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|Data by Research Category|
Dataset: Transect plant line intercepts - percent cover by species
Average percent coverage of each plant species per 5-meter segment along a 30-meter line intercept perpendicular to each of 91 stations on each of the three LTER-I permanent transects. Data consists of week number, transect, station number, species, carbon reduction pathway, habit, form, and average percent cover. It is sorted by transect, station number, then plant species. Measurements are made on 30-meter line intercept transects located perpendicular to each of 91 stations on each of the 2.7 km long Control, Treatment, and Alternate Control Transects established at the beginning of LTER-I. Following January 1, 1987, spring line- intercepts will only record cover of annual species. All perennial cover data will be limited to fall samples. Both annuals and perennials are measured during the fall. Measurements were made biannually from 1982 - 1988. After this they are measured every 5 years. Annuals are measured through 1998; however, after this only perennials are measured and only in the fall. Each plant line transect is divided into 6 5-meter segments. Annuals are measured only in the first meter of segments 1, 2, and 3 and in the last meter of segments 4, 5, and 6. Perennials are measured for the full length of all segments. BACKGROUND. 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.
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. The northeast side of the exclosure is immediately upslope of the College Playa located near the NMSU College Ranch. Three parallel transects (2.7 km in length) run from the middle of the College Playa up into the foot of Mt. Summerford. The Control transect is to the west, the Treatment transect on the east side of the Control transect, and the Alternate Control to the east of the Treatment transect. Each transect is 30 meters wide with a 45 meter buffer zone between each transect. The Treatment transect was treated annually until 1987 with NHNO3 in a concentration equal to 10g N/m2. There are station markers at 30 meter intervals along each transect. Perpendicular to each transect and crossing at each station marker is the 30 meter plant line intercept transect. This extends 15 meters on either side of the station marker. The ends of the plant line intercept transect are marker by short rebar sticking up about 6 inches aboveground. The plant line intercept transects are thus perpendicular to the direction of major drainage flow. There are 91 stations on each of the 3 2.7 km transects with a plant line intercept transect perpendicular to each station.
Methods of recording (field data sheets, instrumental, etc.):
1982 - Spring 1987: data recorded using field data sheets.
Fall 1987 to present: data recorded on audio tape.Methods:
Canopy cover of plant species intercepted by a line stretched the length of the 30-meter plant line transect are measured and recorded for each of 6 5-meter segments. The ends of the line are anchored on permanently placed 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 the line is snagged.
The clothesline is pre-stretched overnight when new to minimize changes in length when stretched tight in the field. The first meter of segments 1, 2, and 3, and the last meter of segments 4, 5, and 6, are marked with enamel paint to indicate a new segment as well as to identify the portion of the segment where annuals are read. The length of the line should be checked before beginning a new season of measurements to ensure that stretching has not distorted line.
Data is recorded by identifying 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 recorded. Multiple readings (intercept observation) can occur for a single plant if vegetation is broken up with open areas along the line intercept. Each new 5-meter line segment is identified as it is encountered. Plant species are recorded as a 4 letter acronym consisting of first 2 letters of genus and first 2 letters of species epithet. If a duplicate acronym results for 2 different species, generally the 3rd letter of the species epithet is then used. Acronyms used are found in the Plant Checklist for the NSF/LTER Jornada Sites.
Data sheets were used to record the data until Week 300. At this time tape recorders were used to record the field data. This data was entered and processed using several programs. INPUT.EXE (Fortran) is used to input tape recorded data. This data is then sorted by transect, station number, plant species, then segment. CONVERT.EXE (Fortran) is used to convert the sorted data to a format that matches that entered from data sheets. SRELCHEK.EXE (QuickBasic) error checks data. (Data must be sorted in the order described above before running SRELCHEK.) Once any corrections are made, LTERCOVR.EXE (Fortran) summarizes and calculates mean percent cover for each species on each 30-meter line transect at each station.
1982 - 1988, biannual (spring = annuals only, fall = annuals & perennials); 1993, 5 year intervals (spring = annuals only, fall = annuals & perennials); 1998 - present, 5 year intervals (fall only = perennials only)
Treatment of data
Beginning in 1992 field data is recorded on audio tape then transcribed to floppy disk using Fortran program INPUT.FOR. This data is then sorted by station, species i.d., and then line segment. It is then converted to a form similar to that recorded on data sheets in prior years. The conversion is done using the Fortran program CONVERT.FOR. This converted form of the data is then analyzed for Mean Percent Cover using the Fortran program LTERCOVR.FOR. A T-test is run on 9 plant species using SAS on the Computer Mainframe.