The following account is based on a recently published WHO document.
1. Nutrient Storage and Cycling:
Ecosystems perform the vital function of recycling nutrients. These nutrients include elements of atmosphere as well as those found in soil, which are necessary for maintenance of life. Biological diversity is essential in this process. Plants are able to take up nutrients from soil as well as from air, and these nutrients can then form the basis of food chains, to be used by a wide range of other life forms.
Soil’s nutrient status, in turn, is replenished by dead or waste matter, which is transformed by microorganisms. This may then feed other species such as earthworms, which also mix and aerate soil and make nutrients more readily available. Ecosystem relationships resemble a web of connection from one living thing to many after living and non-living things. Such relationships allow survival; maintain a balance between living things and the resources (such as food and shelter).
Vegetation is integral to maintenance of water and humidity levels and is essential for maintenence of oxygen/carbon dioxide balance of atmosphere. Due to complex nature of ecosystem relationships, removal or disturbance of one part of ecosystem could affect functioning of many other components of ecosystem. Our knowledge of these relationships is incomplete. Results of disturbance are thus to some extent unpredictable.
Maintaining natural habitats helps ecosystem functions over a wider area. Natural habitats afford sanctuary to breeding populations of birds and other predators, which help control insect pests in agricultural areas, thus reducing need for, and cost of artificial control measures. Birds and nectar loving insects roost and breed in natural habitats. They may range some distance and pollinate crops and native flora in surrounding areas.
Maintaining healthy ecosystems improves chances of recovery of plant and animal populations from unpredictable natural catastrophic events, such as, fire, flood and cyclones and from disasters caused by humans. Inadequately conserved and isolated populations, and ecosystems which are degraded, are less likely to recover.
Populations of biota may end up with small, possibly non-viable, genetic bases, which can lead to extinctions. Poor people are mostly exposed to and are least prepared to cope with unpredictable events such as fluctuations in access to food and other resources or environmental shocks and risks.
Ecosystem degradation exacerbates frequency and impact of droughts, floods, landslides, forest fires and other natural hazards and can intensify competition and potential for conflict over access to shared resources such as food and water. Air purification
Forests canopies serve as particulate filters and chemical reaction sites for regulating atmospheric composition and purifying air. Particulates results from combustion of coal and oil, cement production, lime kiln operation, incineration and agricultural activities. Moist leaf surfaces provide sites for transforming potentially polluting compounds into harmless ones. Nitric oxide produced by soil microbes is a very reactive gas.
As moves through the forest canopy, NO combines with other chemicals on leaf surfaces and does not reach the air above canopy. Otherwise, it would have catalyzed photochemical reactions in atmosphere leading to production of tropospheric ozone. Tropospheric ozone is a greenhouse gas and is also a pollutant that adversely affects plants, animals and humans.
2. Watershed Services:
Forests regulate water flows to downstream areas. Deforestation often leads lo disruption of natural flow pattern causing flood and drought. Forest soils, especially act like massive filters, purify waters as it drips through forests ecosystem. In a healthy middle aged forest, rain falling enters with a nitrogen load of about 8 pounds per acre each year. Stream water leaving this forest often contain less than one tenth of nitrogen entering in rainfall as reported from New England.
3. Potential Pest and Disease Control:
Many weeds, insects, rodents, bacteria, fungi, and other organisms compete with humans for food, shelter and affect food production or spread disease. Certain animals and microbes naturally control some of these pests. Using these natural control agents as models, scientists have developed some biological pesticides to replace traditional pesticides.
In 1950s, small perching birds were declared as enemy in China, following which in 1958 an estimated 800,000 birds were killed in Beijing alone. Major pest outbreaks resulted from this bird eradication program, leading to significant crop losses. Mistake was ultimately realized and bird killing halted.
4. Landscape Stabilization:
Forests and grasslands provide natural protection for soils against erosion in several ways. Plant canopies intercept rainfall and reduce force with which rainwater hits soil surface. Roots bind soil particles in place and prevent them from washing down slopes.
Old root channels minimize powerful force of surface runoff by routing water into soil profile. Human actions like clearing forests and ploughing up grasslands to expand agriculture accelerate erosion, causing loss of useable cropland and other destructive outcomes.
