Conflict between development and the environment remains unresolved, but history teaches us that environmental pollution or stress can be significantly offset through planned development. We rarely consider the stress-tolerance capacity of ecosystems, and this capacity is certainly limited. One of the fragile ecosystems of Bangladesh is the hill ecosystem, mainly because of water scarcity. Accordingly, its stress-tolerance capacity is low. It is a living entity that needs to be addressed scientifically. For this, we need to understand the delicate ecological processes 鈥� eg the hydrological cycle, carbon cycle, nitrogen cycle, etc 鈥� that operate there and on which ecosystem health greatly depends, and vice versa.
The introduction of external forces into a virgin ecosystem 鈥� such as humans, foreign materials for infrastructure, alien plant or animal species, etc 鈥� affects ecological processes, degrades ecosystem health and ultimately reduces productivity. Therefore, for sustainability, an assessment of the carrying capacity of the ecosystem is ideally necessary before planning any development activities. This is something we generally do not care for, and which came to notice during our recent visit to Khagrachari, Rangamati and Bandarban, the natural beauties of Bangladesh.
Below is an overview of the major environmental stresses on the hill ecosystems:
A gradual increase in population and their diversified livelihood needs exert stress on these ecosystems. For example, the introduction of large quantities of building materials (sand, cement, rods, etc.) for infrastructure and housing traps solar heat during the daytime and releases it at night, contributing to local warming. Urbanisation of hills generates huge volumes of wastes (solid, liquid and gaseous), including hazardous medical waste and plastics. The release of untreated sewage certainly defiles the hill environment. For better understanding, imagine hundreds of thousands of people defecating there daily and polluting the environment with potential contaminants such as E. coli and heavy metals (biomagnification occurs as humans occupy the highest trophic level in a food web). Tourist pollution adds an extra burden to the ecosystems. Another potential source of pollution is used lead-acid batteries (commonly used in three-wheelers).
Deforestation, slash-and-burn practices and land conversion lead to land degradation (e.g. soil erosion and landslides). Generally, soils with a slope of more than 20鈥�25 per cent are unfit for cultivation and should be kept covered with forest or grass to avoid soil erosion (Topsoil and Civilisation, 1955). Many hills are being denuded for agriculture, infrastructure development and housing. Crop diversification through the introduction of alien/exotic species causes genetic pollution that stresses the local ecosystem. Native species are evolutionarily committed to protecting their home ecosystem due to long-term adaptation (e.g. hill species are responsible for soil conservation; failing this, they risk extinction). Thus, their root systems, water needs, leaf characteristics, physiology and phenology differ from plain-land species. Even species composition on the north and south sides of a single hill varies due to geography and sunshine. Therefore, before introducing any alien species to hills, there should be careful evaluation of its life-cycle, water and nutrient requirements, edaphic factors, interactions with other species (e.g. community ecology), susceptibility to disease and pests, climatic needs, etc. Otherwise, introduction of new species will negatively impact gene flow, biodiversity and pest incidence (leading to indiscriminate use of agrochemicals), causing environmental degradation and ultimately threatening local food security. Modern agriculture is considered a slow onset of irreversible damage to biodiversity, a natural safeguard for ecosystem functions.
Tourist pollution is a growing concern due to the rapid rise in visitors to the hills. Littering with plastics, food waste and human defecation pollutes natural ecosystems. Noise and vehicular emissions disturb the peaceful environment and wildlife. Construction of unplanned resorts and hotels accelerates deforestation, soil erosion and water contamination, degrading the natural beauty and ecological balance of the hill regions.
Excessive tree cutting for fuelwood, shifting cultivation and illegal logging accelerate deforestation. As a result, soil erosion, loss of fertile topsoil and landslides become more frequent, especially during the monsoon. Illegal hill cutting is a major cause of environmental degradation, destroying natural landscapes, destabilising slopes and disrupting ecological balance. Water- and wind-borne soil erosion causes heavy sediment deposition in river/lake/tank beds, reducing water-holding capacity and increasing susceptibility to climate change, e.g. increased local warming. Low water-holding capacity also reduces the buffering ability of hill ecosystems against environmental stresses.
The widespread use of chemical fertilisers and pesticides in commercial farming damages soil quality. Waste dumping on hillsides contaminates land, reduces soil fertility and disrupts natural nutrient cycles. All these, along with local warming, affect soil biodiversity, increase soil respiration and ultimately increase CO鈧� emissions.
Unplanned urban growth and hillside settlements contaminate streams and lakes with household wastes, untreated sewage, medical waste and plastics. Agricultural runoff carrying pesticides and fertilisers pollutes natural water bodies. The absence of environmentally friendly municipal waste management disturbs aquatic ecosystems. Household runoff containing toiletries and health and beauty products ultimately affects soil, air and water quality. We must therefore be conservative in using such items.
Household emissions, brick kilns, small-scale industries and transport vehicles in hilly towns release harmful smoke and pollutants. In addition, slash-and-burn (Jhum) farming contributes to seasonal air pollution by emitting greenhouse gases and particulate matter. Transboundary pollutants may also contribute to local air pollution.
The large number of autorickshaws and other vehicles in tourist zones generates high levels of noise pollution. Light pollution, especially at night, may cause neurological disorders in resident wildlife and ultimately lead to biodiversity loss.
Pollution and habitat destruction threaten many wildlife species, some already endangered. Large-scale cultivation of alien species and monocultures such as rubber and teak further reduce local biodiversity. Loss of biodiversity reduces the ecosystem鈥檚 defence mechanisms against climate hazards and pest infestation.
Degradation of the hill ecosystem reduces natural resilience to climate vulnerability. Pollution-related environmental changes 鈥� physical (eg local temperature), chemical and biological 鈥� contribute to irregular rainfall patterns, worsening both droughts and flash floods in hilly terrain, hampering ecosystem productivity and ultimately affecting human well-being.
Natural resources are limited, and we must maintain a high standard 鈥� both in quantity and quality 鈥� to ensure health and social security. Unlike other cities or ecosystems in Bangladesh, it is not too late to restore the hill ecosystems. To understand the process of their degradation, long-term monitoring is necessary. This is vital for science-policy interfacing towards functional management.
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Dr Md Sohrab Ali is a former additional director general of Department of Environment. Md Hannan is an assistant director at Department of Environment.