Fine Filter Necessary?
The jury is still out regarding whether the effort required to select and analyze only the Northern Virginia plots created valuable insight for restoration purposes. What appears clear is:
The vast majority of species which did not show up in the Northern Virginia plots were uncommon (Abundance Category of Rare). Therefore, if the uncommon species are not a target of restoration in general, removing these species from the list would appear to have minimal value.
For the species which did show up in the both the statewide and Northern Virginia plots, over 80% have the same abundance (same Mean Cover and Constancy within 10 percentage points).
For the 20% of the species which did have different abundance, the vast majority of those had Constancy below 40% and Cover of 1% or less. Thus, the Common and Dominant species changed little between the two plot sets.
Extensive details about the composition of the four common communities is found in the document below.
Consistency Across Communities
Community by Community Assessment of Changes in Species Abundance for the Statewide and Northern Virginia plot sets
Document: Community by Community Assessment of Changes in Species Abundance for the Statewide and Northern Virginia plot sets
Concerns Regarding Sample Size
The importance of having an appropriate sample size of plots is driven by a need for Precision and Coverage per the chart:
One concern identified early on was how many plots are necessary to create an adequate "sample size" to ensure consistent results with what many more plots will show. The details of that simulation analysis are found below also.
Simulations were run to determine how many plots are necessary for the final species results to approximate the results of a much larger sample size. Plots were selected in random order and the cumulative species identified were calculated as the number of plots increased. For example, a first plot may have 50 species. If you add a second plot that itself also has 50 species, the cumulative species identified would be much less than 100 due to overlapping species between the two plots. The questions evaluated how quickly the total cumulative species increased with increasing sample size, and how quickly the most common species were identified.
Key Findings on Sample Size
The total number of species continues to grow as plots are added. It appears that each plot, more or less, has very uncommon species that add to the cumulative total. This happens for Communities with inherently high and inherently low species diversity.
While the total number of species shows no upward boundary of asymptote, the most common species are established in the plot sets rapidly. As few as 10 plots will identify all of the species with end-constancy >30; and 20 plots will identify all species with eventual constancy >10.
Document: Assessment of how many plots is necessary in order to have a good "sample size"
Assessment of how many plots is necessary in order to have a good "sample size"