Mangrove Changes Research Articles

Impacts of mangrove management systems on mangrove changes in the Northern Coast of Vietnam

Impacts of mangrove management systems on mangrove changes in the Northern Coast of Vietnam

COMMUNITY BASED ANALYSIS ON MANGROVE FOREST CHANGES IN REMBANG DISTRICT, CENTRAL JAVA PROVINCE

Mangrove forest is widely known as valuable resources, which provide goods and services as well as its function to protect coastal area from coastal erosion and promote sedimentation. This study aims to investigate community perspective towards dynamic change of mangrove forest due to coastline change. The research highlights two observations, i.e 1) coastline detection using visual interpretation; 2) community observation towards mangrove forest. Semi-structured questionnaire was applied to analyze the influence of mangrove forest changes to community as well as their adjustment. A proportional random sampling protocol was performed to determine 81 respondents from the village of Pasarbanggi, Tasikharjo and Tunggulsari. The research reveals that the research area exposes to coastline change, which induces mangrove forest dynamic. The dynamic mangrove forest influences local adaptation strategies, and it corresponds to government intervention within mangroves program. Pasarbanggi Village, which received various programs, both from government and other parties, combined with active participation of local people in establishing mangrove, has a stable increase of mangroves area between periods without significant disturbances compared to Tasikharjo Village and Tunggulsari Village. In line with this situation, respondents have different response toward the changes of mangrove forest in their area. Respondents response toward mangrove forest changes correlates to their participation in government mangroves program. Respondents in Pasarbanggi Village are apparently more benefited by the changes of mangroves forest including the direct and indirect benefit from the forest, as well as from mangroves program, compared to another respondent in Tasikharjo Village and Tunggulsari Village.

Contribution of L-band SAR to systematic global mangrove monitoring

Information on the status of and changes in mangroves is required for national and international policy development, implementation and evaluation. To support these requirements, a component of the Japan Aerospace Exploration Agency’s (JAXA) Kyoto and Carbon (K&C) initiative has been to design and develop capability for a Global Mangrove Watch (GMW) that routinely monitors and reports on local to global changes in the extent of mangroves, primarily on the basis of observations by Japanese L-band synthetic aperture radar (SAR). The GMW aims are as follows: (1) to map progression of change within or from existing (e.g. Landsat-derived) global baselines of the extent of mangroves by comparing advanced land-observing satellite 2 (ALOS-2) phased array L-band SAR 2 (PALSAR-2) data from 2014 with that acquired by the Japanese earth resources satellite (JERS-1) SAR (1992–1998) and ALOS PALSAR (2006–2011); (2) to quantify changes in the structure and associated losses and gains of carbon on the basis of canopy height and above-ground biomass (AGB) estimated from the shuttle radar topographic mission (SRTM; acquired 2000), the ice, cloud and land-elevation satellite (ICESAT) geoscience laser altimeter system (GLAS; 2003–2010) and L-band backscatter data; (3) to determine likely losses and gains of tree species diversity through reference to International Union for the Conservation of Nature (IUCN) global thematic layers on the distribution of mangrove species; and (4) to validate maps of changes in the extent of mangroves, primarily through comparison with dense time-series of Landsat sensor data and to use these same data to describe the causes and consequences of change. The paper outlines and justifies the techniques being implemented and the role that the GMW might play in supporting national and international policies that relate specifically to the long-term conservation of mangrove ecosystems and the services they provide to society.

