Beach Vegetation and Plant Distribution Patterns Along the Northern Gulf of Mexico

Barbour, M.; Rajmanek, Davis; Johnson, A.; Pavlik, B.

We sampled the leading 5O + m of beach vegetation along the U.S. portion of theGulf of Mexico with 63 strip transects, made up of contiguous 1 x 1 m quadrats. Only stableor prograding beaches were sampled. Cluster analysis and ordination of samples based on73 taxa revealed three vegetation types: southern Florida, Florida panhandle to Mississippiand Louisiana to Texas. These differed in dominants, species richness, and array ofgrowthforms. In choosing growth form traits, we emphasized leaf characteristics, including thepresence/absence of Kranz anatomy. Environmental factors which were correlated withregional vegetation included sand texture, sand chemistry, topographic. roughness of transects, and climatic or historical factors linked with latitude and longitude. Uniola pani-culata was a leading dominant everywhere except in Louisiana, where it was replaced bySpartina patens. The most arid sites exhibited relatively high cover by taxa with narrow,small, or pubescent leavcs, but were low in cover by succulent, sclerophyllous, or C4 taxa.The coldest and wettest sites exhibited the lowest cover by succulents, but were high inrelative cover by C4 taxa (76%). Only sites relatively undisturbed by hurricanes in the past16 yr were sampled, but even with this constraint, there was a negative correlation betweenspecies richness and severity of past disturbance. Very few taxa exhibited increasing coverwith increasing disturbance.At thc local scale, most taxa were not randomly or uniformly distributed, but rather appeared to peak in cover at prticular distances inland from thc leading edge of vegetation.However, only 37 taxa were widely enough distributed to permit a statistical evaluation oflocal pattern. Six had significantly more cover in the leading 20 m of transectsr all wereprostate forbs, either succulents or C4 plants, and with pubescent leaves, Twelve taxa wereiignificantly more frequent on the most exposcd/stressed prts of transects and 14 weremore frequent on the most protected parts. The former most often were forbs with large,pubescent, or succulent leaves (Atiplex, Cakile, Cassia, Croton, Ipomoea, Oenathera, Pani-cum, Paspalum, Scaevola, Sesuaium); the latter most often were erect or rigid or forbs withsmall, non-pubescent, leaves (Cencbrus, Cbamaescyce, Conltza, Heterotheca, Hydrocotyle,Ioa, Oenotheru, Opuntia, Paronychia, Polygonella, Sporobolus). Several dominant C4 grassesexhibited no pattern (Scbizacbyium, Spartina, Uniola). In general, C4 plants exhibited nosignificant spatial or topographic patterns. Leaf anatomy of 62 taxa examined fell into fivesubjective categories or types, including some which appear to be novel to the literature.The largest fraction (25 taxa exhibited relatively undifferentiated, isolateral mesophylls oftotal thickness averaging 660 um.

Beach Vegetation and Plant Distribution Patterns Along the Northern Gulf of Mexico

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