant communities with more long-lived structure (woody plants)

32. Forest biomass and NPP • Productivity often strongly related to soil fertility or texture (eg N mineralization rate in eastern US) • As community ages, ANPP changes: • Immediately following disturbance ANPP rapid and biomass accumulates quickly • Maximum NPP and living biomass at 50-100 yrs • Leaf biomass is maximal just before canopy closure • Older forests have lower carbon balance – decomposition and respiration/maintenance of nonphotosynthetic tissues

33. Rangeland biomass and NPP • Higher biomass not necessarily related to higher NPP • In dense grasslands removal of dead or “decadent” biomass may stimulate productivity • Indication of coevolution of herbivores and grasses? Ability of grasses to re-grow photosynthetic tissue after removal = herbivore tolerance • Grazing lawns = rapid nutrient cycling and high productivity caused by repeated grazing

34. Factors affecting NPP • Light, temperature • Water (precipitation, evapotranspiration) • Carbon dioxide (high concentrations more influential for C3 than C4) • Nutrient availability (see handout and text P326) • Herbivory – can stimulate (by reducing competition for light) or decrease (by removing photosynthetic tissue) • Fire – usually stimulates: release of nutrients, removal of competition for light and water

35. Variable resources • Resources are not constant in time or space • Ecosystems are limited by a variety of resources • Transient Maxima Hypothesis: TMH • Explains patterns of productivity for non-equilibrium systems. • E.g. tallgrass prairie: at equilibrium, light is limiting (soil resources not utilized to maximum) • When disturbed, light not limiting, productivity increases to utilize available resources (hence increase in productivity with fire or herbivory)

36. Global carbon cycle • Atmospheric carbon flux strongly affected by human activity • Combustion of fossil fuels and clearing of forest releases sequestered carbon into atmosphere • Substantial changes in CO2 since industrial revolution (from 280 ppm to >350 ppm) • Productivity of vegetation affects CO2 concentration in atmosphere