appeared to be accumulating sand and a rapid recovery of both sand and 

 vegetation on this section of Padre Island is anticipated. 



In 1961 Hurricane Carla removed the sand to about 1.2 meters MSL on many 

 north Padre Island areas and essentially eliminated all the plant roots and 

 rhizomes. The 1969 plantings were made at 1.34 meters above MSL, 8 years 

 after the hurricane. With current beach elevations near the normal 1.5 to 1.8 

 meters above MSL, and with much residual plant material, immediate and 

 substantial sand trapping is expected in front of the existing natural and 

 experimental dunes. 



d. Midisland Dune Field . Bare dune fields activated, in part, early 

 this century by overgrazing and drought migrate westward (landward) across 

 Padre Island. The active dunes are so unstable that colonization by plants 

 does not occur. However, after the dune migrates past a given point, it 

 leaves behind a zone of moist sand about 1.5 to 1.8 meters above MSL, which is 

 then rapidly colonized by vegetation (Figs. 16 and 17). 



An area 91 by 46 meters, generally on the north side of the live oak 

 motte, was sampled in the summer of 1973 (Dahl, et al. , 1975). It was found 

 that the most important colonizing species were common bermuda grass, red love 

 grass, and species of Cyperus and Juncus. A resampling of this area was made 

 in July 1981. To show plant successional trends from bare sand to a more 

 mature grassland, samples of the area were made in 76-meter blocks, including 

 an area of mostly bare sand immediately adjacent to the migrating sand dunes 

 (Table 11). The current data, like that of the 1973 sampling, showed that 

 five vegetative species were early colonizers: bermuda grass, red love grass, 

 Fimbristylis spp., Cyperus spp., and needlepod rush (Junaus soirpoides) • 

 Vegetation covered only 2 to 3 percent of the sand surface of the 76 meters 

 most recently abandoned by the migrating dune field. 



The 76 meters farther east had 25 percent vegetation cover and about 11 

 more plant species. Additions to the list of early colonizers were seacoast 

 bluestem, spike rush species (Eleoaharis spp.), prairie senna. Corpus Christi 

 fleabane, beach evening primrose, plains coreopsis (Coreopsis tinctoria) , 

 Texas ironweed (Vemonia Texana) , Juniperleaf polypremum (Polypremum 

 proaumbens) , and green carpet weed (Mollugo vertiaiZlata) . 



From 152 to 229 meters away from the bare dunes, vegetation cover 

 increased to 42 percent, and 25 species were encountered. Between 229 and 305 

 meters away from the migrating dunes, the vegetation ground cover increased to 

 56 percent with 21 species encountered; nine of them dominated the 

 composition. They were: seacoast bluestem, gulfdune paspalum, Paspatum spp., 

 (Faniaum oligosanthes) , red love grass, needlepod rush, prairie senna, camphor 

 weed (Heterotheaa pilosa) , and Corpus Christi fleabane. As the vegetation 

 community became more mature bermuda grass disappeared from the composition 

 (Table 11). 



Depressions holding water for longer periods after rainfall had 

 primarily: American bulrush, spikerush, waterhyssop (Baoopa monnieri) , green 

 carpet weed, and frogfruit (Phyla incisa) • 



During the 8 years from the summer of 1973 to 1981, the bare dune field 

 had migrated about 213 meters landward (west-northwest). Barring a severe 



44 