Variability in mangrove change estimates and implications for the assessment of ecosystem service provision

AbstractAimTo quantify the variability in estimates of change in mangrove area for key countries throughout the tropics, and to highlight potential implications for the assessment of global mangrove ecology, function and conservation.LocationPan‐tropical, covering 15 countries, and accounting for c. 67% of global mangrove area.MethodsWe review 314 national mangrove area estimates (authoritative statements with defined time periods) from various sources. Linear regression models of mangrove area over time were applied to various data point combinations, defined by data source. These included various FAO resources, as well as academic and government statistics and remote sensing studies.ResultsNational trends of change in mangrove area exhibited high variability depending on which data points were modelled. Many countries showed high variability in deforestation rate when the results of all models were combined, e.g. Indonesia had an average deforestation rate of 331.65 (± 222.26) km2 yr−1, Nigeria lost 92.09 (± 188.95) km2 yr−1 and Cuba lost 34.82 (± 142.17) km2 yr−1. The standard deviations were large due to high variability in national estimates, and hence the number of contradictory trends that could be extracted. Conflicting trends of long‐term mangrove loss and gain could be derived for eight of the 15 countries analysed, including Indonesia, Brazil and the Philippines.Main conclusionsThe great variability in trends of mangrove extent suggests that estimates of ecosystem functional loss, biodiversity threat assessments and science‐based conservation policies will be hampered by low confidence in mangrove area dynamics. Variable and inaccurate baseline data feed into various estimates of biodiversity and ecosystem functional loss, such as IUCN Red List assessments and estimates of global carbon emissions from mangrove deforestation. We also require robust information to inform conservation actions and policies hoping to reduce functional loss. Variability has important implications for all ecosystems where statistics are required over large scales.

Assessment of the land use/land cover (LU/LC) and mangrove changes along the Mandovi–Zuari estuarine complex of Goa, India

Land-use/ Land cover change dynamics along the estuarine complex of Mandovi - Zuari in the coastal state of Goa, India is studied by the application of multi-temporal remote sensing data. This tropical estuarine region has faced significant changes in the last few decades due to diverse pressures from various sectors, mainly of anthropogenic origin. Spatial and temporal changes in the LU/LC classes have been evaluated using satellite datasets from Landsat MSS, TM and IRS-LISS III for the years 1973, 1989, 2001 and 2011. Considering a spectrally heterogeneous landscape of the region, the LU/LC changes are identified by using Principal Component Analysis (PCA) as a pre-classification step, followed by the implementation of a combination of supervised and unsupervised classification called Hybrid Classification. The application of PCA has proved to be suitable to successfully identify discrete land surface classes for this study area. An overall accuracy of 95.56% (kappa = 0.9556), 92.93% (kappa = 0.92), 84.64% (Kappa=0.85) and 86.36% (Kappa=0.85) has been obtained for the year 2011, 2001, 1989 and 1973 respectively. The study reveals a gradual increase in built-up area due to urbanization corresponding to a decrease in agricultural land and a considerable loss in beach area. Changes in the mangroves are also assessed within this extent as Goa has significant pockets of mangroves which are located mainly along the estuarine complexes of Mandovi and Zuari (along with the Cumbarjua canal complex). The results highlight an increase in mangrove coverage within the study extent by 1585.8 ha from 1973 to 2011. The mangrove areal extent along Mandovi has increased from 149.45 ha to 1059.77 ha and from 142.95 ha to 676.12 ha along Zuari (including Cumbarjua canal). Increasing awareness and the steps taken by the forest department to provide suitable environment for the growth of mangroves are the main reasons for this increment.

RGB-NDVI color composites for monitoring the change in mangrove area at the Maubesi Nature Reserve, Indonesia

The Maubesi Nature Reserve (MNR) is a protected lowland area in eastern Indonesia that mainly consists of mangrove forest. The objective of this paper was to demonstrate a simple technique to visualize and quantify the change in mangrove area using a 3-year dataset of Landsat TM images acquired in 1989, 2003 and 2009. The normalized difference vegetation index (NDVI) was calculated to determine high and low vegetation biomass in each image. Each NDVI extracted by Landsat image in 1989, 2003 and 2009 was assigned to red, green and blue (RGB) color, respectively, and then combined to make color composites. Additive color theory was applied to interpret mangrove changes within the MNR area on the RGB-NDVI color composite. Changed areas were quantified by performing an unsupervised classification on the RGB-NDVI image with 45 classes that were grouped into eight major mangrove change categories. An Indonesian land cover map was used to assess the accuracy of the classified image. The result showed that 77.13% of the MNR area was unchanged and 22.87% of the MNR area changed over 20 years (1989–2009).

