THE THEMATIC ASSESSMENT REPORT ON INVASIVE ALIEN SPECIES AND THEIR CONTROL
24SUMMARY FOR POLICYMAKERS
subregion from 1970 to 2017. The case studies illustrate a variety of impacts of invasive alien species on both nature and good 
quality of life in different geographic regions, taxonomic groups and realms, but are not meant to be representative. The bottom row 
shows the taxonomic distribution (i.e., plants, invertebrates, vertebrates and microbes, including fungi) of the percentage of invasive 
alien species documented as causing local extinctions of native species (left); the estimated global annual average economic cost of 
biological invasions in billions of United States dollars (centre); and the percentage of the number of documented positive and negative 
impacts of invasive alien species on the constituents of good quality of life (i.e., freedom of choice, health, material and immaterial 
assets, safety, social and cultural relationships) (right). a: {4.3.1, Table 4.3}; b: {4.4.1, Box 4.13}; c: {4.5.1, Table 4.20}. The scientific 
names of the example species are Carcinus maenas (European shore crab); Batrachochytrium dendrobatidis (chytrid fungus); Carijoa 
riisei (branched pipe coral); Wasmannia auropunctata (little fire ant); Lates niloticus (Nile perch); Cenchrus ciliaris (buffel grass); Boiga 
irregularis (brown tree snake); and Reynoutria japonica (Japanese knotweed).
{4.5.1}. In East Africa, management of the invasive alien 
plant Opuntia spp. (prickly pear) requires repeated weeding 
by hand, which is often undertaken by women and children 
and has in many cases become their most time-consuming 
activity (established but incomplete) {5.5.5}. Invasive alien 
species may be introduced for economic development, for 
example through financing large-scale infrastructures (well 
established) {3.2.5, 3.3.1.3, 3.3.1.4, Box 3.11, 3.3.1.1, 
3.3.2.1.1}. In some cases, invasive alien species have been 
unintentionally transported and introduced through 
emergency relief and aid (e.g., seeds of the invasive alien 
plant Parthenium hysterophorus (parthenium weed) arrived 
with grain in aid shipments in several countries) (well 
established) {3.2.2.3}, increasing the risk of possible 
negative impacts on quality of life (established but 
incomplete) {4.5.1, 4.6.3}.
A6 Many invasive alien species have been 
documented on lands managed, used and/or 
owned by Indigenous Peoples and local 
communities (established but incomplete) {Box 2.6; 
4.6}. More than 2,300 invasive alien species have been 
documented on lands managed, used and/or owned by 
Indigenous Peoples, with some negatively affecting their 
quality of life and cultural identities. Indigenous lands in 
Oceania and North America have particularly high numbers 
of recorded invasive alien species (established but 
incomplete) {Box 2.6}. However, numbers of invasive alien 
species are, on average, consistently lower on Indigenous 
lands compared to other lands (established but incomplete)
{Box 2.6}. Many Indigenous Peoples and local communities 
emphasize the inter-relatedness of the land, water and 
humans and other species, which can lead to a range of 
diverse perceptions of specific invasive alien species (well 
established) {1.6.7.1}. In some cases, Indigenous Peoples 
and local communities may consider an invasive alien 
species a valued part of their nature (established but 
incomplete) {1.6.7.1}. There are also examples where 
Indigenous Peoples and local communities have created 
new income sources by relying on invasive alien species 
(well established) {4.5.1, 4.6.2}, but that often occurs 
through necessity rather than choice. However, impact 
reports by some Indigenous Peoples and local communities 
document 68 per cent negative impacts and 32 per cent 
positive impacts on their good quality of life caused by 
invasive alien species (established but incomplete) {4.6.1, 
4.6.3.2, Table 4.33}. Indigenous Peoples and local 
communities often have a good understanding of how the 
complex interactions among drivers facilitate the 
introduction and spread of invasive alien species on their 
lands (established but incomplete) {3.2.3.6, Box 3.15}. For 
example, Indigenous Peoples and local communities 
recognize that the use of invasive alien species for food, 
fibre, income generation or medicinal purposes can cause 
negative impacts on nature's contributions to people and 
their good quality of life (well established) {3.2.3.6, Box 3.6}, 
especially in situations where the native species they 
traditionally depended on for those benefits have declined 
(established but incomplete) {3.2.3.6; 3.2.5}. Impact reports 
by some Indigenous Peoples and local communities 
document 92 per cent negative impacts and 8 per cent 
positive impacts on nature caused by invasive alien species 
(established but incomplete) {Table 4.31}. Negative impact 
reports include water security and human and livestock 
health, as well as acknowledging that invasive alien species 
limit access to traditional lands, reduce mobility and require 
increased labour to manage (established but incomplete)
{Box 4.9, 4.5.1, 4.5.1.4, 4.6.3.1, 4.6.3.2, 5.5.5}. Invasive 
alien species can also adversely affect the autonomy, rights 
and cultural identity of Indigenous Peoples and local 
communities (established but incomplete) {Box 4.15} 
through the loss of traditional livelihoods, knowledge and 
cultural practices (well established) {4.6.3.2}, often leading 
to general feelings of despair, sadness and stress 
(established but incomplete) {4.6.3.2}.
A7 Perceptions of the threat of invasive alien 
species can vary depending on different human 
perspectives (well established) {1.5.2}. Perceptions of 
specific invasive alien species and their value differ among 
and within stakeholder groups and Indigenous Peoples and 
local communities, as different community members can 
experience different impacts depending on gender, age, 
livelihood and a multitude of other factors (established but 
incomplete) {1.5.2, 1.6.7.1, 3.2.1, 5.6.1.2}. Value conflicts 
arise when invasive alien species are considered to be a 
major threat by some stakeholders and beneficial by others 
(well established) {5.6.1.2}. An invasive alien species may 
SUMMARY FOR POLICYMAKERS
19SUMMARY FOR POLICYMAKERS
BACKGROUND
A5 