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The best information on terrestrial habitats relates to forests, which currently occupy approximately 31 per cent of the Earth’s land surface.
Forests are estimated to contain more than half of terrestrial animal and plant species, the great majority of them in the tropics, and account for more than two-thirds of net primary production on land - the conversion of solar energy into plant matter.
The net loss of forests has slowed substantially, from approximately 83,000 square kilometres per year in the 1990s to just over 50,000 square kilometres per year from 2000-2010.
This is mainly due to large-scale planting of forests in temperate regions and to natural expansion of forests. Since newly-planted forests often have low biodiversity value and may only include a single tree species, a slowing of net forest loss does not necessarily imply a slowing in the loss of global forest biodiversity.
The conifer-dominated boreal forests have remained broadly stable in extent in recent years. However, there are signs in some regions that they have become degraded. In addition, both temperate and boreal forests have become more vulnerable to outbreaks of pests and diseases, due in part to an increase in winter temperatures.
Cumulative deforestation of the Brazilian Amazon is nevertheless substantial, reaching more than 17 per cent of the original forest area, and even achievement of the existing government target of an 80 per cent reduction in annual deforestation by 2020 (from the 1996-2005 average) would bring the cumulative loss of forest to nearly 20 per cent.
According to a recent study co-ordinated by the World Bank, 20% Amazon deforestation would be sufficient to trigger significant dieback of forest in some parts of the biome by 2025, when coupled with other pressures such as climate change and forest fires.
The most recent satellite data suggest that annual deforestation of the Brazilian portion of the Amazon has slowed significantly, from a peak of more than 27,000 square kilometres in 2003-4 to just over 7,000 square kilometres in 2008-9, a decrease of over 74 per cent.
However, the same satellite images indicate that a growing area of the Amazon forest is becoming degraded.
Savannas and grasslands, while less well documented, have also suffered severe declines.The extent of other terrestrial habitats is less well documented. It is estimated that more than 95 per cent of North American grasslands have been lost.
Cropland and pasture have replaced nearly half of the cerrado, the woodland- savanna biome of Central Brazil which has an exceptionally rich variety of endemic plant species.
Between 2002 and 2008, the cerrado was estimated to have lost more than 14,000 square kilometres per year, or 0.7% of its original extent annually, well above the current rate of loss in the Amazon.
The Miombo woodlands of Southern Africa, another savanna region with significant plant diversity, are also experiencing continued deforestation.
Stretching from Angola to Tanzania and covering an area of 2.4 million square kilometres (the size of Algeria), the Miombo provide firewood, building materials and extensive supplies of wild food and medicinal plants to local communities across the region.
The woodlands are threatened by clearing land for agriculture, extraction of wood to make charcoal, and uncontrolled bush fires.
Agricultural landscapes maintained by farmers and herders using locally adapted practices not only maintain relatively high crop and livestock genetic diversity, but may also support distinctive wild biodiversity.
These types of landscapes are found worldwide and are maintained through the application of a wide array of traditional knowledge and cultural practices which have evolved in parallel, creating landscapes with globally significant agricultural biodiversity.
Rice-fish agriculture practiced in China has been used since at least the Han Dynasty, 2,000 years ago. In this system, fish are kept in wet rice fields providing fertilizer, softening soils and eating larvae and weeds, while the rice provides shade and food for the fish. The high quality of the fish and rice produced from this system directly benefits farmers through high nutrition, lower labour costs and reducing the need for chemical fertilizers, herbicides and pesticides.
In the valleys of Cusco and Puno in Peru, the Quechua and the Aymara peoples employ a form of terracing which allow them to grow various crops, such as maize and potatoes, as well as graze animals on steep slopes at altitudes ranging from 2,800 to 4,500 meters.
This system supports as many as 177 varieties of potato, domesticated over many generations. It also helps to control soil erosion.
Satoyama landscapes are small mosaics composed of various types of ecosystems including secondary woodlands, irrigation ponds, rice paddies, pastures and grasslands, from which landholders have traditionally harvested resources including plants, fish, fungi, leaf litter and wood, in a sustainable way.
Traditional techniques of managing land for agriculture, some dating back thousands of years, have served an important function in keeping human settlements in harmony with the natural resources on which people depend.
