Published On: 2008-03-29
Environment
Climate change threatens plant diversity in Bangladesh
Dr. Mohammed Kamal Hossain

Forests cover one third of the earth's surface and estimation is that
more than two thirds of all available terrestrial species are found in
the forests. Bangladesh also supports a wealth of plant diversity and
is located in transition of two mega-biodiversity hot spots of
Indo-Malayan region. The country has been endowed with rich plant
diversity because of its fertile alluvial land, warm and humid
climate. More than 5,700 angiosperm species and several sub-species
are available in Bangladesh. The diverse agro-ecological (30
agro-ecological zones) regions or the 12 Bio-ecological zones of the
country have sustained rich genetic resources of crop plants, which
are unique to this country. The forest of Bangladesh covers
approximately 2.60 million ha which is about 17.62 percent of the land
area of the country. Of these, the hills consist of moist tropical
evergreen and semi-evergreen forests, which extend from northeast to
southeast of the country. The forests are generally uneven-aged and
multistoried with the valuable tropical species of Dipterocarpus
turbinatus, D. alatus, D. costatus, Swintonia floribunda, Aphanamaxis
polystachya, Artocarpus chaplasha, Tetrameles nudiflora, Duabanga
grandifolia and Pterygota alata. The understorey is a tangle of
shrubs, creepers, climbers, ferns and orchids. The species were
adapted to the different ecosystems after a long successional process.

Though the native plant species of the country have been enriched with
new species and varieties introduced from abroad, but the invasive
plants are becoming a major threat to natural ecosystems and their
species. The impacts of alien invasive species are immense, insidious
and usually irrecoverable. The scope and cost of alien invasions is
global and enormous, in both ecological and economic terms. But,
unfortunately in Bangladesh introduction of alien invasive species of
flora were deliberate primarily in order to increase productivity to
support the needs of a huge population. The deliberate preferences of
fast growing high yielding cultivars eroded some of the native species
and the genetic resources abruptly. We have scarce information about
the alien species in Bangladesh and their impacts on the ecosystem and
the species.

More than 300 exotic species are supposed to either wildly growing or
cultivated as an economic crop in Bangladesh. Some of the invasive
plants are so well established that have become noxious weeds of
forests and wastelands (Chromolaena odoratum, Mikania cordata, Lantana
camara etc.). Some are considered as noxious weeds of cultivated
fields also (Alternanthera, Scoparia and Heliotropium spp.). Some
troublesome weeds are also found in water land, e.g. Eichhornia
crassipes, Pistia stratiotes. The British mostly contributed to the
introduction of some economically important forest plants form almost
all the continents, e.g. Tectona grandis, Paraserianthes falcataria,
Albizia saman, Xylia dolabriformis, and Swietenia macrophylla. In the
20th century this trend continued to be the same, and some Australian
species (Eucalyptus camaldulensis, Acacia mangium, and Acacia
auriculiformis) are getting preferences in the plantation programs. Of
these, the Acacia auriculiformis is dominating in all the plantation
programmes and growing well in all sorts of degraded lands.

Global climate change is now a reality and the change is mainly
happening due to global warming. Global warming is an issue of much
concern for both the developing and developed countries. The
atmospheric concentration of some gases, mainly carbon-di-oxide has
increased and it forms a layer that traps the heat of the terrestrial
radiation. Consequently, the earth temperature is gradually increasing
and projection is that the global temperature will increase by 1.5 --
2.8 degree Celsius by the middle of this century. The IPCC calculation
projected that if carbon-di-oxide is doubled in the atmosphere, the
mean temperature of the earth will increase by 1.5 -- 4.50C. The IPCC
also forecast that global temperature would rise by 0.20 -- 0.500C in
each decade during 21st century with a consequent rise of sea level by
3--10 cm. Temperature rise will result in melting ice and consequently
the sea level will rise up to 70 cm! The detailed glacial record in
Greenland and Antarctica indicates that the global climate has changed
remarkably within the last couple of decades.

Global climate change has an adverse effect on sea level rise,
increase in force and frequency of floods, tropical cyclones,
tornadoes, drought, rainfall, intrusion of salinity, soil erosion, and
loss of biodiversity and total degradation of the environment.
Moreover, the incidence and extent of malaria, dengue and some other
vector borne diseases are expected to increase with global warming.
The effects of sea level rise and flooding of the low lying coastal
areas threatens the shelters, resources and livelihoods of several
million people in the world. Similarly, a huge population (about 30
million) of Bangladesh living along or very close to the coastal area
will suffer severely. Reduction of fresh water flow and salinity
increase in the Sundarbans has already resulted in top dying of Sundri
trees and gradual changes of the forest composition. If the situation
keeps on prevailing or worsens, then Sundri, the climax species of the
Sundarbans may be replaced by some other species.

Temperature increase by one degree significantly lowers the production
of wheat and potato of the country. Adverse environmental changes will
also affect the production of the major crop rice significantly.
Evidence exists that climate change is seemingly changing the existing
forest covers significantly. Small changes in temperature and
precipitation significantly affects forest growth; even an increase of
one degree in temperature can modify the functioning and composition
of forests. Forest dwelling large animals and 9 percent of all known
tree species are already at some risks of extinction. Climate change
also threatens the forests by pests and fires, making them more
vulnerable to invasive species. Deforestation and land clearing
activities emit about 1.7 billion metric tons of carbon per year into
the atmosphere. Hence, conservation of forests offer important
opportunities to protect biodiversity and slow climate change.

In Bangladesh, due to population pressure, deforestation and changes
of land use pattern, many species of both flora and fauna have became
extinct and many more species are categorized as threatened or
endangered considering their existence in wild or cultivated form. In
addition, Bangladesh will face serious consequences of biodiversity
loss from the global climate change. Considering the present situation
and future need, Bangladesh must address the problem of extinction of
her native plant resources and immediately needs collection,
conservation and management programme for future vulnerable
catastrophic climates. Scientists, policy makers, administrators,
civil society and public representatives including political leaders
could play a vital role to save the diverse plant resources from
extinction. Regional and international cooperation with countries have
much to gain from partnership in research and development programme
devoted to the conservation and use of plant resources.

Dr. Mohammed Kamal Hossain is Professor, Institute of Forestry and
Environmental Sciences, University of Chittagong. E-mail:
hossainmk2001@yahoo.com

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