CHANGES IN THE LANDSCAPE STRUCTURE OF A SOUTHEASTERN WYOMING RIPARIANZONE FOLLOWING SHIFTS IN STREAM DYNAMICS

Throughout western North America, flood regimes have been altered as a result of large-scale water impoundments and diversions, yet the effe cts on riparian landscape structure have not been quantified. Using ae rial photographs and a GIS, we examined changes in the Rawhide Wildlif e Management Area in southeastern Wyoming between 1937 and 1990 after shifts in the frequency and intensity of flooding of the North Platte River. The river declined in wetted area by 75% between 1937 and 1990. Also, the areal proportion occupied by cottonwood (Populus spp.) stan ds with <30% canopy closure increased while stands with >70% canopy cl osure decreased during this period, indicating a shift from young, den se stands to older, more open stands. Some traditional measures of lan dscape structure (i.e. richness, diversity, dominance, average patch p erimeter length, average patch shape), however, appeared insensitive t o these changes. Finally, the proportion of the landscape that changed land types declined with increasing distance from the river. We expec t further modification of the landscape structure, associated with con tinued declines in cottonwood recruitment and increases in cottonwood mortality.