Yesterday evening I went along to the annual Invasive Plant species walk organised by Water of Leith Conservation Trust (WOLCT) for their patrol volunteers. We had a lovely walk trhough the downstream area of Colinton Dell. Hard to believe now, as the rain pours down and the wind howls, but yesterday evening was beautiful and mild and sunny.
The main three invasive plant species that are an issue along the Water of Leith are:
Giant Hogweed is a problem because it can cause burns and scarring if you come into contact with it. It is also very invasive as it produces lots of seeds which can stay fertile for several years. It is however popular with quite a few insect species. WOLCT manages the plant by closely targetted spraying with glyphosate, which is the only herbicide that can control the plant.
Himalayan Balsam is a problem because it is very invasive, as it produces vast numbers of seed. It can totally take over an area and stop anything else from growing during its own season. However, because Himalayan Balsam flowers late, it provides food for bees when there's not much else around. Also it doesn't stop the early spring flowers from thriving. We know from our visits to Dumfriesshire, that areas that are covered in Himalayan Balsam in summer are full of a variety of spring flowers earlier in the year. The real problem occurs by rivers where the growth of this plant can erode riverbanks. Plus it smells vile so I'm more than happy to help WOLCT control it by pulling up the plants I find while I'm patrolling the river.
Japanese Knotweed is one of the most invasive plants in the world. It spreads mostly through its roots and can undermine the foundations of buildings. (If you have Japanese Knotweed in your garden, you are likely to be unable to sell your house). It is very difficult to control, currently the WOLCT is trying to eradicate a patch in Colinton Dell and it will take at least a couple of years more to get rid of it, injecting herbicide into every stem of the plants.
Two other plants are giving some concern in Colinton Dell:
Few flowered leek in some areas of the Dell is already taking over from the native wild garlic. One possible way of controlling its spread is for foragers to pick and eat the leek rather than the garlic. Having said that, the number of dogs that run around (and do other things) in Colinton Dell, makes me nervous of foraging anything that grows on the ground there.
Salmonberries have sprung up in one area of the Dell. I've not really been able to find out much about the status of salmonberries in the UK, they've been here for decades, but I'm only aware of them becoming a problem very recently. WOLCT is looking into how best to control them.