Marsh types (fresh, intermediate, brackish, saline) are assigned to CRMS marsh sites by an algorithm that uses species composition and cover data collected annually from the sites.
Certain species (indicator species), when present at designated abundance levels, are first used to assign marsh types to CRMS sites. A CRMS site is assigned to fresh marsh if one or more of the following species has an average site abundance of 5 percent or greater: Boehmeria cylindrica, Cephalanthus occidentalis, Colocasia esculenta, Decodon verticillatus, Eleocharis baldwinii, Nymphaea odorata, Panicum hemitomon, Sagittaria latifolia, Sagittaria platyphylla, Schoenoplectus deltarum, or if Sagittaria lancifolia or Cladium mariscus have an average site abundance of 50 percent or greater.
A site is assigned to intermediate marsh if Leptochloa fusca, Panicum virgatum, Paspalum vaginatum, Phragmites australis or Schoenoplectus americanus have an average abundance of 50 percent or greater.
If Schoenoplectus robustus, Spartina cynosuroides, or Spartina spartinae have an average abundance of 50 percent or greater, then the site is assigned to brackish marsh.
A site is assigned to saline marsh if Avicennia germinans, Distichlis spicata, or Spartina alterniflora have an average abundance of 50 percent or greater.
When indicator species are present at the appropriate abundance levels the marsh type is assigned to a CRMS site based on the indicator species. When these indicator species are not present or are present below the designated abundance level then the site score (as described below) is used to assign marsh type.
Each plant species in coastal Louisiana is assigned a salinity value according to the marsh type in which it is most commonly found. The marsh type(s) in which species are found at the greatest abundance are used to assign a salinity score as follows: fresh, 0.25; fresh-intermediate, 1.50; intermediate, 2.75; intermediate-brackish, 7.15; brackish, 11.50; brackish-saline, 17.50; saline, 24.00 (Visser et al. 2002). A site score is calculated for each CRMS site using the following equation (Visser et al. 2002):
score = ∑(valuei x abundancei) / ∑(abundancei)
Where valuei is the salinity value assigned to species i and abundancei is the percent cover of species i.
Site scores are then assigned to a marsh type as follows: if the score is less than 1.50 it is fresh, if the score is greater than or equal to 1.50 and less than 7.15 it is intermediate, if the score is greater than 7.15 and less than 15.0 it is brackish, and if the score is greater than 15.0 it is saline.
In some cases a marsh type cannot be assigned to a CRMS site because no species are present (i.e., the site does not contain vegetation or the vegetation is dead) or because the only species that are present are not assigned salinity scores. The following species are excluded from the algorithm because they represent disturbance or occur over a large salinity range, Amaranthus australis, Cyperus odoratus, Echinochloa walteri, Eleocharis sp., Eupatorium capillifolium, Iva frutescens, Leptochloa fusca, Ludwigia sp., Lythrum lineare, Pluchea camphorata, Sesbania drummondii, Sesbania herbacea, Solidago sempervirens, Symphyotrichum subulatum, Symphyotrichum tenuifolium,and Vigna luteola.
Visser, J.M., Sasser, C.E., Chabreck, R.H., Linscombe, R.G. 2002. The impact of a severe drought on the vegetation of a subtropical estuary. Estuaries 25: 1184-1195.