Between 1915 and 1932, more than 100 1m x 1m quadrats were established
across the Jornada Experimental Range to document vegetation dynamics
in dominant grass species over time. Initially the research goal of
the project was to investigate livestock grazing effects on plant
community dynamics. The original sets of quadrats were selected to
represent the major grassland types in the area. Most were placed at
0.8 km intervals along transects radiating from permanent watering
points for livestock. Grassland types represented were (primary
dominants) black grama, tobosa, burrograss, three-awn, blue grama, and
a mixed grass type. The corners of each quadrat are permanently marked
on the ground with angle iron stakes or nails.
Vegetation in the quadrats is monitored by charting. A decimeter grid
was used for charting until 1925, and a pantograph has been used
thereafter. Charting involves 1) drawing the scaled-down locations of
the four corners of the 1m x 1m quadrat on a sheet of paper, 2)
drawing the relative locations of the center of live perennial forbs
and live subshrubs contained in the quadrat, 3) drawing the basal
areas of live perennial grasses contained in the quadrat relative to
the four corners, 4) drawing the canopy areas of live shrubs contained
in or overhanging the quadrat relative to the four corners, and 5)
labeling each item to species, genus, or functional group, whichever
can be most fully resolved. In this way, each chart serves as a map of
each quadrat that can be georeferenced and spatially projected. In
several cases grasses were also measured as a point, particularly if
they could not be identified to species, and are not included in this
data set.
With few exceptions, all 122 quadrats were charted until 1947, and a
portion of the quadrats were charted intermittently between 1947 and
1979. Interest in the project was reinvigorated in 1995, during which
time 112 quadrats were relocated, charted, and documented with GPS
coordinates. An additional 10 quadrats have been located subsequently.
Since 1995 sampling has occurred every 5-6 years.
Maintaining a definitive record of quadrat sampling and charts has
been challenging due to the long-term nature of the project including
changeover of management personnel, periodic abandonment and renewed
interest, plot corners being buried or locations being lost, charts
having gone missing or taken by researchers, changes in taxonomic
classifications, protocols and technology, and incomplete efforts to
compile the data set. At the start of the project, directions for
locating each quadrat were based on features in the landscape that
sometimes did not persist. GPS documentation began in 1995.
Unfortunately, the locations of some quadrats have been lost; however,
this data package contains only quadrats whose locations are currently
known.
Field charts are digitally scanned into high resolution TIFF files.
Scans are then digitized in ArGIS software. Perennial forb and
subshrub location features are recorded in a point shapefile, while
perennial grass basal cover features and shrub canopy cover features
are recorded in a polygon shapefile. Perennial grass stolon features,
if they exist, are recorded in a line shapefile. Known locations of
plot corners are used to spatially project each shapefile, and the
shapefiles are stored in a geodatabase. Attribute tables for each
geodatabase layer are extracted, compiled, and error-checked to
produce the final data tables. This data set is not yet complete;
charts are actively being processed by Jornada Experimental Range
staff and will be updated to this data package as they become
available. See data package knb-lter-jrn.210351002 for perennial forb
and subshrub count data.
