Zonasi dan Struktur Komunitas Mangrove di Pesisir Kabupaten Merauke

Penelitian ini bertujuan untuk mengetahui zonasi dan struktur ekosistem mangrove di wilayah pesisir Kabupaten Merauke tepatnya di Pantai Payumb Distrik Merauke, Pantai Nasem Distrik Naukenjerai dan muara sungai Kumbe Distrik Semangga pada bulan Oktober 2015. Pantai Nasem dan Pantai Payumb dibagi menjadi 2 zona pengambilan sampling sedangkan stasiun muara Sungai Kumbe dibagi menjadi 3 zona. Ukuran transek 100-150m tegak lurus garis pantai dengan ukuran plot 10x10m2. Pada setiap plot sampling dilakukan perhitungan kerapatan jenis, frekuensi jenis dan indeks dominansi. Berdasarkan hasil penelitian diperoleh 15 jenis mangrove yang tersebar di ketiga stasiun yaitu Pantai Nasem 7 spesies, Pantai Payumb 9 spesies dan muara Sungai Kumbe 13 spesies. Vegetasi mangrove di kawasan penelitian disusun oleh 8 genus dan 15 jenis mangrove. Berdasarkan dominansi jenis vegetasi mangrove,   kondisi komunitas di stasiun Pantai Nasem dan Pantai Payumb termasuk dalam kriteria labil dengan tipe substrat berpasir dan dominansi genus Avicennia. Sebaliknya stasiun muara Sungai Kumbe memiliki kondisi komunitas vegetasi yang stabil dengan tipe substrat berlumpur dan dominansi genus Rhizophora. Zonasi ekosistem mangrove pada area pesisir Kabupaten Merauke terdiri dari dua tipe zonasi. Pada daerah pesisir yang berhadapan langsung dengan laut, genus Avicennia merupakan pioneer dalam membentuk zonasi vegetasi mengrove. Sebaliknya pada daerah sungai, genus Rhizophora menjadi pioneer membentuk zonasi pada kedua sisi badan sungai

Monitoring mangrove change using very high spatial resolution satellite images for coastal zone management

