contorta, which had root weight, shoot weight, and stem height declines ranging from 50 to 90% resulting from Compaction caused by some intensive forest management practices compaction of several different soil types (Corns, 1988). can reduce tree growth, but growth reduction is the result of complex Although reduced growth from compaction has been interactions between soil properties and tree physiological processes, which may differ by species. We used a 7 by 7 factorial greenhouse reported across many regions, the effect on individual experiment to create a matrix of bulk density (b) and volumetric tree growth parameters is variable, and overall growth water content (v) to better understand soil compaction effects on response varies for different species and soil types. For seedling growth of: (i) ponderosa pine (Pinus ponderosa var. ponexample, shoot and root weight of Pseudotsuga menziederosa Dougl. ex Laws) grown on Dome and Cohasset soils; (ii) sii var. glauca (Beissn.) Franco and Pinus monticola shortleaf pine (Pinus echinata Mill.) on a Clarksville soil; and (iii) Dougl. ex D. Don seedlings were not affected by comloblolly pine (Pinus taeda L.) on an Argent soil. Models of root length paction after one growing season, but root volume was density (RLD) were developed using multiple regression. The general 41% less for the P. menziesii (Mirb.) Franco seedlings model of RLD ϭ b 0 ϩ b 1 v ϩ b 2 b ϩ b 3 2 v described rooting response and seedling height was 6% greater for P. monticola for the Clarksville-shortleaf and Argent-loblolly soil-species combina-(p ϭ 0.05) (Page-Dumerose et al., 1998). Corns (1988) tions (p ϭ 0.005). However, the ponderosa pine RLD response on Cohasset soil was linear and there was an interaction between v and reported that P. contorta root weight, shoot weight, stem b in the Dome soil. Shoot mass of seedlings growing within the least diameter, and stem height declined due to compaction limiting water range (LLWR) was greater than those growing outside on all four soils tested, but Picea glauca growth on two the range for all soil-species combinations except the Argent-loblolly of the soils did not decline or increased twofold. P. pine (p ϭ 0.05). The loblolly pines had greater shoot mass at v above contorta shoot weight decreased 64% on a silty clay soil the upper LLWR limits (aeration limiting). Least limiting water range when b increased from 1.2 to 1.5 Mg m Ϫ3 , while shoot has potential as a soil quality indicator, but seedling response was not weight decreased 86% on a clay loam soil compacted always associated with LLWR. Root length density (RLD) response to 1.5 Mg m Ϫ3. Wasterlund (1985) also reported species surface models in conjunction with seasonal site water data have differences with Picea abies growth being more impeded potential for determining compaction-induced soil limitations for tree by compaction than Pinus sylvestris L. growth. On sevgrowth, but need to be field tested and calibrated for both soil and species. C.M. Siegel-Issem and J.A. Burger, Dep. of Forestry...

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There has been much concern that traffic associated with the harvesting of intensively managed pine plantations reduces long‐term soil‐site productivity. Trafficking, especially during wet periods, can cause severe soil physical disturbance and redistribution of woody residues. Although the negative effects of soil compaction and rutting on root growth and the importance of organic matter for maintaining site productivity are well known, the connection between these factors and actual changes in soil and site productivity has been difficult to evaluate. Three productive, 20‐ha loblolly pine (Pinus taeda L.) plantations located on fertile “wet pine flats” on the coastal plain of South Carolina were subjected to wet‐ and dry‐weather harvesting and mechanical site preparation. A factorial design was used to evaluate changes in soil‐site quality after 5 yr based on postharvest classifications of soil physical disturbance, harvest residue removal, and the type of site preparation using a recently developed rank diagnostic approach. Trees on disturbed sites performed as well or better than trees on minimally disturbed sites with average levels of harvest residues. Bedding restored relative soil‐site productivity (based on the rank diagnostic) on all but heavily disturbed sites with >25% bare soil; however, these heavily disturbed sites comprised about 5% of the total area harvested. Moderate levels of disturbance may increase relative soil‐site productivity, perhaps by controlling competition or increasing nitrogen mineralization rates. Sites such as these may be good alternatives to more sensitive sites for wet‐weather harvesting.

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Wet-weather logging can cause severe soil physical disturbances and redistribute residues. Although some research indicates negative effects of such disturbances on individual tree growth, the long-term resilience and resistance of soils and the ameliorative effects of site preparation are not fully understood. Three 20 ha loblolly pine ( Pinus taeda L.) plantations located on fertile wet pine flats on the coastal plain of South Carolina were subjected to five treatment combinations of harvest (wet and dry) and site preparation. Mean tree heights were 10.2–11.5 m, and stand biomass ranged between 95 and 143 Mg/ha. A rank diagnostic indicates that wet-weather harvesting did not significantly change site productivity between rotations, and bedding improved site productivity. At the polypedon scale (0.04 ha), there were no significant differences in tree height, biomass, or the rank diagnostic among classes of soil physical disturbances or harvesting residues when bedding was employed. On nonbedded sites, some levels of disturbance appeared to be superior to minimally disturbed sites. Based on 10 year results, wet pine flats are apparently resistant and resilient to the effects of wet-weather harvesting.