We will test directly whether gopher mounds can cause elevation of grasshopper populations by experimentally increasing the density of mounds (using artificial mounds) in a Cedar Creek old field. Artificial gopher mounds were placed in two spatial configurations to increase the local density of mounds in an old field that has relatively low levels of naturally occurring mounds. Artificial mounds are formed from subsurface soil taken from the same depth that pocket gophers move it and are of the same size and bulk density as are naturally produced mounds.
Mound treatments include two spatial arrangements of one elevated density plus a control. Treatments were assigned to 20m x 20m plots, with four replicates of each treatment placed in a random block design. Plots are separated from each other by 10m. Each mound treatment received 25 artificial gopher mounds; control plots are unmanipulated. One mound treatment has the 25 mounds evenly spaced across the plot; the second mound treatment has mounds placed in clusters of 5 at each corner and at the center of the plot.
Mounds were placed in the field in August of 1991. August is the month in which mound building is most pronounced at Cedar Creek, following a summer hiatus in appearance of mounds. Thus, this timing mimics that of the appearance of naturally produced mounds. Grasshoppers and existing gopher mounds were sampled in July of 1991, prior to addition of artificial mounds. Grasshoppers will be resampled in July of 1992 and 1993. Grasshoppers will be sampled by sweeping, using the same methods we currently use to document yearly and seasonal abundance patterns in 22 Cedar Creek oldfields and in LTER experimental plots. For a list of treatments, see the treatment layouts in file trmte92.