5. Flood Mitigation and Buffering Against Ocean Storms:
Floodplains bordering rivers are subject to flooding. Following excessive rains, flood waters flow over riverbanks and into floodplains, forests and wetlands. Some water is soaked up by soil. When floodwaters recede, they leave behind nutrient rich sediment that enhances soil fertility, making these ecosystems extremely productive. Unaltered floodplains provide habitat for many plant and animal species.
High cost of flood damage results in part, from drainage of floodplain wetlands, building of permanent structures on floodplain, and construction of levees. Salt marshes, mangroves forest and other ecosystems buffer the coastline against ocean storms.
Plants in these ecosystems stabilize submerged soil, thereby preventing coastal erosion. These ecosystems are also breeding grounds and nurseries for commercially important fish and vital habitat for many birds and other species.
These ecosystems are being rapidly destroyed, filled in and built upon. Mangroves are more effective than concrete walls in controlling raging floodwaters from tropical storms. Mangrove forests are under assault from coastal development, shrimp aquaculture and unsustainable logging. Countries like Philippines, Bangladesh and Guinea Bissau have lost 70 % or more of their mangrove swamps.
6. Carbon Sequestration and Global Climate:
Land ecosystems are large storehouses of carbon both in plant tissue and in soil organic matter. By absorbing carbon, these ecosystems slow the growth of atmospheric carbon dioxide. Human activities such as burning of fossil fuels are increasing atmospheric concentration of carbon dioxide and other gases. Global average surface temperature rose 0.6° C during 20th century and is projected to rise another 1.4 to 5.8 °C (2.5 to 10.4° F) in 21st century mostly due to human activities.
This temperature rise is associated with more extreme precipitation and faster evaporation of water leading to greater frequency of both very wet and very dry conditions. Global sea level is rising as water expands while warming. Many ecosystems would be highly vulnerable to climate change.
Alpine meadows, mangrove forest and coral reefs are likely to disappear entirely in some places. Other ecosystems are projected to become fragmented or experience major shifts. Services lost through disappearance or fragmentation of certain ecosystems would be costly or impossible to replace.
Vegetation influences climate at macro-and micro-levels. Undisturbed forest helps to maintain rainfall in its immediate vicinity by recycling water vapour at a steady rate back into atmosphere and through canopy’s effect in promoting atmospheric turbulence.
At smaller scales, vegetation has a moderating influence on local climate and may create quite specific micro-climates. Some organisms are dependent on such micro-climates for their existence.
7. Genetic Library Function:
Genetic information stored in natural ecosystem would solve enormous range of challenges. Genetic diversity is a rich, relatively untapped resource for present and future benefits in agriculture and medicine.
Thirteen of the 20 best selling prescriptions drugs in the U.S. are either natural products, that have been slightly modified chemically or manufactured drugs originally obtained from organisms.
Many flowering plants rely on animals to help them mate. Bees, butterflies, beetles, hummingbirds, bats, and other animals transport pollen with enormous benefits to humanity. Approximately one third of world’s food crops depend on these natural pollinators. In the U.S., honey bees pollinate about US $10 billion worth of crops.
Oil palm was introduced into Malaysia from forests of Cameroon in West Africa in 1917. But the weevil that pollinates African oil palm was not introduced at the same time.
For decades, palm growers of Malaysia relied upon expensive, labour intensive hand pollination. In 1980, the weevil was imported to Malaysia, boosting fruit yield in palms 40-60% and generating saving in labor cost of U.S. $140 million per year.
9. Seed Dispersal:
Animals such as toucans, monkeys and fruit bats consume tree fruits and scatter piles of seed rich dung across landscape. This service helps trees to populate their habitat, and migrate across the land in response to a variety of disturbances including climate change. Desertification
Desertification affecting 70% of world’s dry lands is the result of degradation of once fertile arid and semiarid croplands, pastures and woodlands. Deserts have lost their biological or economic productivity. It is due to climate variability and unsustainable human activities such as over cultivation, over grazing, d forestation and poor irrigation practices; Desertification undermines food production destabilization of soil against water and wind.
Degraded land may cause downstream flooding, reduced water quality, sedimentation in rivers and lakes and accumulation of silt in reservoirs and navigation channels. It can cause dust storms that exacerbate human health problems including eye infection, respiratory illnesses, allergies and cases of meningococcal meningitis. Critical habitat for plant and animal species is lost as desertification proceeds, leading to economic losses including those from declining tourism.
