The impact of river modification and dam operation on floodplain vegetation succession trends in the Kootenai River, USA

Abstract

Hydrological alteration caused by dam operation and river modification has changed the dynamics of riparian vegetation in most river floodplain systems. In this study, a dynamic vegetation model was used to analyze the change in floodplain area occupied by individual vegetation types and vegetation succession dynamics as consequences of river modification and dam operation. The vegetation model simulates spatially distributed vegetation types based on simulated river floodplain physical processes. Study periods were classified into historic, pre-dam and post-dam conditions. The statistical t-test was used to analyze changes in the normalized mean area occupied by different vegetation types between different time periods. Furthermore, the Mann–Kendall test was used to evaluate the succession trend of vegetation with respect to spatial area and age.The area occupied by colonization and cottonwood young transition vegetation was similar in historic and pre-dam conditions, but decreased gradually from pre-dam to post-dam conditions. In contrast, the reed and grassland vegetation gradually increased from historic to post-dam conditions. The cottonwood old transition vegetation increased from pre-dam to post dam condition. The average age of the vegetation did not significantly increase or decrease in historic and pre-dam conditions; however, it increased in the post-dam condition. There were no significant differences in the succession trends of vegetation area between historic and pre-dam conditions for most of the vegetation types, except for reed and grassland and cottonwood old transition vegetation. The succession trends of vegetation area were significantly different between pre- and post-dam conditions for all vegetation types except for the wetland vegetation. Our vegetation model illustrated the impact of altered physical processes on riparian ecosystems. Such spatial and quantitative measurements of vegetation distributions can be used to quantify the riparian habitat losses from dam operation, which can help to manage and restore riparian vegetation in human disturbed systems.