1. Seasonal and successional trends in streamflow and N after forest removal in small basins, eastern and northwestern US Julia Jones, Oregon State University David Post, CSIRO, Townsville, Australia Kate Lajtha, Oregon State University

2. Questions 1.What are streamflow responses to forest removal and regrowth across a range of sites? 2. What might be the implications for N fluxes of streamflow-forest interactions? 3. What are the special opportunities in hydrologic research for ecosystem informatics?

3. What are the streamflow responses to forest removal and regrowth as a function of Dry/wet summers Snowpack presence/type Forest type – deciduous broadleaf/evergreen conifer Time since most recent disturbance Andrews WS1,2 2001

4. Even with a treated/control pair, weak causal inferences Instrumented locations of questionable generality Out of date treatments Prediction in ungaged basins Long records Treated/control pairs Complementary information on ecological processes Can pose mechanistic hypotheses to be checked by process studies and modeling Andrews WS9, 2001 Limitations and potentials for “black-box” watershed studies

5. Questions – causes and consequences Causes:  Vegetation physiology  Physical vegetation- atmosphere interactions  Snowpack  Drainage Consequences:  Water availability for plants  Biogeochemistry  Stream ecology Andrews WS 10, 1968

6. Time scales of interest to ecologists and hydrologists Diurnal Storm Seasonal Successional Climate change Evolutionary Andrews WS 10, 1977

7. Instrumented sites (red dots) used in this study– eastern and western forests Deciduous/conifer Seasonal/transient/no snowpack

8. Types of treatments: Intentional  Vegetation manipulation  Drainage manipulation Inadvertent  Natural disturbance  Climate change  Edge effects Andrews WS 1, 1966

9. Analysis of streamflow change in treated/control comparisons Essence of analysis - look at change over time in ratio of treated/control flows Examine daily flows for 5-yr periods, before and after forest removal Consider both absolute and relative changes and their consequences Absolutely large changes Absolutely small, relatively large changes at key periods Consider whole set of basin pairs as ~multifactorial experiment

10. SiteAndrewsCoweetaHubbard Brook NaturalSevere wildfire, 1500s; some wildfire, mid-1800s Severe windthrow during 1835 hurricane Severe windthrow during 1938 hurricane HumanGrazing, burning on non-forest meadows at high elevations, ~1900 Cherokee spring/fall burning, to 1837; Cultivation, grazing, annual burning 1850- ~1900; Complete logging, 1919; Chestnut blight, 1930s-40s; Extensive logging, 1890-1920; Salvage after 1938 hurricane Pre-treatment disturbance histories of sites - state of “control” basins

11. Basin sizes and disturbance histories

12. Lengths of record in experimental basin pairs Vertical lines are 100% clearcut treatments; HBR 2/3 and Fernow 7/4 had herbicide

13. Climates of the sites - Hubbard Brook

14. Climates of Hubbard Brook vs. Andrews Hubbard Brook vs. Coweeta

15. Effect of climate, forest type on streamflow by season - Relative changes - Hubbard Brook 2/3 Relaative change (%) in streamflow

16. Relative changes - Hubbard Brook vs. Andrews Relaative change (%) in streamflow

17. Effect of climate, forest type on streamflow by season - Absolute changes - Hubbard Brook 2/3 Absolute change (mm) in streamflow

18. Absolute changes - Hubbard Brook vs. Andrews Absolute change (mm) in streamflow

19. Effect of time since forest removal, by season Delayed August deficits Persistent spring surpluses and deficits 5-yr post-treatment periods; periods 4-5 are 15-25 years after forest removal Delayed summer deficits Absolute change (mm) in streamflow

20. Effect of time since pre-treatment forest disturbance conifers, seasonal snow conifers, transient.no snow deciduous, seasonal snow deciduous, transient/no snow 1 to 5 yrs after15 to 25 yrs after y = 138Ln(x) - 332 r2 = 0.45 y = 142Ln(x) - 524 r2 = 0.71 Absolute change (mm) in annual streamflow

21. “out of controls?” The treated/control relationship in paired- basin experiments, rather than a black and white one, can be viewed as a function of continuous – and continuously changing – differences between basins in vegetation structure, composition, and climate. Time scales, scaling: Paired-basin records provide the opportunity to quantify and compare streamflow responses at multiple temporal scales, including storm events, seasons, successional periods, and decadal climate change. Regionalization: Small paired-basin experiments permit comparison (prediction?) of streamflow responses across vegetation types and treatments, climates, and basin scales. General lessons about paired-basin studies

22. Hydrologic interactions with basin-scale N fluxes Concentration vs. flux Nitrate vs. dissolved organic N Mechanisms: Biologically controlled (uptake, retention, immobilization) vs. Physically controlled (fast/slow flowpaths, water table variations) or Biophysical interactions – spatial patterns of labile forms, changing flowpaths Three kinds of patterns

23. Coweeta 18 Coweeta 36 Coweeta 18 Coweeta 36 Discharge (mm) Month (Jan-Dec) 5 0 mg/L 5 0 Nitrate concentration (Swank et al., 1997) Coweeta: Very low nitrate concentration, peaks during summer

24. Andrews: DON concentration peaks in fall, as hydrograph rises Vanderbilt et al., 2002 DONprecipdischarge

25. Nitrate concentration (Likens, 1977) Hubbard Brook: high N concentration, peaks during snowmelt 5 0 mg/L Discharge

26. Opportunities for eco-hydrology studies How does vegetation influence water fluxes to/from atmosphere? How does water use influence carbon, nitrogen fluxes?

27. Acknowledgements NSF Long-term studies NSF LTER grants to Andrews, Coweeta, Hubbard Brook USFS support of long-term monitoring at Andrews, Caspar Creek, Coweeta, Coyote Creek, Fernow, and Hubbard Brook Experimental Forests USFS support of Hydro DB Data and expertise were provided by the following USDA Forest Service personnel: C. Creel, G. Downing, R. Fredriksen, D. Henshaw, A. Levno, G. Lienkaemper, J. Moreau, S. Remillard, (Andrews); J. Lewis (Caspar); N. Gardiner, W. Swank, L. Swift (Coweeta); M.B. Adams (Fernow); and J. Campbell, C. Cogbill, J. Hornbeck, W. Martin (Hubbard Brook). We would like to thank J.J. Major and F.J. Swanson for helpful discussions. J. Hornbeck, J. Lewis, J. McDonnell, L. Reid, W. Swank for reviews.