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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), are detailed in a protocol attachment (see "Additional files"), and are 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 data file are specific to the Jornada Basin LTER. To link these codes to recognized taxa, please refer to the "JRN Vascular Plants" EDI package (knb-jrn-lter.210520001 - https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-jrn&identifier=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.