Water and Carbon Cycles in Heterogeneous Landscapes: An Ecosystem Perspective

1. Water and Carbon Cycles in Heterogeneous Landscapes: An Ecosystem Perspective Chapter 4 How water and carbon cycles connect the organizational levels of organisms, ecosystem, and landscape, and what we know of the mechanisms of their operation. • Obstacles that one faces trying to connect these different levels and the ways to tackle them; • Current research questions and approaches;

2. Background • Ecosystem vs landscape • Ecosystem ecology vs landscape ecology • Lack of ecosystem studies at landscape level • Extremely difficulty to measure an ecosystem process (e.g., water and carbon fluxes) • Sound experimental design is extremely difficult to develop • Challenge in scaling (up and down)

3. Spatial display of growing season ecosystem evapotranspiration from eight ecosystems

4. Organizational levels above and below ecosystem. We differentiate between change in organizational level (shown with arrows) and simple aggregation.

5. Major water fluxes in a forested watershed

6. Water Fluxes: Growing season evapotranspiration for five ecosystems and their relative contributions at a landscape scale in northern Wisconsin.

7. Ecosystem transpiration flux saturates with increasing vapor pressure deficit

8. Evapotranspiration (E) – Monteith Model (1965) E is evapotranspiration,  is the slope of the saturation vapor pressure-temperature curve, Rn is canopy net radiation, cp is the specific heat capacity of air, a is the density of air, VPD is vapor pressure deficit from canopy to air, ra is the bulk vegetation aerodynamic resistance, w is the density of water,  is the latent heat of evaporation,  is the psychrometric constant, and rc is canopy resistance. Aerodynamic resistance, ra, is affected by canopy properties and the flow of air through and above the canopy, while rc = (GSL)-1, where GS is canopy average stomatal conductance and L is canopy leaf area.

9. Stomata Conductance (Gs) – Jarvis Model (1976) where -m is the logarithmic sensitivity of the GS response to VPD. GSref is defined as maximum GS at VPD=1 kPa. This model is preferred over the Ball-Berry stomatal conductance model (Ball et al., 1987) because of its use of relative humidity as the driving factor instead of VPD.

10. Topography (A) and ecosystem types (B) of a section of CNNF

11. Seasonal dynamics of simulated and measured ecosystem evapotranspiration and volumetric soil moisture

12. Major Carbon fluxes in a forest

13. Global carbon cycle

14. Atmospheric carbon pools can be reduced by: • 1) Reduce carbon emission from fossil fuel combustion. • 2) Increase carbon storage by: • Increasing ecosystem productivity, and • Decreasing plant decomposition

15. Terrestrial ecosystem carbon cycle - 3 720 Atmosphere -2 X 0 13 39 480 +2 43 74 2 24 80 31 31 140 25 900 Pools Fluxes 1500 units: Pg/yr (1x 1015 g)

16. Forests cover a wide geographical area and contain 80% of all aboveground terrestrial carbon(Waring and Running, 1998) http://www.globalforestwatch.org

17. Small Carbon Storage Fast Fast Large Carbon Storage The ability for terrestrial ecosystems to store carbon depends on the rate at which carbon dioxide is absorbed through photosynthesis and released by decomposition Fast Slow

18. 50N 40N Units: Tons C ha-1 yr-1 30N 120W 110W 90W 70W 100W 80W In the United States, major carbon sinks are in the east part of the continent (Myneni et al., 2001). Units: Tons C ha-1 yr-1

19. Why focus on timber harvesting? Timber harvesting is a major agent of ecosystem disturbance worldwide. Timber harvesting affects microclimate, carbon pool sizes, decomposition, and ecosystem respiration.

20. Decomposition and Respiration They are the primary mechanisms that recycles carbon bound in plant tissue or in organisms back to the atmosphere. These two processes determine the capacity of an ecosystem pool to hold carbon.

21. Swiss-Cheese Mosaic Pine Barrens The Checker-board landscape Spatial Mosaics of Managed Landscapes in N. WI

22. An accurate assessment of the contribution of terrestrial ecosystems to the global carbon budget should consider the diversity of site conditions and developmental stages within the landscape mosaic.

23. Hypothesis The cumulative C fluxes of a landscape are determined by the land mosaic; that is, the various ages and types of ecosystems present, as well as their size and shape. Landscapes are composed of a variety of ecosystems differing in type, age, size, shape, and spatial arrangement. A key question is: Are managed landscapes a C sink or source?

24. (a) (c) (b) Changes in NEP with age (a) and the age structure of a hypothetical landscape (b) together determine the cumulative NEP of the landscape (c) Chen et al. 2004.

25. Autotrophic respiration Leaf gross photosynthesis Net ecosystem exchange Leaf net photosynthesis Leaf respiration Photorespiration Stem respiration Gross primary production Net primary production Root & mycorrhizal respiration Leaf litter respiration CWD respiration Heterotrophic soil respiration Heterotrophic respiration Soil surface CO2 efflux Respiration: forest ecosystem carbon fluxes Atmosphere Photo-tissue Non-photo-tissue CWD Leaf litter Soil Roots Modified from Gifford 2003

27. J-Rover: The Mobile Flux Cart

28. Net ecosystem exchange of carbon (NEE) as a function of ambient photosynthetically active radiation (PAR)

29. Growing season cumulative NEE, ER, and GEP in stands of different ages

30. Landscape-level variation in gross ecosystem productivity, ecosystem respiration and net ecosystem exchange of carbon