Why we work to remove Invasive Species along the River Almond Walkway
Non-native species are those that have been introduced deliberately or accidentally by humans. It is interesting to note that a new Wildlife and Natural Environment Act (Scotland) 2011 is now in force making it illegal to plant any non-native plant in the wild in Scotland. A species is regarded as invasive if it has been introduced by human action to an area where it did not previously occur naturally and has become a pest in the new location, threatening the local biodiversity.
A number of plants occurring along the Almond Walkway are non-native ‘invasive’ species and the following have been cited by Plantlife (http://www.plantlife.org.uk) as among the top 20 alien invasive species which threaten the UK’s flora: Japanese knotweed (Fallopia japonica); Few-flowered leek (Allium paradoxum); Giant Hogweed (Heracleum mantegazzianum); Himalayan Balsam (Impatiens glanduliferum); Rhododendron (Rhododendron ponticum).
Other alien species in the Almond area that threaten biodiversity and require control are: Cherry Laurel (Prunus laurocerasus); Snowberry (Symphoricarpos albus); Himalayan Honeysuckle (Leycesteria formosa).
Japanese Knotweed (by the river’s edge) and Giant Hogweed (a young plant in the foreground)
Japanese knotweed is native in eastern Asia (Japan, China and Korea) and was originally introduced to Scotland as an ornamental plant in the mid 19th century. It is able to regenerate from very small pieces of plant material and its rhizome system can be up to 3 metres deep, making it extremely difficult to eradicate. Once established, it forms dense stands that shade and crowd out all other vegetation, displacing native flora and fauna. Eradication requires that the roots are killed. A good herbicide for use on this plant is glyphosate as it is ’systemic’ i.e. it penetrates through the whole plant and travels to the roots.
Giant Hogweed is a native of South-west Asia which was introduced to Britain as an ornamental in the 19th century. It is phototoxic when the skin is exposed to sunlight. The sap of giant hogweed causes blisters, long-lasting scars and can cause blindness if it comes in contact with eyes. Children should be kept away from giant hogweed. If skin is exposed, the affected area should be washed thoroughly with soap and water and the exposed skin protected from the sun for several days. By forming dense stands, these plants can displace native plants and reduce biodiversity. Eradication may include combinations of specialist herbicidal treatment and removal either mechanically or by hand by trained personnel wearing protective clothing, including eye protection.
Few-flowered leek is a native of the Caucasus region and is very invasive on riverbanks and woodlands especially in Southern Scotland. It competes with native spring flowers. Unfortunately it is very difficult to control and removal by hand has limited success. The best method would be chemical treatment but this would affect other species in the area.
Himalayan balsam is native to the Himalayas and was introduced to the UK in 1839 and is now a naturalised plant, found especially on riverbanks and in waste places where it has become a problem weed. The seed pods open explosively when ripe and each plant can produce up to 800 seeds. These are dispersed widely as the ripe seedpods shoot their seeds up to 7m (22ft) away. The plant tolerates low light levels and also shades out other vegetation, so gradually impoverishing habitats by killing off other plants. Once established along a river bank the seeds can be transported further afield by water. The main method of non chemical control is pulling or cutting the plants before they flower and set seed. Conservation authorities regularly organise ‘balsam bashing’ work parties to clear the weed from marshland and riverbanks.
Rhododendron ponticum is native to southern Europe and southwest Asia and was first introduced to Britain in the late 18th Century. Suckering of the root, together with its copious seed production, has caused it to become an invasive species over much of Western Europe. Once Rhododendron has invaded an area few native plants survive. In woodlands only those trees which manage to grow above the level of the Rhododendron canopy will persist. Conservation organisations in Britain now believe that R. ponticum has become "a severe problem" in the native Atlantic oak woods of the west highlands of Scotland and in Wales and on heathlands in southern England, crowding out the native flora. Control has been by cutting down plants followed up by herbicide use. Injection of herbicide into individual plants has been found to be most effective.
FRAW work party cutting back laurel
Cherry Laurel is native to the Balkan region of southeast Europe and western Asia. It was planted in Great Britain in the 1600s and recorded in the wild by 1886. Benefits have been claimed for this species as a source of nectar and for nesting sites for birds. Also, the fruits are eaten by birds. However it is an extremely invasive plant species, unpalatable and likely toxic to mammals and invertebrates due to the presence cyanide. It spreads aggressively in the shrub layer of woodland, casting a dense shade that excludes other plants. It can be controlled by cutting the stems followed by herbicide treatment of stumps.
Snowberry thicket (winter)
Snowberry is a native of North America and was planted as game cover in the UK in the early 20th century. It is a 1-3m high shrub which spreads by means of suckers to form dense thickets. It has distinctive white berries. It is described by the Forestry Commission in Scotland (http://www.forestry.gov.uk/forestry/INFD-7YBDAR ) as invasive in Scottish woods.
Himalayan Honeysuckle is native to the Himalayas and south western China. It became a popular plant in Victorian shrubberies. Seeds are dispersed both by water and by birds and animals that feed on the ripe fruit. It is regarded as an invasive species in New Zealand and Australia and potentially invasive in the UK.
What is being done to control these species along the River Almond Walkway?
Japanese knotweed: This is being controlled by cutting and herbicide treatment by the Cramond Angling Club and the City of Edinburgh Council Natural Heritage Service
Few-flowered leek: No plans as yet for control but monitoring is planned
Giant Hogweed: This is being controlled by herbicide treatment by the Cramond Angling Club and the CEC Natural Heritage Service
Himalayan Balsam: FRAW members have been helping with pulling out this species in Woodland Compartment 3 and along the river bank
Cherry Laurel: Towards the Cramond end of the Walkway, CEC Natural Heritage Service has been cutting laurel close to ground level. FRAW members have assisted with cutting and burning regrowth. Treatment of stumps with glyphosate is being carried out by trained CEC personnel. As laurel was part of a designed landscape it is planned to retain and control the spread of some plants to provide historical continuity
Rhododendron: Treatment of Rhododendron has been as for Laurel. Further work will be required around the area of the Bughtlin Burn. As for laurel some plants will be retained.
Snowberry: Some Snowberry was cut back by FRAW members at the entrance to the walkway from Queensferry Road, by Dowie’s Mill Cottages and in Woodland compartment 3.
Himalayan Honeysuckle: Cutting back of this species by FRAW members is now providing improved river views.
Ivy growing through wall
In addition to the species described above there are instances when our native Ivy (Hedera helix) requires to be cut back. Ivy is a beneficial plant in many ways as it provides a habitat for wildlife including nesting sites for birds. Growing on trees it may hide signs of decay and on those that are unhealthy there may be a danger of collapse due to the weight and increased wind resistance.
Ivy overhanging the walls at the steps by Jock Howieson’s Cottage has been cut in the area of Jock Howieson’s Cottage to clear the area of excess growth. It has also been cut around a number of trees where it has been identified by CEC Natural Heritage as requiring control.