Himalyan Balsam

Species Description

Scientific name: Impatiens glandulifera

Native to: West and central Himalayas

Habitat: In Britain, Himalayan balsam prefers moist and semi-shaded places, waste ground and thin woodland. It is particularly prevalent along streams and riverbanks, using water to disperse its seeds.

Introduced to the UK in the mid 19th century as an ornamental, this annual plant has spread rapidly. Its success is due to vigorous growth, shade tolerance, effective seed dispersal and high germination rate. The plant can grow to 2 metres in height and forms dense monoculture stands. It out competes other bank-side vegetation, decreasing biodiversity. When the plant dies in the autumn it leaves the bank bare and vulnerable to erosion. In the Ribble catchment, Himalayan balsam is widespread and extensive, particularly along the mid and lower sections of the river.

Further Information

Dispersal and Reproduction

Each plant may produce up to 800 seeds which can be ejected up to 7 metres from the parent. Seeds germinate synchronously in February to March and grow rapidly. Flowering occurs from July to October, with seeds produced from mid-July onwards.

Known Predators

In Britain, sheep and cattle graze balsam indiscriminately, eating leaves, stems and flowers. The elephant hawk-moth and two species of aphid also feed on the plant. Trials of a rust (Puccinia sp.) as a potential new biological control agent are currently underway.

Impacts

Environmental

Balsam shades out and crowds out many native plant species. It also competes with native flowers by exploitation as it produces much nectar, attracting more pollinating insects.

Economic

Having become dominant in its invaded habitat, the shallow root system can promote erosion during autumn and winter, with the subsequent destruction of bankside structure. Dense stands can impede water flow at times of high rainfall, thereby increasing the likelihood of flooding.