There are two types of points available for visualization with the CRMS vegetation layer – marsh type classification and community type classification.
Helicopter surveys of vegetation in coastal Louisiana have been conducted multiple times over the past 70 years in support of Louisiana coastal management activities. The initial surveys (1949, 1968, 1978, 1988 and 1997) were conducted by the Louisiana Department of Wildlife and Fisheries (LDWF). Surveys were completed in 2007, 2013, and 2021 through collaborations with U.S. Geological Survey (USGS), Coastal Protection and Restoration Authority (CPRA), Louisiana State University (LSU), Louisiana State University Agricultural Center (LSU AgCenter), and LDWF. During each survey similar field methodology was used to sample the same stations (points) through time.
These surveys provide important data for federal, state, and local resource managers. The surveys provide information on the condition of Louisiana’s coastal marshes by mapping plant species composition and vegetation change through time. The marsh type delineations, derived from the point data, are intended to represent broad zones of habitat based on observation of vegetation species. The broad zonation does not account for small patches of vegetation that may differ from the generalized marsh type for a given area and was not intended for exact quantification of acreage.
Plant species were identified, and their abundance classified at each point. Based on species composition and abundance, each marsh sampling station was assigned a marsh type: fresh, intermediate, brackish, or saline marsh, or swamp as described below.
Point data are available for 1968, 1997, 2001, 2007, 2013 and 2021. These data can be viewed on the map by clicking the radio button next to “Marsh Type” and selecting the year of choice. Individual points can be clicked on the map (make sure the “Vegetation” layer is activated; to activate click the radio button next to “Vegetation”) and a “pop-up” window will open. This “pop-up” window displays data for the point chosen. Point data can be downloaded by year as well. To access this data, click the reference (book) icon next to “Marsh Type” which will open a “pop-up” window that contains data references and links to the data.
Marsh types (fresh, intermediate, brackish, saline) were assigned to sampling stations by an algorithm that uses species composition and cover data collected during the surveys.
Certain indicator species, when present at designated abundance levels, are first used to assign marsh types to sampling stations.
A sampling station is assigned to fresh marsh if one or more of the following species is present: Boehmeria cylindrica, Cephalanthus occidentalis, Colocasia esculenta, Decodon verticillatus, Eleocharis baldwinii, Nymphaea odorata, Panicum hemitomon, Sagittaria latifolia, Sagittaria platyphylla, Schoenoplectus deltarum, Triadenum virginicum, or if Sagittaria lancifolia or Cladium mariscus have an average site abundance of 50 percent or greater.
A sampling station 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.
A sampling station is assigned to brackish marsh if Schoenoplectus robustus, Spartina cynosuroides, or Spartina spartinae have an average abundance of 50 percent or greater.
A sampling station is assigned to saline marsh if Avicennia germinans, Distichlis spicata, or Spartina alterniflora have an average abundance of 50 percent or greater.
When these indicator species are not present or are present below the designated abundance level then the station 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 station score is calculated for each sampling station 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.
Station 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 sampling station because no species are present (i.e., the sampling station 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.
For more information, see 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.
Using the vegetation observations collected at sampling stations via helicopter survey in 1997, 2001, 2007, 2013, and 2021, stations (points) have been classified into community types using the method described below.
These data can be viewed on the map by clicking the radio button next to “Community Type” and selecting the year of choice. Individual points can be clicked on the map (make sure the “Vegetation” layer is activated; to activate click the radio button next to “Vegetation”) and a “pop-up” window will open. This “pop-up” window displays data for the point chosen. Point data can be downloaded by year as well. To access this data, click the reference (book) icon next to “Community Type” which will open a “pop-up” window that contains data references and links to the data.
One of 11 community types is assigned to sampling stations by an artificial neural network unsupervised classification system that uses species composition (relative cover) data collected from the stations as described previously.
Stations classified as Maidencane communities typically consist primarily of one or more of the following taxa (in decreasing abundance): Panicum hemitomon, Leersia hexandria, Sagittaria lancifolia, Eleocharis sp., Thelypteris palustris, Alternanthera philoxeroides, and Typha sp.
Stations classified as Three-Square communities typically consist primarily of one or more of the following taxa (in decreasing abundance): Schoenoplectus americanus, Spartina patens, Sagittaria lancifolia, Lythrum lineare, Cladium mariscus, Eleocharis macrostachya, and Distichlis spicata.
Stations classified as Roseau Cane communities typically consist primarily of one or more of the following taxa (in decreasing abundance): Phragmites australis, Spartina patens, and Alternanthera philoxeroides.
Stations classified as Paspalum communities typically consist primarily of one or more of the following taxa (in decreasing abundance): Paspalum vaginatum, Schoenoplectus californicus, Spartina patens, Typha latifolia, and Ipomoea sagittata.
Stations classified as Wiregrass communities typically consist primarily of one or more of the following taxa (in decreasing abundance): Spartina patens, Distichlis spicata, and Schoenoplectus americanus.
Stations classified as Bulltongue communities typically consist primarily of one or more of the following taxa (in decreasing abundance): Sagittaria lancifolia, Polygonum punctatum, Alternanthera philoxeroides, Ludwigia grandiflora, and Typha sp.
Stations classified as Needlerush communities typically consist primarily of one or more of the following taxa (in decreasing abundance): Juncus roemerianus, Spartina alterniflora, Spartina patens, and Distichlis spicata.
Stations classified as Bulrush communities typically consist primarily of one or more of the following taxa (in decreasing abundance): Bolboschoenus robustus, Distichlis spicata, Spartina patens, Spartina cynosuroides, Spartina alterniflora, Paspalum distichum, and Juncus roemerianus.
Stations classified as Brackish Mix communities typically consist primarily of one or more of the following taxa (in decreasing abundance): Spartina alterniflora, Spartina patens, Juncus roemerianus, and Distichlis spicata.
Stations classified as Oystergrass communities typically consist primarily of one or more of the following taxa (in decreasing abundance): Spartina patens and Juncus roemerianus.
Stations classified as Saltgrass communities typically consist primarily of one or more of the following taxa (in decreasing abundance): Distichlis spicata, Spartina patens, Spartina alterniflora, and Bolboschoenus robustus.
For more information, see Snedden, G.A., 2019. Patterning emergent marsh vegetation assemblages in coastal Louisiana, USA, with unsupervised artificial neural networks. Applied Vegetation Science 22: 213-229. DOI: 10.1111.avsc.12425.