Multi-Decadal Mangrove Forest Change Detection and Prediction in Honduras, Central America, with Landsat Imagery and a Markov Chain Model

Mangrove forests play an important role in providing ecological and socioeconomic services for human society. Coastal development, which converts mangrove forests to other land uses, has often ignored the services that mangrove may provide, leading to irreversible environmental degradation. Monitoring the spatiotemporal distribution of mangrove forests is thus critical for natural resources management of mangrove ecosystems. This study investigates spatiotemporal changes in Honduran mangrove forests using Landsat imagery during the periods 1985–1996, 1996–2002, and 2002–2013. The future trend of mangrove forest changes was projected by a Markov chain model to support decision-making for coastal management. The remote sensing data were processed through three main steps: (1) data pre-processing to correct geometric errors between the Landsat imageries and to perform reflectance normalization; (2) image classification with the unsupervised Otsu’s method and change detection; and (3) mangrove change projection using a Markov chain model. Validation of the unsupervised Otsu’s method was made by comparing the classification results with the ground reference data in 2002, which yielded satisfactory agreement with an overall accuracy of 91.1% and Kappa coefficient of 0.82. When examining mangrove changes from 1985 to 2013, approximately 11.9% of the mangrove forests were transformed to other land uses, especially shrimp farming, while little effort (3.9%) was applied for mangrove rehabilitation during this 28-year period. Changes in the extent of mangrove forests were further projected until 2020, indicating that the area of mangrove forests could be continuously reduced by 1,200 ha from 2013 (approximately 36,700 ha) to 2020 (approximately 35,500 ha). Institutional interventions should be taken for sustainable management of mangrove ecosystems in this coastal region.

Comparing Mangrove Forest Management in Hai Phong City, Vietnam towards Sustainable Aquaculture

This study examined the driving forces of mangrove change and compared mangrove forest management mechanisms in coastal districts in Hai Phong city, Vietnam. Survey data was used to ascertain the driving forces of mangrove change. The market price approach was used to analyze how local people responded to mangrove forest conservation. The results indicated that implementation of mangrove management instigated by the authorities, community or local people has affected mangrove change. The main driving factor of mangrove degradation in Hai Phong was over expansion of shrimp aquaculture. In Trang Cat commune, Hai An district, the average size of shrimp ponds where expansion was controlled by the local people, was 12.81 hectares. This number was over 53 times higher than in Bang La commune, Do Son district, which was mainly converted from salt ponds. Extensive aquaculture in the former case was the main method of farming which provides low net benefits while the improved shrimp culture in the latter case brings higher net benefits. Mangrove plantation programs funded by the Japanese organizations helped the poor guarantee their lives in Bang La. In Trang Cat, the poorer households would like to participate in mangrove conservation more than richer families. Nevertheless, the upper and rich families in Bang La engaged in mangrove plantation programs did more extensively than the middle and the poor did. Mangrove rehabilitation programs in Bang La have been successfully conducted on account of community-based forest management in cooperation with local authorities. The failure to convert shrimp ponds from mangrove forests was clearly recorded in Trang Cat. This commune needed to replant mangrove in abandoned shrimp ponds and follow the mangrove management mechanism in Bang La.