La situation des mangroves dans le monde reste préoccupante malgré la prise de conscience de leur rôle dans le maintien de la biodiversité côtière. Les pratiques non durables de l’aquaculture extensive sont toujours majoritairement mises en cause. Le besoin d’une meilleure gestion côtière se fait sentir depuis une vingtaine d’années. Il faut reconnaitre que les avancées restent insuffisantes, particulièrement en Indonésie. Ce travail de thèse a été réalisé dans le cadre du projet INDESO. Ses objectifs étaient de décrire les changements dans les mangroves en termes de superficie, de structuration ou de composition spécifique afin d’étudier, à fine échelle spatiale, la diversité des peuplements de palétuviers, leur capacité de régénération et les tendances d’évolution de l’écosystème. Pour cela, j’ai utilisé 28 images satellitaires de télédétection optique à très haute résolution spatiale (THRS) acquises dans la période de 2001 à 2015 sur deux sites d’étude, Bali, Indonésie. J’ai participé aux inventaires forestiers et à l’identification des espèces de palétuviers du stade plantule au stade adulte. J’ai procédé par analyse visuelle des images pour différencier les plantations de palétuviers des forêts naturelles. J’ai examiné les différences entre les signatures spectrales des différentes formations de palétuviers en fonction des configurations angulaires. J’ai réalisé sur chaque image une classification supervisée qui m’a permis de comptabiliser avec une précision de quelques mètres carrés la superficie occupée par les mangroves et d’évaluer la robustesse d’une cartographie à fine échelle de zonations de mangroves.Les résultats obtenus sur l’estuaire du Perancak dégradé par l’aquaculture montrent que la surface de mangrove augmente après 2001 mais que les pratiques de plantations dans cette région n’ont rien à voir avec la réhabilitation de mangroves. Des différences majeures entre plantations et forêts naturelles existent. Ces plantations sont des cultures à très forte densité de Rhizophora, alors que les faciès naturels sont dominés par Avicennia et Sonneratia. Nos résultats montrent que la capacité de régénération dans ces plantations reste très inférieure à celle observée dans les forêts naturelles et que, si régénération il y a, c’est avec des plantules des espèces natives. A partir de l’analyse des imges, nous avons identifié les 136 bassins qui ont fait l’objet de plantations et donné l’année du semis. Le suivi de l’évolution du nombre de pixels classés ‘mangrove’ à l’intérieur de chaque bassin planté montre une grande variabilité des taux d’expansion sur 14 ans, ceci suggérant des conditions environnementales spécifiques à chaque bassin et donc l’inconséquence des pratiques généralisées de plantations à Rhizophora. Enfin, les capacités de colonisation des espèces natives y compris à l’intérieur de certains bassins semblent avérées dans cet estuaire pourtant très fragmenté. Les résultats obtenus sur les mangroves protégées de la région de Nusa Lembongan montrent le potentiel des images multi-spectrales satellitaires THRS pour cartographier différentes zonations de mangroves. Ce potentiel de discrimination est observé assez stable au cours du temps entre 4 espèces. Toutefois, des configurations angulaires avec un soleil de face ou un angle de visée proche de la verticale pourraient générer de la confusion notamment sur les peuplements à canopée ouverte. Nous avons obtenu probablement les premières cartes de mangrove de Nusa Lembongan qui montrent la complexité des zonations forestières et soutiennent l’enjeu de leur protection.L’ensemble de mon travail plaide pour une meilleure interprétation physique de la variabilité des signatures spectrales et texturales de mangrove. Il fournit des recommandations comme la nécessité d’un moratoire sur les monocultures à Rhizophora et des méthodes simples, embryons de futurs observatoires locaux pour l’évaluation et le suivi des plans de gestion côtière mis en place.The situation of world’s mangroves remains a matter of concern, despite the public awareness about their role in the sustainability of coastal biodiversity. Extensive and intensive aquaculture practies are mainly called into question. The need for a better integrated coastal zone management arises since a couple of decades. It must be recognized that progress is insufficient especially in Indonesia.The present PhD work has been carried out in the frame of the INDESO project. The objective was to describe mangrove changes in terms of area expansion, forest structure and species composition before studying, at fine scales, the diversity of mangrove stands, their regeneration capacity and the evolution trends of the whole ecosystem in a given region.In order to achieve this aim, i used 28 very high spatial resolution (VHSR) optical satellite images aquired between 2001 and 2015. I also participated in forest inventories and species identification from the seedling to the adult stages. I visually analysed the set of images for allowing the discrimination of planted mangroves from natural ones. I examined the influence of acquisition geometry parameters on the variability of mangrove spectral signatures. Thanks to supervised maximum likelihood classifications, I succeeded in evaluating the expansion area of mangrove with an accurracy of few square meters and I proceeded in assessing the robustness of fine scale mapping of mangrove zonations.Results obtained in the analysis of the Perancak estuary highlighted that mangrove area is expanding since 2001. The plantation practices were however presented as disrespectful of any sustainable management plan. Indeed, our simple field data indicated strong differences between mangrove plantations and natural forests. Plantations were shown to be cultures of only Rhizophora species with high planting density whereas natural forest stands are composed of Sonneratia and Avicennia mangrove trees. In addition, we highlighted that the regeneration capacity in planted areas remains very lower than the ones clearly observed in natural areas. Moreover, the only regenetive process in plantations seems to be with native species and not with the planted ones. From the analysis of the VHSR images, we identified aquaculture ponds that were planted and their planting year. Consequently, we suceeded in monitoring the mangrove expansion inside every planted pond. Important variability of expansion rate was pointed out, this suggesting contrasting environments in each pond and the inadequacy of cultures of Rhizophora everywhere. The observation of natural colonization in many areas of the estuary, pond floors included, was an interesting point to mention.Besides, results obtained in the study of the protected mangrove region of Nusa Lembongan assessed the potential of multispectral VHSR satellite images for mapping mangrove zonations. Four mangrove zonations mainly dominated by different species exhibit signatures that can be differentiated over years. Different image acquisition parameters may, however, generate confusion in classification. This is particularyly true when forest stands with open canopies are observed with sun frontward or with a near vertical viewing angle because of sun light interaction with the clear waters. We probably obtained the first detailed maps of mangrove zonations in the region. They showed a complex spatial organization of mangrove zonations.The whole of my work advocated for further remote sensing works aiming at the physical interpretation of spectral and textural signatures of mangroves. It provided recommendations such as a moratorium onf Rhizophora plantation and simple methods that will be, we hope, starting points for closing the knowledge gap that hampers monitoring of future coastal zone management plans

Etude des mangroves à partir de l’analyse des changements dans les images de canopée à très haute résolution spatiale pour une meilleure gestion des côtes indonésiennes

