James Bedison Jr., University of Pennsylvania, University of Pennsylvania Dept of E&ES, 240 S. 33rd Street, Philadelphia, PA 19104 and Arthur Johnson, Department of Earth and Environmental Science, University of Pennsylvania, Hayden Hall, 240 S. 33rd Street, Philadelphia, PA 19104.
Changes in soil organic matter in
forest floor soil horizons are examined using data from a long-term soil change
investigation. In 2005 – 2006 we relocated
42 sites originally established in 1932 throughout the Adirondack Park to determine changes in forest
floor soil organic matter from 1932 to 2006.
We excavated quantitative soil pits at each site and used loss on
ignition (LOI) to determine SOM content and
compared these results to previously reported data. Over the 7+ decades, average forest floor (Oe + Oa)
soil organic matter (SOM) content of all sites
decreased significantly (P = 0.01). The overall
changes in forest floor SOM were driven by a significant decrease in both the Oa (P = 0.05) horizon.
Utilizing forest classifications, significant decreases in forest floor
SOM were observed in pine-dominated (P < 0.01) stands. Forest floor SOM
content was, on average, lower in northern hardwood sites during the interval,
but not significantly. The forest floor
SOM changes were unlikey driven by changes in forest
floor depth. There were no overall
significant changes in forest floor depth over the interval in total forest
floor or in either the Oe or Oa horizons.
However, forest floor depths of pine stands decreased significantly (P = 0.02) but, since
pine-dominated sites have shallow forest floors (< 5 cm on average) and are not regionally wide-spread, this difference is
negligible. It is interesting to note
that, although not significant, the average forest floor depths of all forest
types have decreased since 1932.