Survey of giant hogweed, Japanese knotweed and Himalayan balsam on 5 major Lothian rivers, 2003/04

Over the five Lothian rivers surveyed: Fallopia japonica (Japanese Knotweed) was by far the most extensive of the three species, often forming semi-continuous stands along riverbanks which were frequently, on the North and South Esks in particular, within important habitats such as native riparian woodland. The location of populations are hard to predict with frequent isolated stands being found where garden refuse has been dumped or disturbance to the bank has occurred for example. In general the plant occurs much more extensively in and around built-up areas and is much rarer in the more rural locations of the river systems upper reaches. Heracleum mantegazzianum (Giant Hogweed) was the least widespread species which occurred only on the lower Esk in any profusion. Elsewhere it occurred as isolated small stands with at least one record on each catchment. Incidental sightings of this species were also made from the A1 where there are more extensive populations locally. Impatiens glandulifera (Himalayan Balsam) shows a quite distinct pattern of distribution with well-defined upstream and downstream limits between which it occurs at near constant or very high frequency. On the rivers where it occurs the downstream limit is always the sea or a little inland where there is tidal influence as on the River Tyne. On some rivers there are small populations upstream of the main length of affected river.