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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.
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.
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*).