Japanese knotweed (Fallopia japonica) is an invasive exotic species. Found commonly in riparian habitats, it forms dense thickets along the banks of rivers and streams.
The aim of this study was to investigate the effect of Japanese knotweed on stream depth and discharge at baseflow. In early June 2008, pressure sensors were placed upstream, near downstream, far downstream and within a stretch of river containing the study area of Japanese knotweed, which was located along the Third River within the Bonsal Preserve, Montclair, NJ. The study area measured 150 square meters in area and covered about 25 meters of stream bank length. Stream depth, temperature, and discharge were recorded at 15 minute intervals for four months (June through September). Knotweed daily photosynthesis, stomatal conductance, and leaf water potential patterns were recorded during the course of two, day-long samplings at the end of July, 2008. At the beginning of August 2008, all of the knotweed plants in the study area were cut at the base and their leaves were harvested. A leaf mass to leaf area conversion factor was used to calculate LAI for the study area.
Results/Conclusions
Pre-harvest stream water level was found to be significantly lower from post-harvest stream level within the stretch containing knotweed. Furthermore, based on the physiological measurements and an estimated LAI of 4.9, it was estimated that the plants in the study area removed about 3,200 liters of water per day from the soil. These findings suggest that the presence of knotweed within riparian habitats may have even more deleterious effects than simply dominating local flora.