Perennial species canopy cover across grazed/ungrazed fencelines in the Jornada Basin, 1986-2015

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This ongoing data set contains percent canopy cover estimates of perennial plant species from transects that cross a grazed/ungrazed boundary fenceline of a single exclosure on the New Mexico State University Chihuahuan Desert Rangeland Research Center in Dona Ana County, New Mexico, USA. In the spring of 1982, as part of the establishment of the Jornada Long-Term Ecological Research site in southern New Mexico, a 135 ha portion of a 1500 ha, internally drained, watershed was exclosed from grazing by domestic livestock. Prior to exclosure the watershed, as well as the rest of the Jornada basin, had been moderately to heavily grazed for the past 100 years. Concurrent with grazing, the vegetation had undergone a dramatic change from desert grassland, with an almost continuous cover of C4 perennial grasses, to isolated patches of the original grassland in a mosaic with desert shrub dominated plant communities (Buffington and Herbel, 1965). The exclosure lies along a northeast facing piedmont slope at the base of a steep isolated mountain peak, and covers a variety of component landforms from the foot of the mountain to the basin floor. This provided the opportunity to investigate the response of vegetation with respect to landscape characteristics as well as release from grazing. This summary data set consists of percent canopy cover of all perennial plant species from the plant line intercept measurements on either side of the LTER-I exclosure East and West boundary fence. Sampling occurs approximately every five years; it was last conducted in November 2015 and will take place again in 2020.  

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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 clothesline is stretched between the two rebar so it is taut. Before making readings, ensure the line is freed from obstructions so it is perfectly straight between the two rebar. This may require threading the line through large plants or lifting free where sections are snagged. The clothesline used is pre-stretched overnight when new to minimize changes in length when stretched tight in the field. It is marked in 5 meter increments with enamel paint to indicate segment lengths. The length of the line should be 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. We have cross-referenced these 4-letter codes to the codes and species binomials maintained by the USDA Plants database ( 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.

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Data collected approximately every 5 years


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