Behara Satyanarayana

Assessment of mangrove vegetation based on remote sensing and ground-truth measurements at Tumpat, Kelantan Delta, East Coast of Peninsular Malaysia

The lower reaches of River Kelantan form a vast delta (1200 ha) consisting of bay, mangrove and estuary on the northeast coast of Peninsular Malaysia. The present study was conducted to assess the mangrove vegetation at Tumpat based on ground-truth and remote sensing measurements. The mangroves are composed of several species including Nypa fruticans, Sonneratia caseolaris, Avicennia alba, Rhizophora apiculata, R. mucronata and Bruguiera gymnorrhiza, in order of dominance. The point-centred quarter method (PCQM) was used to estimate the stem density (number of stems/0.1 ha) and basal area (m2/0.1 ha) at selected sites on the ground. Recent high-resolution multispectral satellite data (QuickBird 2006, 2.4 m spatial resolution of the multispectral image) were used to produce land-use/cover classification and Normalized Differential Vegetation Index (NDVI) mapping for the delta. The area statistics reveal that mangroves occupy 339.6 ha, while coconut plantation dominates the vegetation (715.2 ha), followed by settlements (621.6 ha), sandbar (148.4 ha), agriculture (89 ha) and aquaculture (42.7 ha). Although the relationship between the spectral indices and dendrometric parameters was weak, we found a very high significance between the (mean) NDVI and stem density (p = 1.3 × 10−8). The sites with young/growing and also mature trees with lush green cover showed greater NDVI values (0.40–0.68) indicating healthy vegetation, while mature forests under environmental stress due to sand deposition and/or poor tidal inundation showed low NDVI values (0.38–0.47) and an unhealthy situation. Overall, a combination of ground survey and remote sensing provided valuable information for the assessment of mangrove vegetation types (i.e. young/growing or mature forest) and their health in Tumpat, Kelantan Delta.

Is Matang Mangrove Forest in Malaysia Sustainably Rejuvenating after More than a Century of Conservation and Harvesting Management

Matang Mangrove Forest Reserve (MMFR) in Peninsular Malaysia is under systematic management since 1902 and still considered as the best managed mangrove forest in the world. The present study on silvimetrics assessed the ongoing MMFR forest management, which includes a first thinning after 15 years, a second thinning after 20 years and clear-felling of 30-year old forest blocks, for its efficiency and productivity in comparison to natural mangroves. The estimated tree structural parameters (e.g. density, frequency) from three different-aged mangrove blocks of fifteen (MF15), twenty (MF20), and thirty (MF30) years old indicated that Bruguiera and Excoecaria spp. did not constitute a significant proportion of the vegetation (<5%), and hence the results focused majorly on Rhizophora apiculata. The density of R. apiculata at MF15, MF20 and MF30 was 4,331, 2,753 and 1,767 stems ha−1, respectively. In relation to ongoing practices of the artificial thinnings at MMFR, the present study suggests that the first thinning could be made earlier to limit the loss of exploitable wood due to natural thinning. In fact, the initial density at MF15 was expected to drop down from 6,726 to 1,858 trees ha−1 before the first thinning. Therefore the trees likely to qualify for natural thinning, though having a smaller stem diameter, should be exploited for domestic/commercial purposes at an earlier stage. The clear-felling block (MF30) with a maximum stem diameter of 30 cm was estimated to yield 372 t ha−1 of the above-ground biomass and suggests that the mangrove management based on a 30-year rotation is appropriate for the MMFR. Since Matang is the only iconic site that practicing sustainable wood production, it could be an exemplary to other mangrove locations for their improved management.

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 peoples 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.

Mangrove species distribution and abundance in relation to local environmental settings: a case-study at Tumpat, Kelantan Delta, east coast of peninsular Malaysia.

We studied mangrove vegetation at Tumpat to estimate different tree structural parameters (e.g., stem density and basal area) at selected sites (PCQ method). There were five dominant taxa in the vegetation, i.e., Sonneratia caseolaris, Nypa fruticans, Avicennia alba, Rhizophora mucronata, and Bruguiera gymnorrhiza in order of importance. Total tree density varied between 79 and 132 stems 0.1 ha -1 , and basal area from 0.14 to 4.9 m 2 0.1 ha -1 . Based on species composition and stem density, the mangrove sites were separable into two groups (Bray-Curtis similarity: 60%). While Group-1 (sites G9, J5, K4, N6 and O4), dominated by S. caseolaris and N. fruticans, was distributed throughout the forest, Group-2 (sites C6 and G6), represented largely by A. alba, was present close to the bay-mangrove boundary. Elevation measurements indicate that Group-1 species occupied low-lying to elevated grounds (0.87–2.23 m above mean sea level) with a (mean) salinity between 0.38 and 14.6 psu, whereas Group2 occurred preferentially at low to medium elevations (0.86–1.29 m) and high salinity (14.6 psu). Discrete mangrove associations (sgroupings) were discerned, wherein the distribution of species was governed by factors such as proximity of land or sea, freshwater input and elevation.

