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Vegetation (Plant) Height


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

Introduction

Vegetation height is measured as the height of the tallest plant part within a 30 cm (12 in) diameter cylinder projected tangent to the transect. It is measured vertically from the soil surface at the center of the cylinder (Figure 17). Vegetation height provides plot-level vertical structure information necessary to predict soil erosion from wind and characterize wildlife habitat. Vegetation height is usually measured at the same time as line-point intercept because it is more efficient, but can be measured separately.

Materials Required

  • Measuring tape (length of transect)—if using a tape measure in feet, use one marked in tenths of feet
  • Two steel stakes for anchoring tape
  • Graduated survey rod or height measuring stick with graduations in centimeters (or 0.5 in) and meters (or ft)
  • 30 cm (12 in) diameter disc or ruler (optional)
  • Clinometer or extendable range pole
  • Electronic device for paperless data collection (preferred) OR clipboard, Line-point Intercept with Height Data Sheet OR Vegetation Height Data Sheet (available in the USDA - ARS Monitoring Manual) and pencil(s)

Standard Method

  • At each designated transect mark, hold the edge of the disc on the opposite side of the tape. Using the disc as a guide, determine the tallest living or dead woody (when present) AND living or dead herbaceous plant (when present) parts intersecting a projected 30 cm (12 in) diameter cylinder tangent to the line (Figure 15).
  • All plant materials existing inside the projected cylinder are considered, whether they are rooted inside or outside the 30 cm (12 in) circular area (Figure 16). It doesn't matter where plants are rooted, only plant materials within the cylinder are observed.
  • Do not stretch or move any plant parts. Ignore any part of the plant that is outside the cylinder.
  • Height is determined as the perpendicular distance (relative to the earth's center, regardless of slope) from the soil surface at the center of the cylinder to the tallest plant element contained within the cylinder.
  • Record height from the center of the cylinder at the soil surface, even if the soil surface is uneven, mounded or bumpy (Figure 17, Table 17). Woody or herbaceous litter are not measured.
2. Record the height of plants 0-2 m (6 ft) tall to the nearest centimeter (0.5 in). Record the height of plants that exceed 2 m (6 ft) in height to the nearest 30 cm (~1 ft).
  • Record the height of the tallest part of the plant inside the cylinder. Record only one height for each plant type (woody or herbaceous) if present. Where no woody or herbaceous vegetation is present, mark “0” on the data sheet.
  • If vegetation is taller than 3 m (~10 ft), a clinometer, phone application, or geometric technique can be used to estimate height. For the geometric option, step back from the cylinder far enough so the tallest point of the plant in the cylinder can be seen. Measure (a) the horizontal distance to that point and (b) the angle (from the soil surface where the observer is standing) to that point. Calculate the height using the following formula: Height = (distance to plant) x (tangent of angle from soil surface). Be sure to measure and set calculators to ‘degrees’ when using this equation.
3. Optional: Species names can be recorded for projects that require species identification of the plant element measured.
4. Optional: Record if the plant element is alive or dead.

Vegetation Height Indicator Calculations

Vegetation height calculations are computed for two reasons: (1) to describe overall height structure on a plot and (2) to describe the heights of the vegetation on the plot. Overall height structure on a plot, described in Steps 1, 2, and 3, is the average height recorded at all measurement intervals including measurements where no vegetation was present and height was recorded as “0”. To describe the vegetation height by structural group (woody or herbaceous) or by species, average the heights recorded when those species or groups occur. Keep in mind that estimating vegetation height only where vegetation was measured (height > 0) may result in variable number of height measurements between plots.

1. Calculate the average vegetation height (vertical structure) for all measurements. An example is shown in Table 18.
  • Add together all height measurements, regardless of species. Divide this sum by the number of samples in this group. Record this value as average overall height on your data sheet.
2. Calculate the average woody height for all measurements (woody vertical structure).
  • Add together all woody species height values. Divide this sum by the number of samples in this group. Record this value as the average woody height on your data sheet.
3. Calculate the average herbaceous height (herbaceous vertical structure).
  • Add together all herbaceous species height measurements. Divide this sum by the number of samples in this group. Record this value as average herbaceous height on your data sheet.
4. Optional: Calculate average of woody or herbaceous heights including only heights > 0.

Vegetation Height Basic Interpretation

Woody and herbaceous height can be important indicators of vertical vegetation structure, especially when interpreted together with Gap intercept and Line-point intercept data. Woody and herbaceous vegetation structure, together with canopy gap size and distribution, are used to characterize wildlife habitat to determine if the site provides adequate thermal, hiding, and/or nesting cover for species of management interest (Table 19).

Vegetation height and canopy gaps are also indicators of potential wind erosion on a site. A site with large canopy gaps and short vegetation is more susceptible to wind erosion than a site with smaller canopy gaps and taller vegetation. Models have been developed that predict wind erosion based on vegetation height, foliar cover and canopy gaps (e.g., Okin 2008*).

Manual

field_methods/vegetation_plant_height.1390872030.txt.gz · Last modified: 2014/01/27 18:20 by jgh