Long-term effects of organic matter removal, compaction, and vegetation control on tree survival and growth in coarse-textured, low-productivity soils

Abstract

The Long-Term Soil Productivity Network is providing a systematic examination of the effects of organic matter removal and compaction on a variety of different soils and forest types across North America. Here we report on the 22nd-year survival and height growth of white oak (Quercus alba), northern red oak (Q. rubra), and shortleaf pine (Pinus echinata) on rocky, nutrient-poor soils that have a low to moderate water holding capacity in the Missouri Ozark Highlands. Treatments included three levels of organic matter removal (sawlog, whole tree, and whole-tree plus forest floor) and three levels of soil compaction (none: bulk density = 1.34 g cm−3; moderate: bulk density = 1.65 g cm−3; and severe: bulk density = 1.78 g cm−3) each with and without vegetation control. Following treatments, bareroot, 1–0 white oak, northern red oak, and shortleaf pine seedlings were planted at a 3:3:1 ratio, approximating the distribution of these species in this region. Within half of each plot, a vegetation control treatment was applied for the first 10 years by treating competing vegetation with herbicide. After 22 years, vegetation control significantly increased biomass and height of all planted species. The average height for northern red oak with vegetation control treatments was 884 cm with vs. 606 cm without; white oak was 837 cm with vs. 424 cm without; shortleaf pine was 1339 cm with vs. 1220 cm without. Moderate compaction increased average white oak height by 15% and severe compaction increased average height by 18% compared to no-compaction treatments. Compaction was not a significant treatment for red oaks or for shortleaf pines. However, the coarse fragments in the study soils appear to have muted much of the compaction to the soil’s fine-earth fraction and may have had the unintended effect of providing partial vegetation control. Whole-tree removal reduced average shortleaf pine heights by 6% vs. sawlog-only removal, while whole-tree + forest floor removal increased heights 3% compared to sawlog harvests. Organic matter removal was not a significant treatment for either oak species. Red oak survival probability was 0.79 with vegetation control vs. 0.34 without; white oak was 0.81 with vs. 0.65 without; shortleaf pine was 0.49 with vs. 0.45 without. Overall, vegetation control was the dominant factor driving survival and growth of oaks, and to a lesser degree, growth of shortleaf pine. Organic matter removal and compaction treatments had relatively little negative effect on height, indicating the resilience of these species to harvest-related disturbances in Ozark Highlands soils.