DOI: 10.5061/dryad.5tb2rbpcm
title: Data for: Plant thresholds and community composition of coastal marsh-forest ecotones in the US Northeast

description: Sea level rise is causing coastal salt marshes to migrate upslope into
 coastal forests and other terrestrial ecosystems.  However, the
 factors that control marsh migration rates are not well understood,
 particularly in the US Northeast, where this phenomenon has received
 little attention. To determine the relationship between environmental
 variables and plant species composition in marsh migration zones, we
 examined plant coverage and environmental data for three sites
 experiencing marsh upslope migration in New Jersey, New York, and
 Massachusetts that varied in slope from 1-3%. We found that only 10% of
 the variation in plant community composition was explained by inundation
 time, while models containing multiple predictor variables, including
 edaphic variables, explained much greater levels of variance. Random
 forest models predicting native halophyte presence /had accuracies of 69 –
 84%, with salinity, flooding duration, and light availability as key
 predictors. The most accurate model for mature tree presence (84%
 accuracy) highlighted salinity and flooding time as the most important
 variables. Threshold Indicator Taxa ANalysis (TITAN) identified plant
 community changepoints at soil salinities of 0.8 and 7.6 PSU, reflecting
 the lower and upper boundaries of the marsh-forest ecotone. Treelines
 varied in elevation by site, suggesting that the amount of tidal flooding
 that trees can withstand varies. These results highlight the importance of
 multiple variables interacting to determine species distributions and
 community composition in marsh-forest ecotones.
description: <em>Site Descriptions</em> Three
 sites in the northeast exhibiting forest retreat along the marsh-forest
 ecotone were chosen for study, including Waquoit Bay (WB), Massachusetts
 (41.5562°, -70.5057°), part of the Waquoit Bay National Estuarine Research
 Reserve. The site has a tidal range of 0.61 m and an ecotone-upland slope
 of 3.45% ± 0.46. The second site, Pine Neck, is part of Pine Neck Preserve
 in East Quogue, NY (40.8422°, -72.5644°) and is managed by the Nature
 Conservancy. This site has a tidal range of 0.78 m and an ecotone-upland
 slope of 2.12% ± 0.58. The southernmost site selected was Egg Harbor, part
 of the Tuckahoe Wildlife Management Area (39.3259°, -74.6502°) in southern
 New Jersey. This site has a tidal range of 1.14 m and has the lowest slope
 of the three, 1.80% ± 0.64. Soils along the marsh-upland border
 transitioned from muck (classified as Freetown and Swansea muck) or
 Transquaking peat at low elevations to sandy soils (Carver coarse sand,
 Deerfield loamy sand, Plymouth loamy sand, Hammonton sandy loam) at higher
 elevations. Sandy soils are ubiquitous along the coastal plain and
 originated from glacial outwash in NY and MA and marine deposition in
 NJ. <em>Field Sampling</em>
 At each site, sampling points were selected to form a grid with
 26.5 m spacing spanning the high marsh and forest edge. We navigated to
 sampling points using a Garmin GPSMap 64st (Garmin Ltd., Olathe, KA). At
 each sampling point, a 0.5 m<sup>2</sup> quadrat was
 haphazardly dropped, and percent cover of understory plant taxa (including
 saplings) was estimated within the plot. The presence of live mature trees
 was noted for a 5 x 5m area centered around the plot. A 100-cc soil ring
 sampler was used to collect a 5cm-deep soil core from each plot. Cores
 were sealed in plastic bags and frozen after returning from the field.
 Light availability for each sampling point was measured for five minutes
 at a height of 3 m using a Photosynthetically Active Radiation (PAR)
 sensor (Odyssey Light Meters, Dataflow Systems Ltd., Christchurch, NZ)
 relative to a sensor placed in an unobstructed canopy to correct for cloud
 cover. Depth to groundwater was recorded as either: (a) the maximum depth
 where water could be obtained using a pushpoint porewater sampler designed
 to sample saturated groundwaters (MHE products, East Tawas, MI, USA) or
 (b) depth to water table measured in a shallow borehole. All groundwater
 depths greater than 84 cm were recorded as &gt;84 cm.