Variations of chlorophyll-a in the northeastern Indian Ocean after the 2004 South Asian tsunami

Analysis of satellite remote sensing data has revealed changes in distribution of chlorophyll-a (Chl-a) and sea surface temperature (SST) in the Indian Ocean during the South Asian tsunami in December 2004. Chl-a data derived from Moderate Resolution Imaging Spectroradiometer (MODIS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) images were examined for the period from 1998 to 2005. Around the epicentre of the Sumatra earthquake, the Chl-a concentration was found to increase prior to the main event on 26 December 2004 and then decrease during the tsunami event, while a high SST (∼30–31°C) was observed in and around the epicentral region. Chl-a concentrations in the coastal waters of the Southeast Asian countries were remarkably low during and after the tsunami. Similar but relatively small variations in Chl-a and SST were observed during the second earthquake on 28 March 2005. Analysis of Chl-a, SST, wind and upwelling water has provided information for understanding the changes in Chl-a concentration during the tsunami. A very large offshore phytoplankton bloom (∼300 km2) appeared to the southeast of Sri Lanka about 3 weeks after the tsunami; this might have been caused by a tropical storm that could be responsible for the enhancement of nutrients.

Multivariate methods distinguishing mangrove community structure of Coringa in the Godavari Delta, East coast of India

Multivariate analysis (PRIMER) based on mangrove tree density and basal area measurements in Coringa, a Bay-Mangrove ecosystem in the Indian sub-continent, revealed 6 different floristic groups. While Group-1 and Group 2 characterized by a combination of Sonneratia apetala and S. caseolari-Avicennia alba, reflected conditions typical of low-lying swamps, Group-3, consisting of Xylocarpus mekongensis, Rhizophora mucronata, R. apiculata and Bruguiera gymnorrhiza, was found close to the sea where high saline conditions prevailed. Group-4 species, Avicennia marina, A. officinalis and Excoecaria agallocha, represented widespread distribution and were found almost everywhere within Coringa. Group-5 consisted of Lumnitzera racemosa, Ceriops decandra and Aegiceras corniculatum which occurred at sites not very far from the influence of Gautami-Godavari estuary, suggestive of their preference to low salinity regimes. Finally, Group-6 typically represented by Bruguiera cylindrica was seen interiorally at sites under the direct influence of Bay waters. Delineation of sample sites and species records based on extensive field data will be invaluable for appropriate management (e.g. plantation) and conservation measures for Coringa.

The final spawning ground of Tachypleus gigas (Müller, 1785) on the east Peninsular Malaysia is at risk: a call for action.

Tanjung Selongor and Pantai Balok (State Pahang) are the only two places known for spawning activity of the Malaysian horseshoe crab - Tachypleus gigas (Müller, 1785) on the east coast of Peninsular Malaysia. While the former beach has been disturbed by several anthropogenic activities that ultimately brought an end to the spawning activity of T. gigas, the status of the latter remains uncertain. In the present study, the spawning behavior of T. gigas at Pantai Balok (Sites I-III) was observed over a period of thirty six months, in three phases, between 2009 and 2013. Every year, the crab’s nesting activity was found to be high during Southwest monsoon (May–September) followed by Northeast (November–March) and Inter monsoon (April and October) periods. In the meantime, the number of female T. gigas in 2009–2010 (Phase-1) was higher (38 crabs) than in 2010–2011 (Phase-2: 7 crabs) and 2012–2013 (Phase-3: 9 crabs) for which both increased overexploitation (for edible and fishmeal preparations) as well as anthropogenic disturbances in the vicinity (sand mining since 2009, land reclamation for wave breaker/parking lot constructions in 2011 and fishing jetty construction in 2013) are responsible. In this context, the physical infrastructure developments have altered the sediment close to nesting sites to be dominated by fine sand (2.5Xφ ) with moderately-well sorted (0.6–0.7σφ), very-coarse skewed (−2.4SKφ), and extremely leptokurtic (12.6Kφ) properties. Also, increased concentrations of Cadmium (from 4.2 to 13.6 mg kg−1) and Selenium (from 11.5 to 23.3 mg kg−1) in the sediment, and Sulphide (from 21 to 28 µg l−1) in the water were observed. In relation to the monsoonal changes affecting sheltered beach topography and sediment flux, the spawning crabs have shown a seasonal nest shifting behaviour in-between Sites I-III during 2009–2011. However, in 2012–2013, the crabs were mostly restricted to the areas (i.e., Sites I and II) with high oxygen (5.5–8.0 mg l−1) and moisture depth (6.2–10.2 cm). In view of the sustained anthropogenic pressure on the coastal habitats on one hand and decreasing horseshoe crabs population on the other, it is crucial to implement both conservation and management measures for T. gigas at Pantai Balok. Failing that may lead to the loss of this final spawning ground on the east coast of P. Malaysia.

