Changes in global mangrove distributions
Encyclopedia
Global mangrove
distributions have fluctuated throughout human and geological
history. The area covered by mangroves is influenced by a complex interaction between land position, rain
fall hydrology
, sea level
, sedimentation
, subsidence
, storms and pest-predator relationships). In the last 50 years, human activities have strongly affected mangrove distributions, resulting in declines or expansions of worldwide mangrove area. Mangroves provide several important ‘free services’ including coast
al stabilization, juvenile fish habitats, and the filtration of sediment and nutrients ). Mangrove loss has important implications for coastal ecological
systems and human communities dependent on healthy mangrove ecosystems. This Wikipedia
page presents an overview of global Mangrove Forest
biome
trends in mangrove ecoregions distribution, as well as the cause of such changes.
Percentage of original area lost per year
(based on data from ) (Annual loss rates calculated from the mean number of years between original area and present area for each region: 24, 25, 7, 11, and 17
years for Asia, Africa, Australia, the Americas, and the world, respectively.)
The present annual rate of loss is estimated at just over 2% per year. The most recent and comprehensive global assessment of mangrove distribution was conducted by the Food and Agriculture Organization of the United Nations (FAO
) which assessed trends from 1980 to 2005. In the 1980s and 1990s the greatest amount of loss occurred, while in the period of 2000 to 2005 the rate has fallen significantly across all regions. Some projections estimate that worldwide mangrove area will decline by a further 25% by 2025, particularly in developing nations.
of mangrove ecosystems has been instrumental in the loss of mangroves. Commonly, they have been undervalued and considered ‘wastelands’ with low productivity
. Concerns for the fate of mangroves have historically been restricted to scientific communities
, with little transfer of knowledge to local
communities and governments. Mangroves are a common pool resource
, creating difficulties in enforcing restrictions on exploitative activities.
More recently, perceptions have shifted to a broader acknowledgment within communities and governments of the value of mangroves in coastal ecosystems and local communities. The declining rate of mangrove loss since 2000 across all regions is indicative of this, bringing forth an increasing number of conservation
projects and legislation
Fig xxxx. (Refer to conservation section)
. Mangrove losses to climate change are considered a probable long term threat to future distributions. Despite a wide variety of factors linked to mangrove loss (insert figure of causes), the main drivers of recent (i.e. after 1980) mangrove destruction are linked to four main activities: urban sprawl
, tourism
, agriculture
and aquaculture
. The causes of declines in mangrove areas vary between regions. In Asia
, the Caribbean
and Latin America
, aquaculture and tourism development are the greatest threat. In Oceania
, tourism development is the greatest threat while in Africa
, conversion of mangroves for agricultural and urban development is most apparent.
Urban expansion – As population density increases at the coast, areas of mangrove forest have been replaced to provide urban and industrial
lands.
Tourism – infrastructure supporting tourism often requires the reclamation of substantial tracts of mangrove forests. In the Americas and Oceania, tourism is a major driver of mangrove loss. Where tourism is a main contributor to an economy
(such as Pacific Island nations), construction of resort
s and related infrastructure
s have reduced mangrove area in past decades.
Agriculture – Conversion of mangrove forests for agriculture has occurred across all regions historically, freeing up land for activities such as rice or salt
production (.
Aquaculture – This activity is considered the greatest contributor to worldwide mangrove loss. Since the 1980s, shrimp
aquaculture dramatically increased, replacing mangroves with ponds and degrading surrounding areas with associated pollution ( Aquaculture has dramatically affected some regions. For example, 50-80% of mangroves were lost in Asia in the past decades. Asia, the Caribbean and Latin America have been most affected by aquaculture
energy and short canal
lengths to the coast. Consequently, vast tracts of mangrove forest have been replaced by numerous ponds. Compounding mangrove losses is the short life span of individual ponds (5–10 years), imposing a shifting cultivation
pattern to shrimp farming.
After 1980, shrimp farming became far more intensive
, with high productivity (per unit area) ponds proliferating across the landscape. Dramatic reductions in mangrove forests were reported with shrimp pond intensification. In Thailand
, mangrove forests literally halved between 1975-1993 The impact of such losses has been linked to the disruption of ecological
and economic functioning of mangroves. For example, loss of income for local Thai fisherman has been reported due to reduced catches from the degradation of juvenile
fish habitat.