 <em>Lab Analyses</em> In the lab,
 edaphic conditions were characterized for salinity, redox, moisture, bulk
 density, and organic matter content. Redox was measured from the center of
 each core using a Sper Scientific benchtop meter (Sper Scientific, Ltd.,
 Scottsdale, AZ). Soil cores were then dried at 70° C until the mass no
 longer decreased after consecutive measurements. Gravimetric moisture
 content was measured as the percentage mass lost during drying. Soil bulk
 density was calculated by dividing the dry mass by the volume of the core.
 Soil organic matter content was measured using Loss on Ignition (LOI),
 where samples were combusted at 550° C for four hours, and organic matter
 content was recorded as the percentage mass that was lost through
 combustion. A volume of deionized water equal to 5x the soil mass was
 added to 3-5 cc of dry soil, vortexed for 10 seconds, held overnight,
 centrifuged for 5 minutes at 2500 RPM, and salinity was measured on the
 supernatant using a conductivity/temperature probe attached to a YSI
 Professional Plus meter (Xylem Inc., Yellow Springs, OH). Salinity was
 measured on duplicate soil subsamples for three plots per site. Salinity
 is reported as the 5:1 slurry of deionized water and dry soil. The average
 water:soil ratio of the samples we collected was similar at 3:1.
 *Geospatial Measurements * Elevations of the
 sampling points were extracted from bare-earth Digital Elevation Models
 (DEMs) derived from LiDAR surveys. A comparison with static GPS measures
 (10 per site spanning the marsh to the forest) found an average difference
 between LiDAR and GPS-measured elevations of 0.02 m. To compare elevations
 of tree boundaries among sites, the lower tree boundary was digitized
 manually from high-resolution (0.6 m) aerial imagery acquired in 2018/9
 from the National Agriculture Imagery Program (NAIP). Living trees that
 were within 15 m from their nearest neighbor were included as part of the
 boundary, while trees &gt;15 m from nearest neighbors were excluded.
 Boundaries were digitized 3 times so that digitizer error could be
 estimated as the standard deviation of the mean elevation from each
 attempt. The upper boundary of salt-tolerant plants was delineated through
 field surveys using a Garmin 64st (Accuracy ± 3 m) (Garmin Ltd., Olathe,
 KS), where the uppermost boundary of salt-tolerant plants was delineated.
 The uppermost salt-tolerant plants were most commonly <em>Baccharis
 halimifolia</em> or <em>Phragmites australis</em>. The
 elevation distribution of this field-derived demarcation was estimated
 using bare-earth DEMs in ArcGIS Pro (version 3.2.1, ESRI, Redlands, CA,
 USA). Because tidal range varied between sites, elevations standardized
 for tidal range (<em>z</em>*) were generated as the elevation
 in meters relative to mean sea level, divided by the tidal range (z* =
 (Z-MSL)/(MHHW-MSL)), where <em>z</em> = mean elevation of the
 boundary, and MSL and MHHW = tidal datums acquired from VDatum.