The situation of world’s mangroves remains a matter of concern, despite the public awareness about their role in the sustainability of coastal biodiversity. Extensive and intensive aquaculture practies are mainly called into question. The need for a better integrated coastal zone management arises since a couple of decades. It must be recognized that progress is insufficient especially in Indonesia.The present PhD work has been carried out in the frame of the INDESO project. The objective was to describe mangrove changes in terms of area expansion, forest structure and species composition before studying, at fine scales, the diversity of mangrove stands, their regeneration capacity and the evolution trends of the whole ecosystem in a given region.In order to achieve this aim, i used 28 very high spatial resolution (VHSR) optical satellite images aquired between 2001 and 2015. I also participated in forest inventories and species identification from the seedling to the adult stages. I visually analysed the set of images for allowing the discrimination of planted mangroves from natural ones. I examined the influence of acquisition geometry parameters on the variability of mangrove spectral signatures. Thanks to supervised maximum likelihood classifications, I succeeded in evaluating the expansion area of mangrove with an accurracy of few square meters and I proceeded in assessing the robustness of fine scale mapping of mangrove zonations.Results obtained in the analysis of the Perancak estuary highlighted that mangrove area is expanding since 2001. The plantation practices were however presented as disrespectful of any sustainable management plan. Indeed, our simple field data indicated strong differences between mangrove plantations and natural forests. Plantations were shown to be cultures of only Rhizophora species with high planting density whereas natural forest stands are composed of Sonneratia and Avicennia mangrove trees. In addition, we highlighted that the regeneration capacity in planted areas remains very lower than the ones clearly observed in natural areas. Moreover, the only regenetive process in plantations seems to be with native species and not with the planted ones. From the analysis of the VHSR images, we identified aquaculture ponds that were planted and their planting year. Consequently, we suceeded in monitoring the mangrove expansion inside every planted pond. Important variability of expansion rate was pointed out, this suggesting contrasting environments in each pond and the inadequacy of cultures of Rhizophora everywhere. The observation of natural colonization in many areas of the estuary, pond floors included, was an interesting point to mention.Besides, results obtained in the study of the protected mangrove region of Nusa Lembongan assessed the potential of multispectral VHSR satellite images for mapping mangrove zonations. Four mangrove zonations mainly dominated by different species exhibit signatures that can be differentiated over years. Different image acquisition parameters may, however, generate confusion in classification. This is particularyly true when forest stands with open canopies are observed with sun frontward or with a near vertical viewing angle because of sun light interaction with the clear waters. We probably obtained the first detailed maps of mangrove zonations in the region. They showed a complex spatial organization of mangrove zonations.The whole of my work advocated for further remote sensing works aiming at the physical interpretation of spectral and textural signatures of mangroves. It provided recommendations such as a moratorium onf Rhizophora plantation and simple methods that will be, we hope, starting points for closing the knowledge gap that hampers monitoring of future coastal zone management plans.La situation des mangroves dans le monde reste préoccupante malgré la prise de conscience de leur rôle dans le maintien de la biodiversité côtière. Les pratiques non durables de l’aquaculture extensive sont toujours majoritairement mises en cause. Le besoin d’une meilleure gestion côtière se fait sentir depuis une vingtaine d’années. Il faut reconnaitre que les avancées restent insuffisantes, particulièrement en Indonésie. Ce travail de thèse a été réalisé dans le cadre du projet INDESO. Ses objectifs étaient de décrire les changements dans les mangroves en termes de superficie, de structuration ou de composition spécifique afin d’étudier, à fine échelle spatiale, la diversité des peuplements de palétuviers, leur capacité de régénération et les tendances d’évolution de l’écosystème. Pour cela, j’ai utilisé 28 images satellitaires de télédétection optique à très haute résolution spatiale (THRS) acquises dans la période de 2001 à 2015 sur deux sites d’étude, Bali, Indonésie. J’ai participé aux inventaires forestiers et à l’identification des espèces de palétuviers du stade plantule au stade adulte. J’ai procédé par analyse visuelle des images pour différencier les plantations de palétuviers des forêts naturelles. J’ai examiné les différences entre les signatures spectrales des différentes formations de palétuviers en fonction des configurations angulaires. J’ai réalisé sur chaque image une classification supervisée qui m’a permis de comptabiliser avec une précision de quelques mètres carrés la superficie occupée par les mangroves et d’évaluer la robustesse d’une cartographie à fine échelle de zonations de mangroves.Les résultats obtenus sur l’estuaire du Perancak dégradé par l’aquaculture montrent que la surface de mangrove augmente après 2001 mais que les pratiques de plantations dans cette région n’ont rien à voir avec la réhabilitation de mangroves. Des différences majeures entre plantations et forêts naturelles existent. Ces plantations sont des cultures à très forte densité de Rhizophora, alors que les faciès naturels sont dominés par Avicennia et Sonneratia. Nos résultats montrent que la capacité de régénération dans ces plantations reste très inférieure à celle observée dans les forêts naturelles et que, si régénération il y a, c’est avec des plantules des espèces natives. A partir de l’analyse des imges, nous avons identifié les 136 bassins qui ont fait l’objet de plantations et donné l’année du semis. Le suivi de l’évolution du nombre de pixels classés ‘mangrove’ à l’intérieur de chaque bassin planté montre une grande variabilité des taux d’expansion sur 14 ans, ceci suggérant des conditions environnementales spécifiques à chaque bassin et donc l’inconséquence des pratiques généralisées de plantations à Rhizophora. Enfin, les capacités de colonisation des espèces natives y compris à l’intérieur de certains bassins semblent avérées dans cet estuaire pourtant très fragmenté. Les résultats obtenus sur les mangroves protégées de la région de Nusa Lembongan montrent le potentiel des images multi-spectrales satellitaires THRS pour cartographier différentes zonations de mangroves. Ce potentiel de discrimination est observé assez stable au cours du temps entre 4 espèces. Toutefois, des configurations angulaires avec un soleil de face ou un angle de visée proche de la verticale pourraient générer de la confusion notamment sur les peuplements à canopée ouverte. Nous avons obtenu probablement les premières cartes de mangrove de Nusa Lembongan qui montrent la complexité des zonations forestières et soutiennent l’enjeu de leur protection.L’ensemble de mon travail plaide pour une meilleure interprétation physique de la variabilité des signatures spectrales et texturales de mangrove. Il fournit des recommandations comme la nécessité d’un moratoire sur les monocultures à Rhizophora et des méthodes simples, embryons de futurs observatoires locaux pour l’évaluation et le suivi des plans de gestion côtière mis en place

