Rainfall during the sampling period (793 days) was
9,143 millimeters. Mean and maximum rainfall by sampling
period (mean of 16 days) were 189 and 563 millimeters,
respectively. Surface runoff averaged 0.6 millimeters and
1.2 millimeters by sampling period for the control and
experimental plots, equal to 0.25 and 0.48 percent of mean
rainfall, respectively. Disturbance of the soil environment
by removal of earthworms doubled runoff and increased the
transport (erosion) of soil and organic material by a factor of
4.4. When earthworms were removed, the erosion of mineral
soil (soil mass left after ashing) and the transport of fine litter
were increased by a factor of 5.3 and 3.4, respectively. It is
assumed that increased runoff is a function of reduced soil
porosity, resulting from decreased burrowing and reworking
of the soil in the absence of earthworms. The background,
or undisturbed, downslope transport of soil, as determined
from the control plots, was 51 kilograms per hectare and the
“disturbance” rate, determined from the experimental plots,
was 261 kilograms per hectare. The background rate for downslope transport of fine litter was 71 kilograms per hectare
and the disturbance rate was 246 kilograms per hectare. Data
from this study indicate that the reduction in soil macrofauna
population, in this case, earthworms, plays a key role in
increasing runoff and soil erosion and, therefore, has important
implications for forest and water management.