Vegetative Assessment of Wetland Sites

Quadrant Sampling Protocol

I.    Purpose:

          Hydrology, soils and vegetation are used to evaluate and delineate wetlands.  The goal of the quadrant sampling protocol is to monitor the condition and development of wetland ecosystems in the Boquet River Watershed.  Special attention will be paid to non-native and invasive plant species because they alter ecosystem health.            

II.   Equipment:

            1.         Waterproof data sheet & clipboard

            2.         Pencil

            3.         Base map

            4.         One square meter quadrant frame made up of PVC pipe & connectors

            5.         Inelastic cords, measuring 3.09 and 8.92 meters, attached to fiberglass                          center stake     

            6.         Metric diameter (dbh) tape measure

            7.         Plant identification handbook

            8.         Global positioning unit (GPS)

            9.         Waterproof hip waders

            10.       Raincoat          

            11.       Insect repellant

            12.       Hat

            13.       Head Net

            14.       Drinking water

III.  Procedure:

            The procedure can be divided into three sections.  The first section (procedure1 to 3) consists of preliminary field activities.  The second section (procedure 4-10) describes how to perform the quadrant sampling in the field.  The third section (procedure 10-14) outlines methods for quantifying data collected during the quadrant sampling. 

1.  One comprehensive vegetative assessment will be carried out at each wetland site during the growing season, between June 15 and August 15. 

2.  Use the PVC piping to construct a quadrant measuring 1m x 1m on the inside of the square.

3.  There are numerous sampling points at each wetland site, use a separate data sheet for each.  At the top of each data sheet record the following information: name of wetland, transect number, date of visit, quadrant sampling point “name”, and GPS unit. 

4.  Locate each sampling point using the base map and GPS unit.  Each wetland site includes a number of lines called transects, identified by Roman numerals.  The individual sampling points, identified by capital letters, are positioned along each transect.  Together, a Roman numeral and a capital letter “name” an individual sampling point.  In addition to the base map, sampling points are marked by orange-tipped PVC pipes standing between 1.22 and 1.83 meters above ground.  Each marker is labeled with sampling point name and GPS coordinates. 

CAUTION:  GPS coordinates may vary slightly.

5.  Determine the number of strata at each sampling site.  That is, count the number of distinct vegetative layers.  A maximum of four strata can exist:

               a.  Tree: any woody plant with a diameter breast high (dbh) ≥ 8 cm

               b.  Sapling/Shrub: any woody plant ≥ 1m. tall but with a dbh < 8cm

               c.  Herb: all non woody plants and woody plants < 1m. tall

               d.  Woody Vine: woody climbing plants ≥ 1m. tall

Note: Overlap may exist within vegetation strata.  For example, Sapling/Shrub may occupy the same area as Woody Vine or Tree.  In the Herb layer non woody plants such as cattail may exceed the one meter height limit.  However, woody plants must measure less than one meter to be considered a part of the Herb layer.

6.  Use a circular quadrant with an area of 250m² to sample areas with Woody Vine and Tree.  Utilize a smaller circular quadrant, with an area of 30m², to sample for Sapling/Shrub.  Sample Herbaceous plants growing beneath the water (submerged) and those with most vegetative parts above water (emergent) using the square meter quadrant constructed of PVC piping. 

7.  Tree Stratum Sampling:  Record the identity of each individual tree by scientific name given in plant identification handbook.  Include each individual’s diameter at breast high (dbh), a standard tree dimension.  Measure 1.37m (4.5 feet) from the ground and mark that height with chalk, pin, etc. on your chest for consistency in dbh measurement.  Standing close to and facing the tree, wrap diameter tape around tree to measure and record dbh (cm) at this height.  Diameter Tape is calibrated to measure the trunk’s diameter rather than measure its circumference based on a pre-defined conversion factor.  Where multiple trunks arise from a common basal point, each trunk is treated as a separate individual if it has diverged from the others below breast height, or 1.37m, from the ground.

8.  Woody Vines Stratum Sampling:  Woody vines are likely to be uncommon in our area.  If any are present, record the number of stems for each species in the 250m² quadrant.

9.  Sapling/Shrub Stratum Sampling:  Identify each sapling/shrub occurring within the 30m² quadrants.  Estimate height of plant and record the scientific name of each individual sapling/shrub.  Use one line per individual.  

10.  Herb Stratum Sampling:  Place the 1m² quadrant on the ground at the sampling point.  Identify each species of plant with foliage extending into the quadrant and estimate its percent coverage of the quadrant.  Estimate and record the percent cover by species.  Note that each row in the data sheet table is intended for a separate species, not for separate individuals. 

11.  Calculate and record basal area for tree stratum sampling.  Basal area is a measurement used to estimate the amount of space occupied by tree stems.  It is expressed in square center meters and can be calculated as follows:

·        “Basal area of an individual tree is equal to the diameter at breast height (dbh) of the tree squared, times the conversion factor 0.7854.” 

·        Individual tree BA = (dbh)² x 0.7854

For example, if dbh measures 18cm:

                                                   BA = (18 cm)² x 0.7854

                                                   BA = 254.4696 cm²

Note: All the data should be recorded using the metric system.

12.  Height class is an indication of dominance used for the sapling/shrub layer.  Taller species, or those with greater biomass, control or influence the amount of light the rest of the community receives.  Use estimated heights and the following table to determine height class.

13.  Record the relative dominance of species in the herb stratum.   Relative dominance is the ratio of the coverage of a single species to the total coverage of all species sampled in a given area.  It can be calculated by using the following equation:

·        (Amount of species “A” / Total amount of all species) x 100

Note: If there is bare ground in the quadrant, the relative dominance is of the portaion that is vegetated.  However, please RECORD THE PERCENT OF THE QUADRANT THAT IS VEGETATED on the data sheet.

14.  The dominant species within a community may be the most abundant, take up the most space, or make the greatest contribution to energy flow or nutrient cycling. Another measure of relative dominance useful in describing each stratum is the 50/20 Rule.  If a particular species accounts for more than 50% of the total coverage of vegetation in the stratum, or for at least 20% of the total coverage in the stratum which the species was found, that species is defined as dominant. This is called the 50/20 rule.  Specifically, steps in selecting dominant species by the 50/20 rule are as follows:

a) Estimate the absolute percent cover of each species in the first stratum. Since the same data may be used later to calculate the prevalence index, the data should be recorded as absolute cover and not converted to relative cover.

b) Rank all species in the stratum from most to least abundant.

c) Calculate the total coverage of all species in the stratum (i.e., sum their individual percent cover values). Absolute cover estimates do not necessarily sum to 100%.

d) Select plant species from the ranked list, in decreasing order of coverage, until the cumulative coverage of selected species exceeds 50% of the total coverage for the stratum. If two or more species are equal in coverage (i.e., they are tied in rank), they should be selected as a group. The selected plant species are all considered to be dominants. All dominants must be identified to species.

e) In addition, select any other species that, by itself, is at least 20% of the total percent cover in the stratum. Any such species is also considered to be a dominant and must be accurately identified.

f) Repeat steps 1-5 for any other stratum present. Combine the lists of dominant species across all strata. Note that a species may be dominant in more than one stratum (e.g., a woody species may be dominant in both the tree and sapling/shrub strata).

If you have comments/questions, please contact Dr. Meiyin Wu, Dr. Dennis Kalma or Boquet River Association . 

This page was last updated on January 08, 2007 .