INVASIVE ALIEN SPECIES:
A THREAT TO THE
BIODIVERSITY AND
ENVIRONMENT
BY
ZAHIDULLAH KHAN
PhD Scholar QAU Islamabad
Introduction
Plants originally originated in specific
habitats, under particular set of edapho-climatic
conditions and historically flourished their for
thousands of years with out mixing with flora of
another region. This was because natural
biogeographic barriers isolated the continental
biota for millions of the years. So that each
biogeographic zone of the world was occupied by
specific type of flora, different from that of
another such region.
Introduction
However the increased travel, transport, trade and
tourism associated with globalization have lead to the
drastic breaching of biogeographic barriers resulting in
mixing or homogenization of the earths biota at local,
regional, continental and global levels.
This
intentional
or
unintentional
human
aided
introductions of taxa from one part of the globe into
another part of the globe is causing severe harm to the
environment, economies, human health and biodiversity.
Therefore invasion ecology is now a days the most rapidly
developing field of biology and is the area of most intense
research the world over. However in Pakistan even the
scientific community is not aware of this global issue in the
era of biodiversity.
Concepts & Terminology
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Alien terminology:
Terms & concepts crucial to invasion Biology are often
ambiguous, problematic & non-operational.
Native or Indigenous:
Taxa in a given area that have originated & evolved their
without human involvement
& that have inhabited that
area historically for thousands
of years are called indigenous
or native.
Concepts & Terminology
Endemic:
Taxa that are confined,
restricted, peculiar and specific
to a particular locality, or geographic
zone, or a country and that don’t
occur elsewhere on the surface
of the globe.
Alien:
(non-native, exotic,
introduced, non-indigenous,
anthropochores, neophytes,
adventives, immigrants)
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Plant taxa in a particular area that have been introduced by
humans intentionally or unintentionally to areas outside their
place of origin & natural range of distribution are called Alien.
Concepts and terminology
Invasive:
According to the Global Invasive Species Program
(GISP):
“Invasive alien species (IAS) are non-native
organisms that cause, or have the potential to
cause, harm to the environment, economies, or
human health. Invasive alien species (IAS) are
one of the most significant drivers of
environmental change worldwide.”
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Invasive alien species are globally recognized as
the second greatest threat to the biodiversity
after direct habitat destruction.
Invasive species have the potential to spread
vigorously and quickly, out-compete native plant
species and degrade natural ecosystem.
What makes an invasive, invasive?
Typical characteristics of (IAS)
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Aliens that are successful invaders are species
that have some advantage over native species.
Introduced from other habitats
Rapid growth & maturity
Prolific seed production
Aggressive spreaders and prolific reproducers
Highly successful seed dispersal, germination
and colonization
Rampant vegetative spread
Typical characteristics of
(IAS)
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Ability to outcompete native species for space,
water, food, and other essential resources
Adapt to a variety of conditions
No natural predators, parasites, etc
High cost of removal and control
Are difficult to control or eliminate once
established
Impacts of invasive species
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Direct costs in lives (diseases), crop losses
reduced ecosystem function/services
biodiversity loss
Compete with & replace rare and endangered
species
Encroach upon limited habitat of rare and
endangered species
Reduce or eliminate localized or specialized
native plant communities, such as TDDF
Margalla hills
Disrupt insect-plant associations necessary for
seed dispersal of native plants
Impacts
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Disrupt native plant-pollinator relationships
Reduce eliminate host plants for native insects
and other wildlife
Hybridize with native plant species, altering
their genetic makeup & reduce gene pool.
Serve as host reservoirs for plant pathogens and
other organisms that can infect and damage
desirable native and ornamental plants and
Impacts
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Replace nutritious native plant foods with
lower quality sources
Kill trees and shrubs through girdling
Increase the incidence of plant disease
and stress in forested areas
Prevent seedling establishment of native
trees and shrubs
Reduce vigor of mature trees through
shading
Impacts
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Reduce the amount of space, water, sunlight and
nutrients that would be available to native
species
Increase erosion along stream banks, shorelines
and roadsides
Change characteristics of the soil structure and
chemistry
Alter hydrological flows and conditions
Pathways of Introduction
Pathways include:
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movement of goods (species translocated in containers,
planting media, untreated wood packaging, some food
products)
movement of people (by air, road, rail and sea transport)
postal and courier services (including biological material
purchased via the Internet)
agriculture and forestry (direct introductions of crops and
livestock, unintentional introduction of pests and
diseases)
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horticulture (dispersal of ornamentals from
gardens, ponds etc.)
