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Robert Slesak – Oregon State University Stephen Schoenholtz – Virginia Tech

Soil C Cycling Following Timber Harvest in Response to Logging Debris Retention and Herbicide Application. Robert Slesak – Oregon State University Stephen Schoenholtz – Virginia Tech Timothy Harrington – PNW Research Station, USFS. Background. Uncertainty in response of

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Robert Slesak – Oregon State University Stephen Schoenholtz – Virginia Tech

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  1. Soil C Cycling Following Timber Harvest in Response to Logging Debris Retention and Herbicide Application Robert Slesak – Oregon State University Stephen Schoenholtz – Virginia Tech Timothy Harrington – PNW Research Station, USFS

  2. Background • Uncertainty in response of soil microbial respiration (SMR) to harvesting(disturbance) • Net effect of management practices on soil C pools • Site Productivity - Reduced soil C (soil OM) may reduce longterm soil quality

  3. Study Objectives • Treatment effects on SMR • Importance of modified soil enviro. or C input from treatments on response • Determine ifDOC concentrations • vary with treatment • Relationships between DOC and • soil respiration (see you in • New Orleans)

  4. Experimental Approach • Experimental unit = individual tree (4m2 area centered on tree) • Logging debris at either 0, 40, 80% ocular coverage • With or without sustained herbicide application • 2 sites with contrasting soil characteristics and precipitation • Treatments applied in March 2005

  5. Measures • Monthly in situ SMR • Soil temperature (0-10 cm) • Soil water DOC with tension lysimeters (60 cm) • Lab incubations (3 annually) • - constant temp and moisture • - SMR and DOC

  6. Matlock – microbial respiration

  7. Molalla – microbial respiration

  8. Lab-field comparison for April Matlock No significant differences in lab or field No significant differences in lab Sig. main effect of herbicide (p<.05) In field Molalla Suggests effect in field at Molalla probably due to modified environment

  9. Lab-Field comparison for July Matlock Significant effect of debris (p=.05) In field No significant differences in lab No significant differences in field (herb p=.11) Significant effect of debris (p=.04) and herb (p=.03) in lab Molalla Matlock – field effects probably due to modified environment Molalla – field environment may be inhibiting treatment effect - variance may mask field effect (may be C effect from herbicide)

  10. Soil Water DOC Matlock Debris F=2.19, p=.12 Molalla Debris F=5.94, p<.01

  11. Conclusions • Control of competing vegetation and logging debris reduces microbial respiration for part of the growing season - length of time varies by site • Modified SMR due primarily modified soil environment • - temperature alone does not explain response • - soil moisture most likely plays important role • Some evidence for C input effect or modified microbial community • DOC “loss” greatest in the absence of logging debris (non-sig. Matlock) • Combined (SMR+DOC) C flux greatest for 0% debris retention • - losses may be offset by C inputs (NWC) • - losses may not be greater than reference (WC) • Total soil C at end of experiment will determine net change in pool

  12. Questions?

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