Negative impacts of invasive species on forests and forestry

Invasive species negatively impact the forest sector in economic, ecological, environmental, social and health terms.


The most direct economic impact of invasive species on the forest sector is related to the loss or reduced efficiency of production. Invasive species, in particular insect pests and diseases, can damage trees in all stages of development and affect the ability of both natural and planted forests to meet their management objectives. The introduction and spread of invasive species can have major implications for trade which will depend on the policy response of trading partners to news about outbreaks, the importance of the traded commodities, the extent of the damage, and the demand and supply elasticities. In addition, the associated control costs, including the costs of inspections, monitoring, prevention and response, of even just a few species can be enormous. Invasive species can also generate substantial costs to the forest sector in lost conservation values and ecosystem services.

Ecological and environmental

The ecological and environmental impacts of invasive species can be felt by all levels of organization including the gene, species, habitat and ecosystem level.

Genes. If introduced or spread into habitats with closely related species, alien species could interbreed with native species resulting in changes to the genetic makeup of either species which could result in a reduction in the survival of either species, creation of a more successful invader, or the creation of hybrids that could be more susceptible to certain pests and pathogens. Of recent concern to the forest sector is the impact of possible introduction of new tree genotypes (non-local provenances or genetically improved planting stock) resulting in the creation of hybrids and the resulting loss of gene pools that may have acquired specific characteristics through local adaptation.

Species. Invasive species can influence species diversity, richness, composition and abundance. At the species level, direct effects of invasive species occur through processes such as the predation of, competition with, and pathogen and parasite transmission to individual organisms, eventually leading to population declines and species extinctions.

Habitats. Through their impacts on species and ecosystem processes, invasive species can result in the fragmentation, destruction, alteration or complete replacement of habitats which in turn, has cascading effects on even more species and ecosystem processes.

Ecosystems. The impacts of invasive species at the ecosystem-level include changes to trophic structures, changes in the availability of resources such as water and nutrients, and changes in the disturbance regime of an ecosystem.

Social and health

As a result of the negative impacts of invasive species on native forest biodiversity, a loss of food sources and traditional medicines may be experienced thereby compromising not only the health of local people but also the livelihoods of those dependent on the collection and sale of such items for income. For small-scale landowners, invasive species can also decrease the value of their land.

Forest workers, as part of their jobs, and people living in and around forests are more exposed to invasive alien species such as the reservoirs and hosts of many emerging infectious diseases such as Lyme disease, human immunodeficiency virus (HIV), Ebola and Marburg hemorrhagic fevers, malaria, yellow fever, leishmaniasis, trypanosomiasis and Kyasanur forest disease. People living in and around invaded forest areas may also suffer allergic or other negative reactions to the invasive species themselves or to the measures used to control them such as pesticides and biological controls.

last updated:  Tuesday, April 21, 2009