Frequently asked questions related to the recent mangrove assessment

  • What are mangroves and why should we worry about the loss of them?

  • Mangroves are tidal forests commonly found along sheltered coastlines in the tropics and subtropics. They protect the coast against erosion due to wind, waves and water currents and protect coral reefs, seagrass beds and shipping lanes against siltation. Mangroves also host a number of different animal species - including endangered mammals, reptiles, amphibians and birds - offer nutrients to the marine food web and provide spawning grounds to a variety of fish and shellfish, including several commercial species. Mangrove deforestation threatens the survival of these species and contributes to land erosion and salinization of coastal soils.

    Mangroves are also a source of a vast range of wood and non-wood forest products including timber, fuelwood, charcoal, fodder, honey, medicine and thatch. In many developing countries, coastal communities rely on mangrove forests to provide fuelwood for cooking as well as protein in the form of fish and shellfish. It represents a vital resource for their daily subsistence.

    High population pressure in coastal areas has, however, led to the conversion of many mangrove areas to other uses, including infrastructure, aquaculture, rice and salt production.

  • What¿s the purpose of the study?

  • Despite the existence of numerous case studies describing mangrove losses over time, scarce information exists on status and trends in mangrove areas at the global level. The primary purpose of this initiative is to facilitate access to this information by policy-makers, planners and mangrove managers worldwide.

  • What was the methodology used to determine these estimates?

  • The majority of the recent figures were provided by countries as part of the Forest Resource Assessment (FRA 2000). An extensive literature search and requests for information sent to the networks and individual specialists worldwide yielded additional information on both current and past extent. An initial screening of results included weeding out duplicates, discarding rough "guesstimates"and selecting just one estimate for those years where more than one was available. This was followed by regression analyses (best fit of linear, polynomial, logarithmic and power curves) of existing reliable data over time which provided estimates for 1990 and 1980 and an extrapolated estimate for 2000 for each country.

    Where insufficient information was available for the trend analysis, i.e. only one estimate within the last 30 years (less than 1 percent of the total mangrove area), the area was assumed to have remain constant unless qualitative information indicated otherwise.

    Where recent information was unavailable (about 3.5 percent of the total mangrove area), the extrapolation to Year 2000 was based on the overall forest change rate as reported in the Global Forest Resources Assessment 2000 (FAO 2001) applied to the latest reliable estimate.

  • What definition has FAO used for this study?

  • FAO has used the definitions used in the individual assessments. So the definition differs from country to country and from assessment to assessment within individual countries. However, mangroves form a very distinct forest type and the definitions employed only varied to a minor degree.

  • How reliable are the estimates?

  • As with all analyses, the results depend on the quality of the inputs. In this particular case, the majority of the most recent figures were provided by the countries as part of FRA 2000. As regards the trend analysis, changes in definitions and methodologies between assessments and surveys make it difficult to compare results over time.

    The new estimates provided by this study for 1980 and 1990 and the most recent reliable estimate for 1992 (area weighted average year) are presumed to be the best available in that they are primarily based on information from inventories and aerial surveys. The extrapolation to Year 2000 is, by nature, less reliable - particularly where few or no recent assessment results were available. This estimate is thus only indicative and likely to change as and when results from ongoing and future assessments become available.

  • How do the results compare with previous studies?

  • The results indicate that previous estimates of the total mangrove area made in the early 1980s (including the global estimate provided by FAO/UNEP as part of FRA 1980) were too low (primarily due to the limited number of countries included), whereas those made in the 1990s were too high.

  • Which countries have the largest deforestation rates?

  • In absolute terms, the highest rates of deforestation in the 1980s were found in Brazil, Indonesia, Pakistan, Australia and Mexico. This is not surprising since these countries are among those with the largest areas of mangroves. The same countries (except for Pakistan which has been replaced by Papua New Guinea) top the list of countries with the largest losses of mangroves in the 1990s, although the rates have diminished substantially in most of these.

    In relative terms, countries with high deforestation rates include Singapore, Benin, Dominica, Brazil and Côte d¿Ivoire in the 1980s and Côte d¿Ivoire, Honduras, China, Congo and Barbados in the 1990s.

    Conversely, a number of countries have registered a positive change over time, including Bangladesh, where the largest mangrove area (The Sundarbans Reserved Forest) is well protected and substantive and successful efforts have been made in coastal afforestation, particularly on land formed by accretion. Kuwait also registers a positive trend as mangroves have been planted as an introduced species. For other countries, an apparent positive trend may be due to changes in methodology or definition or due to the discovery of new mangroves areas not previously included (e.g. United Arab Emirates).

    The relatively large mangrove deforestation rates in Asia, the Caribbean and Latin America in the 1980s reflect large scale conversion of mangroves for aquaculture and tourism infrastructure. Most countries have now banned the conversion of mangroves for aquaculture purposes and require environmental impact assessments prior to large-scale conversion of mangroves areas for other uses.

