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 creosote bush 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 creosote bush site blocks. 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.
The entire canopy cover (cm) in increments of 0.1 to 1.0 for each
species and the maximum height (cm) was recorded. For plants, canopy
cover is measured in terms of the number of 10-cm squares occupied by
the species on the quadrat. Values ranged from 0.1 to 100. For large
cover values (5+), increments of 1.0 or 0.5 were used. The cover
values for all individual plants of a given species in the quadrat was
summed to get one overall cover value. For live plants, the maximum
height in centimeters for that plant species in the quadrat is also
recorded. For annuals, the highest part of the plant, whether it is a
reproductive structure or vegetative structure was used. For
perennials, including perennial grasses, the highest vegetative
structure and NOT any reproductive structures were used. The height
for bare branches is from the ground to the highest point if the bare
branch is the highest point for the species. If a plant is dead, but
still rooted in the soil, it is stated as "dead" in the
condition column. For dead plant foliage, cover only (not height) was
measured.
The data were entered in the field on to micro-cassette tape
recorders. The taped recorded data were then entered on to MS Excel
spreadsheets.
Twice a year in the spring and fall from 1995-2005, vegetation data in
each quadrat was measured. After 2005, sampling frequency changed to
once every 5 years in the fall. Further details on measurements and
data preparation can be found in the SMES vegetation quadrat protocol
included with this package. This study is ongoing.
