Climate change: Impact on forests

Climate change: Impact on forests
Mohammed Abdul Baten and Ronju Ahammad

IT is beyond doubt that Bangladesh is one of the badly affected countries from the impacts of climate change. Therefore, it is no more any fashion rather an imperative to call for effective measures for combating climate change. Of late, the government has given an announcement to create a fund for the purpose amounting to estimated three billion taka in the current fiscal year, which will be allocated to various adaptation and mitigation strategies against already set paradigm of bad consequences from the climate change such as losses from frequent cyclones in the south, drought in the northern region and decreasing agriculture productivity with recurring food.

Though rest of the world is now emphasising on the restoration of and increasing green areas to combat climate change, yet we are still far from the reality. Most of our efforts to the green future concept are a matter of discourse in documents and seminars other than practice. The shirking of responsibility natural forests and afforestation with invasive exotic species in the form of social forestry or other schemes may not contribute to the battle against climate change at an expected level, many scientists revealed in their studies.

Evidently, rapid transformation of land-uses, in particular deforestation is releasing back the stored carbon from forest into the atmosphere and thus increasing global warming. So, in the face of climate change, the effective management of forests for both goods and services to human well being becomes a challenge. For Bangladesh, this may be greater than others.

The Kyoto Protocol, an international agreement between the parties to climate change has recognised the important role of forests for reducing carbon dioxide, and they initiated the strategy of Clean Development Mechanism (CDM) for high greenhouse gas emitters like USA, EU to buy carbon credit through afforestation scheme. In reality, carbon trade encourages plantation of fast growing monoculture species irrespective of biodiversity which in turn degrades the previous natural forest structure that generally coped successfully with different events like solar radiation and various natural hazards.

Not only forest maintains biodiversity as a whole, but also provides subsistence livelihood to nearly 400 million people of the world who are living in and around the forests. International Institute for Environment and Development (IIED) estimates that climate change will increase the vulnerability of the most poor communities (approximately 1.2 billion people) in tropical region because of their livelihood dependency on natural resources.

The Intergovernmental Panel on Climate Change (IPCC) projected that the state of tropical forest ecosystems is likely to be worsen from climate change. Bangladesh being in the tropical region, different physical effects of climate change including increased temperature and precipitation, increased salinity and extreme weather events such as floods, cyclones and droughts will have profound negative impacts on its forests.

Bangladesh is characterized by both natural and plantation forests which, however, account for 17.5 percent of the total land in documents, but only 6-7 percent in reality. The notable natural forest ecosystems are tropical wet evergreen and semi-evergreen forest (hill forests), moist deciduous forestry (sal forest), tidal forest (mangrove forest), and village forestry. The plantation forests are now increasing under the auspices of social forestry programme to ensure people participation and their socio-economic benefits. Each forest type possesses particular stand structure, composition and functional groups (i.e., the groups of species that perform multiple functions in an ecosystem such as pollination, nitrogen fixation, predation, decomposition etc.) and also builds site specific responses to climate variability.

However, continuous deforestation (approximately 3.3 percent per year) in this region is reducing natural forest stocks, threatening valuable wildlife, and thus degrading micro-climate in both forest and adjacent regions.

Because of the increased rainfall in monsoon, water runoff rate on the forest floor has increased from the previous one. As a result, rapid soil erosion causes nutrient leaching and destroys micro-orgainsim and reduces overall site quality for better forest growth in the previously dense hill forests of Chittagong, Chittagong Hill Tracts (CHT), Sylhet, and Cox's Bazar. Most of the forests are also likely to be affected from the absence of ecological memory that is the network of species for interaction between each other and environment, and building the capacity for reorganisation within or outside the forest patch after different perturbations. Researches shows that regeneration rate of Garjan (Dipterocarpus Spp) in the Chittagong and CHT has declined considerably in the last decades. The monoculture plantation of Teak in CHT also exacerbates soil erosion because of poor undergrowth during heavy rainfall. Forestry experts find monoculture seldom leaves the land very productive for further recolonisation.

Moreover, the increasing frequency of flood, as a consequence of climate change, and its prolongation also triggers the mortality of some homegarden species such as jackfruit, papya and bamboo mainly found in the plainland village forests.

Over the last fifty years, the sal forests, situated in central and north-western region have decreased drastically due to illegal deforestation. Only a few areas reminiscent of the original forest remains, while government is trying to reforest the area with some so called fast growing exotic species such as Akashi (Acacia auriculiformis) and Eucalyptus (Eucalyptus camaldulensis). Many forest scientists argue that these exotic species are detrimental to biodiversity of the area may and transform the local ecosystem into aridity through their increased water uptake characteristics. Besides, climate change might increase the temperature in north-western region which infact alters the ecological processes in the Modhupur and Barind tracts through increased evapo-transpiration causing moisture stress (water deficiency) in winter, thus affecting the survival of sal forest ecosystem. Agricultural practices are now common phenomena in and around the previous forest patches instead of earlier forest based landuses.

Being the largest single tract of mangrove forests in the world, the Sunderbans, a World Heritage Site is already affected with climate change impacts, importantly from increasing salinity and extreme weather events like tropical cyclones. Though, the main causal factors of top dying is yet to be known, but, some researchers predict that top dying of sundari trees (Heritiera fomes) is likely to be the consequence of slow increase of salinity over a long period of time. Salinity increase also affects the species' combination and regular successional patterns in the Sundarbans as some non-woody shrubs and bushes replace the tree species, reducing the forest productivity and habitat quality for valuable wildlife. World Wildlife Fund for Nature Conservation ( WWF ) estimates that due to sea level rise, nearly 7500 hectare of mangrove forest in the Sundarbans are projected to be flooded. Many researches have shown that tropical cyclones destroy the mangrove forests to a large extent. For instance, in the recent past, cyclone Sidr has destroyed one-third of the Sundarbans.

Forest ecosystems may be or not adaptive to climate variability will depend on the complex interactions of multiple organisms ranging from trees, animals to micro-organisms. Very often the presence of functional groups and response diversity (i.e., diversity of responses to environmental change among species that contribute to the same ecosystem function) of species within the forests determine the adaptive capacity to the impacts of climate change.

Recent studies show that massive afforestation with exotic species wouldn't be a pragmatic solution for the adaptation to the climate change. Rather, it is suggested that as implications of response, diversity and functional diversity-biodiversity should be conserved in their natural habitat by protecting existing natural forests, minimising soil disturbances, reducing carbon loss from soil, preventing potential loss of mycorrhizae and increasing freshwater inflow in the saline affected mangrove regions.

Mohammed Abdul Baten and Ronju Ahammad write from Stockholm Resilience Centre, University of Stockholm, Sweden

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