Kim Littke Rob Harrison David Briggs University of Washington

1. Understanding Site-Specific Factors Affecting the Nutrient Demands and Response to Fertilizer by Douglas-fir • Kim Littke • Rob Harrison • David Briggs • University of Washington Center for Advanced Forestry Systems 2010 Meeting

2. Rationale • Nitrogen fertilization is a common practice in Douglas-fir forests of the Pacific Northwest • The Regional Forest Nutrition Research Project studied the effect of N fertilization over western Washington and Oregon • However, growth response to N fertilization was widely variable • No site and soil factors have been confirmed as response predictors for Douglas-fir Center for Advanced Forestry Systems 2010 Meeting

3. Objectives • Test soil variables including bulk density, nutrient pools, temperature, and moisture • Record non-soil variables such as site index, LAI, elevation, slope, precipitation, air temperature, and relative humidity • Determine which factors can predict N fertilizer response • Focus on variables that are easily obtained Center for Advanced Forestry Systems 2010 Meeting

4. Experimental Plan • 15-30 year-old Douglas-fir stands in British Columbia, Oregon, and Washington • Range of landform, elevation, and slope • Measure DBH, height, and crown height of 48 dominant Douglas-fir • Pair trees according to the best matches for DBH and crown height • Fertilize one tree per pair with 224 kg N/ha • Select up to 20 pairs per installation Center for Advanced Forestry Systems 2010 Meeting

5. Paired Tree Design Center for Advanced Forestry Systems 2010 Meeting

6. Paired Tree Installations • Red Markers – Glacial parent material • Green Markers – Sedimentary parent material • Blue Markers – Igneous parent material Center for Advanced Forestry Systems 2010 Meeting

7. Progress • 60 Douglas-fir installations • 2 ponderosa pine • 25 glacial • 19 sedimentary • 18 igneous • 59 installations have soil sampled and weather stations installed • Complete weather station data for one growing season for 31 installations • Six installations with two-year growth data Center for Advanced Forestry Systems 2010 Meeting

8. Site Quality Center for Advanced Forestry Systems 2010 Meeting

9. Soil Nitrogen to 1 Meter Glacial North to South Sedimentary Center for Advanced Forestry Systems 2010 Meeting

10. Basal Area Growth Percent Center for Advanced Forestry Systems 2010 Meeting

11. Height Growth Percent Center for Advanced Forestry Systems 2010 Meeting

12. Volume Growth Percent Center for Advanced Forestry Systems 2010 Meeting

13. Foliage Area after fertilization • Control • Fertilized Center for Advanced Forestry Systems 2010 Meeting

14. Foliar N Concentration Center for Advanced Forestry Systems 2010 Meeting

15. Basal Area Growth Response Center for Advanced Forestry Systems 2010 Meeting

16. Height Growth Response Center for Advanced Forestry Systems 2010 Meeting

17. Timeline • Two-year growth data for 28 installations fall 2010 • Foliage, forest floor, and soil sampling • 26 installations will be measured fall 2011 • Four-year growth data to be measured 2011, 2012, and 2013 • Background soil samples to be finished spring 2010 • Weather stations maintained twice yearly Center for Advanced Forestry Systems 2010 Meeting

18. Deliverables and Budget • Establishment of Paired Tree Installations throughout the Pacific Northwest • Derive a model to predict fertilizer response based on site and soil factors • $20,000 for the next year • Other support from: • Stand Management Cooperative • Agenda 2020 Center for Advanced Forestry Systems 2010 Meeting

19. total funding $195,078

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