description: # Data for: Plant thresholds and community composition of coastal
 marsh-forest ecotones in the US Northeast
 [https://doi.org/10.5061/dryad.5tb2rbpcm](https://doi.org/10.5061/dryad.5tb2rbpcm) Data includes the following files: Ecotone_PlantSpp-EnvData.csv, EggHarborSamplingPoints.zip, PineNeckSamplingPoints.zip, WaquoitSamplingPoints.zip, EggHarborWatershed.zip, PineNeck_Watershed.zip, WaquoitWatershed_final.zip, EggHarborUpperBorder.zip, PineNeckUpperBorderWaypoints.zip, WaquoitUpperMarshBoundary.zip,EggHarborTreeline_C_points.zip, EggHarborTreeline_D_points.zip, EggHarborTreeline_E_Points.zip, PineNeckTreeline_B_Points.zip, PineNeckTreeline_C_Points.zip, PineNeckTreeline_D_Points.zip, Waquoit_Treeline2_Points.zip, Waquoit_Treeline3_Points.zip, and Waquoit_Treeline4_points_v2.zip. ## Description of the data and file structure The three zipped files: EggHarborSamplingPoints.zip, PineNeckSamplingPoints.zip, and WaquoitSamplingPoints.zip are shapefiles for sampling points at Egg Harbor, Pine Neck, and Waquoit Bay. Within each zipped file is a set of files that are used together to display spatial vector data. These files include a .shp file that contains the geometry or shape, a .shx file that is the index file to link the geometry and data, a .dbf that contains the attribute table or tabular data, a .prj file that contains projection information, a .cpg file that defines which character encoding is used for strings in the .dbf file, a .xml file (might be shown as HTML file) that contains detailed metadata about the shapefile, a .sbn or spatial index file, and a .sbx file supports the .sbn by storing bounding box info for quick access.  The three files: EggHarborWatershed.zip, PineNeck_Watershed.zip, WaquoitWatershed_final.zip are zipped polygon shapefiles of the watershed boundaries for the sites, delineated using Digital Elevation Models (USGS 2014/5/8) and the Watershed tool in ArcGIS Pro (version 3.2.1, ESRI, Redlands, CA, USA). Within each zipped file is a set of files that are used together to display spatial vector data. These files include a .shp file that contains the geometry or shape, a .shx file that is the index file to link the geometry and data, a .dbf that contains the attribute table or tabular data, a .prj file that contains projection information, a .cpg file that defines which character encoding is used for strings in the .dbf file, a .xml file (might be shown as HTML file) that contains detailed metadata about the shapefile, a .sbn or spatial index file, and a .sbx file supports the .sbn by storing bounding box info for quick access. The three files: EggHarborUpperBorder.zip, PineNeckUpperBorderWaypoints.zip, and WaquoitUpperMarshBoundary.zip, are zipped polygon shapefiles showing the uppermost distribution of halophytic, or salt-tolerant vegetation at each site. Within each zipped file is a set of files that are used together to display spatial vector data. These files include a .shp file that contains the geometry or shape, a .shx file that is the index file to link the geometry and data, a .dbf that contains the attribute table or tabular data, a .prj file that contains projection information, a .cpg file that defines which character encoding is used for strings in the .dbf file, a .xml file (might be shown as HTML file) that contains detailed metadata about the shapefile, a .sbn or spatial index file, and a .sbx file supports the .sbn by storing bounding box info for quick access. Nine files depict treelines, or the lower boundary between trees and salt marsh plants, at research sites (three from each site to capture uncertainty from heads-up digitization): EggHarborTreeline_C_points.zip, EggHarborTreeline_D_points.zip, EggHarborTreeline_E_Points.zip, PineNeckTreeline_B_Points.zip, PineNeckTreeline_C_Points.zip, PineNeckTreeline_D_Points.zip, Waquoit_Treeline2_Points.zip, Waquoit_Treeline3_Points.zip, Waquoit_Treeline4_points_v2.zip. Within