In the area of the Burstow Stream as it runs through Brook Wood and beyond the group is involved in the control of Himalayan Balsam plants. Volunteers across Britain are working to stem the invasion of this plant as it threatens to take over vast tracts of the countryside. Teams of workers, many voluntary as is the Horley Conservation Group, are pulling up 'jungles' of Himalayan Balsam, a relative of the Busy Lizzie garden plant while it is flowering and before it can fire its seeds (maybe 2,500 per seed pod) up to 20 feet away to start new colonies.Himalayan balsam has swamped riverside areas throughout the country. Countless miles of riverbank and hundreds of acres of countryside are now swamped by the balsam, which was introduced into Britain as a garden plant and 'escaped' into the wild in the early 20th century.
Like so many introductions from abroad, the move to bring a foreign species into Britain has backfired spectacularly and damaged our eco-system.Concerted efforts are being made to wipe out the plant in the wild before it takes over.
Himalayan Balsam is so strong and invasive that it can even overpower vast beds of native plants like stinging nettles and bramble bushes. Because it grows well over 5ft tall, it stops sunlight reaching other plants so they wither and die. And unlike most native plants, it can fire its seeds to far-flung corners to start new beds next year. However, it is easily uprooted by hand because it grows in moist soil. Cutting the plant shorter or knocking it over fails to stop it spreading. One reason for the success of the plant is its extremely high nectar production which is about 47 times more than our native great willowherb or 23 times more than our native purple loosestrife. This allows it to attract pollinators such as bumblebees away from native species, so reducing their seed set by as much as 25%