LONG ISLAND VEGETATION 



207 



The middle of the Juneus gerardi Association shows about 57 per 

 cent of salt. Where the Scirpus robustus has invaded farthest 

 from the fresh water marsh the salt content is 13 per cent. Aspid- 

 ium thelypteris marks the zero line of salinity in this marsh. 

 Another soil factor in salt marshes demanding attention is the 

 presence of gases, especially hydrogen sulphide. This is elimi- 

 nated in striking quantities when the soil is disturbed particularly 

 toward the outer margin. 



The Baccharis Association. On the southeast side of Lloyds 

 Neck the Juncus-gerardi Association is followed by a shrub belt 

 in which Baccharis halimifolia and Iva oraria are the characteristic 

 plants. The presence of such secondary species as Solidago sem- 

 pervirens, Limonium carolinianum, Panicum virgatum, Myrica 

 carolinensis, Agrostis alba maritima, Rhus copallina, and Andropo- 

 gon scoparius clearly indicate the fact that this association is on the 

 tension line between salt and fresh water. In all the local marshes 

 it occupies a narrow border line. This association may also be 

 seen in the marshes of Lloyds Point and Centerport. The further 

 development of this association brings in the scrub oaks and their 

 associates of the Pine Barrens Formation. 



Many of the larger salt marshes are situated at the heads of the 

 harbors. The adjoining uplands are composed of unconsoli- 

 dated rock and the drainage is for the most part underground. As 

 a result when the surface of the salt marsh approximates the ex- 

 treme high tide level the ground water becomes fresh and the suc- 

 cession passes into the fresh water marsh. Even though some of 

 the area be invaded by the extreme tide of autumn and winter, 

 the seepage of fresh water outward is so constant that plants 

 which are not at all halophytes are uninjured. 



The Swamp Formation. The Scirpus Association. The 

 dominant plants are Scirpus americanus, Scirpus rohustus, and 

 Hibiscus moscheutos. These occupy the tension line and with- 

 stand occasional inundations of brackish water. Chemical tests 

 between tides show the absence of chlorides in the middle of this 

 association. Ptilimnium capillaceum, Pluchea camphor ata, Aster 

 novi-belgii litoreus, Asclepias incarnata pulchra, Lysimachia ter- 

 restris, Eleocharis rostellata, and Aspidium thelypteris are the com- 