World’s human population is becoming increasingly urban. Land-use changes and pollution associated with urbanization cause loss of plant and animal habitat and diminish stabilization function.
Urbanization often leads to increased erosion and reduced natural watershed control of floods. Filling in of wetlands for urban expansion eliminates their water cleansing function.
11. Wetland Drainage:
Over the 20th century, some 10 million square kilometers of wetlands have been drained globally, an area about the size of Canada. In the lower 48 states of the U.S., drainage has reduced wetlands areas by half, mostly for agriculture. In the process, critical wildlife habitat has been lost, as have floodplains which are safety valves for flood events and natural filters for flowing waters.
12. Pollution control:
Pollution of air, rain (and snow), surface waters and land diminishes ecosystem services in many ways. Air pollutant ozone reduces growth of agricultural crops and plants in natural ecosystems. Pollution of rain with sulfur and nitrogen compounds results in acid rain that damages plants impoverishes soils and acidifies surface waters, killing plant and animal inhabitants. Nitrogen pollution causes harmful algal bloom and depletes water of oxygen, sometimes severely causing death of major fish.
Heavy metals from smelters accumulate in soils, killing plant life and thus creating erosion problems. Persistent organic pollutants, such as, DDT and PCBs can alter food webs and thereby diminish ability of ecosystems to deliver services such as pest control.
Ecosystems and ecological processes play an important role in breakdown and absorption of many pollutants, created by humans and their activities. These include wastes such as sewage, garbage and oil spills. Components of ecosystems from bacteria to higher life forms are involved in these breakdown and assimilative processes.
Excessive quantities of any pollutant, however, can be detrimental to integrity of ecosystems and their biota. Some ecosystems, especially wetlands, have qualities that are particularly well suited to breaking down and absorbing pollutants.
Natural and artificial wetlands are being used to filter effluents to remove nutrients, heavy metals and suspended solids, to reduce biochemical oxygen demand and destroy potentially harmful microorganisms. Human activities have concentrated heavy metals, radioactive elements and other toxins in various places, rendering some locations unusable and dangerous.
In cleaning up such contaminated sites, the capacity of vascular plants to concentrate toxic elements without harming themselves can be utilized. Mustard plants accumulate lead and certain ferns sop up arsenic in a small pond contaminated with Strontium 90 near Chernobyl nuclear power plant.
Cesium 137 and other harmful radioactive substances released during reactor fire in 1986. Scientists grew sunflowers on small Styrofoam rafts, and with roots of sunflowers dangling in water, sunflowers rapidly accumulated levels thousand times higher than concentrations in water.
13. Sediment and Soil Detoxification, Soil Formation Fertility:
Microbes detoxify some human generated wastes. Oil spilled into estuaries and marine ecosystems poses health risks to humans and other species. When certain compounds from petroleum hydrocarbons adhere to sinking particles, they settle to sediment surface, where naturally occurring microbes can detoxify compounds and ultimately degrade them to carbon dioxide and water. Soils with their active microbial and animal populations have capacity to supply adequate nutrients to plants in suitable proportions.
Soil animals and microbes break down organic matter and release nutrients into soil solution. Electrical charges carried by tiny soil particles give them ability to retain these nutrients and release them to plant roots. Biodiversity helps in formation and maintenance of soil structure and retention of moisture and nutrient levels.
Loss of biological diversity through clearing of vegetation has contributed to salinisation of soils, leaching of nutrients, and accelerated erosion of topsoil, reducing land’s productivity. Trees, on the other hand, lower water table and remove deposited salt from upper soil horizons.
Soil protection by maintenance of biological diversity can preserve the productive capacity of soil, prevent landslides, safeguard coastlines and riverbanks and prevent degradation of coral reefs and riverine and coastal fisheries by siltation.
Trees and other vegetation also assist in soil formation. A significant contribution is introduction of organic matter through litter formation, decay and regeneration of tiny fibrous roots, both of which facilitate microbial activity.
Root systems break up soil and rock leading to, amongst other things, penetration of water. Root systems also bring mineral nutrients to surface through root uptake. Organic matter formed by decay of tiny fibrous roots can also bind with minerals, such as, iron and aluminum, which can reduce potential deleterious effects of these minerals on other regulation.