A team of international mangrove forest experts suggesting optimistic cause for global mangrove conservation

February 26th 2020

More than a decade ago, a team of mangrove experts warned that mangrove forests were being lost faster than almost any other ecosystem, including coral reefs and tropical rainforests. Nonetheless, the situations are getting better now. An international team of 22 researchers led by National University Singapore (NUS) from 24 institutes including Dr Stefano Cannicci from The Swire Institute of Marine Science and School of Biological Sciences, the University of Hong Kong (HKU), found that there is now cause for optimism, with the global loss rate of mangrove forests less alarming than previously suggested.

After studying various earlier presented works, the team found that globally, mangrove loss rates have reduced by almost an order of magnitude between the late 20th and early 21st century – from what was previously estimated at 1% to 3% per year, to about 0.3% to 0.6%. The drastic drop in the loss rate is attributed greatly to the successful mangrove conservation efforts. This heightens conservation optimism amongst broader projections of environmental decline.

A commentary summarising the team’s findings was published in the scientific journal Current Biology. This international effort was the result of the Fifth International Mangrove Macrobenthos and Management conference (MMM5), the world’s largest mangrove conference which was held for the first time in Singapore last year.

“The team deduced that the reduction in mangrove global loss rates has resulted from improved monitoring and data access, changing industrial practices, expanded management and protection, increased focus on rehabilitation, and stronger recognition of the ecosystem services provided by mangroves,” explained Associate Professor Daniel Friess from the Department of Geography of NUS.

Dr Cannicci from HKU said: “I am very proud of being one of the academics who warned about world mangrove loss a decade ago, since I think that the paper published at that time contributed to a turn the tide on mangrove degradation. There are still dangers and we still have to manage and preserve mangroves worldwide, but the perception about their importance for humankind has definitely changed. In particular, a recent survey held in Hong Kong by me showed that mangroves area in Hong Kong has increased in the last 20 years and that these ecosystems are huge reservoirs of crab, mollusca and insect diversity.”

Dr Cannicci said the data discussed in the present paper strongly support the need to implement good practices in conservations, also for Hong Kong mangroves. He remarked: “Although small and limited in size, HK mangroves harbour a magnificent diversity of plant and animal species. Eight species of trees, 53 species of crabs and 42 species of snails have been recorded in these forests, which is more than is known for the mangrove forests of the whole African continent.”

After years of degradation, mangroves in Hong Kong now cover about 350 ha (Hong Kong Island has an area of about 7859 ha). Distributed across about 40 forests, they represent the largest remaining mangrove patch within the Pearl River Delta, with the largest one distributed along the coast of Deep Bay. There are also many small, but pristine patches in the North East New territories and a small one located on Hong Kong Island.

Positive change in mangrove conservation
Mangrove forests occur along the shorelines of more than 100 countries and are incredibly important as they offer numerous critical benefits to people, including protection from coastal erosion and storm as well as cyclone damage, natural filters for pollution and sediment, carbon sequestration which helps to mitigate climate change, and provide millions of people with products such as fuelwood, construction materials and fisheries resources, since mangroves act as nursing grounds for many coastal fishes.

“There is strong evidence that positive conservation change is occurring. Mangrove conservation has gained substantial momentum, with greater public and government awareness leading to investment and on-the-ground action. However, despite recent mangrove conservation successes, tempered optimism is necessary, as conservation gains are not evenly spread, nor guaranteed into the future,” cautioned Associate Professor Friess.

Mangroves under threat in emerging deforestation frontiers
The team found that mangroves continue to be threatened by aquaculture, agriculture and urban development across the world, particularly for new deforestation frontiers that are emerging throughout parts of Southeast Asia and West Africa. Southeast Asia is a traditional hot spot of mangrove deforestation as mangroves are cut down to make space for aquaculture ponds, cleared for rice paddy cultivation, and reclaimed for industrial and port development.

“Emerging deforestation frontiers need to be addressed early. Improved environmental governance and increased public intervention can help secure positive conservation outcomes in these locations. We need to take decisive steps to improve the success and scale of mangrove rehabilitation, and increase the resilience of mangroves to sea-level rise to maintain the current progress in mangrove conservation,” commented Dr Candy Feller from the Smithsonian Environmental Research Center, one of the contributors to the study.

