Mass of the forest floor (kg/m²)
 

As the graph shows, the mean mass of the forest floor decreased in 1990 and then increased again in 1998.  The large standard error values make it difficult to draw conclusions from these values.  This appears not to be due to a single variable skewing the average, but to wide variability in the sample area. For data tables with the full set of values, please click on the graph.



 

The average masses of organic matter (OM) in the forest floor show a slight trend of increase across the eighteen years.  However, large error bars indicate a large variability within the samples.  Since the means for 1990 and 1998 are the result of only 5 samples, it is possible that small sample size and natural variation could create the false appearance of a trend.  For data tables with the full set of values, please click on the graph.



 

Percent Organic matter in the Forest Floor (LOI%)(LOI=Loss on Ignition)

Between 1980 and 1998, the LOI in the forest floor showed a trend of increase.  The graph of the means shows a large jump in the forest floor data from 1990, and then a return to levels near that of 1980.  Closer examination of the data suggests that the percentage for 1998 has been skewed by one sample that is exceptionally low.  When the data is averaged without this sample, the average is 77.0 %, fairly close to the value for 1990, suggesting a possible trend of increase.  However, the small number of samples makes this easily skewed by variation among sample location.



 

Mineral Soil Percentage Organic Matter (LOI%)

Throughout the soil profile, the percentage of organic matter in mineral soil stayed generally the same.  This is important because it indicates that changes in the distribution of the minerals that complex with organic matter are not due simply to an increase in the amount of organic matter at a particular depth.

The uppermost thickness segment did show an increase of ~3 %.  This may be due to natural variation and a small number of samples.  The interface of the forest floor and the upper mineral soil, although quite distinct, is still variable even over the 15 x 15 cm area from which it was removed. Very slight collection differences and decisions as to how much to include could easily obscure differences between years.  Below 2 cm, the percentages do not appear to deviate until the 16-20 cm thickness layer, which also shows a slight increase, which may simply be attributable to one sample with a high LOI%.  For the entire set of values, please click on the graph.
 
 

Bulk Density of the Mineral Soil (g/cm³)

The bulk density of the mineral soil increased with depth in both years sampled. Plowing would homogenize the density throughout the profile and a graph of it would appear as a vertical line.  Since the end of plowing, greater organic matter and microbial activity in the upper horizons gradually has reduced the density, causing the curve seen above.  Variations between sampling years are most likely due to sampling variation. The patterns observed in bulk density are exactly the type of  natural soil processes which are associated this the reestablishment of the "native" soil profile in this plowed system.  For the full set of values, please click on the graph.

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