Spartina is grown in experimental elevation planters placed in draining ponds on the salt marsh platform. The planters are constructed from PVC pipes of varying lengths. All of the PVC pipes are open at the bottom, and flush to the mudflat surface of the pond, resulting in the tops of the pipes being situated at various relative elevations within the tidal range. Plants growing in the shorter PVC pipes are flooded for a longer duration of each tidal cycle than plants growing in the taller PVC pipes. The growth response of S. alterniflora when exposed to different flood frequencies is monitored by monthly estimates of biomass (determined non-destructively from plant heights) and by destructive 'harvesting' of all above- and belowground plant material at the end of the growing season.
Experimental Elevation Planters:
There have been two experimental elevation planters located at Law's Pt. Each planter has 6 replicate pots each of 6 levels. Pots are constructed from varying lengths (in 15-cm increments) of 6" diameter PVC pipe. All of the PVC pipes are open at the bottom, and flush to the mudflat surface of the pond, resulting in the tops of the pipes being situated, step-wise, at various relative elevations within the tidal range. The entire structure resembles a staircase. The six replicate pots at the lowest level of the planters are ~0.5m above MSL. Pots at the highest level of the planters are ~0.1-0.2m above MHHW. Planter A was established at Site#1 in 2002. In 2008 two additional elevations were added to Planter A. Planter A was dismantled after the 2009 experiment. Planter P was established at Site#2 in 2006.
Replicate pots are filled with sediment from the draining pond in which they are situated in either late fall or early spring. Between mid-April and mi-May, plugs of S. alterniflora are collected from the marsh platform near the planter, and transplanted into the pots. Every attempt is made to ensure that all plugs are the same size (surface area and depth) and contain the same number of plants of about the same height. However, often times the natural marsh is not yet well established, and there is variability within the initial plantings. Marsh plugs are approximately 4-5" in diameter and 5-6" in depth. In 2011 marsh plugs were 2" diameter x 6" deep, and in 2013 marsh plugs were 4" diameter x 6" deep.
Standing biomass in the replicate pots are estimated approximately monthly in 2002, 2003, 2008-2011 and 2013. The height of each plant (excluding flowers) in each pot is measured and read (along with level and replicate information) into a digital recorder. Plant height data are transcribed into an EXCEL spreadsheet, and processed with FORTRAN algorithms (Morris and Haskin, 1990, Ecology 71(6):2209-2217) to convert plant height to plant weight.
At the end of the growing season (mid-Aug to mid-Nov), the planter is 'harvested'. The contents of each replicate pot (live shoots, dead shoots, roots, rhizomes, peat, sediment, dead belowground macro organic matter) are removed from the planter. Shoots are clipped at the sediment surface, sorted into live and dead plants, counted, dried (60C) and weighed. Belowground portions from each pot are seived (2.5mm) to collect all plant material (live and dead), dried (60C) and weighed.
Various monitoring , planting , and harvesting protocols have been used throughout the years to accomodate various experimental goals (e.g. fertilization, plant age, plant species, belowground biomass distribution, substrate type). Only data from untreated, single year replicates of S. alterniflora are included in this dataset. Following are exceptions to the general protocol described above. In 2002, the harvest occured after all plants had senesced, therefore aboveground peak biomass was estimated from July plant height data. In 2002 only half the pots were harvested. In 2003, the harvest occured after all plants had senseced, therefore aboveground peak biomass was estimated from July plant height data. In 2003, only half the pots were 1yr old. In 2005, belowground material was sorted into live and dead, and only live belowground material was retained. In 2006, plant density was not determined. In 2011, a substrate experiment was conducted in the planter; only half the pots were filled with natural (control) sediments collected as described above. Belowground material was seived to 1mm; only live roots and rhizomes were retained. In 2013, plants were not harvested, therefore peak aboveground biomass was estimated from August plant height data. For 2014, the harvest data (density, AG biomass and BG biomass) are for plants that were planted in spring 2013 and overwintered.
Elevations of the pots relative to NAVD88 are determined approximately annually by FastStatic measurements using a Trimble 4800 receiver and TSC-1 controller (from UNAVCO www.unavco.org).
Collections occur approximately monthly from May through September. Database is updated once annually, usually in the winter. Study and data collection are ongoing as of Sept 2019.
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