THE THEMATIC ASSESSMENT REPORT ON INVASIVE ALIEN SPECIES AND THEIR CONTROL
12SUMMARY FOR POLICYMAKERS
KEY
MESSAGES
A. Invasive alien species are a 
major threat to nature, nature's 
contributions to people, and good 
quality of life
Alien species are being introduced by human 
activities to all regions and biomes of the 
world at unprecedented rates. Some become 
invasive, causing negative and in some cases 
irreversible impacts on nature, including loss 
of uniqueness of biological communities, 
contributing to the unparalleled degree of 
deterioration of the biosphere upon which 
humanity depends.
KM-A1 People and nature are threatened by 
invasive alien species in all regions of Earth 
{A1} (Figure SPM.2). More than 37,000 established 
alien species have been introduced by human activities 
across all regions and biomes of Earth, with new alien 
species presently being recorded at an unprecedented 
rate of approximately 200 annually. Studies with evidence 
of negative impacts exist for more than 3,500 of these 
species, which are categorized as invasive alien species. 
The proportion of established alien species known to be 
invasive varies among taxonomic groups, ranging from 
6 per cent of all alien plants to 22 per cent of all alien 
invertebrates. Twenty per cent of all impacts are reported 
from islands. A disproportionate number of documented 
negative impacts have been reported in terrestrial realms, 
especially in temperate and boreal forests and woodlands 
and cultivated areas (including agricultural land). About 
one quarter of documented negative impacts have been 
reported from aquatic realms, especially from inland surface 
waters/waterbodies and shelf ecosystems. In addition to 
their impacts on nature, about 16 per cent of invasive alien 
species have negative impacts on nature's contributions to 
people, and about 7 per cent on good quality of life.
KM-A2 Invasive alien species cause dramatic and, 
in some cases, irreversible changes to biodiversity 
and ecosystems, resulting in adverse and complex 
outcomes across all regions of Earth, including 
local and global species extinctions {A2, A3} 
(Figure SPM.3). Invasive alien species have contributed 
solely or alongside other drivers to 60 per cent of recorded 
global extinctions, and are the only driver in 16 per cent of 
the documented global animal and plant extinctions. Biotic 
homogenization, whereby biological communities around the 
world become more similar, is a major negative impact of 
invasive alien species, with consequences for the structure 
and functioning of ecosystems. Changes in the properties 
of ecosystems, such as soil and water characteristics, 
account for more than a quarter of documented impacts. 
The magnitude and types of impacts vary for different 
invasive alien species and across ecosystems and regions. 
The majority of documented global extinctions attributed 
mainly to invasive alien species have occurred on islands 
(90 per cent), and local extinctions account for 9 per 
cent of documented impacts of invasive alien species on 
islands. Some areas, despite being protected for nature 
conservation or being remote, are also vulnerable to the 
negative impacts of invasive alien species.
KM-A3 The economy, food security, water 
security and human health are profoundly and 
negatively affected by invasive alien species {A4, 
A5} (Figure SPM.3). In 2019, global annual costs of 
biological invasions were estimated to exceed US$423 
billion. The vast majority of global costs (92 per cent) accrue 
from the negative impacts of invasive alien species on 
nature's contributions to people or on good quality of life, 
while only 8 per cent of that sum is related to management 
expenditures of biological invasions. The benefits to people 
that some invasive alien species provide do not mitigate or 
undo their negative impacts, which include harm to human 
health (such as disease transmission), livelihoods, water 
security and food security, with reduction in food supply 
being by far the most frequently reported impact (more than 
66 per cent).
KM-A4 Invasive alien species can add to 
marginalization and inequity, including, in some 
contexts, gender- and age-differentiated impacts 
{A5, A6}. People with the greatest direct dependence 
on nature, including those involved in gender- and agespecific activities, such as fishing or weeding, may be 
disproportionately affected by invasive alien species. 
More than 2,300 invasive alien species are found on lands 
managed, used and/or owned by Indigenous Peoples 
across all regions of Earth, threatening their quality of life 
and often leading to general feelings of despair, sadness 
and stress. Indigenous Peoples and local communities, 
ethnic minorities, migrants, and poor rural and urban 
communities are disproportionately impacted by invasive 
alien vector-borne diseases. Biological invasions negatively 
affect the autonomy, rights and cultural identities of 
Indigenous Peoples and local communities through the loss 
of traditional livelihoods and knowledge, reduced mobility 
and access to land, and increased labour to manage the 
invasive alien species. Impact reports by some Indigenous 
Peoples and local communities document 92 per cent 
SUMMARY FOR POLICYMAKERS
The thematic assessment report on
INVASIVE ALIEN SPECIES
AND THEIR CONTROL
Figure SPM 1 Key concepts within the biological invasion process.7