Article by Abigail Pedlow
Himalayan Balsam is one of those plants marked with a star on the new green flora card. It’s a problem plant because it spreads along our river banks, out-competing the native vegetation (at 200 cm it’s the tallest annual plant in the UK). Because it is an annual and shallow-rooted as well it causes erosion when banks are left bare at this time of year, and even in summer the shallow roots don’t bind the banks together in the way that native plants such as Hemp-agrimony do.
Its bright pink, showy, flowers are popular with bees, but even this is bad news for the native plants - they get ignored and left un-pollinated.
Like most ‘invaders’, it has exceptional dispersal properties – in this case the explosive nature of the seed-pods flinging seeds up to 5 m.
|
Source |
Date |
Spread |
|
White’s Flora of Bristol |
1912 |
2 locations |
|
BRERC (Flora of the Bristol Region) |
2000 |
149km squares in Avon |
|
BRERC database |
2003 |
274km squares in Avon |
Send us records to help us monitor this problem plant, and help target action.
From Tim Corner
Most general field surveys, whether carried out by consultants or wildlife organisations, such as BRERC or Avon Wildlife Trust, tend to be based on botanical survey methods. The main reason for this is that unlike animals, plants don’t move around. Or do they? They might not get up and walk away, or fly off to the other side of the hill, but they do spread about and some plants spread very fast indeed.
An example is Japanese Knotweed. This is an introduced, exotic, non-native plant virtually unheard of by most people 20 years ago. Now it can be found all over the place, particularly in hedgerows, woodland, along streams and riverbanks and waste ground. It spreads vegetatively, not needing to pollinate, and small fragments of the plant thrown in the air by hedge cutting will grow. It has proven to be near impossible to eradicate from the countryside and shades out, competes and destroys other plants living in its midst, including our native species.
An example of a plant threatened by Japanese Knotweed is Herb Paris. Herb Paris is considered a good indicator of ancient woodland for the following reason - in order to reproduce itself the conditions have to be just right and it can take many years for this to occur. For example a plant clinging on in a shady area of a dense wood may need the odd oak tree to crash to the ground, thereby creating just the right amount of light and space around it. Of course it needs the falling tree to miss it.
Herb Paris is a small plant usually with 4 leaves arranged in a whorl. It flowers on the top of the whorl of leaves and, when it is successful in flowering and producing seed, it spreads into the world by way of the seed simply falling off and onto the ground next to it.
It takes many years for Herb Paris to go hardly anywhere at all. Meanwhile, Japanese Knotweed is charging around the countryside at a rate of knots…
Are either of these plants growing near you? Please send your records.