Douglas-fir plantation productivity: effects of organic matter retention, competing vegetation, and soil compaction

Transcription

1 Douglas-fir plantation productivity: effects of organic matter retention, competing vegetation, and soil compaction Investigators: Tim Harrington and Connie Harrington, USDA Forest Service Tom Terry, Weyerhaeuser Company Rob Harrison, University of Washington Stephen Schoenholtz, Virginia Tech and those scientists in training...

2 Some of the participating organizations...

3 Study context: extending the LTSP network Does manipulating organic matter, soil porosity, and the complexity of the plant community affect a forest site s productive capacity? Powers et al. 2004

4 Approach: compare productivity across a wide range of organic matter, vegetation, and soil treatments

5 Site characteristics Fall River Matlock Molalla Matlock soils silt loam very gravelly loamy sand cobbly loam Fall River rainfall site index planted Molalla Grove soil series near Matlock

6 Precipitation and temperature differences Fall River: coldest Matlock: wettest Molalla: warmest & driest

7 Dominant effect: competing vegetation Competing vegetation effects Organic matter retention effects

8 100 Matlock Molalla Fall River How does Douglas-fir development compare among sites? Survival (%) Stem diameter (mm) Stem only, NWC Stem only, WC Piled, NWC Piled, WC Whole tree, NWC Whole tree, WC Height (cm) Years since treatment

9 Interacting effects of organic matter retention and competing vegetation Douglas-fir stem volume (cm 3 ) Matlock Molalla 0% debris, NWC 40% debris, NWC 80% debris, NWC 0% debris, WC 40% debris, WC 80% debris, WC Years since treatment Individual-tree study

10 Soil water: primary driver of productivity Direct relationship of diameter growth to soil water content at Fall River Diameter growth (mm) r = 0.66 p < Soil water content (m 3 m -3 ) Competing vegetation effects Organic matter retention effects

11 Organic matter retention effects on competing vegetation: Reduced herb abundance Competing vegetation cover (%) Matlock Herbs, NWC Herbs, WC Woody, NWC Woody, WC Molalla Logging debris cover (%) Individual-tree study: vegetation present

12 Nitrogen losses: small and short term Organic matter retention effects Competing vegetation effects Nitrate-N (mg L -1 ) Soil water nitrate-n (60cm depth) by herbicide treatment and site 7.0 Matlock NWC 6.0 Matlock WC Molalla NWC 5.0 Molalla WC Jan-06 Mar-06 May-06 Jul-06 Sep-06 Nov-06 Jan-07 Mar-07 May-07 Jul-07

13 Soil compaction effects: small to non-detectable Stem diameter (mm) control compacted Height (cm) Fall River Matlock Molalla Third-year size of Douglas-fir: differences not statistically significant

14 Soil microbial community responses: fate of carbon Microbial respiration by woody-debris retention at Molalla debris 40 debris 80 debris Organic matter retention effects CO2 flux (umol m 2 sec -1 ) Microbial respiration by herbicide treatment at Molalla Sep-05 Nov-05 Jan-06 Mar-06 May-06 Jul-06 Sep-06 Nov-06 Jan-07 Mar-07 May-07 Jul-07 Sep CO2 flux (umol m 2 sec -1 ) Competing vegetation effects 1.0 NWC WC Sep-05 Nov-05 Jan-06 Mar-06 May-06 Jul-06 Sep-06 Nov-06 Jan-07 Mar-07 May-07 Jul-07 Sep-07

15 The Next Steps linking similar data sets collaborative relationship 5 th -yr data in 2008 characterizing the drivers how do they work? formulating decision-analysis systems how will this work be supported? predicting management consequences model validation