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Plant species richness is defined as the total number of species in an area and is one indicator of biodiversity. The Modified Whittaker approach discussed here is based on Stohlgren et al. (1995) and Bull et al.(1998), which can be found in Herrick et al. 2005. This method is very time intensive.
This method is time consuming and has high sampling costs associated with it. To save time and cost it is sample fewer transects (one can be sufficient) at more locations.
Guide. U.S. Department of Agriculture, Forest Service. Washington, D.C.
Because the Modified Whittaker approach is time intensive, the simplest alternative is to use the minimum estimate of species richness calculated from Line-point intercept method. However, this will miss most species. The Line-point intercept estimate of species richness can be further supplemented by conducting a thorough search for exotics and other species of interest throughout the plot area. Another alternative is to search the 10 x 30 m plot without subplots. This is appropriate if the species-area curve is not required.