Maintaining current progress in mangrove conservation
Even mangrove rehabilitation is lauded as a method to offset historical as well as ongoing losses and can yield long-term ecosystem service provision, the team found that successful rehabilitation is still a challenge to achieve at scale. Current mangrove rehabilitation projects around the world can fail because key ecological thresholds and rehabilitation best practices are ignored – for instance, planting in low-intertidal locations that are not suitable for mangrove growth and using non-native species that can quickly become invasive, which gives rise to myriad ecological impacts on the intertidal zone.

“Ensuring that mangrove conservation gains are not short-lived will require continued research, policy attention, and renewed efforts to improve the success of mangrove rehabilitation at a scale that will be ecologically impactful,” said Dr Erik Yando, Research Fellow at the NUS Department of Geography.

To ensure that the mangrove conservation gains are not short-lived, continued research, policy attention, and renewed efforts to improve the success of mangrove rehabilitation at a scale are required. The international team will continue to monitor mangrove deforestation and conduct studies to assess the benefits and values of mangroves in Southeast Asia.

(The press release is adapted from the press release of NUS)

Image download: www.scifac.hku.hk/press

The article: “Mangroves give cause for conservation optimism, for now” in Current Biology
Link of the article: https://www.cell.com/current-biology/fulltext/S0960-9822(19)31687-2

For more information about Dr Stefano Cannicci’s research, please visit: https://www.imeco-lab.com/

For media enquiries, please contact Ms Cindy Chan, Assistant Communications Director of Faculty of Science (Tel: 3971 5286; email: cindycst@hku.hk) or Dr Stefano Cannicci from The Swire Institute of Marine Science and School of Biological Sciences, The University of Hong Kong(email: cannicci@hku.hk).

Image 1: A crab resting on the mangrove in Ting Kok, Tai Po. 一隻螃蟹在大埔汀角的紅樹林上歇息 (Photo credit: The Swire Institute of Marine Science and School of Biological Sciences, TheUniversity of Hong Kong) (圖片來源:港大太古海洋生物研究所及生物科學學院。

Image 2: The international team found now cause for optimism for global mangrove conservation. 國際紅樹林專家組對現時的紅樹林保育情況感到樂觀(Photo credit: The Swire Institute of Marine Science and School of Biological Sciences, The University of Hong Kong)(圖片來源:港大太古海洋生物研究所及生物科學學院。

十多年前,一支研究紅樹林生態的國際專家小組聯手敲響警號,警告全球紅樹林面積正大幅度減少,速度甚至比其他生態系統如珊瑚礁及熱雨林還要快。專家小組最近的研究發現,由於各地採取了有效的應對方案,紅樹林的保育情況比預期理想。

團隊把研究結果比對之前的數據,發現20世紀末至21世紀初,全球紅樹林減少的速度減慢了大約十倍,由之前估計每年減少1%3%,下調到0.3%0.6%。研究結果已於學術期刊 《當代生物學》(Current Biology)發表。

研究由新加坡國立大學牽頭,有來自全球24間學院,包括香港大學太古海洋生物研究所及生物科學學院副教授Stefano Cannicci博士等22位紅樹林專家參與,他們欣喜見到紅樹林面積減少的速度未如預期般惡劣,對全球紅樹林的保育情況轉趨樂觀。

今次研究是「第五屆國際紅樹林大型底棲動物與管理大會」的成果,那是全球最大規模討論有關議題的會議,剛於去年在新加坡舉行。

新加坡國立大學地理學系副教授 Daniel Friess解釋研究結果說:「專家小組推斷,全球紅樹林減少的速度放緩,是由於多方面的因素,包括在監察和數據搜集上有所改善,工業作業方式的轉變,林木管理及保護工作得以擴大,人們對修復保育的關注增加,以及對於紅樹林對生態系統的貢獻的認知加强等,都有積極正面的影響。」

香港大學的Cannicci 博士表示:「我很榮幸參與這次紅樹林研究。十多年前發表的一篇學術文章,我有份提出社會需要正視紅樹林面積減少的問題,當時文章引起社會廣泛關注,之後引發了各種應對方案,令問題得以舒緩。今天,大眾對保育紅樹林的意識雖然提高了,可是對其生態的威脅依然未完全解除,全球仍需繼續保育及管理工作。今次我們發表的學術文章,促使全球各地包括香港,盡力落實保育紅樹林的有效方案與措施。我最近對香港紅樹林的一項研究亦顯示,本港紅樹林的面積在過去20年有所增長,孕育了大量螃蟹、軟體動物和昆蟲等物種。」

