Cristina M. Siegel1, James Burger1, D. Andrew Scott2, Felix Ponder3, and Robert F. Powers4. (1) Department of Forestry, Virginia Tech, 228 Cheatham Hall, Blacksburg, VA 24061, (2) USDA-FS (Forest Service), USDA-FS Southern Research Station, 2500 Shreveport Hwy, Pineville, LA 71360, (3) Lincoln University, U.S. F.S. Northern Research Station, Foster Hall, Room 208, Jefferson City, MO 65102, (4) PSW Research Station, USDA Forest Service, 3644 Avtech Parkway, Redding, CA 96002
Assessing tree growth response to applied compaction has been difficult due to inherent heterogeneity in soil properties. In addition, the effects of compaction on tree growth and soil properties vary for different sites, species and over time. We determined potential compaction-induced soil limitations to tree growth as a function of several fundamental soil physical properties by field-validating root growth models derived under controlled greenhouse conditions. We determined the extent to which these models predicted tree growth by comparing model predictions with measured seasonal net tree productivity, soils and climate data. On 0.2-ha plots, ranging from non- to severely compacted, Pinus ponderosa, P. echinata and P. taeda were grown on a Haploxeralf soil from California, a Paleudult from Missouri, and a Paleudalf from Mississippi, respectively. Soil properties measured included soil strength, bulk density and soil water content, which was measured continuously through one growing season. Net primary productivity (NPP) was determined by sequential root corings, diameter growth and litterfall. Using the models, we determined soil sufficiency for root growth (SSRG) for each soil-species combination for one growing season. The relationship between SSRG, root and shoot growth varied by soil and species. These models could be used for estimating forest productivity decline across a gradient of disturbance conditions and hydrologic regimes.