1. Hydraulic redistribution of soil water in two old-growth coniferous forests: quantifying patterns and controls Principles underlying the hydraulic redistribution of water by large trees: A review of Warren, et al. 2007

2. Biologically-mediated hydraulic redistribution of water: How? Plants photosynthesize during daylight Plants transpire water through stomata to fix carbon for growth; occurs along water potential gradients Plants cease transpiration during darkness Roots still drawing water to saturate tissues, alter soil water potentials

3. Biologically-mediated hydraulic redistribution of water Hydraulic redistribution of soil water (HR), in which root systems passively transfer water from moist to drier soil along a water potential gradient (  ) is a widespread phenomenon…” –Warren, et al 2007. Upward or downward through soil Also referred to as hydraulic lift

4. Biologically-mediated hydraulic redistribution of water Can be explained by water potential gradients –At night, the plant is at equilibrium with root water potential Soil properties and hydraulic conductivity explained by Darcy’s Law

5. Darcy’s Law Formulated by Henry Darcy in 1856 Describes the rate of flow of water through porous media “The rate of flow of water in porous media is proportional to, and in the direction of, the hydraulic gradient and inversely proportional to the thickness of the bed” Ward & Trimble Environ. Hydrology, P. 434

6. Darcy’s Law Can be modified to find K/  instead of a velocity (V): K = qL / Ah K: Hydraulic conductivity q: rate of outflow L: length of core sample A: Core cross-sectional area h: depth of the constant head applied -Ward & Trimble Environ. Hydrology, P. 79

7. The Research… Warren, J.M., Meinzer, F.C., Brooks, J.R., Domec, J.C. & R. Coulombe (2007). Hydraulic redistribution of soil water in two old-growth coniferous forests: quantifying patterns and controls. New Phytologist, 173: 753-765. Look to explain hydraulic lift through the natural variability in water potential gradients and seasonal courses of root conductivity (soil/plant biophysical properties)… An experiment in the WA/OR Cascades is born…

8. Two old-growth forests Deschutes Nat. Forest (OR) –Metolius Research Natural Area Gifford Pinchot Nat. Forest (WA) –Wind River Canopy Crane Facility Both have pronounced dry seasons (50- 150 days) and deeply-rooted (2-3m) conifers (Pseudotsuga menziesii & Pinus ponderosa)

9. Measuring water potential Soil  measured using thermocopule psychrometers at depths 20-100cm Plant  measured using pre-dawn removed shoots and a Scholander pressure chamber –Establish  values for both P. ponderosa & P. menziesii

10. Soil Volumetric Water Content (  ) Quantified with multi-sensor probes every 10-30 minutes at various locales Averaged for each depth Daily water-depletion rates were calculated between daily max and min 

11. Darcy’s Law Revisited Can be modified to find K/  instead of a velocity (V): K = qL / Ah K: Hydraulic conductivity q: rate of outflow L: length of core sample A: Core cross-sectional area h: depth of the constant head applied -Ward & Trimble Environ. Hydrology, P. 79

12. Modification of Darcy’s Law by Warren, et al Q p = KA  / L ≈ (100-PLC)A  / L Q p : Potential water flux (max value= 1) A: Cross-sectional area K: Root hydraulic conductivity  : Change in soil  between two points separated by distance L PLC: % loss of root conductivity

13. Putting it all together… They found a positive linear relationship between overnight recovery of  and  R 2 >.7 For a given value of soil , soil  was.01-.05 Mpa greater during nocturnal periods than during daytime periods

14. What does it mean? Soil moisture affects understory plant performance, distribution Hydraulic lift may change with global climate –Reduced precipitation >> Larger role hydraulically lifted water plays in ecosystems? Increased ambient CO 2 means more closed/fewer stomata –Does this mean less transpiration (less negative H 2 0 potential in leaves?)

15. Future Work Global and continental runoff balance? Global and continental streamflow? Transpiration’s role in the global hydrologic cycle with changing hydraulic lift? How do belowground biotic processes affect/ how are they affected by abiotic (water table, etc) processes?