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 are measured from a vegetation
measurement frame placed over the quadrat, which is 1 meter by 1
meter, and partitioned into a grid of 100, 10 cm by 10 cm squares.
Fraction of canopy cover for each species present was recorded in
increments of 0.1, to a maximum of 1.0 for each square in the
quadrat frame. Maximum height (cm) was also recorded, by species,
for each square. For plants, total canopy cover is measured by
summing fractional covers, by species, for all 100 10x10 squares in
the quadrat. Total cover values range from 0.1 to 100%. 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%. 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
plants cover only (not height) was 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
"Jornada_086_small_mammal_exclosure_quad_his.txt".