Mapping changes in the largest continuous Amazonian mangrove belt using object-based classification of multisensor satellite imagery

Mapping and monitoring mangrove ecosystems is a crucial objective for tropical countries, particularly where human disturbance occurs and because of uncertainties associated with sea level and climatic fluctuation. In many tropical regions, such efforts have focused largely on the use of optical data despite low capture rates because of persistent cloud cover. Recognizing the ability of Synthetic Aperture Radar (SAR) for providing cloud-free observations, this study investigated the use of JERS-1 SAR and ALOS PALSAR data, acquired in 1996 and 2008 respectively, for mapping the extent of mangroves along the Brazilian coastline, from east of the Amazon River mouth, Pará State, to the Bay of São José in Maranhão. For each year, an object-orientated classification of major land covers (mangrove, secondary vegetation, gallery and swamp forest, open water, intermittent lakes and bare areas) was performed with the resulting maps then compared to quantify change. Comparison with available ground truth data indicated a general accuracy in the 2008 image classification of all land covers of 96% (kappa = 90.6%, tau = 92.6%). Over the 12 year period, the area of mangrove increased by 718.6 km2 from 6705 m2 to 7423.60 km2, with 1931.0 km² of expansion and 1213 km² of erosion noted; 5493 km² remained unchanged in extent. The general accuracy relating to changes in mangroves was 83.3% (Kappa 66.1%; tau 66.7%). The study confirmed that these mangroves constituted the largest continuous belt globally and were experiencing significant change because of the dynamic coastal environment and the influence of sedimentation from the Amazon River along the shoreline. The study recommends continued observations using combinations of SAR and optical data to establish trends in mangrove distributions and implications for provision of ecosystem services (e.g., fish/invertebrate nurseries, carbon storage and coastal protection).

Does spatial scale affect the pattern of mangrove change under different rainfall regimes? An example in southeast Queensland, Australia

AbstractThe aim of this study was to investigate the interactions of natural and anthropogenic variables at different spatial scales related to changes in mangrove distribution during a relatively wet period (1972–1990) and a dry period (1991–2004) in subtropical eastern Australia. Previous research has demonstrated that mangroves are encroaching into salt marsh. Mangrove spatial change in southeast Queensland is related generally to landscape variables especially during the relatively wet period. What has not been explored is the spatial scale of the influence under the two rainfall regimes (wet and dry) and that is the aim of this paper. Ten sites were examined at different levels of resolution including catchment, sub‐catchment and two buffer zones (1000 and 500 m), under the period of relatively higher and lower rainfall. Land use was ascertained from Landsat satellite imagery using Maximum Likelihood Classification techniques. Partial least squares regression analysis was used to study the relationships between the predictor variables and the rate of change in the mangrove distribution. The research has found that the impact of land use/cover on the encroachment of mangrove into saltmarsh can vary and appears to be related to rainfall patterns, which in turn affect hydrological connectivity. A major finding of this research was that the changing spatial patterns of mangroves during the wet period was more a function of land use/cover pattern and population density at the sub‐catchment level, whereas during drier periods it was more affected by the local effects of nearby land use/cover in buffer zones.

Mapping of mangrove forest land cover change along the Kenya coastline using Landsat imagery

Mangroves in Kenya provide a wide range of valuable services to coastal communities despite their relatively small total area. Studies at single sites show reductions in extent and quality caused by extraction for fuel wood and timber and clearance for alternative land use including saltpans, aquaculture, and tourism. Such studies suggest that Kenyan mangroves are likely to conform to the general global trend of declining area but there are no reliable recent estimates of either total mangrove extent or trends in coverage for the country. The total extent of Kenyan mangroves was estimated at four points in time (1985, 1992, 2000 and 2010) using Landsat satellite imagery. Due to its medium resolution, Landsat may underestimate mangrove areas in Kenya where relatively small, linear, coastal features occur. There is also a high frequency of clouds in the coastal areas which can cause data gaps during analysis. However comparison with aerial photographs taken in 1992 showed satisfactory levels of accuracy (87.5%) and Cohen’s Kappa (0.54) validating its use in this context. These 1992 data provided an independently validated baseline from which to detect changes (fore- and hind-casted) in other periods after removing cloud coverage. We estimated total mangrove coverage in 2010 at 45,590 ha representing a loss of 18% (0.7% yr−1) in the 25 years between 1985 and 2010. Rates of mangrove loss for Kenya varied both spatially and temporally with variations possibly due to legislative inadequacies and differences in habitat alteration patterns. Hence freely available Landsat images proved adequate to detect changes in mangroves and revealed that Kenya shows rates of decline similar to (although slower than) global estimates.