In many parts of the world, these systems are being lost, due partly to the intensification of production, and partly to abandonment linked to migration from rural to urban areas.
In some cases, this trend may create opportunities for biodiversity through the re-establishment of natural ecosystems on abandoned farmland.
However, the changes may also involve important losses of distinctive biodiversity, among both domesticated and wild species, and of ecosystem services provided by managed landscapes.
Abandonment of traditional agricultural practices may cause loss of cultural landscapes and associated biodiversity.
The condition of many terrestrial habitats is deteriorating.
The global analysis of land degradation and improvement estimated that nearly one quarter (24%) of the world’s land area was undergoing degradation, as measured by a decline in primary productivity, over the period 1980-2003. Degrading areas included around 30% of all forests, 20% of cultivated areas and 10% of grasslands.
When ecosystems become fragmented they
may be too small for some animals to establish
a breeding territory, or force plants and
animals to breed with close relatives.
The in-breeding of species can increase
vulnerability to disease by reducing the
genetic diversity of populations. A study in the central Amazon region of Brazil found that forest fragments of less than one square kilometre lost half of their bird species in less than fifteen years.
In addition, isolated fragments of habitat make species vulnerable to climate change, as their ability to migrate to areas with more favourable conditions is limited.
Aquatic habitats such as mangroves, seagrass beds, salt marshes and shellfish reefs continue to decline in extent.
This is threatening highly valuable ecosystem services including the removal of significant quantities of carbon dioxide from the atmosphere; but there has been some slowing in the rate of loss of mangrove forests, except in Asia.The quantity of carbon buried each year by vegetated coastal habitats such as mangroves, salt marshes and seagrass beds has been estimated at between 120 and 329 million tonnes. The higher estimate is almost equal to the annual greenhouse gas emissions of Japan.
Mangrove forests are highly-productive ecosystems in the inter-tidal zones of many tropical coastlines.
They not only provide wood for local communities, but also act as nursery areas for a wide range of commercially-valuable fish and crustacean stocks, and act as vital energy barriers, protecting low-lying coastal communities from offshore storms.The rate at which mangroves are declining globally seems to have reduced more recently, although the loss is still disturbingly high. During the 1980s, an average of 1,850 square kilometres was lost each year. In the 1990s the annual average dropped to 1,185 square kilometres, and from 2000-2005 it was 1,020 square kilometres - a 45% reduction in the annual rate of loss.
Seagrass beds or meadows, fringing coastlines throughout the world, perform a number of vital but under recognized ecosystem functions, including support for commercial fisheries, a food source for species such as manatees and dugongs, and the stabilization of sediments.
It is estimated that some 29% of seagrass habitats have disappeared since the 19th century, with a sharp acceleration in recent decades.
Since 1980, the loss of seagrass beds has averaged approximately 110 square kilometres per year, a rate of loss comparable to mangroves, coral reefs and tropical forests.
Salt marshes, important as natural storm
barriers and as habitats for shorebirds,
have lost some 25% of the area they
originally covered globally, and current
rates of loss are estimated to be between
one and two per cent per year.
Salt marshes are especially important
ecosystems for removing carbon dioxide
from the atmosphere.
For example in the United States they are estimated to account for more than one-fifth of the carbon absorbed by all ecosystems, despite covering a relatively small area.
Tropical coral reefs contribute significantly to the livelihoods and security of coastal regions in the areas where they occur.
They also contribute through tourism based on their aesthetic beauty, income and nutrition from the fish species they support, and protection of coastlines from storms and waves.
Although they cover just 1.2% of the world’s
continental shelves, it is estimated that between
500 million and more than one billion people rely
on coral reefs as a food resource.
Around 30 million people in the poorest and most
vulnerable coastal and inland communities are
entirely dependent on resources derived from
coral reefs for their well-being.
They also support between one and three million species, including approximately 25% of all marine fish species.
The condition of deep-water habitats has started to cause concern, as awareness increases of the impacts of modern fishing technology, especially bottom-trawling, on ecosystems.
Bottom-trawling and use of other mobile fishing gear can have an impact on seabed habitats equivalent to the clear-cutting of rainforests. Species from the deep ocean have become increasingly targeted as more accessible fish stocks become depleted and more strictly regulated. Fish stocks assessed since 1977 have experienced an 11% decline in total biomass globally, with considerable regional variation. The average maximum size of fish caught declined by 22% since 1959 globally for all assessed communities.
