Twenty-year effects of mechanical site preparation and windrow burning treatments on soil properties and Pinus contorta var. latifolia nutrition in sub-boreal British Columbia

Abstract

This study examined mechanical site preparation and windrow burning effects on soil properties and lodgepole pine (Pinus contorta var. latifolia) foliar nutrients on a sub-boreal site in north–central British Columbia, Canada. After two decades, there were no adverse long-term effects on soil bulk density. Rather, bulk densities to 20 cm depth declined continuously in all treatments including the control. Coarse mixing was associated with lasting increases in organic matter-related properties [total carbon (C) and nitrogen (N), ammonium-N, C/N] compared with the control, whereas plow-inverting, disk trenching, fine mixing and windrow burning had no lasting effects on these attributes. In contrast, windrow burning caused persistent increases in pH and related properties (cation exchange capacity, exchangeable calcium and potassium) relative to the control. Mechanical treatments had more short-lived effects on these properties, with the exception that coarse mixing caused significant 20-year reductions in pH relative to the control. There were slight deficiencies of foliar N, sulfur (S) and boron according to published thresholds. None of the treatments affected foliar N, and the effects on total S and sulfate-S were highly variable and not statistically significant. Boron deficiency in the control and mechanical treatments worsened between years 10 and 20, whereas levels on burned windrows were continuously high.

Keywords:

• Foliar nutrients
• lodgepole pine
• mechanical site preparation
• soil bulk density
• soil nutrients
• windrow burning

Acknowledgements

We thank Dr Robert McMinn, Marvin Grismer, BC Ministry of Forests and Range (MFR) staff, and contractors who were involved initially in the installation, measurement and maintenance of the study site. We are also grateful to Anne Macadam and Rick Trowbridge for collection of year 10 soil data and to Marvin Grismer, Cosmin Man, Torsten Kaffanke and David Sword for soil and foliar sampling in year 20. Our appreciation also goes to Clive Dawson and staff at the Ministry of Forests and Range Analytical Laboratory (Victoria) for soil and foliar sample preparation and analysis. Thanks to Richard Kabzems, Marty Kranabetter, John McClarnon and Allan Powelson of MFR, and to Paul Sanborn of the University of Northern BC (Prince George) for input during the study and the preparation of the manuscript. Funding for the study was provided by MFR, Canada–British Columbia Economic and Regional Development Agreements (FRDA), Forest Renewal BC (FRBC) and BC Forest Investment Account: Forest Science Program. Funding assistance does not imply endorsement of any statement or information in this paper.