Mangrove zonation dynamics in the Deep Bay area using multi-source time-series satellite images

Ph.D.Mangrove deforestation is occurring globally at a rapid rate and is causing serious ecological and economic losses at all scales. Monitoring the mangrove changes is an important step for mangrove management and conservation. Zonation of mangrove species (ZMS) is the predictable and discrete ordering of mangrove species caused by a unique, intertidal environment. Mangrove zonation pattern is formed by complex abiotic and biotic environmental factors and, at the same time significantly influences the associate flora and fauna communities even the whole coastal ecosystem and local carbon cycle. Dynamic of mangrove zonation could be an indicator for local environmental change and, at the same time drive corresponding changes of the environment. Therefore, mapping ZMS and analyzing its long-term change is critical to understanding the mangrove community and the whole ecosystem. This dissertation combined spatial analysis methods to multi-source time-series satellite images aiming to investigate the characteristics and inner structures of mangrove zonation in the Deep Bay Area during the past three decades. The major findings of this study are summarized as follows.Firstly, mangroves in Mai Po Nature Reserve have shown a clear sequence of species zonation pattern in the past three decades. Generally, during most of the study period, there has been a sequence of three banded zones perpendicular to the shoreline from high tide to low tide level in Mai Po, dominated by mature Kandelia obovata (KO1), Avicennia marina (AM) and younger Kandelia obovata (KO2), respectively, while in Futian Nature reserve, the zonation pattern was not that clear during the past three decades.Secondly, spatial analysis method standard deviational ellipse (SDE) could enhance mangrove zonation understanding by adding unique directional change information to compensate for the spatial extent. According to the SDE analysis results based on medium resolution images, the rotation change results in the past three decades shown that the three types species KO1, AM and KO2 in Mai Po continuously spread in a northwestern direction over the study period. The X and Y deviation changes show that KO1 and Acanthus ilicifolius (AI) distributed in a relatively larger area in Mai Po, whereas AM and KO2 tend to be restricted to a relatively smaller area. Additionally, the moving trend results of the ellipse centers indicate a similar moving trend of the centers of the four types of species over the past three decades, moving to the northwest, and indicating a consistent zonation moving trend.Thirdly, different features of native and exotic species were found through the spatial analysis results. Native mangrove stands in the Deep Bay Area show relatively clearer zonation during the past three decades, presenting a sequence of the species in this tide-dominated shore with higher aggregation and reunion degree. In comparison, the distribution pattern of exotic species is in higher degree of fragmentation and less connectivity. According to the analysis results of some landscape metric indexes such as Aggregation Index (AI), Contiguity Index (CONTIG_MN), Clumpiness Index (CLUMPY), Proportion of Like Adjacency Index (PLADJ), Interspersion Juxtaposition Index (IJI) and Effected Mesh Size index (MESH) of both native and exotic species, the overall higher indexes value of native species KO and AM indicates that these native species tend to form dominant patch types with higher connectivity in the inner species zones, while the lower value of exotic Sonneratia spp. indicates the exotic species zones show higher degree of fragmentation with more small patches existing in them.The major outcomes of this research provide results of how the zonation pattern was changing during the past three decades in the Deep Bay area and what different features the native and exotic species were demonstrated through the zonation changing process in the Deep Bay area. Pixel-based SDE and patch-based Landscape Metrics were proven to be effective methods in measuring and describing the spatial distribution pattern of mangrove zonation based on both high and medium level satellite images. This study that focused on the three-decade historical change of mangrove zonation could be an effective reference for other mangrove ecologists and policy makers for mangrove protection and management.紅樹林森林的破壞和砍伐正在全球迅速發生，並造成各種規模的嚴重生態和經濟損失。監測紅樹林的變化是紅樹林管理和保護的第一個重要步驟。紅樹林物種的分區ZMS是由獨特的潮間帶環境引起的紅樹林物種的可預測的離散排列順序。紅樹林分區模式是由複雜的非生物和生物環境因素形成的，同時顯著影響了相關的動植物群落甚至整個沿海生態系統和當地的碳圈。紅樹林分區的動態可以作為當地環境變化的指標，同時也可以推動相應的環境變化。因此，繪製ZMS並分析其長期變化對於了解紅樹林群落和整個生態系統至關重要。本文將空間分析方法與多源多時相長時間序列衛星影像相結合，旨在研究近30年來後海灣地區紅樹林分帶性的特徵和內部結構。本研究的主要發現總結如下。首先，米埔自然保護區的紅樹林在過去近三十年中顯示出明顯的物種分區格局序列。總體上，在研究期間的大部分時間裡米埔呈現出從高潮到低潮位的三個垂直於海岸線的序列帶狀區域，分別以成熟秋茄（KO1），白骨壤AM）和新生秋茄(KO2)為優勢物種。而在福田自然保護區，過去近三十年的分區模式並不那麼明顯。其次，空間分析方法標準偏差橢圓（SDE）可以通過添加獨特的方向變化信息來補充空間範圍信息，從而增強對紅樹林分區的理解。根據基於中等尺度分辨率影像SDE的分析結果，在過去的近三十年中，KO1,AM和KO2三種類型的旋轉角度變化表明，在研究期間米埔的主要红樹林物種在西北方向不斷擴散。X和Y偏差變化表明KO1和老鼠簕AI）分佈在米埔的相對較大的區域，而AM和KO2傾向於限制在相對較小的區域。此外，橢圓中心的移動趨勢結果表明過去近三十年中四種類別的中心有向西北方向移動的類似移動趨勢，並表明一致的分區移動趨勢。第三，本研究通過空間分析結果發現了本地和外來物種的不同特徵。在過去近三十年中，後海灣地區的原生本地紅樹林物種顯示出相對清晰的分區，在這個以潮汐為主的海岸中呈現出一系列具有更高聚集和團聚度的物種。相比之下，外來物種的分佈格局具有更高的碎裂程度和更少的連通性。根據對本地和外來物種的聚合指數（AI），鄰接指數CONTIG_MN），聚集指數CLUMPY），類鄰接指數比PLADJ），交叉並置指數IJI和影響網格尺寸指數MESH等景觀指標的分析結果本地物種KO和AM的整體較高指數值表明這些本地物種傾向於形成主要的斑塊類型，在內部物種區域具有較高的連通性，而外來海桑屬物種的較低值表明，外來物種區域表現出更高程度的碎裂，其中存在更多的小斑塊。這項研究的主要成果提供了過去近三十年在後海灣地區的分區模式如何變化的結果，以及通過後海灣地區的分區變化過程證明了本土和外來物種的不同特徵。基於像素的SDE和基於斑塊的景觀指標可以有效地測量和描述基於高水平和中等水平衛星圖像分類解譯的紅樹林分區的空間分佈模式。這項關注紅樹林分區近三十年歷史變化的研究可以成為其他紅樹林生態學家和政策制定者紅樹林保護和管理的有效參考。Liu, Mingfeng.Thesis Ph.D. Chinese University of Hong Kong 2019.Includes bibliographical references (leaves 90-106).Abstracts also in Chinese.Title from PDF title page (viewed on 14 May, 2021)