slight increases noted. Seashore dropseed tended to decline or 

 remain the same. There were no significant increases. 



(2) Invasion of Unplanted Species . Invasion of unplanted 

 species into experimental dunes has been slower than anticipated. 

 For example, the 1,200-foot sea oats dune has been under test 

 since March 1969, yet only four species other than those planted 

 occurred commonly enough to be considered a significant invader (Table 9) 

 Gulf croton and the Ipomoea spp. occur sporadically. .This lack 

 of unseeded species in dunes from experimental plantings after 

 7 or 8 years is best explained by comparing species composition 

 on mature dunes of the area formed naturally to the unplanted study 

 area and the dunes from experimental plantings of this study. 

 Gulf croton, beach evening primrose, Physalis species, beach morning 

 glory, and other grasses are relatively common in mature, naturally 

 formed dunes. These species are also much more common on the 

 unplanted, naturally formed dunes in this study. Apparently, 

 if a dune forms naturally with the pioneering plants available 

 to the area, some species remain from previous successional stages 

 and they are a natural component of the mature dune at successional 

 climax. However, some of the pioneer successional stages have 

 been bypassed through planting a grass monoculture. Hence, some 

 normal dune species were unable to find a niche and become established. 

 It becomes apparent that a multispecies dune will develop very 

 slowly if originated from grass plantings. 



V. DISCUSSION 



1 . Evaluation of Dune-Widening Methods . 



During experimental plantings from 1969 to 1974, the 1,200- 

 foot bitter panicum and the dune-width extension plantings were 

 specifically made to find the most effective way to widen the base 

 of dunes constructed from vegetation plantings. In February 1972, 

 600 feet of beach was planted with bitter panicum. The north 

 300 feet was 50 feet wide with individual transplants spaced 

 2 feet apart in rows 2 feet apart. The plantings from 300 to 600 

 feet were the same except planting width was 100 feet. In April 

 1972, another 600 feet was added to the south end of the February 

 planting. The plantings width was 50 feet for the 600 to 900 feet, 

 and 100 feet for the 900 to 1,200 feet. However, individual 

 transplants were placed 2 feet apart in 4-foot rows rather than 

 in 2 -foot rows. 



Data accumulated during the past 2 years for the 1,200-foot 

 bitter panicum dune are in Tables 5 and 6 and Figures 10, 16, and 

 17. Briefly, the results of this study are: 



(a) A 50-foot-wide planting trapped all available sand 

 from the beach, so it was unnecessary to plant a 



48 



