Effects of intensive forest management on soil phosphorus (P)are unclear and may impact long-term site productivity. We assessed changes in P availability over 10 years associated with harvest intensity (bole-only vs. whole-tree harvest)and vegetation control treatments (initial vegetation control (IVC)vs. five years of annual vegetation control (AVC))using a P fractionation procedure. Fractions were characterized at 0–15, 15–30, and 30–60 cm soil depths in two coast Douglas-fir (Pseudotsuga menziesii (Mirb.)Franco var. menziesii)plantations with strongly contrasting soil properties near Matlock, WA (young soils formed in glacial outwash)and Molalla, OR (relatively old soils formed in igneous residuum and exhibiting andic properties). Al and Fe concentrations associated with short-range order minerals were greater at Molalla than Matlock and generally decreased with depth at both sites. We observed decreases in most total-P and P-fraction concentrations across the three soil depths at the Molalla site. Effects were less pronounced and generally inconsistent at the Matlock site. Decreases in total P and P fraction concentrations were greatest in the AVC treatments at Matlock, but opposite trends were observed at Molalla where decreases were greatest with IVC. There was no difference between harvest treatments on the change in P fractions in most instances, with the exception of the 30–60 cm depth at Matlock where concentrations of some P fractions were maintained or increased with bole-only harvesting. Ten-year responses indicate harvest intensity has limited effects on long-term productivity associated with soil P because of the large size of the soil P pools and the relatively small changes in soil P that occurred with treatment. Decreases in P concentrations with AVC at Matlock and IVC at Molalla were larger than the other treatments and highlight the important role of vegetation in P dynamics following harvesting at these sites.
Bibliographical noteFunding Information:
This is a product of the Sustainable Forestry component of Agenda 2020, a joint effort of the USDA Forest Service Research and Development and the American Forest and Paper Association. Funds were provided by the USDA Forest Service Pacific Northwest Research Station, Virginia Tech, Green Diamond Resource Company, and Port Blakely Tree Farms, LLC. The authors are grateful to Randall Greggs and Mike Warjone for providing critical financial and logistical support that made this study possible. Special thanks to J. Dollins for assisting with field work and sample preparation, and Stephanie Duston for her assistance in the laboratory.
© 2019 Elsevier B.V.
- Long-term soil productivity
- Scotch broom
- Selective dissolution extraction
- Site-specific response