Productivity and soil properties 45 years after timber harvest and mechanical site preparation in western Montana

Abstract

Site preparation following timber harvests is widely used to increase seedling establishment postharvest. Historically, dozer piling and ripping were the most common forms of site preparation in the Intermountain West. Less commonly, terracing of hill slopes was another form of site preparation on the Bitterroot National Forest in western Montana from 1961–1970 on marginally productive lands. Our objective was to compare soil physical and chemical propertie sa s well as timber productivity as evidenced by diameter-at-breast height (dbh) between terraced and standard-site preparation methods as well as unharvested stands. We collected and analyzed soil samples for bulk density, mineral cations, total C, total N, organic matter, particle size, and pH, forest floor measurements, tree dbh, and ground cover. Even after 45 years, visual soil disturbance in site-prepared stands was still observable with a majority of sites having some degree of compaction or rutting damage. Many soil chemical and physical properties were not significantly different among the two site treatments and the unharvested control stands. However, soil organic matter was significantly lower in the terraced and standard site-prepared stands than in the unharvested stands. Ponderosa pine dbh was greater in the terraced stands than in the nonterraced stands, but understory species diversity was low. The loss of surface soil organic matter and understory species associated with both forms of site preparation is a concern for future forest management. Leaving forest residue during harvest operations, limiting travel routes during management operations, and minimizing forest floor displacement may allow for limited soil impacts on future site-prepared stands.