Preliminary estimates suggest that between 30-50 % of the cold-water coral reefs in the Exclusive Economic Zone of Norway (that is, within 200 nautical miles of the Norwegian coast) have been impacted or damaged by bottom trawling.
Other documented cases of damage caused by reef trawling have been observed in the Faroe Islands, Denmark and Iceland. All three countries have now closed some coral areas to trawling.
Deep-water habitats are considered especially vulnerable because species of the deep ocean tend to be slow-growing and long-lived. Cold-water corals are also considered in some studies to be particularly susceptible to impacts from ocean acidification.
Decades of catch records enable trends to be recorded in the average position of caught fish in the food web (the Marine Trophic Index), and thus to monitor the ecological integrity of marine ecosystems. Despite the intense pressure on fish stocks, the Index has shown an increase of 3% globally since 1970.
However there is substantial regional variation in the Marine Trophic Index, with declines being recorded in half of the marine areas, including the world’s coastal areas.
The largest proportional fish stock increases are in the Mediterranean and Black Seas, West Central Pacific and Southwest Pacific.
Although these increases may indicate a recovery of higher predator species, they are more likely a consequence of fishing fleets expanding their areas of activity, thus encountering fish stocks in which larger predators have not yet been removed in such numbers.
Marine Protected Areas (MPAs) cover approximately half of one per cent of the total ocean area.
The open ocean is virtually unrepresented in the protected area network reflecting the difficulty of establishing MPAs on the high seas outside exclusive economic zones. Of 232 marine eco-regions, only 18% meet the target for protected area coverage of at least 10%, while half have less than 1% protection. In various coastal and island regions, the use of community-based protected areas, in which local and indigenous peoples are given a stake in conservation of marine resources, are becoming increasingly widespread, and have shown promising results.
The worlds fisheries employ approximately 200 million people and provide about 16 percent of the protein consumed worldwide and have a value estimated at $82 billion US dollars.
About 80 percent of the world marine fish stocks for which assessment information is available are fully exploited or overexploited.
The value of the ecosystem services provided by coral reefs ranges from more than US$ 18 million per square kilometer per year for natural hazard management, up to US$ 100 million for tourism, more than US$ 5 million for genetic material and bioprospecting and up to US$ 331,800 for fisheries.
The annual economic median value of fisheries supported by mangrove habitats in the gulf of california has been estimated at US$ 37,500 per hectare of mangrove fringe.
The value of mangrove as coastal protection may be as high as US$ 300,000 per kilometer of coastline.
In the Ejido (communally owned land) of Mexcaltitan in Mexico, the direct and indirect value of mangroves contribute to 56 percent of the Ejidos annual wealth increase.
In the past decade, more than 12,000 square kilometres in the South Pacific have been brought under a community-based system of marine resource management known as Locally-Managed Marine Areas (LMMA).
The initiative involves 500 communities in 15 Pacific Island States. It has helped achieve widespread livelihood and conservation objectives based on traditional knowledge, customary tenure and governance, combined with local awareness of the need for action and likely benefits
These benefits includes recovery of natural resources, food security, improved governance, access to information and services, health benefits, improved security of tenure, cultural recovery, and community organization
Results of LMMA implementation in Fiji since 1997 have included: a 20-fold increase in clam density in the tabu areas where fishing is banned; an average of 200-300% increase in harvest in adjacent areas; a tripling of fish catches; and 35-45% increase in household income.
estuary biomes where a source of fresh water, such as a river, meets the ocean
intertidal zone part of the ocean that is closest to land; parts extend
above the water at low tide
neritic zone part of the ocean that extends from low tide to the edge
of the continental shelf
ocean upwelling rising of deep ocean waters that occurs when prevailing winds blow along surface waters near a coastline
oceanic zone part of the ocean that begins offshore where the water measures 200 m deep or deeper
pelagic realm (also, pelagic zone) open ocean waters that are not close
to the bottom or near the shore
photic zone portion of the ocean that light can penetrate
planktivore animal species that eats plankton
predator animal species that hunt and are carnivores or “flesh eaters”
thermocline layer of water with a temperature that is significantly
different from that of the surrounding layers
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