Assessing forest products usage and local residents' perception of environmental changes in peri-urban and rural mangroves of Cameroon, Central Africa

BackgroundDeforestation is one of the most ubiquitous forms of land degradation worldwide. Although remote sensing and aerial photographs can supply valuable information on land/use cover changes, they may not regularly be available for some tropical coasts (e.g., Cameroon estuary) where cloud cover is frequent. With respect to mangroves, researchers are now employing local knowledge as an alternative means of understanding forest disturbances. This paper was primarily aimed at assessing the mangrove forest products usage, along with the local people's perceptions on environmental changes, between Littoral (Cameroon estuary) and Southern (mouth of the Nyong River and Mpalla village) regions of Cameroon.MethodsThe data from both locations were obtained through conducting household interviews and field observations.ResultsIn the Cameroon estuary (Littoral region), 69.23% of respondents (mostly elders) could distinguish two to four mangrove plants, whereas the informants (65.45%) in the mouth of the Nyong River and Mpalla village (mostly young people interviewed from the Southern region) are familiar with only one or two commonly found mangroves. Also, more respondents from the Cameroon estuary are depending on mangroves for fuelwood (Rhizophora spp.) and housing (Rhizophora spp., Avicennia germinans (L.) Stearn and Nypa fruticans (Thumb.) Wurmb.) purposes, in contrast to Nyong River mouth and Mpalla village. Although local people perceived wood extraction as a greater disruptive factor, there are several causes for mangrove depletion in the Cameroon estuary. Among others, over-harvesting, clear-felled corridors, sand extraction and housing were found important. Furthermore, a decline in mangrove fauna composition (in terms of fishery products) was recorded in the Littoral as well as Southern regions. However, the causes of such perceived negative changes were not similar in both cases.ConclusionsFindings of this study highlight the need to improve sustainable management of the mangrove ecosystems through afforestation (in large impacted areas), selective removal of senescent tree stems and branches (in little damage stands), regulating sand extraction and housing activities, and creating awareness and law enforcement.

Geoinformatics in mangrove monitoring: damage and recovery after the 2004 Indian Ocean tsunami in Phang Nga, Thailand

Abstract. In the aftermath of the 2004 Indian Ocean Tsunami, it has been proven that mangrove ecosystems provide protection against coastal disasters by acting as bioshields. Satellite data have been effectively used to detect, assess, and monitor the changes in mangroves during the pre- and post- tsunami periods. However, not much information regarding mangrove restoration or reforestation is available. Rather than undertaking time-consuming fieldwork, this study proposed using geoinformatic technologies such as Remote Sensing (RS), Geographic Information System (GIS), and Global Positioning System (GPS) to monitor the mangrove recovery. The analysis focused only on the tsunami-impacted mangrove areas along the western coast of the Tai Muang, Takuapa and Khuraburi Districts of Phang Nga Province, southern region of Thailand. The results consisted of 2 parts, first: the supervised classification of main land uses, namely forest, mangrove, agricultural land, built-up area, bare soil, water body, and miscellaneous covers in ASTER images, was conducted using the maximum likelihood method with higher than 75 % for overall accuracy. Once the confusion between classes was improved in post-processing, the accuracy of mangrove class was greater than 85 % for all dates. The results showed that the mangrove area in 2005 was reduced by approximately 5 % (1054.5 ha) from 2003 due to the impact of the 2004 Indian Ocean Tsunami. Although the recovery program (replacing the same species of dead mangrove trees, mainly the Rhizophora apiculata Bl and Rhizophora mucronata Poir, in situ) had started by mid-2005, the areas gradually decreased to approximately 7–8 % in 2006 and 2010 compared with the reference year of 2003. Second, the recovery trend was observed in the Normalized Difference Vegetation Index (NDVI) fluctuation curve and the supporting field survey data. The recovery patterns were summarized into 2 categories: (i) gradually recovery, and (ii) fluctuating recovery. The gradually recovery category that implied the homogeneous pattern or uniform reforestation was observed in the seriously damaged area where most of the mangrove trees were swept away during the tsunami. This pattern covered approximately 50.35 % of the total reforested area. The NDVI time series of the uniform or homogeneous reforested mangrove at the sampled plots has gradually increased after 2005. The fluctuating recovery category that implied the heterogeneous pattern or non-uniform reforestation was observed in partially damaged areas where some of the mangrove trees were swept away and broken but still some trees were remained in the area. The heterogeneous patterns covered approximately 49.65 % of the total reforested area.