On the Fate of Floating Marine Debris Carried to the Sea through the Main Rivers of Indonesia

Plastic debris has become an acute marine pollution concern worldwide in modern times. Indonesia is particularly impacted because of its high population density, heavy rainfall rate and numerous coastlines. A Lagrangian analysis was performed to simulate the fate of fictive marine debris drifting along surface currents, including tides and Stokes drift. The fictive particles were released according to the discharge rate of 21 Indonesian rivers and advected over 4 years. Most of the particles were stranded along Indonesian coasts (60%), before 6 months had elapsed (84%) and within a range of 1000 km (76%). The time variability exhibited two seasonal peaks, one centered on January-February and one on June-July, consistent with in situ observations. However, the results underline the complexity of performing direct comparisons between in situ observations and numerical simulations for stranded waste due to limited measurements and the heterogeneity of field methods and protocols

On the Fate of Floating Marine Debris Carried to the Sea through the Main Rivers of Indonesia

Plastic debris has become an acute marine pollution concern worldwide in modern times. Indonesia is particularly impacted because of its high population density, heavy rainfall rate and numerous coastlines. A Lagrangian analysis was performed to simulate the fate of fictive marine debris drifting along surface currents, including tides and Stokes drift. The fictive particles were released according to the discharge rate of 21 Indonesian rivers and advected over 4 years. Most of the particles were stranded along Indonesian coasts (60%), before 6 months had elapsed (84%) and within a range of 1000 km (76%). The time variability exhibited two seasonal peaks, one centered on January-February and one on June-July, consistent with in situ observations. However, the results underline the complexity of performing direct comparisons between in situ observations and numerical simulations for stranded waste due to limited measurements and the heterogeneity of field methods and protocols

Multitemporal analysis of high spatial resolution optical satellite imagery for mangrove species mapping in Bali, Indonesia

