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Plant Species Inventory

from the USDA-ARS Monitoring Manual for Grassland, Shrubland and Savanna Ecosystems


A plot-level species inventory provides a rapid estimate of species richness. A thorough search of the plot can detect less-frequently occurring species that may not have been recorded in cover measurements (e.g., Line-point intercept). For a more intensive species richness measurement, see the modified Whitaker species richness.

Materials Required

  • Measuring tapes (transect lengths)
  • Stopwatch
  • Pin flags to mark unknown plants
  • Plant identification keys and books
  • Four 1.5 m (5 ft) PVC pipes (optional)
  • Compass
  • Electronic device for paperless data collection (preferred) OR clipboard, Species Inventory Data Sheet (Available in Appendix B of the Monitoring Manual), and pencil(s)

Standard Method

1. Set up the species inventory plot.

The species inventory area is within at least a portion of the area covered by the Line-point intercept transects.

  • A square or rectangular sub-plot shape created by connecting the ends of the plot transects is recommended for a systematic species search (Figure 32a). Lay out the transect tape on at least one side of the square or rectangle to define the sub-plot boundaries so that the data recorder can see the boundaries within which to conduct the reconnaissance for species inventory. Record both the size and shape of the plot searched.
  • Optional: For compatibility with NRI, the cumulative species inventory plot area is 1,641 m2 (17, 662 ft2) (Figure 32c).
  • Always inventory the same plot area for all plots within a project and for repeat visits to plots.
2. Systematically and uniformly search the entire plot for 15 minutes.
  • Area is searched by one individual, although a recorder may stand off-plot to record data. Do not re-search any areas already searched.
  • Area search occurs after Vegetation height, Line-point, and Gap intercept measurements on transects are complete.
  • Work from the corners of the plot toward the sub-plot center in a systematic, or zig-zag search pattern (Figure 32). If external boundary tapes are not used, it may be helpful to attach a PVC pipe to the end of each transect to identify plot corners, and then use compass bearings to ensure position within the sub-plot.
3. Record each species found within the plot.
  • At least 50% of a plant base must be rooted inside the plot boundary to be recorded.
  • Record each species found within the plot in the “Species” column of the data sheet using (a) a national standard species code (in the U.S. use the PLANTS - database, (b) scientific name or © common name. Each species is listed only one time.
  • Mark unknown plant species with a pin flag and return to identify them after the search time has expired. Do not spend any of the 15 minute search time deliberating about species identification, or looking through plant species lists or books to identify unknowns. Assign a personal, temporary ID to questionable plants if necessary (e.g., “Yellow Aster 1”, “Yellow Aster 2”, “Spikey grass”, “Black stemmed shrub”, etc.), and write out their full identifications after the 15 minute search period to save time. If field identification is not possible, take geo¬tagged (except for NRI) photographs of the unknown plant. Be sure to include a photo ID card in the photo. If possible, collect and press a plant specimen from nearby, but off-plot, for later identification (see Plant Identification, page 14). This specimen needs to include as many potentially identi¬fying elements as possible, including leaves, stems, flowers, and fruits.
  • If species is not known, use the following codes and add sequential numbers as necessary:

AF# = Annual forb (also includes biennials)
PF# = Perennial forb
PG# = Perennial graminoid
SH# = Shrub
TR# = Tree

Quality Assurance Checklist

  • Each data sheet is complete. Observer, recorder, date, plot name, sub-plot area, sub-plot shape, and search time are recorded.
  • Unknown plants are described according to unknown plant protocols, photographed, and a specimen collected when possible.
  • Data collection team confirms species list is complete and correct.
  • Number and type of species are consistent with plot observations.
  • Boundaries of search area are clearly marked.
  • A recorder, in addition to recording species, can also ensure the observer is moving through the plot quickly enough to cover the entire search area in 15 minutes.

Species inventory indicator calculations

1. Count the total number of species recorded.
  • Only count each species once.
  • Count every plant species, even if its identification is unknown (e.g., PG01, PG02).
  • Only include species recorded in other methods (e.g., Line-point intercept, Vegetation height) if (a) they were also captured during the species inventory or (b) the transects are wholly contained within the species inventory sub-plot.
2. Determine functional groups (e.g., shrubs, perennial grasses). Record the number of species in each functional group.
3. Identify potential species of management concern for the plot and record presence or absence of these species.

Vegetation Height Indicator Calculations

Species inventories detect the presence of rare or invasive species which may not be detected by cover or density measurements along transects due to their infrequent occurrence, rarity, or recent establishment. This method can identify areas where additional plant surveys are needed. A plot-level species inventory also provides information on species richness, one indicator of biodiversity. Plot biodiversity indicators must be evaluated within the context of the ecological potential of the plot (e.g., as defined by an ecological site description). Consequently species richness, like bare ground and other indicators, cannot be directly compared among sites with different soils and climate.

Ecological heterogeneity can also affect richness: a plot that spans several soil types will likely have higher biodiversity than a plot located on a single soil. Similarly, a plot that includes several ecological states on the same or different soils is likely to have more species. Species richness may even be higher in a somewhat disturbed or degraded state than in an undegraded state as invasives colonize, but do not entirely replace spe¬cies native to the area. Within-plot comparisons over time must be carefully interpreted for the same reasons.

Consequently, caution should be used when comparing plots using species richness as an indicator of site biodiversity. Interpretation of species richness should always be made in an ecological context together with indicators derived from Line-point intercept, Gap intercept, and Soil stability.


field_methods/plant_species_inventory.1391041648.txt.gz · Last modified: 2014/01/29 17:27 by jgh