Cannicci 博士認爲,今次對全球紅樹林生態環境的研究結果顯示,良好的保育政策和實行方式非常重要,應該在全球包括香港大力推行。他説:「香港的地方雖小,但這裏的紅樹林孕育了非常豐富和多樣化的植物和動物物種,根據我們的記錄,當中包括8種樹木、53種螃蟹和42種蝸牛等軟體動物,物種的種類比整個非洲大陸的紅樹林已知所蘊藏的還要多。」

香港的紅樹林經歷多年的生態環境破壞惡化,目前總面積只有350公頃(香港島的面積大約是7859公頃)。現時全港有大約40個紅樹林叢林,是珠江三角洲中所餘最大的叢林組,其中最大面積的散佈在深水灣沿岸一帶,新界東北也有零星散佈,在香港島也有一個小紅樹林。

保育紅樹林的好處

全球超過100個國家的海岸線目前都有紅樹林的蹤影,它對人類和整個生態系統有著非常重要的角色,包括防止堤岸崩決、抵禦風暴、阻隔沙塵污染物,以及透過碳封存減輕氣候變化帶來的影響等。它又為人類提供木材燃料和建築材料,孕育近岸的魚類提供豐富漁獲作為食物。

Friess 博士認為:「有很強的證據顯示,各種保育措施正有效地實行。政府和大眾對紅樹林保育的關注增加,吸引了更多保育資金和實際行動以付諸實現。不過,保育的成果在分佈上似乎並不十分平均,我們亦未能保證這些措施能繼續有效執行,因此大家需要時常提高警覺,確保紅樹林保育工作得以持續進行。」

新興地方發展對紅樹林的威脅

研究團隊發現紅樹林仍然受着漁業及農業發展、全球都市化等因素的威脅,尤其在東南亞和西非一些新興開發林地的地區。東南亞向來是去紅樹林化比較嚴重的地域,大片紅樹林遭砍伐,以騰出空間興建魚塘和稻田,甚至用作興建工業區及港口。

研究團隊成員、 Smithsonian Environmental Research Center Candy Feller 博士表示:「有關機構應盡快停止在紅樹林的開發行為並加強環境管制,希望可以為這些地區的保育帶來正面影響。除此之外,我們應該採取有效手段去修復紅樹林,提升它們對水位上升的防禦力。」

繼續刻下紅樹林保育工作

雖然紅樹林修復計劃能夠補償一直以來的損失,長遠有助回復紅樹林的生態功能,但研究團隊發現,大規模的紅樹林修復計劃往往遇上巨大挑戰,令目前全球的一些紅樹林修復計劃有機會以失敗告終,這主要是由於欠缺對生態系統的約制及有效實行的方式的認識,例如種植在潮汐間過低不適合紅樹林生長的位置,或種植非原生物種,而這些品種很快變得富侵略性,以致大規模地破壞附近的生態環境。

新加坡國立大學的研究員Erik Yando博士在總結時呼籲:「我們必須對紅樹林的保育政策作長遠打算,只有持之以恆,才可以為紅樹林的復修及生態平衡帶來正面影響。」

研究團隊將繼續監察全球紅樹林面積縮減的問題,以及在東南亞一帶進行有關保育紅樹林所帶來的益處的相關研究。團隊認爲,要確保紅樹林保育計劃有效並得以延續,必須繼續投入科研工作、重視政策,以及加大力度改善紅樹林的修復工作等。

(新聞稿取材及翻譯自新加坡國立大學的原新聞稿)

圖片下載: www.scifac.hku.hk/press

有關文章: “Mangroves give cause for conservation optimism, for now”  —- 《當代生物學》
連結: https://www.cell.com/current-biology/fulltext/S0960-9822(19)31687-2

有關Stefano Cannicci 博士的研究可參閱以下網址:https://www.imeco-lab.com/

傳媒查詢,請聯絡港大理學院助理傳訊總監陳詩迪(電話:3917-5286; 電郵:cindycst@hku.hk)或港大太古海洋生物研究所及生物科學學院副教授 Stefano Cannicci博士(電郵:cannicci@hku.hk)。

 

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