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Thirty Years of Change in Forest Soils of the Allegheny Plateau, Pennsylvania

^a USDA-Forest Service, Northeastern Research Station, 234 Mirror Lake Road, Campton, NH 03223
^b USDA-Forest Service, Northeastern Research Station, Irvine, PA 16365
^c USDA-Forest Service, Northeastern Research Station, Delaware, OH 43015

View larger version (33K): [in a new window]   Fig. 1. Sampling layout showing the spatial relationships between the original pit sampled in 1967 (shown as a diamond), the four pits sampled in 1997 (shown as squares), and the forest floor pin-block transects sampled in 1997, 1998, and 1999 (shown as circles).

View larger version (25K): [in a new window]   Fig. 2. Results of reanalysis of pH (standard units) and exchangeable Ca, Mg, and Al (cmolc kg–1) in archived soil samples. Original analyses are shown on the x-axes; new analyses, after 30 yr of storage, are shown on the y-axes. The dashed line represents a 1:1 line; solid lines are the regression line describing the relationship between original and new analyses.

View larger version (35K): [in a new window]   Fig. 3. Variation in pH (standard units) and exchangeable Ca, Mg, and Al (cmolc kg –1) in the Oa/A horizon at each of the four study sites, and for all sites combined. The value for the 1967 pits represents a single measurement. The bars represent the mean and standard error of measurements for the 1997 pits (n = 4 per site) and pin-blocks (n = 10 per site, per year). DD, Dewdrop, FC, Fools Creek; HC, Hearts Content; NB, North Branch.

View larger version (39K): [in a new window]   Fig. 4. Depth profiles of pH (standard units) and exchangeable Ca, Mg, and Al (cmolc kg–1) at each of four study sites. The closed circles represent the data collected from the original pit dug in 1967. The open circles represent the data collected from four pits dug in 1997, located 10 m away from the original pit, in each of the four cardinal directions. The dotted horizontal line shows the average depth of the top of the fragipan, where present. A fragipan was found at three of the five pits at DD, all five pits at FC, and one of five pits at HC.