  • Deforestation is one thing, but what about degradation of the mangroves?

  • The study did not provide information on the rate of mangrove degradation due to the lack of comprehensive and comparable data.

  • To what extent have countries been involved and the figures validated?

  • All countries were asked to provide information on current forest area according to forest types for FRA 2000, using their own classification system. Since mangroves form a distinct and relatively easy forest type to define, most countries which have mangroves provided specific information on their extent. The list of the most recent estimate is mostly based on this information.

    A broad literature search and requests for information sent to mangrove networks and individual specialists worldwide yielded additional information, particularly on past estimates. More than 2 800 national and subnational datasets have been collected so far, covering 121 countries and areas where mangroves are known to exist, with the earliest estimates dating back to 1918 and the 1920s. The information has been analysed with the assistance of mangrove experts throughout the world, in many cases including government officials. (A list of people contacted for individual countries is available in one of the Working Papers in press.) However, the full data set has not been sent to all countries for validation, but will be included as part of the documentation for the next interim Global forest resources assessment to be released in 2005.

  • Can I access and use the original data?

  • The database containing all the original data and the source of these will soon be accessible on our Web site and in printed form, including detailed information on the analysis undertaken by FAO, facilitating the analysis of the primary data by others.

    For more details on the change rate over time, please refer to FAO, in press. Status and trends in mangrove area extent worldwide. By Wilkie, M.L. and Fortuna, S. Forest Resources Assessment Working Paper No. 63. Forest Resources Division. FAO, Rome. (Unpublished)

    In addition, the most recent, reliable estimate by country presented on this Web site is updated as and when new information becomes available, and may thus also differ from the figures provided in SOFO 2003.

  • How often will the information be updated and when will the next assessment take place?

  • The information in the database will be continuously updated in terms of the most recent, reliable estimate by country. A revised estimate for 2000 based on new information will be released in 2005 and again in 2010. We actively encourage countries, organizations and individuals to send us their information in order to make the data base as complete as possible.

  • Why do some of the figures on this Web site differ from those provided in the State of the World¿s Forests 2003?

  • Whereas the area figures for 1980, 1990 and 2000 and the area changes over time in the tables on this Web site are identical to those presented in the State of the World¿s Forest (SOFO) 2003, the figures for the average annual change in percentage differ for some countries. In SOFO 2003, the annual changes in mangrove areas for the two decades 1980-1990 and 1990-2000 were presented as the average annual change in percentage of the 1980 and 1990 mangrove area respectively [(Area2000/Area1990 -1)*100/10].

    To facilitate comparison with the relative changes in overall forest cover in individual countries - as reported for example in the Global Forest Resources Assessment 2000 - the compound rate of change for each decade [((Area 2000/Area 1990)^0.1-1)*100] has been employed for the tables on this Web site, resulting in slightly higher relative figures for some countries.

    Both the absolute and the relative change figures are averages for the decade and do not capture variations in these rates within the period. For more details on the change rate over time, please refer to FAO, in press. Status and trends in mangrove area extent worldwide. By Wilkie, M.L. and Fortuna, S. Forest Resources Assessment Working Paper No. 63. Forest Resources Division. FAO, Rome. (Unpublished) In addition, since each country estimate on this Web site is updated as and when new information becomes available, information may differ from the figures provided in SOFO 2003.

  • How is this information going to make a change / What next?

  • In addition to providing evidence of the continued high rate of deforestation in mangroves, compared to the average deforestation rate for all forest types combined, the database gives an indication of which countries have the highest rate of deforestation in relative and absolute terms and thus which countries might be of a high priority for support by FAO and others. It also shows where information is lacking and efforts should be made to obtain more recent and reliable area estimates. We will be liaising closely with individual countries to assist them in obtaining more recent and reliable information through our programme on national forest assessments. This provides assistance and capacity building to individual countries and offers any technical assistance they may need in mangrove conservation, rehabilitation, management and sustainable use, building on our vast experience in this field, which includes more than 60 field projects in 35 different countries over the last 30 years.

  • What else is FAO doing on mangroves?

  • FAO's activities related to mangroves commenced in the 1950s and can be grouped according to the main activities of the Organization as a whole:

    • The collection, analysis and dissemination of information related to mangroves; development of awareness raising material, guidelines and case studies on best practices in mangrove conservation, management and sustainable utilization;

    • Provision of a neutral forum for technical and policy discussions including support to the international dialogue on forests and promotion of international cooperation;

    • Provision of technical and policy advice to governments on conservation and sustainable utilization of mangrove ecosystems and their resources;

    • Institutional strengthening and capacity building - including direct development assistance via an extensive field programme (more than 60 mangrove-related mangrove projects in 35 different countries over the last 30 years).

    last updated:  Thursday, May 19, 2005