Some consider that the number of shrimp farms in South-east Asia peaked in the late 1990s, with the rate of mangrove loss declining accordingly. This decline is in part due to increased conservation
and restoration
projects, and improved management
practices.
related threat to mangrove regions. The natural ability of mangroves to ‘keep up’ with rising sea level
through peat
or sediment
accumulation could be exceeded, leading to mangrove die back.Low island
mangroves are most at risk, as demonstrated in Bermuda
, where sea level rise has exceeded peat accumulation rates periodically, resulting in landward die back of mangrove stands. Climate change may reduce global mangrove area by 10-15%, but it is a long term, less significance threat to the current 1-2% annual loss from human activities.
programmes. Globally, this stability and expansion is far outweighed by the magnitude of mangrove loss from human activities.
;. Mangroves naturally encourage sediment
deposition by slowing currents
and attenuating waves. However, with high sediment
inputs, the elevation of inter-tidal flats can rise above the low tide limit of the original mangrove forest, resulting in a seaward expansion of new mangrove habitat
. Once new mangroves establish, they too begin to trap more sediment, raising the tidal flat elevation and generating more mangrove habitat. Seaward expansions are likely in regions with modified catchments (i.e. deforestation or urban development) with high topography where high sediments loads are delivered to mangroves at the coast. Extremely high rates of sediment input can exceed tolerance thresholds
and induce mangrove die backs. Excess sedimentation is the primary control, but nutrients (i.e. from agricultural runoff) can enhance mangrove expansion, particularly when combined with high levels of sedimentation
. Seaward expansions highlight the interconnectivity of mangrove ecosystems to adjacent catchments and the need to consider catchment alteration when managing mangroves.
(NZ), temperate
mangroves (Avicennia marina) are common in estuaries, harbours and tidal creeks north of 38° latitude. Following European colonization, mangrove area declined, but since the 1970s rapid, ongoing seaward expansion has occurred in many areas. For example in the last 50 years mangrove area has expanded 120% in Tuaranga Harbour. Such expansion is strongly correlated with elevated rates of sediment deposition. Catchment
activities such as deforestation
and more recently, urban development have been blamed for the expansion.
Considerable debate over whether to protect or remove NZ mangroves exist. Proponents for protection cite the ecological and coastal protection values of mangrove stands, while removal advocates aim to restore recreational values and prevent encroachment into non-mangrove ecosystems. A shift in the management strategy of regional councils from protection to mangrove ‘management’ has occurred recently Removals may take place when human amenities or non-mangrove habitats are deemed threatened by mangrove encroachment. Some researchers caution comparisons being made between NZ and tropical mangroves, suggesting NZ mangroves are unique in their ecology and require a tailored management
approach.
expansions are documented in a number of regions (Thailand
, Australia, and Hawaii
). The cause of landward expansions is not always clear. In Eastern Australia expansions have replaced salt marshes with various suggestions for the cause of landward expansion (increased rainfall, changes in hydrology, to local subsidence). Expansions in Hawaii are thought to be the result of invasions by exotic
mangrove species.
has undertaken extensive coastal afforesation (mass plantings) projects since 1966, leading to an increase in mangrove area in recent decades; 2005;. Many nations with mangroves have signed on to the 1971 Ramsar Convention
on wetlands in the last two decades, making a commitment to wetland
preservation. However, the adoption of protective legislation
is not evenly spread. For instance, community initiatives to protect mangroves are common in Africa but little legislation exists compared to other regions, such as Asia.
, as well as a largely universal acknowledgement amongst communities and governments of the ecological and economic values. Despite this awareness, global mangrove area continues to decline through human activities. A lack of communication between biologists, effected residents, and governments could partly account for this. Calls have been made for greater collaboration
between international researchers and residents of affected nations.
Efforts to assess changes in worldwide mangrove distribution have been hindered by a lack of long term data, or limited to no data at all for some nations. Without accurate data on distributions, an accurate forecast of mangrove loss or expansion becomes problematic. This in turn may hinder the progress of conservation
projects.
Despite large volumes of scientific literature
on mangroves, many uncertainties still exist. These include how mangroves will response to increases in greenhouse gases and sea level, sustainable yields for silviculture, the difference in ecological functioning between tropical and temperate
species, and why within the same species we get seaward and landward expansions. Obtaining this knowledge will help nations to better predict future mangrove behavior, and administer appropriate management
policies.
Mangrove ecoregions
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
distributions have fluctuated throughout human and geological
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
history. The area covered by mangroves is influenced by a complex interaction between land position, rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
fall hydrology
Hydrology
Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...
, sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
, sedimentation
Sedimentation
Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...
, subsidence
Subsidence
Subsidence is the motion of a surface as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation...
, storms and pest-predator relationships). In the last 50 years, human activities have strongly affected mangrove distributions, resulting in declines or expansions of worldwide mangrove area. Mangroves provide several important ‘free services’ including coast
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...
al stabilization, juvenile fish habitats, and the filtration of sediment and nutrients ). Mangrove loss has important implications for coastal ecological
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
systems and human communities dependent on healthy mangrove ecosystems. This Wikipedia
Wikipedia
Wikipedia is a free, web-based, collaborative, multilingual encyclopedia project supported by the non-profit Wikimedia Foundation. Its 20 million articles have been written collaboratively by volunteers around the world. Almost all of its articles can be edited by anyone with access to the site,...
page presents an overview of global Mangrove Forest
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
biome
Biome
Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a...
trends in mangrove ecoregions distribution, as well as the cause of such changes.
Global trends
In the last 5 decades, worldwide mangrove area has fallen across all regions. Different data sources or survey methods make estimates more problematic, as many nations have high variations of mangrove change.Percentage of original area lost per year
- Asia: 1.52%
- Africa: 1.25%
- Australia: 1.99%
- Americas: 3.62%
- The World: 2.07%
(based on data from ) (Annual loss rates calculated from the mean number of years between original area and present area for each region: 24, 25, 7, 11, and 17
years for Asia, Africa, Australia, the Americas, and the world, respectively.)
The present annual rate of loss is estimated at just over 2% per year. The most recent and comprehensive global assessment of mangrove distribution was conducted by the Food and Agriculture Organization of the United Nations (FAO
Fão
Fão is a town in Esposende Municipality in Portugal....
) which assessed trends from 1980 to 2005. In the 1980s and 1990s the greatest amount of loss occurred, while in the period of 2000 to 2005 the rate has fallen significantly across all regions. Some projections estimate that worldwide mangrove area will decline by a further 25% by 2025, particularly in developing nations.
The role of perception
People’s perceptionPerception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
of mangrove ecosystems has been instrumental in the loss of mangroves. Commonly, they have been undervalued and considered ‘wastelands’ with low productivity
Productivity
Productivity is a measure of the efficiency of production. Productivity is a ratio of what is produced to what is required to produce it. Usually this ratio is in the form of an average, expressing the total output divided by the total input...
. Concerns for the fate of mangroves have historically been restricted to scientific communities
Scientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...
, with little transfer of knowledge to local
Local
Local usually refers to something nearby, or in the immediate area.It may be used in many ways, some of which are related to this general meaning, others which are not:* Local, local anesthesia* Local, a.k.a. union local or local union* Local, a.k.a...
communities and governments. Mangroves are a common pool resource
Common-pool resource
In economics, a common-pool resource , also called a common property resource, is a type of good consisting of a natural or human-made resource system , whose size or characteristics makes it costly, but not impossible, to exclude potential beneficiaries from obtaining benefits from its use...
, creating difficulties in enforcing restrictions on exploitative activities.
More recently, perceptions have shifted to a broader acknowledgment within communities and governments of the value of mangroves in coastal ecosystems and local communities. The declining rate of mangrove loss since 2000 across all regions is indicative of this, bringing forth an increasing number of conservation
Conservation biology
Conservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction...
projects and legislation
Legislation
Legislation is law which has been promulgated by a legislature or other governing body, or the process of making it...
Fig xxxx. (Refer to conservation section)
Causes of decline
A variety of factors have led to the declining trends in mangrove distribution (refer to table fig of causes). These factors are predominantly anthropogenic in origin, as mangrove destruction is positively correlated to human population density. Up to 35% of mangrove forests worldwide have been lost since 1980, reflecting the increased pressure from high population densities residing at the coastCoast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...
. Mangrove losses to climate change are considered a probable long term threat to future distributions. Despite a wide variety of factors linked to mangrove loss (insert figure of causes), the main drivers of recent (i.e. after 1980) mangrove destruction are linked to four main activities: urban sprawl
Urban sprawl
Urban sprawl, also known as suburban sprawl, is a multifaceted concept, which includes the spreading outwards of a city and its suburbs to its outskirts to low-density and auto-dependent development on rural land, high segregation of uses Urban sprawl, also known as suburban sprawl, is a...
