THE THEMATIC ASSESSMENT REPORT ON INVASIVE ALIEN SPECIES AND THEIR CONTROL
14SUMMARY FOR POLICYMAKERS
(Figure SPM.5). Many invasive alien species have been 
intentionally introduced outside their natural range around 
the world for their perceived benefits without consideration 
or knowledge of their negative impacts, but there have 
also been many unintentional introductions, including as 
contaminants of traded goods and stowaways in shipments. 
Indirect drivers of change, particularly those associated 
with economic activities, of which international trade is the 
most important, are increasingly facilitating transport and 
introduction, the early stages of biological invasion. Direct 
drivers, particularly land- and sea-use change and climate 
change, are increasingly important later in the biological 
invasion process, facilitating the establishment and spread 
of invasive alien species, with fragmented ecosystems being 
more vulnerable to invasive alien species. Transport and 
utility infrastructures in terrestrial and aquatic environments 
can create corridors that facilitate the spread of invasive 
alien species, including into remote, undisturbed and 
protected areas. For some invasive alien species, the spread 
is immediate, but others only begin to spread long after 
first introduction, meaning that currently observed threats 
of invasive alien species can lead to underestimation of the 
magnitude of the future impact. Invasive alien species may 
increase in numbers after a long period at low density as 
a result of changes in interactions with other species, for 
example as a result of the introduction of a missing dispersal 
agent or the removal of a competitor.
KM-B2 The threats from invasive alien species are 
increasing markedly in all regions of Earth, with 
the current unparalleled high rate of introductions 
predicted to rise even higher in the future {B10} 
(Figure SPM.4). The number of alien species has been 
rising continuously for centuries in all regions, and the global 
economic costs of invasive alien species have quadrupled 
every decade since 1970. Even without the introduction 
of new species, already established alien species given 
the opportunity, may continue to expand their geographic 
ranges into new countries, regions and ecosystems, 
including remote environments. Under a "business-asusual" scenario, which assumes that trends of drivers will 
continue as observed in the past, by 2050 the total number 
of alien species globally is expected to be about one-third 
higher than in 2005. However, the number of alien species 
worldwide is expected to increase faster than predicted 
under the business-as-usual scenario.
KM-B3 The ongoing amplification of drivers of 
change in nature may substantially increase the 
number of invasive alien species and their impacts 
in the future {B9, B11, B12, B14}. The causal links 
between indirect and direct drivers imply that ongoing 
and future amplification of these drivers will increase the 
frequency and extent of biological invasions and the impacts 
of invasive alien species, which, in some cases, may 
exacerbate the impacts of other drivers. At a global scale, 
the number of invasive alien species and their negative 
impacts are likely to increase due to the amplification of 
multiple drivers including but not limited to demographic, 
economic and land-use and sea-use change while noting 
regional variation. Additionally, climate change will further 
exacerbate the establishment of some invasive alien species 
and will be a major cause of future establishment and 
spread. Delays in the response of invasive alien species 
to drivers of change may result in a long legacy of future 
biological invasions due to past and present amplification 
of drivers.
KM-B4 The magnitude of the future threat 
from invasive alien species is difficult to predict 
because of complex interactions and feedback 
among direct and indirect drivers of change in 
nature {B10, B13, B14}. Climate change interacting with 
land- and sea-use change is predicted to profoundly shape 
and amplify the future threat from invasive alien species. 
Interactions among climate change, land-use change 
and invasive alien species can alter and intensify natural 
disturbance regimes, such as wildfires. Variations in human 
perceptions and values add yet another level of complexity, 
as sociocultural drivers interact with other indirect drivers 
and influence direct drivers. Such interactions may lead to 
unprecedented numbers of invasive alien species, with the 
consequent amplification of their impacts.
C. Invasive alien species and their 
negative impacts can be prevented 
and mitigated through effective 
management
Curbing the rising number of invasive alien 
species and reducing their spread and 
impacts are achievable through management 
actions in the short as well as long term. 
There are many decision frameworks and 
approaches for supporting management of 
invasive alien species at all stages of the 
biological invasion process. Prevention is the 
best option, but early detection, eradication, 
containment and control are also effective in 
specific contexts. Management of biological 
invasions benefits from engagement with 
stakeholders and Indigenous Peoples and 
local communities.
KM-C1 The number and impacts of invasive alien 
species can be reduced through management of 
biological invasions {C15, C16, C17, C18, C22, 
C23} (Figure SPM.6, Table SPM.1). There are decision-
SUMMARY FOR POLICYMAKERS
The thematic assessment report on
INVASIVE ALIEN SPECIES
AND THEIR CONTROL
B. Globally, invasive alien species 
and their impacts are increasing 
rapidly and are predicted to 
continue rising in the future