Invasive Species


Alien, invasive species are a problem all over the world and Essex is no different. A PowerPoint slide show about invasive species can be downloaded here (5.4MB PPT).

What are alien, invasive species?

 Alien species are species that are found out of their normal range and are considered to be 'non-native'. In most cases, species that move to a new location do not survive because they are not adapted to the environmental conditions, predators or diseases.  However, if a species is able to survive, it may compete with native species for resources such as food and habitat. These 'alien invasive species' pose one of the greatest threats to biodiversity worldwide because they can alter the relationships in the ecosystem, create significant changes in the habitat and may drive native species to extinction.

The problem of non-native species in Essex

Many alien, invasive species have been recorded in Essex. For example, Japanese Knotweed has been found in several sites around Colchester and Brentwood, Himalayan Balsam on at least 35 river banks in NE Essex, and Signal Crayfish in every Essex river. Muntjac deer are present throughout the county and the increasing numbers are having a significant impact in many of our woodlands.

Large numbers of muntjac can have an adverse effect on woodland vegetation because they browse on herbs, shrubs and young trees, which results in a change in the vertical structure of the woodland. These deer reduce the height of low growing shrubs, such as heather Calluna vulgaris, and prevent taller species, such as hazel Corylus avellana, from reaching their full height. This results in woodlands with a ground layer and a high canopy, but a sparse middle layer. The food and egg-laying plants of butterflies and other invertebrates, such as snails, may be destroyed, thus reducing the diversity of the woodland and affecting birds and mammals by removing food sources.

The pages within this section of the website give more detail about species that are of particular concern in Essex.  You can find further information about invasive plant species on the Plantlife website.

How do alien invasive species get into the countryside?

These species may arrive by accident, for example, deer escaped from deer parks, or they may be released by design, for example, planting Spanish bluebells rather than native bluebells in woods, and Mink released intentionally from fur farms. You can help by:

  •     composting garden plants rather than disposing of them in the countryside
  •     not releasing non-native garden or aquarium plants into the wild
  •     buying native stock - aquatic species, wildflowers, trees and shrubs
  •     not releasing non-native fish into ponds, streams or rivers
  •     not releasing non-native amphibians or reptiles into the countryside

What are we doing about the problem?

We aim to identify the alien, invasive species causing most damage in Essex, together with their distribution throughout the county. We will then produce guidance on appropriate control measures and identify resources, such as funding for control and organisations providing information and advice for the public.

What you can do to help

If you see any of the following non-native, invasive species, tell us where you see them and approximately how many you see. If possible, please use a full Ordanance Survey grid reference (2 characters, 10 digits).

We will use this information to record the locations of sightings in Essex.  This information will be of help to researchers, both within Essex and on a national scale.
High risk species (causing the greatest damage)
Japanese knotweed Fallopia japonica
Himalayan Balsam Impatiens glandulifera
Floating pennywort Hydrocotyle ranunculoides
Water fern Azolla filiculoides
Australian stone-crop Crassula helmsii
Spanish bluebell Hyacinthoides hispanica
Signal crayfish Pacifastacus leniusculus
Chinese mitten crab Eriocheir sinensis
Mink Mustela vison
Muntjac deer Muntiacus reevesii

Low or medium risk species (causing less damage)
Giant hogweed Heracleum mantegazzianum
Parrots feather Myriophyllum aquaticum
American bullfrog Rana catesbeiana
Pacific wireweed Sargassum muticum
Wakame kelp Undaria pinnatifida
Red-eared slider Trachemys scripta elegans
Zebra mussel Dreissena polymorpha
Topmouth gudgeon Pseudorasbora parva
Ruddy duck Oxyura jamaicensis


You can also visit the website of PlantTracker from where you can download a smartphone app from the iTunes app store or Android Market that shows you how to identify each species and enables you to easily submit geo-located photos whenever you find one.  The app now features 14 invasive plant species and also includes a "Confusion Species" gallery for each one, to help you separate some of the similar looking plants you might encounter.  Submit your discoveries and help to build a map of the location of invasive plant species.