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Impaired soil quality due to compaction and organic matter removal following forest harvesting and mechanical site preparation is of concern, especially on calcareous soils which are believed to be particularly sensitive to disturbance. This study set out to determine the effects of organic matter removal and compaction on soil quality and seedling productivity on calcareous soils of a localized disturbance landscape (2.25 m 2 ). Here we report ten year post-establishment results of Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) and lodgepole pine ( Pinus contorta var . latifolia Engelm.) seedlings across four sites in southern British Columbia, Canada with eight treatment levels incorporating different quantities of organic matter removal and soil compaction. Pine seedlings suffered high rates of mortality when planted in deposits across all sites while Douglas-fir seedling mortality was high when planted in compacted undisturbed treatments at two sites and in deposits on the remaining sites. Douglas-fir volume was greatest on the deposit treatment regardless of site but grew significantly better on the non-calcareous site. Pine seedlings outgrew Douglas-fir seedlings and, after ten years, seedlings were largest on a mildly calcareous site. Seedling growth was generally found to be negatively affected by calcareous soils and compaction; however, the specificity of results, in terms of species and site interaction and changing response as the seedlings aged, reinforced the importance of treatment effects on soil quality and forest productivity across the entire length of a stand rotation. [ABSTRACT FROM AUTHOR]

• Vegetation control yielded significantly better growth for the two tree species. • Organic matter (forest floor) removal negatively affected Douglas-fir growth. • Compaction significantly affected Douglas-fir survival and may affect future growth. • Amelioration currently not significantly different, but some grew better. • Vegetation competition was more of a problem on treatments that mixed soil. Understanding the relationship between soil disturbance and tree growth is key to sustainable forest management. We report fifteen-year tree growth results of Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) and western white pine (Pinus monticola Dougl. ex D.Don) growth following clearcut harvesting and installation of three replicates of the international Long-Term Soil Productivity (LTSP) trial protocols. Additional amelioration plots were also established on each replicate site to study rehabilitation of the most severe disturbance, treatment of Armillaria root disease, and enhancement of soil organic matter. Stark differences were found among the various treatments and species. Vegetation control resulted in significantly better growth for both tree species across the core LTSP treatments and amelioration treatments. On the core LTSP treatments, organic matter removal had a significant negative effect on Douglas-fir growth. Amelioration treatments resulted in similar survival and similar or better volume growth than the core LTSP treatments, with the exception of poor volume growth after compaction rehabilitation with no organic matter returned into the soil. Compaction significantly influenced Douglas-fir survival and was often higher on moderate compaction plots. On some sites there was decreased survival and growth associated with heavy compaction that will likely influence longer-term outcomes with a more variable and changing climate. Overall, results to date on the core LTSP treatments, amelioration treatments, and adjacent miniplots reported elsewhere suggest that forest floor removal causes negative growth and, combined with severe compaction, caused both negative growth and poor survival. In the Interior Northwest it is still prudent to minimize soil disturbance and leave organic matter onsite unless there is site specific evidence to the contrary. Additional work is required to reap the full, long-term benefit of the installations. Recommendations are provided highlighting the critical work that should be completed in the near future before biological evidence is lost to decay, including suggestions for further data analysis and extension, the need to continue LTSP core, amelioration and miniplot measurements to demonstrate and calibrate sustainable forest resource management. Our data suggest considering changes to current soil disturbance policy and forest operations based on the current results regarding forest floor displacement. [ABSTRACT FROM AUTHOR]