Winter 2004

Alien plants in the sand-dunes

Article by Phil Smith

From spring to autumn, the sandhills are a riot of colour with sheets of attractive wild flowers, appealing to botanist and lay person alike. But hang on; how many are genuine British plants? Recent studies show that an increasing proportion of our dune flora is non-native. Indeed, out of a grand total of about 1000 higher plants, around 320 (or 32%) are aliens. Where do these plants come from and what sort of impact are they having on our internationally important sand-dunes?

Russian Vine To the general public, perhaps the most familiar member of the alien flora is the Evening-primrose Oenothera, sometimes called the "dusk beacon", whose tall yellow flower-spikes enliven the dunes from July to September. There are actually four species on the Sefton Coast and none is native, though the first record here was as long ago as 1801. Evening-primroses are typical of a group that botanists call "neophytes" (literally "new plants"), which have arrived in the last 500 years or so. Evening Primrose A recent catalogue lists 4,000 of them in the British Isles, more than double the native flora! Most neophytes are garden-escapes, but some arrived as seed-impurities in grain or wool. Others originated in bird-seed or food refuse, including sewage, and a few in ships' ballast. Evening-primroses mostly come from the Americas, were first grown in Britain in 1629 as ornamentals and have been known in the wild since about 1650. Their roots were occasionally eaten but cultivation for the medicinal oil-containing seeds came much later.

Sea BuckthornFortunately, like most neophytes, the Evening-primroses seem to have little or no adverse effect on the sand-dunes, but this is not always the case. A few are known as "high-impact" neophytes. These are aggressive aliens that invade natural habitats, out-competing native flora and its associated animal life. The most notorious of these on the Sefton Coast is the dreaded Sea Buckthorn Hippophae rhamnoides, a spiny shrub with orange berries that was introduced from eastern England by the Lords of the Manor in about 1900 to help stabilise blowing sand. Unfortunately, the demise of rabbits in the mid 20th Century meant that the buckthorn was able to spread widely, choking floristically rich slacks and fixed dunes. Massive efforts have been made in recent decades to get it under control.

Also damaging to some aspects of duneland ecology are the non-native trees, mostly Corsican Pine Pinus nigra laricio from the Mediterranean, which were planted, partly to create shelter and partly as a crop, from the late 19th Century onwards. Although some plants and animals have found a home in the plantations, many local specialities are excluded, while the shelter-belt effect has encouraged other trees, such as the White Poplar Populus alba from Eastern Europe and the American Balsam Poplar Populus x jackii, to colonise what were previously open sandhills. The pines and poplars also suck up more water than dune vegetation and help to dry up slacks, upon which so much of our important flora and fauna depends.

Balsam Poplar

Other high-impact neophytes on the dunes, though on a much smaller scale, include garden escapes, such as Japanese Knotweed Fallopia japonica, the related Russian Vine Fallopia baldschuanica, Japanese Rose Rosa rugosa, Snow-in-summer Cerastium tomentosum, White Stonecrop Sedum album and Spanish Bluebell Hyacinthoides hispanica. Spanish Bluebell The latter, in particular, is a problem because it hybridises with our native Bluebell H. non-scripta and replaces it. Indeed, the hybrid H. x variabilis is now the commonest bluebell on the Sefton Coast.

Bulbs, like the Bluebell, seem to do particularly well on the sand-dunes. Presumably, the well-drained soil and summer drought suit their life-styles. From March to May, one can easily find such well-known garden bulbs as Glory-of-the-snow Chionodoxa and Grape-hyacinth Muscari, while the variety and splendour of Daffodil Narcissus cultivars rivals most gardens. The pale-blue Spring Starflower Tristagma uniflorum, a beautiful, little-known bulb, was found well-established on several dune sites in 2004.

Spring Starflower

The early-flowering species are soon replaced by tulips Tulipa and then by the white flowers of Star-of-Bethlehem Ornithogalum umbellatum and, in shady places, Lily-of-the-valley Convallaria majalis. Late summer bulbous plants include the very common Montbretia Crocosmia x crocosmiiflora and, rarely, the impressive Giant Montbretia C. masoniorum, which is popular in gardens as the cultivar "Lucifer". Fortunately all these plants are relatively innocuous. Giant Montbrietia

Garden escapes are, of course, more frequent where housing estates abut onto the dunes. This is well shown by the species lists for three dune areas which I have studied recently (Table 1). Queen's Jubilee Nature Trail has only 19% aliens because it is separated from housing by Victoria Park. However, Falklands Way and Kenilworth Road dunes have 35% and 42% non-native plants respectively, reflecting the proximity of residential development to both sites.

Table 1. The number and proportion of alien plants on three dune sites.

Name of siteArea (ha)No. vascular plants No. introduced plants % aliens
Queen's Jubilee Nature Trail92284419
Kenilworth Road624110242
Falklands Way1233011735

It's not hard to find a reason for these trends. The deliberate dumping of garden refuse is a common problem all along the coast. Not only does it lead to alien plant introductions, but it also adds nutrients to dune soils, resulting in the spread of harmful plants like nettles. It also goes without saying that it is extremely damaging visually. Sefton Council has a collection service for garden waste, so there is absolutely no excuse for it. I, for one, hope that it will be stopped.

Garden waste causes soil enrichment

So, let us continue to enjoy our sand-dune flora, while recognising that all is not as it seems. Many non-native plants represent a colourful and interesting addition to the biodiversity of the sandhills, but some create major problems that cost money and manpower to put right. I hope you will agree that we all have a responsibility not to add to those problems.