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habitat restoration and landscaping (use of
non-native genotypes of native plants, escapes
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Plants (Grasses) as packing material
Hypotheses that allow
naturalization and invasion:
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Enemy Release
Highly competitive
Extra resources
New niche with little overlap
Competitive release from generalist predators or
herbivores
Disturbance for colonization
Invasive Aliens in Pakistan
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Total Flora about 6000
Aliens +1000
Invasive more than 70 species
Drastic Invasive 16 species
Lantana camara, Brousonettia papyrifera,
Eucalyptus
camaldolensis,
Parthenium
hysterophorus,
Leucanea
leucosephala,
Leptochloa chinensis, Eicchornia crassipes,
Prosopis juliflora, Salvinia molesta, Ipomoea
carnea,
Lolium
temulentum,
Xanthium
stromarium, Bromus unioloides, Phalaris
minor
Invasive Aliens of
Islamabad
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Broussonetia papyrifera
Lantana camara
Parthenium hysterophorus
Prosopis juliflora
Sylibum marianum
Bromus unioloides
Broussonetia papyrifera
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Paper Mulberry:
Origin: East Asia
Planted during
the 1960s
Prime objective:
greening the town
control soil erosion
Act as an aggressive tree
Replaced native flora in
a few decades.
Broussonetia papyrifera cont….
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pollen allergy during
the months of
March and April.
CDA had so far
chopped 36, 000
mature trees,
14,000 in the last
two years
Considerable measures
are still required
to ensure the control
of paper mulberry
from high infestatio
area and the adjacent regions
Lantana camara
Lantana: native to the US
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and Mexico.
Among the ten worst
weeds of the world
Form continuous thickets at
the infected sites in Pakistan.
Due to its aggressive behavior
it has replaced native flora
wooden barriers are visible in
highly infested Margalla
Hills, around Rawal Lake and
in Potohar plateau and the
Salt Range
Lantana camara cont…..
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Occupied a lot of natural
grazing ground & is
threatening wildlife.
hazardous to animals
and humans
leaves and seeds are toxic
to (livestock)
Plant acts as potential breeding
place for Tsetse Fly
Studies show the allopathic
impacts on soil micro flora
& fauna
Parthenium hysterophorus
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Native to the subtropics of
North and South America
Introduced from India
in to Pakistan
in 1970s
Invading aggressively in:
• wasteland, degraded areas,
rocky crevices, along water
channels, roadsides, and
railway tracks, cultivated land
Parthenium hysterophorus
cont….
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This noxious weed affects
• crop production
• animal husbandry
• human health
• and biodiversity
Contains Parthenin
lactones which are
Lethal to humans,
Animals and agriculture.
Invasive Plant Control
Methods
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an amount of Rs. 102 m have been allocated
for a project to deal with the IAS problem in
the country.
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Physical (Mechanical)
Chemical (Herbicide Application)
Biological
Mechanical eradication
Mechanical:
Hand pulling,
Cutting,
weed wrench
and wood talon
Brush hog or tractor
 Mowing
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Covering
 Grazing
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root talon
weed wrench
Mechanical + Chemical
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Cut plant followed by direct herbicide
application to cut
 cut stump painting
 bark injection
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Concerns with Mechanical
Removal
•Erosion caused by disturbed soil
can be an avenue of entry for
other invasive plant species
• Disturbance of nesting areas
Bark injection
Chemical
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Chemical
 Foliar: wipe-on, backpack sprayer,
spray bottle, boom applicator
 for some plants cut and
spray of regrowth will
minimize the amount of
chemical used.
 Basal Bark
 Pre emergent
 (rarely used in natural areas)
Concerns with Herbicide Use
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Contamination of surface or ground water
Accidental application to desired species
Disturbance of nesting areas
EXOTIC/INVASIVE
Management Issues
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1. Invasive species will not stop their spread at county,
state, or national borders
2. New invasive species will arrive
3. Rate of introductions will probably increase because of
increasing worldwide trade + global climate change
4. Coordinated efforts at all levels (county, state, national,
international) are needed for effective education and
prevention, early detection & rapid response, and control
5. Adequate funding is essential to success
Outline (Research)
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Biotic Invasions
Inventory (where are all the places that the exotic plants live)
Monitoring for population increase
[Density]
[Spread]
Monitoring for impact
The Decision to Manage
RESOURCES FOR MORE
INFORMATION
Global Context - IAS Databases
Global Invasive Species Database (GISD)
URL: http://www.issg.org/database and http://www.invasi
vespecies.net/database
100 of the World’s Worst Invasive Alien Species (in
GISD)
Global Compendium of Weeds (GCW)
URL: http://www.hear.org/gcw/alpha_select_gcw.htm
European Information System on Invasive Alien
Species – Regional Biological Invasions Centre (RBIC)
North European and Baltic Network on Invasive Alien
Species (NOBANIS) Database
URL: http://www.nobanis.org/Search.asp