If my goal of vegetation sampling is to determine plant species diversity of a heterogeneous area (eg. lowland, montane), what is the appropriate sampling deign and how to determine sampling size?
Depends on if your goal is representativity or maximize diversity.
If you want a general representativity of your landscape you could utilize a remote sensing image over the area and randomize your plots. This would represent the proportional habitats and species within them equally.
If you want to maximize diversity of your landscape it would be better to stratify your method to include many micro-habitats that are more likely to contain rare species that aren't common in the general landscape.
When it comes to sampling size (size of each plot) it will also depend on how uniform each plot is and the time it would take to inventory it. I would suggest either 1m x 1m or 5m x 5m, both are standard plot-sizes.
Thank you Carl for your immediate response. Very helpful!
How about determining the number of sampling units eg how many 1x1 quadrat will be established in a homogeneous area? May I know how vegetation scientists accomplish this task? No data on variability is available..
For sampling forested area you might use larger plots, 10 X 10 to40 X 40 m
The study of vegetation in Europe has mainly followed the method of Braun-Blanquet or S.I.G.M.A. (International Station of Géobotanique Méditerranéenne et Alpine), also called "the School of Phytosociology of Zürich-Montpellier". You will find abundant bibliography on the subject in the Internet. In this method you will find the definition of the minimal sampling area.
Greetings
I entered "MINIMAL SAMPLING AREA" in google. I found the info below from this link: http://www.sci.sdsu.edu/SERG/techniques/mfps.html
" An accurate estimate of the necessary number of quadrats can be determined by plotting data for a given feature (i.e. percent cover) vs. number of quadrats. The appropriate quadrat number will correspond to the point at which the curve plateaus (Figure 1) Barbour et al., 1987). Some field researchers sample until the standard error of the quadrat is within a previously decided, acceptable boundary. A standard error of + or - 15-20% of the mean (i.e. two thirds of all quadrats supply data that fall within this range about the mean) is sometimes used (Barbour et al., 1987)"
Hello Mark Anthony; Your last comment accurately describes how to determine sample number. However, you might want to think about WHERE you place those plots. Be sure to determine that the area being sampled actually is as homogeneous as your eye thinks it is. Cheers, Jim Des Lauriers
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