Greenham and Crookham Commons Management Plan 2009-2014: Invasive alien species
07 Aug 2004: Himalayan balsam near Goldfinch Bottom

Invasive or potentially invasive alien species recorded on Greenham and Crookham Commons.

When assessing the need to control exotic species, each should be assessed on its effect on native biodiversity which could, in some cases, be positive. The table below is an overview of management policies for significant non-native species currently known to be present. There are, additionally, scattered instances of various garden escapes. These are generally tolerated unless they appear to be invasive or otherwise damaging.


Latin name Common name Compartments Species and management information
Impatiens glandulifera Himalayan balsam 5D This plant can quickly spread and dominate the ground layer in wet areas. Remove plants every year before seed develops by pulling, cutting stem below first node (e.g. by scything), or lopping/slashing heads. Stack arisings in discrete piles or dispose off site. Focus on areas where dense thickets occur but pull lone individuals when sighted. Requires annual management.
Alnus cordata Italian alder 13, 16, 18 Planted around the main control tower car park and throughout compartment 13 this tree seeds profusely. A selective gradual thinning of Italian alder each year in favour of native species to be undertaken in compartment 13. Cut and treat all specimens in the main car park.
Buddleia spp. Buddleia 3, 5 Species of buddleia do provide a rich source of nectar for butterflies and other insects. One spot in particular offers a great way for the public to see a variety of butterflies easily. A continual monitoring of the spread of the current extent should be undertaken regularly where any additional plants should be removed. Isolated individuals can be left if not detrimental to surrounding vegetation.
Acer pseudoplatanus Sycamore Throughout woodlands Sycamore contributes to the diversity of the common. Where woodland management occurs each tree should be assessed in context with other nearby species. They can either be coppiced to allow an understorey in the absence of other species, thinned in favour of native species or 'ring barked' to create standing deadwood. They may have a positive effect in some areas as the flowers may provide an early food supply for dormouse.
Crassula helmsii New Zealand pygmyweed or swamp stonecrop Throughout most of the ponds This 'weed' is widespread across the site and management to reduce its dominance needs to be undertaken. Due to its extent, the ability to be moved around the site by cattle, and the potential cost, a targeted approach is needed. The Pond Management Plan, to be produced in the first year of this plan, will consider the effects of this invasive species and how to manage it. The aim is to target the more ecologically rich ponds first with the long term goal of containing its spread through seasonal management.
Rhododendron spp. Rhododendron 1D, 2, 13, 17 This species can spread and dominate woodland areas, shading areas of woodland floor to the detriment of native ground flora. All plants should generally be cut and the stumps treated.
Gaultheria spp. Gaultheria 1D This species of Erica is found in parts of the woodland in small numbers and is not particularly invasive. Plants found should be removed and stumps treated where they start to spread.
Crocosmia spp. Crocosmia 5C This garden escape has spread through some of the wetlands in this area. Its spread should be controlled by pulling.
? a fern, species uncertain 5C Another garden escape is found in the gullies around this compartment, and should be controlled by pulling.
? Bamboo 17B Escaped from at least 2 gardens, this plant quickly spreads in wetland areas. Cut and remove from site over winter and follow up with treatment with glyphosate on the new shoots in spring. Repeat every year until eradicated or under control. This is to be combined with liaising with nearby properties from which spread has emanated.
Lophocolea semiteres a liverwort 9, 10, 11, 12, 16 Invasive liverwort from South America, South Africa and Australasia found across the common. This particular species forms blankets on bare soil which puts it in direct competition with closely related liverwort species (Lophocolea bidentata and Lophocolea heterophylla) and also low-growing bryophytes such as Archidium alternifolium and Pleuridium acuminatum. Further study of the extent and impact of this liverwort invasion is required. See Bryophytes and lichens on Greenham and Crookham Commons (NatureBureau 2009).
na Introduced fish spp. Main, large ponds Where large fish are introduced into ponds they can have a reducing effect on newt and invertebrate populations. All movement of fish requires a licence so contractors would most likely be used to remove them.
Quercus cerris Turkey oak 5, 15 Turkey oak is a host of the knopper gall wasp, which poses a threat to our native oak species. All younger turkey oaks to be removed where they compete with native trees in woodland or with heathland and grassland areas. Certain more mature existing specimens should be retained to maiantain the habitat they provide for (e.g.) invertebrates. The spread should be monitored regularly.
Quercus ilex Holm oak 13 Remove trees where they compete with native trees in woodlands or with heathland and grassland areas, but maintain some for diversity where conflict is not an over-riding factor. Specifically for compartment 13, selectively fell in this plantation area as part of glade clearance but retain some specimens. The spread should be monitored regularly.
Hippophae rhamnoides Sea buckthorn 13 This plant is normally a management issue for coastal sand dunes where it can spread and dominate. The spread and dominance of the few individuals of this plant on the common should be checked yearly. A few individuals should be retained for diversity as the berries can provide autumn food.
Pacifastacus leniusculus American signal crayfish Potentially, all ponds Presence on the common is anecdotal and not currently confirmed. Any of this species found in the ponds will need to be removed. The main effect of the American signal crayfish (and other similar introduced species found in lesser abundance) is their competition for food. They also harbour desease which affects the native white clawed crayfish. It is an offense to return an American signal crayfish to a water course if it is captured or removed.
Pelophylax ridibundus Marsh Frog 14 Confirmed presence only in the pond immediately southeast of Estovers. It is thought unlikely that the marsh frog will spread easily to other ponds on site, due its reluctance to venture more than a few metres from water. No control action is currently (Feb 2016) planned.
Fallopia japonica Japanese knotweed 5A (Oct 2013), potentially all Highly vigorous and invasive, forming dense thickets up to 3 m tall and outcompeting native plants. Propagation is vegetative, via rhizomes and sections of the crown and stems. Control by cutting down, and injecting glyphosate into the hollow stems. Cutting methods that produce fragments, such as flailing, should be avoided as just a small part of the stem can produce a new plant. Burn the cut material.