General study design
There are 15 net primary production (NPP) monitoring sites located
in 5 vegetation communities that represent the major vegetation
types of the Jornada Basin. These vegetation zones and their
associated NPP sites (3 per zone) are: 1) creosotebush scrub
(CALI, GRAV, SAND), 2) tarbush flats (EAST, TAYL, WEST), 3)
grassland (BASN, IBPE, SUMM), 4) mesquite dunes (NORT, RABB,
WELL), and 5) playa (COLL, SMAL, TOBO). Grids of permanent 1
square meter replicate quadrats have been established at each site
for long-term monitoring of net primary production. Grids consist
of 49 quadrats arranged in a square 7 x 7 pattern, with quadrats
10 m apart. (Exception: P-COLL, the College Ranch playa, has 48
quadrats arranged in a 3 x 16 pattern). Quadrats are permanently
marked with aluminum nails inserted into the soil at two diagonal
corners; quadrats are identified by nearby rebar stakes and tags
(numbered 1-49, starting at the northwest corner and wrapping back
and forth in a north-south direction). NPP observations, both
non-destructive (this package) and off-grid harvests began in
April 1989.
Site maps may be available on request from the Data Manager
(currently missing).
Non-destructive quadrat measurement methods
This data package contains the non-destructive measurements of
vegetation cover, height, and other attributes in permanent NPP
quadrats. From these dimensional measurements, volume can be
calculated for each species in each quadrat. These volumes can be
used with the allometric equations derived from a reference
harvest dataset (see EDI package knb-lter-jrn.210011004) to
estimate the biomass of permanent quadrat species on a seasonal
basis. These methods were first established by Huenneke et
al. (2001), were updated by Peters et al. (2012), and are detailed
in a protocol attachment (see "Additional files") and
outlined below.
Standing biomass is sampled three times a year: in winter
(February - March), before shrubs begin spring growth; in spring
(May), when shrubs and spring annuals have reached peak biomass;
in fall (late summer; October), when summer annuals have reached
peak biomass but before killing frosts. At each sample date, each
site is visited (order of sampling may vary, according to
phenological stage of sites) and the dimensions of each plant on
each quadrat are measured and recorded. Recorded for each
observation are: date, zone, plot, quadrat #, species (4 letter
acronym), observation # (one for each measurement of that species
in that quadrat), cover (percentage of quadrat covered by canopy
of that individual or species), height (vertical extent of that
individual or species), count (if multiple individuals with the
same dimensions are present), and phenological stage
(Flowering/fruiting or Vegetative). Plants rooted outside but
reaching into the quadrat are measured in terms of their vertical
and horizontal extent only in the rectangular volume above the
quadrat. Large plants (e.g., shrubs) are broken down into
individual branch systems or other sub- volumes and recorded as
separate observations. Cacti are measured for number of pads
(count), average length of pad (height), and average width of pad
(diameter).
Early sample periods included measurements of diameter, rather
than cover, for some species; see data files from those periods.
IMPORTANT NOTES
NOTE 1: These data are not appropriate for
estimates of percentage cover. NPP-associated percent cover
measurements were developed for and are used solely to provide the
best estimate of biomass production. Because the methodology
results in measurements of overlapping subcanopy systems and
canopies of adjacent individuals, NPP percent cover measurements
are not an appropriate measure of actual aerial plant cover. Doing
so will result in inflated numbers for the "actual"
vegetative cover.
NOTE 2: Plant species codes in the
"spp" column of the data file are specific to the
Jornada Basin LTER. However, USDA Plants Database codes
(plants.usda.gov) have been assigned to most of these local codes
in a separate column. Further details for linking the local codes
to currently recognized taxa may be found in the "JRN
Vascular Plants" EDI package (knb-lter-jrn.210520001).
Additional files
The field quadrat protocol included with this package
(nppfield_protocol_master_for-distribution.pdf) provides details
on field methods.
Derived data packages
knb-lter-jrn.210011001 - Quadrat biomass by species and season
knb-lter-jrn.210011003 - Annual NPP summaries by site
References
Huenneke, Laura F., Dennis Clason, and Esteban Muldavin.
"Spatial heterogeneity in Chihuahuan Desert vegetation:
implications for sampling methods in semi-arid ecosystems."
Journal of Arid Environments 47, no. 3 (2001): 257-270.
Peters, Debra PC, Jin Yao, Osvaldo E. Sala, and John P. Anderson.
"Directional climate change and potential reversal of
desertification in arid and semiarid ecosystems." Global
Change Biology 18, no. 1 (2012): 151-163.