Status of the undisturbed mangroves at Brunei Bay, East Malaysia: a preliminary assessment based on remote sensing and ground-truth observations

Brunei Bay, which receives freshwater discharge from four major rivers, namely Limbang, Sundar, Weston and Menumbok, hosts a luxuriant mangrove cover in East Malaysia. However, this relatively undisturbed mangrove forest has been less scientifically explored, especially in terms of vegetation structure, ecosystem services and functioning, and land-use/cover changes. In the present study, mangrove areal extent together with species composition and distribution at the four notified estuaries was evaluated through remote sensing (Advanced Land Observation Satellite—ALOS) and ground-truth (Point-Centred Quarter Method—PCQM) observations. As of 2010, the total mangrove cover was found to be ca. 35,183.74 ha, of which Weston and Menumbok occupied more than two-folds (58%), followed by Sundar (27%) and Limbang (15%). The medium resolution ALOS data were efficient for mapping dominant mangrove species such as Nypa fruticans, Rhizophora apiculata, Sonneratia caseolaris, S. alba and Xylocarpus granatum in the vicinity (accuracy: 80%). The PCQM estimates found a higher basal area at Limbang and Menumbok—suggestive of more mature vegetation, compared to Sundar and Weston. Mangrove stand structural complexity (derived from the complexity index) was also high in the order of Limbang > Menumbok > Sundar > Weston and supporting the perspective of less/undisturbed vegetation at two former locations. Both remote sensing and ground-truth observations have complementarily represented the distribution of Sonneratia spp. as pioneer vegetation at shallow river mouths, N. fruticans in the areas of strong freshwater discharge, R. apiculata in the areas of strong neritic incursion and X. granatum at interior/elevated grounds. The results from this study would be able to serve as strong baseline data for future mangrove investigations at Brunei Bay, including for monitoring and management purposes locally at present.

The advantages of using drones over space-borne imagery in the mapping of mangrove forests

Satellite data and aerial photos have proved to be useful in efficient conservation and management of mangrove ecosystems. However, there have been only very few attempts to demonstrate the ability of drone images, and none so far to observe vegetation (species-level) mapping. The present study compares the utility of drone images (DJI-Phantom-2 with SJ4000 RGB and IR cameras, spatial resolution: 5cm) and satellite images (Pleiades-1B, spatial resolution: 50cm) for mangrove mapping—specifically in terms of image quality, efficiency and classification accuracy, at the Setiu Wetland in Malaysia. Both object- and pixel-based classification approaches were tested (QGIS v.2.12.3 with Orfeo Toolbox). The object-based classification (using a manual rule-set algorithm) of drone imagery with dominant land-cover features (i.e. water, land, Avicennia alba, Nypa fruticans, Rhizophora apiculata and Casuarina equisetifolia) provided the highest accuracy (overall accuracy (OA): 94.0±0.5% and specific producer accuracy (SPA): 97.0±9.3%) as compared to the Pleiades imagery (OA: 72.2±2.7% and SPA: 51.9±22.7%). In addition, the pixel-based classification (using a maximum likelihood algorithm) of drone imagery provided better accuracy (OA: 90.0±1.9% and SPA: 87.2±5.1%) compared to the Pleiades (OA: 82.8±3.5% and SPA: 80.4±14.3%). Nevertheless, the drone provided higher temporal resolution images, even on cloudy days, an exceptional benefit when working in a humid tropical climate. In terms of the user-costs, drone costs are much higher, but this becomes advantageous over satellite data for long-term monitoring of a small area. Due to the large data size of the drone imagery, its processing time was about ten times greater than that of the satellite image, and varied according to the various image processing techniques employed (in pixel-based classification, drone >50 hours, Pleiades <5 hours), constituting the main disadvantage of UAV remote sensing. However, the mangrove mapping based on the drone aerial photos provided unprecedented results for Setiu, and was proven to be a viable alternative to satellite-based monitoring/management of these ecosystems. The improvements of drone technology will help to make drone use even more competitive in the future.

Variations in mangrove regeneration rates under different management plans: An analysis of Landsat time-series in the Matang Mangrove Forest Reserve, Peninsular Malaysia

The Matang Mangrove Forest Reserve (MMFR) has been under silvicultural management using a 30-year rotation cycle since 1902. Whereas two artificial thinnings in 15 and 20-year-old stands yield mangrove poles, the clear-felled greenwood from 30-year-old stands is used for charcoal production. Although the reserve appears to be (economically) sustainable in terms of wood production, there is insufficient information on mangrove regeneration and growth dynamics within the MMFR to confirm this. In the present study, we investigate changes in mangrove regeneration rates after clear-felling by analysing a Landsat time-series (1986–2016) using the BFAST algorithm. We created an image-stack from 1986 to 2016 and calculated different vegetation indices (e.g. NDVI) for each image. Based on the vegetation indices, we could identify the clear-felling activities and observe different trends in the mangrove regeneration rate. We will further analyse the time series using the trend and seasonal components of the BFAST algorithm.