Changes in coastal wetland habitats in Careel Bay, Pittwater, N.S.W., from 1940 to 1996

Between 1940 and 1996 the saltmarsh habitats of Careel Bay were significantly reduced in size, while the mangrove habitat of the bay expanded, in both a landward direction, encroaching upon the saltmarsh habitats, and a seaward direction. This is one of many examples of mangrove incursion upon saltmarsh habitats along the New South Wales coastline. Natural and anthropogenic influences upon Careel Bay were examined in an effort to determine possible causes. Patterns of change in regional sea level, sedimentation and increase freshwater delivery were found to coincide with the mangrove and saltmarsh changes, partly due to influences of the urbanization of the catchment.

Assessing the extent of mangrove change caused by Cyclone Vance in the eastern Exmouth Gulf, northwestern Australia

Changes in mangal area were quantified in the eastern Exmouth Gulf over six years (1999–2004) after Cyclone Vance using Landsat TM satellite imagery and aerial photography. Vance was the strongest tropical cyclone ever to impact the Australian mainland before 2006 and produced wind gusts of more than 280 km h −1. Image data were processed using ENVI™ and IDRISI™ software. Three sets of Landsat TM images from 1999 (a few days before the cyclone), 2002 and 2004 were used, along with 2004 digital aerial photography. A ‘common’ subset of 904 km 2 was selected from all images and classification was developed using ISODATA™ unsupervised classification to identify spectrally distinct areas followed by principal component analysis (PCA), vegetation indices and supervised classification. Some 12,800 ha of mangrove habitat was present before the cyclone and approximately 5700 ha (44%) was removed by it. Most mangroves lost (74%) between 1999 and 2004 were converted either to bare sediment or to live saltmarshes and this occurred mostly between 1999 and 2002. Five basic categories of damage were conspicuous from imagery and field observations, and evidence suggests that much of the loss was due to the longer term consequences of sediment deposition or smothering, rather than the immediate effects of wind or waves. Mangroves exhibited accelerated recovery between 2002 and 2004, and around 1580 ha regenerated during this time, amounting to a return of 68% of their former coverage. At this recovery rate we estimate that they should have returned to their pre-cyclone area by 2009. Over half of the saltmarsh habitats (54%) were removed by the cyclone (4060 ha) but their recovery has been far more rapid than mangroves. After 5 years, saltmarshes had returned to 87% of their previous area. The 5700 ha of mangrove habitat damaged by Cyclone Vance exceeds any anthropogenic impact that has ever taken place in Western Australia by several orders of magnitude.

Natural and anthropogenic changes to mangrove distributions in the Pioneer River Estuary (QLD, Australia)