each zipped file is a set of files that are used together to display spatial vector data. These files include a .shp file that contains the geometry or shape, a .shx file that is the index file to link the geometry and data, a .dbf that contains the attribute table or tabular data, a .prj file that contains projection information, a .cpg file that defines which character encoding is used for strings in the .dbf file, a .xml file (might be shown as HTML file) that contains detailed metadata about the shapefile, a .sbn or spatial index file, and a .sbx file supports the .sbn by storing bounding box info for quick access. The attached file "Ecotone_PlantSpp-EnvData.csv" includes 122 fields: Site, Date, Point, Lat, Long, Poaceae_sp, Poaceae1_eh, Poaceae1_wb, Poaceae1_pn, Poaceae2, Poaceae3, Poaceae4, Poaceae5, Juncaceae1, Cyperaceae, CHMA, POSP, FRSP, QUAL, GAPR ,HYVE, LOIN, LYBO, MISC, Moss, RUSP, UnForb, UnForb1, UnForb2, UnForb3, UnForb4, AMSP, GABA, GAFR, ILGL, KAAN, MOCA, UnS5, UnShrb, Unshrb4, UnShrub2, UnShrub3, VACO, ACRU, JUVI, ILOP, NYSY, ScrOak, UnOak2, UnT1, UnT2, PAQU, SMSP, SODU, TORA, UnV, Unvine, AGST, DISP, JUGE, SPAL, SPPA, AGMA, ATPA, IRVE, LICA, PLMA, SADE, SOSE, SULI, SUMA, SYSP, TRMA, BAHA, IVFR, PHAU, Wrack, Dead, Bare, Total, ST_Gram, ST_Shrub, ST_Herb, Phrag, SI Phrag_Stems, Light, WaterDepth (cm), Redox, moisture_percent, Salinity, LOI, Bulk Density, Elevation_NAVD88, z_minusMHW, z_minusMSL, z_star, FloodingDuration, QUSP_s, NYSY_s, JUVI_s, ACRU_s, QUIL_s, ILOP_s, SAAL_s, NYSY_s, PIRI_s, QUAL_s, QURU_s, QUIL_s, QUPH_s, QUVE_s, QUSP__s, ACRU_t, JUVI_t, ILOP_t, SAAL_t, and Total_Trees. The field Site includes one of three site codes: WB, PN, EH, which represent Waquoit Bay, MA (WB), Pine Neck Preserve, NY (PN), or Egg Harbor, NJ (EH). The field Date includes the sampling date in the format of MM/DD/YYYY. The field Point is a number 1-48, where each site (WB or PN, or EH) has a certain number of sampling points (1-41 for WB, 1-43 for PN, or 1-48 for EH). The field Lat is the latitude in decimal degrees north. The field Long is the longitude in decimal degrees west. The 6-79 fields represent a visual estimate of percent cover (0-100%) for understory plant species, plants, wrack, dead material, or bare ground observed in the field in 0.5m2 quadrats. Poaceae_sp, Poaceae1_eh, Poaceae1_wb, Poaceae1_pn, Poaceae2, Poaceae3, Poaceae4, Poaceae5, Juncaceae1, and Cyperaceae are different unknown species of the grass (Poaceae), Rush (Juncaceae), and Sedge (Cyperaceae) families. CHMA is *Chimaphila maculata.* POSP is *Polypodiopsida* sp. FRSP is *Fragaria* sp. QUAL is *Quercus alba.* GAPR is *Gaultheria procumbens.* HYVE is *Hydrocotyle verticillata.* LOIN is *Lobelia inflata.* LYBO is *Lysimachia borealis.* MISC is *Mikania scandens.* Moss is an unknown moss species. RUSP is *Rubus* spp. UnForb, UnForb1, UnForb2, UnForb3, and UnForb4 are four different species of unknown forbs. AMSP is *Amelanchier* sp. GABA is *Gaylusacia baccatta.* GAFR is *Gaylusacia frondosa.* ILGL is *Ilex glabra.* KAAN is *Kalmia angustifolia.* MOCA is *Morella caroliniensis.* UnShrub5, UnShrb, Unshrb4, UnShrub2, and UnShrub3 are different species of unknown shrubs. VACO is V*accinium corymbosum.* ACRU is *Acer rubrum.* JUVI is *Juniperus virginiana.* ILOP is *Ilex opaca.* NYSY is *Nyssa sylvatica.* QUIL is *Quercus ilicifolia.* Quercus_species is unknown oak. UnTree1 and UnTree2 are unknown tree species. PAQU is *Parthenocissus quinquefolia.* SMSP is *Smilax* spp. SODU is *Solanum dulcamara.* TORA is *Toxicodendron radicans.* UnVine is unknown vine1. Unvine2 is unknown vine2. AGST is *Agrostis stolinifera.* DISP is *Distichlis spicata.* JUGE is *Juncus gerardii.