II. STUDY AREA 



Padre Island has a subtropical, semiarid climate, moderated by maritime 

 tropical air from the Gulf of Mexico. The summer months are hot, with little 

 daily or weekly variation. Winter (December to February) is mild with wide 

 fluctuations in temperature; freezing temperatures are infrequent. 

 Precipitation is irregular, both monthly and annually, with no sharply defined 

 seasons. Within the last century, the annual precipitation at Corpus Christi, 

 the nearest station with long-time weather data, has ranged from 1222 

 millimeters in 1888 to 136 millimeters in 1917, with an average of 678 

 millimeters. Excessive precipitation associated with hurricanes, usually in 

 late summer and early fall, biases the annual average precipitation upward. 

 Without the hurricanes, the annual average would be lower and more indicative 

 of the stress associated with semiarid lands where droughts are frequent but 

 irregular (Carr, 1966). The average temperature for Corpus Christi is 21.7° 

 Celsius (Department of Commerce, 1970), 



Two principal wind regimes dominate the Texas coastal zone — persistent 

 southeasterly winds from March to September and north-northeasterly winds from 

 October to February (Behrens, Watson, and Mason, 1977). However, prevailing 

 winds (disregarding windspeed) are onshore 11 months of the year (Dahl, et 

 al., 1975). Northerly winds are associated with frontal passages and are 

 usually strong with concurrent precipitation. However, some northers are dry, 

 creating small dunes along the beach with each passage. Prevailing winds then 

 transport this sand back to the foredunes. 



The coastal topography of the mainland adjacent to Padre Island is rela- 

 tively flat with soils developed from Pleistocene and recent unconsolidated 

 clastic sediments. The soils of Padre Island developed on recent marine and 

 eolian soils (Brown, et al., 1976). The sand particle size is predominantly 

 fine to very fine. Soils vary in salt content and in amounts of shell and 

 organic matter. The highest organic matter content from beach sands was 0.1 

 percent. Shell fragments were generally less than 1 percent (Dahl, et al., 

 1975). 



A schematic cross-sectional profile of north Padre Island and the 

 dominant plants of major communities are in Figure 2. North Padre Island is 

 predominantly a grassland of midheight. Seacoast bluestem iSchizachyriim 

 s oopariim var . littovalis) , seashore dropseed (Sporobolus Virginians), 

 gulfdune paspalum (Paspalnm mono st achy um) , and saltmeadow cordgrass (Spartina 

 patens) are species that commonly occur from the foredune across the island. 



The number of species on the shoreface of the dunes is limited, with sea 

 oats (Uniola paniaulata) the dominant sand-trapping plant. Other species 

 capable of trapping or binding sand are saltmeadow cordgrass, seashore 

 dropseed, bitter panicum (Paniaum amarwri) , railroad vine (Ipomoea pes-Capvae) , 

 and gulf croton (Croton punctatus) . After dunes have been started by pioneer 

 vegetation, forbs such as beach groundcherry (Physalis viscosa) , beach evening 

 primrose (Oenothera drummondii) , and prairie senna (Cassia fasaiaulata) often 

 become common. 



Of particular interest to this study is the vegetation of the backshore 

 and the foredune foreslope, and the natural succession of plants from a 

 barren, hurricane-planed backshore to a continuous, mature foredune ridge. 

 Sea purslane (Sesuvium portulaoastrim) , one of the first species to reappear 