, tourism
Tourism
Tourism is travel for recreational, leisure or business purposes. The World Tourism Organization defines tourists as people "traveling to and staying in places outside their usual environment for not more than one consecutive year for leisure, business and other purposes".Tourism has become a...
, agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
and aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
. The causes of declines in mangrove areas vary between regions. In Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, the Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
and Latin America
Latin America
Latin America is a region of the Americas where Romance languages – particularly Spanish and Portuguese, and variably French – are primarily spoken. Latin America has an area of approximately 21,069,500 km² , almost 3.9% of the Earth's surface or 14.1% of its land surface area...
, aquaculture and tourism development are the greatest threat. In Oceania
Oceania
Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...
, tourism development is the greatest threat while in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, conversion of mangroves for agricultural and urban development is most apparent.
Urban expansion – As population density increases at the coast, areas of mangrove forest have been replaced to provide urban and industrial
Industry
Industry refers to the production of an economic good or service within an economy.-Industrial sectors:There are four key industrial economic sectors: the primary sector, largely raw material extraction industries such as mining and farming; the secondary sector, involving refining, construction,...
lands.
Tourism – infrastructure supporting tourism often requires the reclamation of substantial tracts of mangrove forests. In the Americas and Oceania, tourism is a major driver of mangrove loss. Where tourism is a main contributor to an economy
Economy
An economy consists of the economic system of a country or other area; the labor, capital and land resources; and the manufacturing, trade, distribution, and consumption of goods and services of that area...
(such as Pacific Island nations), construction of resort
Resort
A resort is a place used for relaxation or recreation, attracting visitors for holidays or vacations. Resorts are places, towns or sometimes commercial establishment operated by a single company....
s and related infrastructure
Infrastructure
Infrastructure is basic physical and organizational structures needed for the operation of a society or enterprise, or the services and facilities necessary for an economy to function...
s have reduced mangrove area in past decades.
Agriculture – Conversion of mangrove forests for agriculture has occurred across all regions historically, freeing up land for activities such as rice or salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
production (.
Aquaculture – This activity is considered the greatest contributor to worldwide mangrove loss. Since the 1980s, shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
aquaculture dramatically increased, replacing mangroves with ponds and degrading surrounding areas with associated pollution ( Aquaculture has dramatically affected some regions. For example, 50-80% of mangroves were lost in Asia in the past decades. Asia, the Caribbean and Latin America have been most affected by aquaculture
Mangrove loss case study: Shrimp aquaculture in South-east Asia
In many South-east Asian nations, shrimp aquaculture has been instrumental in mangrove loss, particularly in the 1980s and 1990s. Due to high economic returns, shrimp farming was promoted to improve economic conditions in many countries. The social and economic benefits of shrimp farming are substantial. Shrimp farms are located close to the coast to reduce costs by using tidalTide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
energy and short canal
Canal
Canals are man-made channels for water. There are two types of canal:#Waterways: navigable transportation canals used for carrying ships and boats shipping goods and conveying people, further subdivided into two kinds:...
lengths to the coast. Consequently, vast tracts of mangrove forest have been replaced by numerous ponds. Compounding mangrove losses is the short life span of individual ponds (5–10 years), imposing a shifting cultivation
Shifting cultivation
Shifting cultivation is an agricultural system in which plots of land are cultivated temporarily, then abandoned. This system often involves clearing of a piece of land followed by several years of wood harvesting or farming, until the soil loses fertility...
pattern to shrimp farming.
After 1980, shrimp farming became far more intensive
Intensive
In grammar, an intensive word form is one which denotes stronger or more forceful action relative to the root on which the intensive is built. Intensives are usually lexical formations, but there may be a regular process for forming intensives from a root...
, with high productivity (per unit area) ponds proliferating across the landscape. Dramatic reductions in mangrove forests were reported with shrimp pond intensification. In Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, mangrove forests literally halved between 1975-1993 The impact of such losses has been linked to the disruption of ecological
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
and economic functioning of mangroves. For example, loss of income for local Thai fisherman has been reported due to reduced catches from the degradation of juvenile
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
fish habitat.
Some consider that the number of shrimp farms in South-east Asia peaked in the late 1990s, with the rate of mangrove loss declining accordingly. This decline is in part due to increased conservation
Conservation biology
Conservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction...
and restoration
Restoration ecology
-Definition:Restoration ecology is the scientific study and practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human intervention and action, within a short time frame...
projects, and improved management
Management
Management in all business and organizational activities is the act of getting people together to accomplish desired goals and objectives using available resources efficiently and effectively...
practices.
