Each study site is 1 km by 0.5 km in area. Four replicate
experimental blocks were randomly located at each study site
depending on whether the site was grazed. The blocks are all
oriented on a site in an X/Y coordinate system, with the access road
to each site forming the X axis. The compass orientation at the
Jornada grassland site is to the north, and Jornada creosotebush
site is oriented to the south. Treatments within each block include
one unfenced control plot (Treatment: C; control); one plot fenced
with barbed wire, hardware cloth, and poultry wire to exclude
rodents, rabbits, and cattle (Treatment: R; rodent); one plot fenced
only with barbed and poultry wire to exclude cattle and rabbits
(Treatment: L; lagomorph); and one plot fenced with barbed wire to
exclude cattle (Treatment B; bovine). Cattle exclosure plots with
barbed wire occur only at the black grama grassland site where
cattle were present, for a total of 4 treatment plots at each of the
four grassland site blocks. There are only 3 treatment plots at each
of the creosotebush site blocks because grazing is excluded from the
entire creosotebush site. The treatments were randomly assigned to
each of the three or four possible plots in each block
independently, and their arrangements differ from block to block.
Each of the plots in a replicate block is separated by 20 meters.
Each plot measures 36 meters by 36 meters. Thirty-six sampling
points are positioned at 5.8-meter intervals on a systematically
located 6 by 6 point grid within each plot. A permanent one-meter by
one-meter vegetation measurement quadrat is located at each of the
36 points. All cover values here are measured from a vegetation
measurement frame placed at this quadrat, which is 1 meter by 1
meter, and partitioned into a grid of 100, 10 cm by 10 cm squares.
Leaf litter includes all detached (unrooted) dead plant material on
the soil surface, including woody branches. Each year in spring and
fall from 1995-2005, leaf litter percent cover was determined by
summing the estimated cover for each of the 100, 10 cm squares. For
total cover values less than 5%, increments of 1% were used. For
cover values greater than 5%, estimates were made to the nearest 5%.
Only leaf litter cover that is in the open and not within clumps of
grass, etc. Some leaf litter cover has distinctive margins and is
easy to define and measure. However, much leaf litter consists of
many diffuse small patches that are separated by bare soil, and
distributed throughout the quadrat. For such diffuse cover, we
determined the actual cover in one typical 10 by 10 cm square (e.g.,
0.3), then counted the number of squares with diffuse cover (e.g.,
5), and multiplied the number of squares by the actual cover for a
typical square (e.g., 0.3 X 5 = 1.5, then rounded to 1.0 or 2.0, or
if the value had been greater than 5, rounded to the nearest
increment of 5.0 ) for the total litter cover. All litter cover is
pooled into one observation, and no height is measured.
From 1995 to 2005, vegetation data for all quadrats was measured
twice a year in the spring and fall. After 2005, sampling frequency
changed to once every 5 years in the fall. This study is ongoing.
Field observations were recorded on micro-cassette tape recorders.
Further details on measurements and data preparation can be found in
the SMES vegetation quadrat protocol included with this package
("SMESvegquadprotocol.pdf"). A comment history is found in
the file "JRN086_small_mammal_exclosure_quad_his.txt".
