Spartina pectinata Plant Association 



SPAPEC; prairie cordgrass 

 MTNHP rank: G3/S3 



Environment: This is perhaps the most abundant of naturally occurring wetland types on BLM land 

 in Carter County. It occurs in floodplains of ephemeral and permanently flooded streams in 

 subirrigated settings. In rangelands on shale substrates where there is otherwise little or no 

 permanent standing water, intermittent drainages are usually damned to create stockponds; narrow 

 and patchy wetland habitat above and below stockponds is often dominated by the rhizomatous grass 

 Spartina pectinata. Two relatively undisturbed examples of SPAPEC were sampled, one in an 

 intermittent wash off a shale ridge system, headwaters of Short Creek, and another in the more or 

 less permanently flooded canyon bottom of East Fork Little Powder River. The Short Creek site 

 occurs in a landscape of low-relief uplands dominated by sagebrush steppe (ARTTSW / ELYLAN) 

 while the Little Powder River site is in a box canyon which cuts eroded breaklands and benchlands 

 dominated by silver sage (ARTCAN/PASSMI) and grasslands (STICOM/CARFIL) with scattered 

 ponderosa pine. Adjacent wetland types at the Little Powder River site were dominated by 

 Equisetum laevigatum and Scirpus pungens. 



Vegetation: The two sampled plots represent a broad range in hydrological conditions to which 

 Spartina pectinata is adapted and functions as a dominant. The plot in an ephemeral wash has about 

 50% cover by Spartina pectinata with near complete cover (of both live foliage and litter) in patches 

 which form terraces in a mosaic with bare soil of recent alluvial deposition. There is little cover by 

 other species, the grasses Agrostis scabra and Poajuncifolia and forbs Aster falcatus, Polygonum 

 ramosissimum, and Thermopsis rhombifolia form a distinctive assemblage, but occur in only trace 

 amounts. The plot in the permanently saturated, low gradient floodplain contrasts by being less 

 patchy and by having a taller, more dense sward of Spartina pectinata (about 90% cover), significant 

 cover (about 10%) by Scirpus pungens and a different assemblage of characteristic tall, wet-site 

 forbs {Asclepias speciosa, Rumex crispus, and Solidago canadensis). 



Soils: The floodplain site exhibited soils with strong gleying and no evidence of mottling. The other 

 site, located in an intermittent wash, possessed neither wetland soil feature but, owing to its 

 topographic position below and adjacent to an acid shale ridge system, its soil reaction was 

 moderately acid (see inset below), with a hydrogen ion concentration more than 1 00 times greater 

 than any SPAPEC site sampled to date (Hansen et al. 1995). Conductivities indicate only mildly 

 saline conditions. Appraising soil texture by feel indicates both soils were silt loams. 



Comments: An "upland marsh" habitat type dominated by Spartina gracilis (71% cover) and 

 Muhlenbergia asperifolia (10% cover) was described in southern Carter County in the bentonite 

 mining district (Ecological Consulting Service 1975). Hansen et al. (1995) include wetlands 



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