Global climate change and mangrove loss
Increases in temperature, CO2, precipitation, storms, and sea level are likely to threaten mangroves in the future. Sea level rise is considered the greatest climate changeClimate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
related threat to mangrove regions. The natural ability of mangroves to ‘keep up’ with rising sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
through peat
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...
or sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
accumulation could be exceeded, leading to mangrove die back.Low island
Low island
A low island is, in geology , an island of coral origin. The term applies whether the island was formed as a result of sedimentation upon a coral reef or of the uplifting of such islands...
mangroves are most at risk, as demonstrated in Bermuda
Bermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...
, where sea level rise has exceeded peat accumulation rates periodically, resulting in landward die back of mangrove stands. Climate change may reduce global mangrove area by 10-15%, but it is a long term, less significance threat to the current 1-2% annual loss from human activities.
Global trends
Several nations have experienced an expansion of their mangrove area. These expansions include human activities promoting seaward or landward expansion from climatic or other local factors, as well as conservation and reforestationReforestation
Reforestation is the natural or intentional restocking of existing forests and woodlands that have been depleted, usually through deforestation....
programmes. Globally, this stability and expansion is far outweighed by the magnitude of mangrove loss from human activities.
Seaward expansion and human activity
Seaward mangrove expansion is considered a natural response to high inputs of sediment and nutrients from human activity in adjacent catchmentsCatchment area (human geography)
In human geography, a catchment area is the area and population from which a city or individual service attracts visitors or customers. For example, a school catchment area is the geographic area from which students are eligible to attend a local school...
;. Mangroves naturally encourage sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
deposition by slowing currents
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
and attenuating waves. However, with high sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
inputs, the elevation of inter-tidal flats can rise above the low tide limit of the original mangrove forest, resulting in a seaward expansion of new mangrove habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
. Once new mangroves establish, they too begin to trap more sediment, raising the tidal flat elevation and generating more mangrove habitat. Seaward expansions are likely in regions with modified catchments (i.e. deforestation or urban development) with high topography where high sediments loads are delivered to mangroves at the coast. Extremely high rates of sediment input can exceed tolerance thresholds
Thresholds
Thresholds is the second full-length studio album from Florida death metal band Nocturnus. It was released in 1992 by Earache Records and follows the band's debut album The Key....
and induce mangrove die backs. Excess sedimentation is the primary control, but nutrients (i.e. from agricultural runoff) can enhance mangrove expansion, particularly when combined with high levels of sedimentation
Sedimentation
Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...
. Seaward expansions highlight the interconnectivity of mangrove ecosystems to adjacent catchments and the need to consider catchment alteration when managing mangroves.
Case study: New Zealand mangroves
In New ZealandNew Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
(NZ), temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
mangroves (Avicennia marina) are common in estuaries, harbours and tidal creeks north of 38° latitude. Following European colonization, mangrove area declined, but since the 1970s rapid, ongoing seaward expansion has occurred in many areas. For example in the last 50 years mangrove area has expanded 120% in Tuaranga Harbour. Such expansion is strongly correlated with elevated rates of sediment deposition. Catchment
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
activities such as deforestation
Deforestation
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....
and more recently, urban development have been blamed for the expansion.
Considerable debate over whether to protect or remove NZ mangroves exist. Proponents for protection cite the ecological and coastal protection values of mangrove stands, while removal advocates aim to restore recreational values and prevent encroachment into non-mangrove ecosystems. A shift in the management strategy of regional councils from protection to mangrove ‘management’ has occurred recently Removals may take place when human amenities or non-mangrove habitats are deemed threatened by mangrove encroachment. Some researchers caution comparisons being made between NZ and tropical mangroves, suggesting NZ mangroves are unique in their ecology and require a tailored management
Management
Management in all business and organizational activities is the act of getting people together to accomplish desired goals and objectives using available resources efficiently and effectively...
approach.
