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".
