Invasive species
Some alien invasive species of flora threaten to alter the landscape they invade. Rhododendron Rhododendron ponticum forms dense thickets, out-competing native plants in woodlands. Japanese knotweed Fallopia japonica, introduced as an ornamental plant, has infested a wide range of habitats, including river banks. When it dies back in winter the banks are left bare and vulnerable to erosion. Curly leaved waterweed Lagrisiphon major is commonly sold as an oxygenating plant. It has had a serious impact on Lough Corrib, carpeting extensive areas, excluding light and restricting angling, boating and other water based activities. These are just some examples.
Species which are native can also be invasive, encroaching on land where it is not being grazed. Examples are blackthorn and even hazel in the Burren where scrub expansion is increasing by almost 5% annually. Land abandonment is of increasing concern because of the decline in traditional agricultural practices which preserved unique landscapes and habitats of high ecological value. Poor market prices, alternative off-farm employment opportunities and certain agricultural policies favour land abandonment in remote, inaccessible areas often with difficult, unproductive soils.