Landward Expansion
In contrast to seaward expansions in NZ, landwardLandward
Landward is a long-running television programme focusing on agricultural and rural issues, produced and broadcast by BBC Scotland. Until 2007, it aired on Sunday mornings in Scotland, replacing the similar show Countryfile which aired elsewhere in the UK; however in 2007 Landward moved to a regular...
expansions are documented in a number of regions (Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, Australia, and Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
). The cause of landward expansions is not always clear. In Eastern Australia expansions have replaced salt marshes with various suggestions for the cause of landward expansion (increased rainfall, changes in hydrology, to local subsidence). Expansions in Hawaii are thought to be the result of invasions by exotic
Exotic
Exotic can mean:*In mathematics:**Exotic R4 - differentiable manifold homeomorphic but not diffeomorphic to the Euclidean space R4**Exotic sphere - differentiable manifold homeomorphic but not diffeomorphic to the ordinary sphere*In physics:...
mangrove species.
Expansion through conservation and restoration
More recently, awareness of the economic, social, and ecological values of mangroves have led to an increase in the number of initiatives to protect and restore mangrove areas. Broader recognition of the connection of mangroves to coastal food chains, coastal protection and socio-economic welfare has driven recent conservation. For example, BangladeshBangladesh
Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...
has undertaken extensive coastal afforesation (mass plantings) projects since 1966, leading to an increase in mangrove area in recent decades; 2005;. Many nations with mangroves have signed on to the 1971 Ramsar Convention
Ramsar Convention
The Ramsar Convention is an international treaty for the conservation and sustainable utilization of wetlands, i.e., to stem the progressive encroachment on and loss of wetlands now and in the future, recognizing the fundamental ecological functions of wetlands and their economic, cultural,...
on wetlands in the last two decades, making a commitment to wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....
preservation. However, the adoption of protective legislation
Legislation
Legislation is law which has been promulgated by a legislature or other governing body, or the process of making it...
is not evenly spread. For instance, community initiatives to protect mangroves are common in Africa but little legislation exists compared to other regions, such as Asia.
Challenges, limitations and future suggestions
Much attention has been given to mangroves by the scientific communityScientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...
, as well as a largely universal acknowledgement amongst communities and governments of the ecological and economic values. Despite this awareness, global mangrove area continues to decline through human activities. A lack of communication between biologists, effected residents, and governments could partly account for this. Calls have been made for greater collaboration
Collaboration
Collaboration is working together to achieve a goal. It is a recursive process where two or more people or organizations work together to realize shared goals, — for example, an intriguing endeavor that is creative in nature—by sharing...
between international researchers and residents of affected nations.
Efforts to assess changes in worldwide mangrove distribution have been hindered by a lack of long term data, or limited to no data at all for some nations. Without accurate data on distributions, an accurate forecast of mangrove loss or expansion becomes problematic. This in turn may hinder the progress of conservation
Conservation biology
Conservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction...
projects.
Despite large volumes of scientific literature
Scientific literature
Scientific literature comprises scientific publications that report original empirical and theoretical work in the natural and social sciences, and within a scientific field is often abbreviated as the literature. Academic publishing is the process of placing the results of one's research into the...
on mangroves, many uncertainties still exist. These include how mangroves will response to increases in greenhouse gases and sea level, sustainable yields for silviculture, the difference in ecological functioning between tropical and temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
species, and why within the same species we get seaward and landward expansions. Obtaining this knowledge will help nations to better predict future mangrove behavior, and administer appropriate management
Management
Management in all business and organizational activities is the act of getting people together to accomplish desired goals and objectives using available resources efficiently and effectively...
policies.
Summary
Mangrove loss has been a worldwide trend for the last 50 years due primarily to anthropogenic activities that compete for land area. Expansions in mangrove area do occur, but have a limited ability to offset the extensive losses. Recently the rate of loss has been declining due to a greater awareness of mangrove values, with legislation and conservation projects becoming more commonplace. It can only be hoped that this declining rate of loss continues, allowing future generations to appreciate the many benefits of mangroves.See also
- MangroveMangroveMangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
- Mangrove Forest biome
Mangrove ecoregions
- Ecological values of mangroveEcological values of mangroveMangrove ecosystems represent natural capital capable of producing a wide range of goods and services for coastal environments and communities and society as a whole. Some of these outputs, such as timber, are freely exchanged in formal markets...
- Coastal biogeomorphologyCoastal biogeomorphologyOver the past two decades, biogeomorphology has developed as an established research field examining the interrelationship between organisms and geomorphic processes in a variety of environments, both marine, and terrestrial...
- Coastal erosionCoastal erosionCoastal erosion is the wearing away of land and the removal of beach or dune sediments by wave action, tidal currents, wave currents, or drainage...