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  1. Laragin
  2. Mid-Atlantic
  3. Monday, September 08 2014, 03:41 AM
Hello everyone,

Got a question to throw out there. I'm a student and fairly new to the wetlands world. I'm surveying some plots in the mid-atlantic region and trying to use the 50/20 rule for dominants. My question is how does it come into play in regard to invasives. I have some plots with stiltgrass all over the place. Are invasives counted when tallying up percentages in my subplots and then not counted when applying the 50/20 rule?? I'm not sure and would like to hear any advice from you all out there.

Thank you in advance!
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Edward Bonner Accepted Answer Pending Moderation
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Even though it is an invasive, you should treat it as you would any other plant in your plots when you apply the 50/20 rule. If we treated invasives differently from native species, the vast majority of our wetland delineations would be problematic. When you are identifying your dominant species, remember to do it based upon the comminity layer. In this case stilt grass would be your herbaceous layer. Stilt grass is also known as Microstegium or Eulalia. My expectation is that you are finding this throughout a forested area and most likely a forest that has had some historic disturbances. The disturbance may not be readily apparent. It might have been farming, logging or drainage alterations. Further, these disturbances may have been on the site or on adjacent land areas. I believe it is listed as Fac so it may not necessarily throw your results askew. Stilt grass can be very aggressive and tolerate a wide wetness regime. If you think it may be affecting your results you might want to do your analysis with and without the species and see if you come up with different results.
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  1. more than a month ago
  2. Mid-Atlantic
  3. # 1
Laragin Accepted Answer Pending Moderation
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Thank you for the helpful clarification. I've lined it up so I can easily see how percentages turn out with and without an invasive. You are correct in that it doesn't seem to skew things too much. But I did find in one of my plots that was heavy with the Microstegium that if I removed from my calculation then the next herbaceous species on the list jumped from below the 20% mark to over the 20% mark. But that was the only case I've found so far. I've got more plots to go so I'll see if I run into that scenario again. You are also correct on it being land that was once disturbed or at least adjacent to disturbed land...so good call there. Once again, thank you for help!
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  1. more than a month ago
  2. Mid-Atlantic
  3. # 2
Prachi Patel Accepted Answer Pending Moderation
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Just curious, on what's the 50/20 rule. I'm from Great Lakes Region in Canada and as such may be this is not relevant to my region. Here in Ontario we use 50/50 rule for wetland delineation i.e 50% wetland and 50% upland. Is 50/20 - to specify dominance of plant species from the 50% wetland species?
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  1. more than a month ago
  2. Mid-Atlantic
  3. # 3
Patrick Murphy Accepted Answer Pending Moderation
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The 50/20 rule is different. It is used to determine which species in a particular stratum are the dominants. The rule goes something like this. If a species has 20% of the RELATIVE cover in a stratum, it is a dominant. All the species with the highest RELATIVE cover are added up until the total sum of the relative cover equals or just exceeds 50%. Those species are also dominants. For example, if you have species with the following RELATIVE cover, the first three are dominant and the others are not, 25, 20, 5, 3, 2, 2, 1. The first two are dominants because the equaled or exceeded the 20% criteria, and the 5% was included because it could be added to the other two to total the 50% criteria.

Also, if you just so happen to have a tie with the last item to add, for example if two species had the 5% value, then both of them would be dominants.
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  1. more than a month ago
  2. Mid-Atlantic
  3. # 4
Prachi Patel Accepted Answer Pending Moderation
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Thanks Patrick, that was helpful.
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  1. more than a month ago
  2. Mid-Atlantic
  3. # 5
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