Invasive species: impacts on forests and forestry
Response includes eradication, containment, control and mitigation.
When the preventative and early detection measures have failed to stop the introduction of invasive species, eradication is the preferred next method of action. Eradication involves the elimination of the entire population of an alien species, including resting stages, in managed areas. As a rapid response to early detection of an alien species, eradication is often the key to a successful and cost-effective solution. Careful analysis of the costs involved and the likelihood of success must be made before any eradication attempts are made. Some groups of organisms are more suitable for eradication such as plants, terrestrial vertebrates, some terrestrial invertebrates and in some cases insects. Also, well established populations and large areas of infestation are unsuitable for such programmes.
Successful eradication programmes must:
- be scientifically based;
- ensure that all individuals of the target population are susceptible to the technique being used thus ensuring that eradication of all individuals is achievable;
- build support from the public and all relevant stakeholders;
- ensure that the legal and institutional framework is sufficient for dealing with the issue;
- secure sufficient funding;
- ensure through prevention measures that there is no immigration of the target species into the area;
- put in place a method to detect the last survivors;
- include a subsequent monitoring phase to ensure that eradication has been achieved, and to prevent re-invasion;
- ensure that techniques are environmentally, socially and ethically acceptable;
- include any necessary measures to restore ecosystems after eradication.
Eradication programmes involve several control methods as outlined in the control section below.
Containment is a special form of control aimed at restricting the spread of an invasive species and to contain the population in a defined geographical range. The methods used are the same as those described for prevention, eradication and control. An important component of containment programmes is the ability to rapidly detect new infestations of the alien species spreading from the defined containment area or into new areas, so that control measures can be implemented quickly. In cases where eradication is not possible, containment of the invasive species into a defined area can be very effective in saving other regions of a country.
The long-term reduction in density and abundance of an invasive species to below a pre-set acceptable threshold is the aim of control programmes. Suppression of invasive populations below such thresholds can favour native species. Control methods including mechanical control, chemical control, biological control, habitat management, and hunting or a combination of these, have all been used successfully in controlling invasive species.
Not all options for the control of invasive species are practical, effective, economically justifiable, or environmentally sound for application in forests. In the forest sector, control measures should be integrated to maximize yield and profit while minimizing negative environmental impacts. Some other options that are suitable include cultural techniques, such as seedling management, planting patterns, buffer zones, ecoclimatic matching, pest and pathogen resistance; mechanical methods, such as cutting, bulldozing and shading; biological control; and integrated pest management.
If eradication, containment and control methods have failed in managing an invasive species, the only option is to accept the species while mitigating the impacts to other species and the environment. The focus here is on protecting the native species rather than harming the alien species. Mitigation methods can include translocation of a population of species to an ecosystem that has not been invaded and alterations in the behaviour of desired species such as conditioning species to use breeding areas inaccessible to the invaders or artificial feeding sites.