International audienceMapping zonations of mangrove species (ZMS) is important when assessing the functioning of such specific ecosystems. However, the reproducibility of remote sensing methods for discriminating and mapping mangrove habitats is often overstated due to the lack of temporal observations. Here, we investigated the potential use of temporal series of high-resolution multispectral satellite images to discriminate and map four typical Asian ZMS. This study was based on the analysis of eight images acquired between 2001 and 2014 over the mangrove area of Nusa Lembongan, Bali, Indonesia. Variations between years in the top-of-atmosphere reflectance signatures were examined as functions of the acquisition angles. We also applied maximum likelihood supervised classification to all of the images and determined the variability in the classification errors. We found that the distinction between spectral signatures of ZMS characterized by a close canopy was fairly independent of the season and sensor characteristics. By contrast, the variability in the multispectral signatures of ZMS with open canopies and associated classification errors could be attributed to variability in ground surface scattering. In both cases, sun-viewing geometry could alter the separability between ZMS classes in near-nadir viewing or frontward sun-viewing configurations, thereby explaining why the overall accuracy of ZMS classification might vary from 65% to 80%. Thus, multitemporal analysis is an important stage in the development of robust methods for ZMS mapping. It must be supported by physical-based research aiming to quantify the influences of canopy structure, species composition, ground surface properties, and viewing geometry parameters on ZMS multispectral signatures

Mangrove monitoring for mangrove conservation and adaptive management

Mangroves are important ecosystems that provide a huge range of benefits for coastal communities. The management of mangroves requires multiple methods and approaches that contribute to answering the policy relevant questions. Our site is in the Perancak estuary, Bali, where mangroves were degrading in 1980's due to the conversion of mangrove forests to aquaculture ponds and later reestablished in early 2000 when many aquaculture ponds were abandoned due to economic crisis and the diseases. Monitoring of mangroves in this area has been conducted since 2004, aiming to identify the ecological processes in mangrove ecosystems that support mangrove conservation initiatives and coastal management. The study showed the recovery in net primary productivity (NPP) and carbon sequestration capacity of mangroves in abandoned ponds. Our results support the view that mangroves are highly productive ecosystems that can recover from disturbances even from extensive land conversion through destruction of mangrove trees, and undertake reshaping of hydro-biogeochemical processes. Mangrove extent can grow by self-regeneration and replantation throughout the 7.5 km² estuary, this resulting in the reverse process of aquaculture site conversion into mangroves areas. In the frame of the INDESO project (Infrastructure Development for Space Oceanography) mangrove changes in this region are monitored in support of a series of very high resolution satellite images acquired since 2001. The analysis of these data supports the definition of keystone regions for monitoring biodiversity recovery and ecosystem protection. Our goal is to provide recommendations for sustainable management of mangrove coasts that are understandable to local government and stakeholders, including the recommendation that supports the establishment of Regional Marine Conservation Area (or Kawasan Konservasi Laut Daerah, KKLD) of the Perancak estuary. (Résumé d'auteur

Temporal stability of mangrove multispectral signatures at fine scales

International audienceSustainable management of mangroves depends on our ability to maintain ecosystem functions. It requires a careful monitoring of several forest characteristics such as the species composition. Very high resolution multispectral satellite images provide pivotal information at the individual tree scale that may support identification and mapping of species of mangrove trees emerging at the canopy level. In this study, we showed that fine scale spectral responses of four common Asian mangroves species were and remained distinct over one decade and, independently of both the satellite sensors and the angular configurations of image acquisitions. We began an important radiative transfer modeling work to interpretation such promising observation

13 years of change in the extent and physiognomy of mangroves after shrimp farming abandonment, Bali, Indonesia

International audienceThere is a need to document how fast mangrove coasts are changing. Within the framework of the INDESO project, we are implementing methods for monitoring changes in Indonesian mangroves over the past decade. The Perancak river estuary, Jembrana, Bali was selected as a pilot site to analyze the impact of aquaculture and plantation practices in a 7 km² mangrove area. During the 80’s, most of the mangrove forest was converted to shrimp ponds. However many of shrimp ponds have been abandoned since the 90’s and covered by mangroves through plantation programs. We based our analysis on a temporal series of VHR satellite images acquired from 2001 to 2014 aiming to assess the vegetation change over 13 years in the study site. We mapped and quantified the trends of evolution in mangroves in terms of surface extents, forest types and forest structure (young, adult, mature). Our results showed that the Perancak estuary is undergoing the greening, i.e. increasing extent and continuous growing of mangroves. With this approach, we proved that both sustainable and unsustainable coastal zone management practices such as mangrove deforestation, plantation or protection, can be identified and mapped from VHR satellite image