We analyzed a time series of aerial photographs and Landsat satellite imagery of the Pioneer River Estuary (near Mackay, Queensland, Australia) to document both natural and anthropogenic changes in the area of mangroves available to filter river runoff between 1948 and 2002. Over 54 years, there was a net loss of 137 ha (22%) of tidal mangroves during four successive periods that were characterized by different driving mechanisms: (1) little net change (1948–1962); (2) net gain from rapid mangrove expansion (1962–1972); (3) net loss from clearing and tidal isolation (1972–1991); and (4) net loss from a severe species-specific dieback affecting over 50% of remaining mangrove cover (1991–2002). Manual digitization of aerial photographs was accurate for mapping changes in the boundaries of mangrove distributions, but this technique underestimated the total loss due to dieback. Regions of mangrove dieback were identified and mapped more accurately and efficiently after applying the Normalized Difference Vegetation Index (NDVI) to Landsat Thematic Mapper satellite imagery, and then monitoring changes to the index over time. These remote sensing techniques to map and monitor mangrove changes are important for identifying habitat degradation, both spatially and temporally, in order to prioritize restoration for management of estuarine and adjacent marine ecosystems.

Coastal Ecosystems and Tsunami Protection after the December 2004 Indian Ocean Tsunami

An exploratory study was conducted on the role of coastal ecosystems in protecting communities from the December 2004 Indian Ocean tsunami, focusing on mangrove forests on the Andaman coast of Thailand and how well villages were undertaking environmental conservation. Remote sensing analysis identified predisaster mangrove change and postdisaster structural damage and landscape changes. Field data from five sites (20 villages), gathered via the VIEWS™ data collection system, validated and supplemented this analysis. Key informants at several of these villages were also interviewed. A preliminary comparison of villages that otherwise faced similar tsunami exposure suggests that the presence of healthy mangroves did afford substantial protection. Village performance in mangrove conservation and management efforts, and thus the presence of healthy forests, is influenced by both social capital and the design of external aid delivery programs.

Mangrove Forest Cover Change in the Bangladesh Sundarbans from 1989-2000: A Remote Sensing Approach

This paper quantifies mangrove forest cover change in the Sundarbans of southwest Bangladesh from 1989 to 2000 using Landsat Thematic Mapper satellite imagery. We used three image processing techniques: normalized differential vegetation index (NDVI), maximum likelihood classification, and subpixel classification. We compared change detection results using the three image processing methods. Traditional classifiers, such as maximum likelihood algorithms, do not reveal the true nature of this mixed water‐forest environment. Both NDVI and subpixel classification revealed similar spatial distributions of areas that were deforested from 1989 to 2000. These areas are in the southeastern comer and the western edge of the Bangladesh Sundarbans.

Planning Strategies for Mangrove and Saltmarsh Changes in Southeast Australia

Estuarine habitats of southeast Australia have been undergoing changes characterized by a reduction of saltmarsh and an increase of mangroves. Incorporated into these changes have been mangrove migration into saltmarsh areas, thus contributing to the latter's decline. At the same time, rapid and extensive change in the catchments of many estuaries has occurred as a result of urban and rural development. It has been estimated that the changes observed between mangrove and saltmarsh wetland vegetation is caused by a series of processes, including urbanization and increased population pressure, increased rainfall, increased nutrients, mangroves recolonizing previously cleared areas, engineering works and subsequent altered tidal patterns, sea-level rise, and subsidence of intertidal flats. Planning strategies are suggested that can be implemented in an integrated manner to mitigate the threats from these processes and to ensure the sustainable management of mangrove and saltmarsh wetlands.

GIS-based integration of interdisciplinary ecological data to detect land-cover changes in creek mangroves at Gazi Bay, Kenya

5 Laboratory of Forest Management and Spatial Information Techniques, Universiteit Gent, Coupure 653, B-9000 Gent, Belgium /ha) and complexity indices (1.86 and 1.12) at Makongeni and Kinondo 1, respectively, reflected intense human pressure in these areas. Areas that were easily accessible or close to human settlements appeared more vulnerable. Accrued information from a socioeconomic survey carried out over the same period corroborates the hypothesis that human influence was a major contributor to these changes. Historic aerial photographs together with satellite imagery indicate less than 20% decrease in coverage of R. mucronata between 1965 and 1992, but an increase of almost 35% in sand cover over the same period. The approach that was used in this study, one largely unprecedented in the East African region, was useful in drawing the conclusion that human influence was the most probable trigger of the observed changes.