Controls on soil organic matter content within a northern hardwood forest

Forest soils can act as both sinks and sources for atmospheric CO2 and therefore have an important role in the global carbon cycle. Yet the controls on forest soil organic matter content (SOM) distribution at the scale of operational land management scales within forest types are rarely quantified in detail. To identify factors that influence the spatial distribution and accumulation of SOM in forests, soils and stand composition data from 42 even-aged northern hardwood forest plots were analyzed using multiple linear regression and non-parametric statistical approaches. The analysis included three layers of SOM pools (forest floor, 0-20 cm mineral soil, and 20+ cm, mineral soil) over three spatial scales (point, plot and regional). The largest amounts of total SOM (mean=289, std dev=70 Mg ha(-1)) occurred in deep and well drained soils located on gently grading slopes. When soil layers were analyzed separately, the following relationships were observed: 1) highest forest floor SOM occurred under mixed species composition as opposed to stands dominated by sugar maple, 2) highest 0-20 cm mineral SOM occurred at high elevations (greater than 450 m) in moderately well drained soils, and 3) highest 20+ cm mineral SOM also occurred at high elevations and when soils were deeper. Further analysis of 0-20 cm mineral layer revealed that lower rock volume and finer soil texture resulted in higher SOM at a single point. When SOM that was predicted from models based on plot-specific attributes (soils series, slope and aspect) were compared to soil survey SOM estimates, the mean SOM values for both approaches were similar (253 and 269 Mg ha(-1) respectively). Easily identifiable characteristics such as mixed stand composition, the presence of forest floor and E horizon thickness may be used as field indicators of SOM storage. The variety of controls identified in this study should be considered when assessing soil carbon response to management options and future changes in climate. (C) 2008 Elsevier B.V. All rights reserved.