Effects of site preparation on ponderosa pine (Pinusponderosa), associated vegetation, and soil properties in south central Oregon

Abstract

Eight years after installation, six site preparation treatments were compared for effects on soil chemical and physical properties, nonconiferous vegetation, and the survival and growth of planted ponderosa pine (Pinusponderosa Laws.). Treatments included a logged-only control, ripping, brush blading, disking, chemical spraying (herbicide), and chemical spraying followed by disking. The brush-blade and chemical–disk treatments showed the greatest reduction in nutrient levels (total N, S, and C, and extractable P) compared with the control within the lower zone of soil sampled (15–25 cm depth). The chemical-only and disk-only treatments resulted in smaller decreases in nutrient levels, while ripping appeared to have only minor effects on soil chemical properties. Similar trends were noted in the upper soil zone (0–10 cm), although the differences were not statistically significant. Brush blading and both disking operations increased soil bulk density in the upper soil zone, but not in the lower soil zone. Aboveground biomass of shrubs was highest on the control treatment, followed by the rip, disk, brush-blade, chemical, and chemical–disk treatments. Pine survival was 78% or better for all treatments except the rip and control. The chemical–disk and chemical treatments resulted in the best height growth, followed by the disk, brush-blade, rip, and control treatments. A strong negative correlation existed between the amount of brush and pine biomass after 8 years. This study illustrates the importance of weed control to achieve maximum survival and early growth of planted pines in south central Oregon.