Invasive Non-Native Species in NPT

Of these, Himalayan Balsam (or Indian Balsam), Japanese Knotweed and Rhododendron are notorious, but each species in this list has a significant impact on one or more of our principal habitats (see Table 2). Other potentially invasive species in the county such as Lupin, Chinese Bramble, American Skunk Cabbage and Henry’s Honeysuckle could pose a threat in the future.

Several other neophyte species which are abundant and aggressive competitors, particularly in early successional or ruderal environments, include some Stonecrop species, Bilbao Fleabane and Hoary Mustard, but none of these have significant effects on local biodiversity. Similarly, there are a number of garden throw-out species which are widespread and persistent in the county, notably Dotted Loosestrife and Montbretia, which we believe are not having significant effects on biodiversity at present.

Interesting problems are posed by some garden plants that have become established and/or naturalised in some habitats where they might cross fertilise and hybridise with native species. Two significant examples are given by Spanish (and Hybrid) Bluebell and the silver-blotched leaf form of Garden Yellow Archangel. The extent to which Spanish/Hybrid Bluebell has hybridised with native Bluebells and the effect that this may have on the genetic purity of local native Bluebell populations is largely unknown. At the moment there is little evidence that there is cause for concern but it seems prudent to eradicate naturalised Spanish/Hybrid Bluebells from areas where they could hybridise with native Bluebells e.g. in ancient woodland and hedgerow. Similarly, it would be wise to control naturalised populations of Garden Yellow Archangel, which is much more vigorous and competitive than our native Yellow Archangel.

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With regards to invasive non-native fauna in NPT, we have records for a number of species, including:

• American Mink

• Grey Squirrel

• Red-eared Terrapin

• Egyptian Goose

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Of these, perhaps the most common is the Grey Squirrel, which is ubiquitous across NPT and commonly seen across our parks, gardens and woodlands. The Grey Squirrel is a North American species, which is highly competitive with the native Red Squirrel, as well as transmitting a disease (Parapoxvirus) which has decimated the Red Squirrel populations in Wales. Red Squirrels were once found across the whole of NPT but by 1999 they had disappeared from the county and from much of Wales as a whole. This decline in the Red Squirrel has been attributed to the Grey Squirrel, though habitat loss, road traffic and other predators are also likely to have had an impact. Likewise, a similar correlation can be seen between the decline of the Water Vole and the spread of the American Mink, which has been blamed for the decline of Water Vole in other areas across the UK. We do not have substantial evidence of other non-native fauna causing significant problems in NPT, though this is not to say it is not occurring.

Brief descriptions of the INNS of most concern in NPT and a summary of their main impacts is given below. A wider list of INNS problematic across the whole of Wales has been collated and details of this list can be found on the Wales Biodiversity Partnership website.