Note: the methods for this data set are exactly the same as those for
knb-lter-jrn.210120002. However, this data set beings earlier (1982
instead of 1986) but is limited to 6 species (Bouteloua eriopoda,
Dasyochloa pulchella, Larrea tridentata, Acourtia nana, Pleuraphis
mutica, and Scleropogon brevifolius) and 3 genera (Aristida,
Gutierrezia, and Sporobolus) due to the limited taxonomic resolution
of the 1982 sampling.
Along the East Boundary fence line of the exclosure, the east side is
ungrazed (control) and the west side is grazed (treatment). Along the
West Boundary fence line, the east side is grazed and the west side is
ungrazed. Each plant line transect is divided into 6 5-meter segments.
Permanently marked 30m line transects were located at about 50m
intervals along the two parallel long axis fences of the LTER
exclosure which begins immediately above the College Playa and extends
toward Mt. Summerford. This is the northern portion of Pasture 10 of
New Mexico State University Chihuahuan Desert Rangeland Research
Center (formerly known as College Ranch). These fences run
approximately north to south (NNE to SSW) up the slope of the
watershed, traversing the component landforms characteristic of the
bajadas of the Basin and Range Province.
The line transects are perpendicular to the fences and cross them at a
fence post (either T-post or wood post) on the downslope side. They
are thus perpendicular to the direction of major drainage flow. The
line transects are identified by an aluminum tag wired to the fence
post. The letter on the tag i.d. identifies the fence (E=East or
W=West); the number is the station number (East: 1-30; West: 1-31).
Canopy cover of only perennial species intercepted by a line stretched
the length of the 30-meter line transect are measured and recorded for
each of 6 5-meter segments. The ends of the line are anchored by
3/8" rebar extending about 6 inches out of the ground.
When measurements are to be made, a length of high tensile clothesline
is stretched between the two rebar so it is perfectly straight between
the two rebar and as close to the ground as possible. This may require
threading the line through plants or lifting free where sections are
snagged. The clothesline used is pre-stretched a minimum of 24 hours
when new to minimize changes in length when stretched tight in the
field. It is then marked in 5 meter increments with enamel paint to
indicate segment lengths. The length of the line is checked before
beginning a new season of measurements to ensure that stretching has
not distorted the line. Data is recorded by identifying the Station
number (metal tag is located on fence post) and Segment number. The
5-meter segments are numbered 1 through 6 beginning at the west end of
the line (right end if facing upslope). Length of each plant species
that is intercepted by line is measured with a meter stick and
recorded. Multiple readings (intercept observation) can occur for a
single plant if vegetation is broken up with open areas along the line
intercept. The effective minimum gap size used is 1 cm. Beginning and
end of each new 5-meter line segment is identified as it is
encountered.
Plant species are recorded as 4-letter codes, generally consisting of
first 2 letters of genus and first 2 letters of species epithet. A
number will be used after a 4-letter code to represent an unknown
genus or family. The first 4 letters in this case represent the genus
or family. We have cross-referenced these 4-letter codes to the codes
and species binomials maintained by the USDA Plants Database
(plants.usda.gov). Summary data presented in this data set is the
average percent cover for the outer-most 2 5-meter segments for the
respective treatment (grazed or ungrazed). The term outer-most is
relative to the fence. The 5-meter segment on either side of the fence
is not included in the cover estimates due to fence line effect
disturbances; e.g., cattle trails, tumbleweeds trapped along fence,
etc. This summary data does not include the first year of measurement
in 1982 because of numerous problems with species codes used that
could not resolved.