* SPAL is *Spartina alterniflora.* SPPA is *Spartina patens.* AGMA is *Agalinis maritima.* ATPA is *Atriplex patula.* IRVE is *Iris versicolor* LICA is *Limonium carolinianum.* PLMA is *Plantago maritima.* SADE is *Salicornia depressa.* SOSE is *Solidago sempirvirens.* SULI is *Sueada linearis.* SUMA is *Sueada maritima.* SYSP is *Symphyotrichum* sp. TRMA is *Triglochin maritima.* BAHA is *Baccharis halmifolia.* IVFR is *Iva frutescens.* PHAU is *Phragmites australis.* Column 80 is the total percent cover observed. Columns 81 to 86 are total percent covers for different plant groups where ST_Gram is salt-tolerant graminoids, ST_Shrub is salt-tolerant shrubs, ST_Herb is salt-tolerant herbs, Phrag = Phragmites australis, and SI = salt-intolerant plants. Phrag_stems is the number of live* Phragmites* stems rooted in the quadrat. Columns 87-98 are environmental variables that were measured from soil samples or in situ: Light, WaterDepth_cm, Redox, moisture_percent, Salinity, LOI, BulkDensity, Elevation_NAVD88, z_minusMHW, z_minusMSL, z_star. Light is light availability, measured as a percentage of total light available relative to a reference sensor in an unobstructed forest. WaterDepth is the depth to the water table in cm measured during summer at low tide. Redox was measured in mV using a redox probe. moisture_percent is the percentage of mass lost from drying soil samples. Salinity is the soil salinity measured from 5:1 water:dry soil extracts in PSU. LOI or Loss on Ignition is a measure of organic matter content, measured as the percentage of mass lost through combustion. BulkDensity is the mass of dry soil divided by the volume, measured in g/cm 3. Elevation is the elevation of the sampling plot in meters relative to the North American Vertical Datum of 1988 (NAVD88), extracted from USGS Digital Elevation Models (DEMs). The variable z_minusMSL is the plot elevation minus mean sea level in meters determined from the NOAA VDatum tool. The variable z_minusMHW is the plot elevation in meters minus mean high water determined from VDatum. The variable z_star is the plot elevation standardized to tidal range, where z = (elevation-MSL)/(MHHW-MSL). The variable FloodingDuration is the percentage of time the surface is flooded, calculated using the Vulntoolkit R package and water level logger data collected at the sites from 2020 - 2021. Columns 99-105 (QUUP_s toto SAAL_s) are counts of saplings within 5 x 5 m plots centered around the understory vegetation plots. QUSP_s is number of *Quercus sp.* saplings. NYSY_s is number of *Nyssa sylvatica* saplings. JUVI_s is number of *Juniperus virginiana* saplings. ACRU_s is number of *Acer rubrum* saplings. QUIL_s is number of *Quercus ilicifolia* saplings. ILOP_s is number of *Ilex opaca* saplings. SAAL_s is number of *Sassafrass* *albidum* saplings. Columns 106-117 (NYSY_t - SAAL_t) are the counts of mature trees found in 5 x 5 m plots centered around the understory vegetation plots. NYSY_t is number of *Nyssa sylvatica* trees. PIRI_t is the number of *Pinus rigida* trees.  QUAL_t is the number of *Quercus alba* trees.  QURU_t is the number of *Quercus rubra* trees.  QUIL_t is the number of *Quercus ilicifolia* trees.  QUPH_t is the number of *Quercus phellos* trees. QUVE_t is the number of *Quercus velutina* trees.  QUSP_t is the number of *Quercus sp.* trees.  ACRU_t is the number of *Acer rubrum* trees. JUVI_t is the number of *Juniperus virginiana* trees. ILOP_t is the number of *Ilex opaca* trees. SAAL_t is the number of *Sassafrass* *albidum *trees. Total_Trees is the total number of trees found in the 25m^2 plots. ## Sharing/Access information Water level data from 2020 - 2021 can be accessed here: * [https://doi.org/10.5061/dryad.ghx3ffbvz](https://doi.org/10.5061/dryad.ghx3ffbvz) ## Code/Software None included.