MID-TEXAS COASTAL MARSH CHANGE (1939-1991) AS INFLUENCED BY LESSER SNOW GOOSE HERBIVORY

Emergent coastal marshes of the San Bernard National Wildlife Refuge ( SBNWR), were evaluated from 1939 to 1991 using aerial photography and a geographic information system (GIS). Vegetated marsh was transformed to mudflats and open water in areas heavily utilized by wintering les ser snow geese (LSG). Unvegetated mash increased from less than 4% in 1939 to 21% in 1991. Rate of denudation increased after 1965 when LSG numbers of 300,000 in the 1950's increased to nearly 1,000,000 by the 1970's. Over time, some mudflats have revegetated, while others have b ecome deep, open-water areas. Extremes of inter- and intra-annual tide levels, surface water and interstitial soil water salinity, and preci pitation were also experienced during this time period. Repeated and i ntense herbivory by LSG followed by frequent tidal inundation, high so il and water salinities and extended droughts results in vegetation lo ss and the potential for accelerated soil erosion.