Himalayan balsam © David Kilbey

Features from Wildlife magazine Wildlife articles 2008 -- Spring 2008 -- ::Severn Barrage ::The Variety of life ::A year at Willsbridge ::Willsbridge comes of age ::Reaching out - Willsbridge ::Round the reserves Wildlife articles 2007 -- Autumn 2007 -- ::Thinking BIG ::Watery webs:the pond network ::Wildlife in the landscape ::Variety of life ::How to be a climate friend ::Seasonal stroll - Walborough ::Round the reserves -- Summer 2007 -- ::The Folly Farm appeal ::Weston Big Wood-biodiversity at its best ::The variety of life ::How to capture a butterfly ::How to get to know an orchid ::Seasonal stroll - WestonBigWood ::Reserves update -- Spring 2007 -- ::Folly Farm - a very special place ::Making a difference at Folly Farm ::How find the magic at Folly Farm ::Seasonal stroll at Folly Farm ::Magic spots at Folly Farm ::Batscapes ::Climate challenge ::Variety of Life - the Ponways project ::Round the reserves Wildlife articles 2006 -- Autumn 2006 -- ::The Severn Estuary ::Bird Watch results ::How to identify garden birds ::Making space for wildlife ::How does your garden grow? ::Round the reserves -- Summer 2006 -- ::Going for green ::Stand up and be counted ::Happy birthday NSLMP ::Holi day - a riot of spring colour ::Avon's species-rich grassland ::How to photograph dragonflies ::The Big Switch ::Round the reserves -- Spring 2006 -- ::How to identify winter water birds ::Make 2006 the year you... ::Invasive invasion ::Sowing the seeds: Willsbridge Mill ::Round the reserves Wildlife articles 2005 -- Autumn 2005 -- ::Indentify common funghi ::Build a hedgehog hideaway ::Big Bird Watch ::Champions for wildlife ::Round the reserves ::Seeds of the futre: Willsbridge Mill -- Summer 2005 -- ::Restoring Folly Farm ::How to become bee-friendly ::How to identify the butterflies of spring ::Save our seas ::The variety of life: hedgerows ::Round the reserves ::25 Ways to make a difference -- Spring 2005 -- ::The variety of life: water voles ::The Avon Biodiversity Action Plan ::How to take really good wildlife photos ::How to help your garden grow ::Round the reserves ::Seasonal strolls: Browns Folly ::Sowing the seeds: for wildlife for people ::Sowing the seeds: looking back

Invasive evasion

Did you know that many familiar British plants have actually been introduced from other countries, some many hundreds of years ago?

This fact causes vigorous debate amongst botanists about what plants should actually be regarded as native or non-native to the British Isles. There is general agreement that harmless additions to the colours and textures of the countryside are acceptable, but there are a number of invasive species which have spread so rapidly, outcompeting the local native vegetation. As a result they dominate some habitats such as river banks and ponds, which then threatens the survival of the native animals that depend on the original habitat. Our temperate climate is very favourable to these species which can produce huge amounts of seed or reproduce via small parts of the plant. They're also not easy to control by the more acceptable herbicides such as glyphosphate, and clearance programmes are costing surprisingly vast sums - up to £300million nationally to tackle Himalayan balsam for example. So great is the problem, that it's now illegal under the Wildlife and Countryside Act 1981 to introduce certain species into the wild. Three spectacular nuisances were the result of the Victorian passion for plant collecting to enhance the gardens of country houses.

Himalayan balsam
The wonderful pink haze that lines many local rivers and streams such as the Frome and the Malago, is the result of the spread of Himalayan balsam. First recorded in Britain in 1839, it holds the record as the UK's tallest annual plant, growing up to three metres. As well as overshading and outcompetiing the river/stream bank vegetation, the autumn dieback leads to soil being washed away into the rivers. Its quirky seed dispersal also ensures dispersal - as soon as a ripe pod is touched the seeds are fired at breathtaking speed up to a distance of seven metres away. Its seed can remain viable for up to two years and of course is waterborne.

