There was a negative correlation between knotweed invasion and the species richness and abundance of native understory herbs, shrubs, and juvenile trees. The carbon to nitrogen ratio of senesced knotweed leaves was 52:1, a value 38 to 58% higher than dominant native riparian species. Analysis of nutrient reabsorption from senescing leaves revealed that knotweed reabsorbed 75.5% of its foliar nitrogen prior to litterfall. In contrast, native species reabsorbed 5 to 33%, thus contributing a greater proportion of their nitrogen resources to riparian soils and aquatic environments through leaf litter.
Reductions in juvenile coniferous and broadleaf trees associated with knotweed invasion may limit development of overstory trees and alter the successional trajectory of these riparian forests. Loss of riparian trees can have long lasting and detrimental effects on bank stability, hydrology, nutrient loading, habitat quality and productivity of adjacent lotic systems. Additionally, leaf litter from riparian vegetation comprises a primary source of nutrients and energy in forested streams and backwater channels. By displacing native vegetation and altering the species composition and nutrient quality of litter inputs, knotweed invasion can affect the structure and productivity of riparian forests and adjacent aquatic habitats.
