THE THEMATIC ASSESSMENT REPORT ON INVASIVE ALIEN SPECIES AND THEIR CONTROL
28SUMMARY FOR POLICYMAKERS
numbers of alien species being introduced (Figure SPM.4). 
Some of these have become invasive (well established) {2.1, 
3.2.3}. Even without the introduction of new species, given 
the opportunity, many already-established alien species in a 
region may continue to expand their geographic ranges and 
spread into new countries and regions (well established)
{2.6.1}, including into remote environments such as 
mountain, polar (i.e., Antarctica and the Arctic) and desert 
ecosystems (well established) {2.5.2.8, 2.5.2.7, Box 2.7, 
Box 3.11}. Under a "business-as-usual" scenario, which 
assumes the continuation of past trends in drivers, the total 
number of alien species is projected to further increase 
globally, and by 2050 is expected to be approximately 
36 per cent higher than in 2005 (established but incomplete)
{2.6.1}. As trends in major drivers are predicted to 
accelerate in the future (well established) {3.1.1}, the 
number of alien species worldwide is expected to increase 
faster than predicted under the "business-as-usual" scenario 
(established but incomplete) {2.6.1}. There is a lack of 
quantified projections for invasive alien species under 
different scenarios (Table SPM.A1), which impedes a 
comparison of trends for alternative futures (well established)
{2.6.5}. Projections of long-term trends for invasive alien 
species numbers are not available but they are expected to 
be similar to those for established alien species (established 
but incomplete) {2.2.1}. The documented global economic 
cost of biological invasions has increased fourfold every 
10 years since 1970 (Figure SPM.3) and is anticipated to 
continue rising (established but incomplete) {Box 4.13}.
B11 The increase in the transport and introduction 
of invasive alien species worldwide is primarily 
influenced by economic drivers, especially the 
expansion of global trade and human travel 
(Figure SPM.5) (well established) {2.1.2, 3.1.1, 
3.2.3}. There has been a fivefold increase in the size of the 
global economy over the last 50 years (well established)
{3.1.1}. International trade, which has increased nearly 
tenfold over the same period, represents the most important 
pathway through which invasive alien species are 
transported worldwide (Figure SPM.5) (well established)
{3.1.1, 3.2.3.1}. There is a strong link between the volume 
of commodity imports and the number of invasive alien 
species in a region, and patterns in the global spread of 
species mirror shipping and air traffic networks (well 
established) {3.2.3.1}. The construction of shipping canals 
(e.g., Suez, Panama) has connected previously separated 
marine and freshwater regions, facilitating the spread of 
invasive alien species through species migration, ballast 
water transfers (Box SPM.2) and biofouling (well 
established) {3.2.3.1, 3.3.1.3}. For example, 150 years after 
the opening of the Suez Canal, marine alien species are still 
being newly recorded in the Mediterranean Sea (well 
established) {Box 3.7}. Biosecurity measures at international 
borders have not kept pace with the growing volume, 
diversity and origins of global trade (including e-trade) and 
travel (well established) {3.2.4.2, 3.2.3.4, 5.6.2.2}. Projected 
growth in international trade and the movement of people, 
including tourism, will lead to further pressure on border 
inspection regimes and could soon overwhelm the 
biosecurity capability of most countries (well established)
{3.2.3.1, 6.3.1.4}.
B12 Accelerated establishment and spread of 
invasive alien species within countries are 
primarily driven by direct drivers, notably changes 
in land- and sea-use (Figure SPM.5) (well 
established) {2.2.1, 3.3.1, 3.6.2}. Land- and sea-use 
changes may increase the vulnerability of natural 
ecosystems to the establishment and spread of invasive 
alien species through increasing fragmentation and habitat 
disturbance, for example by changing grazing, fire regimes, 
soil disturbance, or watershed flow (well established)
{3.3.1.2, 3.3.1.5}. Transportation and utility infrastructures 
such as roads, tracks, railways, pipelines, canals and 
bridges, among others, can create corridors that facilitate 
the spread of invasive alien species, including into remote, 
undisturbed and protected areas (well established) {3.3.1.3, 
Box 2.7, Box 3.7}. Marine and aquatic infrastructure may 
alter seascapes and the functioning of marine ecosystems, 
facilitating the spread of invasive alien species (established 
but incomplete) {3.2.2.4, 3.3.1.4, 5.6.1.4}. The numbers of 
invasive alien species were reported to be 1.5 to 2.5 times 
higher on pontoons and pilings than on natural rocky reefs 
(established but incomplete) {3.3.1.4}. More generally, 
land-use change can facilitate biological invasions through 
alteration of processes that cause natural disturbance of 
landscapes, such as wildfire or grazing regimes (established 
but incomplete) {3.3.1.5}. In several regions of the world, 
grazing by feral alien ungulates (horses, camels, buffalo, 
pigs) facilitates the spread of invasive alien plants, 
sometimes through complex species interactions involving 
the suppression of native species and the facilitation of other 
alien species (well established) {3.3.1.5.1}. As a specific 
example, invasive alien ungulates (wild boar, deer) can 
transport invasive ectomycorrhizal (root associated 
symbiotic) fungi, which are beneficial for the establishment 
and spread of alien pine trees, over long distances, 
rendering habitats susceptible to pine invasion (well 
established) {Box 3.10}. Climate change, along with the 
continued intensification and expansion of land-use change 
may lead to future increases in the establishment and 
spread of invasive alien species in disturbed habitats and in 
nearby natural habitats (established but incomplete) {3.3.4}.
B13 No driver acts in isolation, and interactions 
among drivers are amplifying biological invasions, 
leading to outcomes that can be difficult to predict 
(well established) {2.6.1, 3.1.5, 3.5}. The outcomes of 
interactions among multiple drivers, including feedback, are 
complex and varied (well established) {1.3.3, 3.1.5, 3.5}. 
Some of the highest current rates and greatest magnitudes 
SUMMARY FOR POLICYMAKERS
19SUMMARY FOR POLICYMAKERS
BACKGROUND
A GLOBAL DISTRIBUTION OF ESTABLISHED ALIEN SPECIES 