Japanese knotweed
Probably the best known of all these problem species is Japanese knotweed. Introduced for ornamental planting in the mid-19th Century, it was first recorded in the wild in 1900, and particularly spread in the late 1970s. There are in fact four species in this country now, Himalayan knotweed, Indian knotweed, giant knotweed, and a hybrid between Japanese and giant knotweed. They are all mainly female which means that the spread is vegetative; a portion of root as small as the tip of the little finger can produce a new plant. Stands of Japanese knotweed have an enormous rhizome system which can extend for 7 metres to a depth of 3 metres. The edible young shoots were known as bambard by Bristol youngsters who discovered their rhubarb-like property on Bristol bomb sites and also used the hollow bamboo-like stems as pea-shooters.

Giant hogweed
The damp-loving and architecturally stunning giant hogweed is a perennial which can grow to five metres high. It was brought from the Caucasus by Victorian horticulturalists in 1893. This plant so impressed the Victorian garden designer, John Louden, that he gave seeds to friends for dispersal in places as far apart as the north of England, Ireland and Norway. What no-one bargained for was its massive seed production, which is easily dispersed by water and viable for up to 15 years. It has attracted notoriety because of its ability to cause painful blisters, with resulting skin discolouration that can last up to six years. A plant chemical called furocoumarin is contained in the sap of stem hairs and the underside/edges of leaves, and contact with this makes the skin hypersensitive to bright sunlight. In fact, our native common hogweed and wild parsnip also have this ability but are less likely to attract attention.

Pond pests
Below are a few introduced species to be shunned when thinking about a new pond, or, if you already have these plants, don't let them escape!

Australian swamp stonecrop
The tiny Australian swamp stonecrop (or New Zealand pigmyweed) is spreading in local ponds and other slow moving water-bodies. This plant is a small succulent and has three different shapes depending on whether it is terrestrial, emergent or submergent. Once established, it can spread from minute fragments, smother native plants and quickly take over. It was introduced from Tasmania in 1911 and sold as an oxygenating plant and was first recorded in the wild in 1956. Its recent spread is believed to have been through garden centres and aquatic nurseries, but being so small it's very easy to transfer it unknowingly with other plant material.

Parrot's feather
It's easy to see why parrot's feather is a popular garden pond plant. It comes from lowland central South America and was first found in the wild in 1960. Looking superficially like our native water violet, its attractive, delicate frond-like foliage stands proud above the water. Only the female plant is found here so its rampant growth is vegetative, from small stem fragments. Like Australian swamp stonecrop it continues to live even when the pond dries out.

Water fern
The water fern is a Latin American introduction and also has a delicate appearance with its small red curled fronds, but will very quickly completely cover the surface of any water body that its vegetative parts come into contact with. In the winter, it can completely avoid detection by sinking to the pond bottom.

Innocents abroad
Unfortunately some of these plants can still be found in garden centres and aquarium shops, often not adequately labelled, so that you could unwittingly introduce them to your garden even when trying to stay native. And although it can be useful to receive cleared out plants from friends when stocking up a new pond, beware of what you might be innocently taking in. If your new pond is in an area near rich aquatic plantlife (for instance, close to countryside ditches) it could be interesting to let the pond vegetate naturally. But don't forget - it's illegal to actually dig up any native wild plant that isn't your own.

Dumping disaster
And remember - don't dump garden waste in semi-natural habitats - it's also illegal! As well as fuelling the local environment with extra nutrients it doesn't need, some of these species will take hold, interfering with the local ecosystem. Compost garden waste or take them to a recycling centre.

For further information, including guidance on control, the Environment Agency website is particularly useful: www.environment-agency.gov.uk. You ca also find more about native and non-native species on Kew Gardens' website www.or.uk/go wild/wild science/invasive-action.html