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). NPP observations, both
non-destructive and off-grid harvests (this package) began in
April 1989.
Site maps may be available on request from the Data Manager
(currently missing).
Reference harvest methods
This data package contains the volumetric and aboveground biomass
data from vegetation harvested outside the permanent NPP quadrats.
These measurements comprise a reference dataset from which biomass
is regressed against plant volume to create allometric models that
estimate biomass from non-destructive volume measurements in
permanent quadrats (see package 210011002). These methods were
first established by Huenneke et al. (2001) and were updated by
Peters et al. (2012). They are detailed in an attached protocol
document (see "Additional files"), and are outlined
below.
Off-quadrat plant harvests at each site occur on the same day that
non-destructive measurements are collected inside the permanent
quadrats. Plant samples selected for harvest vary by species,
functional type, abundance, phenological stage, phenotypic
plasticity, and other criteria. Dominant species, and others
showing significant differences among sites in past regressions,
are harvested from each site; for other species, samples may be
taken in smaller numbers at any one site and samples from
different sites may be pooled in the regression (see species
list). Sample sizes are 15 for dominants, 10 for most other
species (see species list). The range of cover values to be
harvested is based on the range of cover values recorded from the
permanent quadrats. Plants to be harvested are found in areas
typical of those encountered in the permanent quadrats, and
sampling avoids plants obviously damaged by livestock or previous
harvests, or otherwise not representative of plants within
permanent quadrats.
Once suitable plants are identified, their horizontal cover and
vertical height are measured in the field as for the quadrats.
Volumes are then harvested, returned to the laboratory, held in a
cold room (4 degree Celsius), sorted (dead material discarded,
unless obviously from the current season of growth), dried (55
degree Celsius), and weighed to nearest 0.01 g. Dominant shrubs
(Larrea, Flourensia, Prosopis) are separated into leaves, stems,
and reproductive material (either before or after weighing of
total biomass); these components are weighed separately.
During the first five years of the study, off-quadrat reference
harvests of species occurring in the NPP quadrats were common. As
allometric models have become more robust, harvests for many
species have ceased, and only a limited subset of highly variable
or newly occurring species are harvested each year.
IMPORTANT NOTES
NOTE 1: 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
A harvest protocol included with this data package
("Harvestprotocol.pdf") provides details of field and
laboratory methods used to create these data.
Derived data packages
knb-lter-jrn.210011001 - Quadrat biomass by species, site, 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.