Climate Change and Hong Kong Ecology

“Climate change is obvious; we’re breaking temperature records,” says Lam Chiu-ying, a former director of Hong Kong Observatory who, although retired, retired is highly active in various conservation and environmental initiatives. Lam is a keen naturalist – formerly serving as chairman of the Hong Kong Birdwatching Society, so is aware of changes underway in the natural world. “We have plants moving upwards on slopes,” he says. “And for high altitude species like some birds, the vegetation they depend on may disappear, so once they have reached the top of hills, they can only move up to heaven.”

            Lam also worries about impacts of sea level rise and storm surges, particularly in urban areas and the northwest New Territories – noting that, “According to the Observatory, surges that occurred once in 50 years at the beginning of this century will happen once a year by end of this century.”

            Even without storm surges, the marshes at Deep Bay in northwest Hong Kong will be regularly inundated by tides from 2075 onwards, according to a computer-based analysis by a team at WWF Hong Kong. This could severely impact the Mai Po Marshes Nature Reserve, and the team advocates protecting nearby fishponds from development, in order to help safeguard the wetlands; while also noting coastal wetlands can help protect against sea level rise and storm surges.

            Of course, the impacts of global warming are global, and set to increase. “Climate Change is the defining issue of our time and we are at a defining moment,” says an article on the United Nations (UN) main website. “From shifting weather patterns that threaten food production, to rising sea levels that increase the risk of catastrophic flooding, the impacts of climate change are global in scope and unprecedented in scale.” With all life on earth affected by these impacts, albeit to widely varying extents, the UN even has a website devoted to climate change and biodiversity worldwide.

            In 2018, aiming to play a role in trying to combat climate change, Lam became chairman of a sub-group under Hong Kong’s Council for Sustainable Development, after the government asked the council to conduct a public engagement exercise on climate change, and long-term decarbonisation.

            “The plan was for an 18-month public engagement, to end in the middle of 2019, after which we would draft proposals for the council, which would make policy recommendations,” said Lam. While Lam did survey a few sectors regarding their thoughts, the public consultation was delayed … and delayed; and he came to believe the administration wanted to avoid making significant changes that would impact people’s lifestyles.

            Though the consultation was held, Lam’s sub-group was only allowed to see a four-page draft report, in May 2021. Believing this far from adequate for devising a strategy for the next three decades, he resigned from the group. “These administrative officers think action will block economic development, and have never felt urgency in dealing with climate change,” he says.

            However, there are changes underway, including in Hong Kong’s ecosystems, that indicate there is an urgent need for action.    

Changes often mysterious, and how should we humans help?

However, unlike increasing temperatures or rising sea level, it is by no means straightforward to link changes in plant and animal communities to climate change. “Many people might judge climate change is often responsible for changes in species distributions,” says Dr Benoit Guénard of the University of Hong Kong’s School of Biological Sciences. “I’m not as confident, especially in sub-tropical regions. Hong Kong was mostly deforested by the 1600s, and the forests are recovering, so more species can find suitable habitats.”

            A fellow entomologist and colleague of Guénard in the School of Biological Sciences, Dr Timothy Bonebrake, is working on topics including habitats and climate interactions, and similarly notes Hong Kong presents a unique challenge, given there are many places with forest recovering. “This means there are changes to ecological communities – including butterflies, moths, and birds,” he says. “You need care if you see a new species, and say, ‘Oh, it’s because of warming,’ as it could be because the habitat is changing.”

            One species that may have arrived in response to warming temperatures is the black-and-white Courtesan butterfly, which was first recorded in Hong Kong 2007, and is now fairly widespread. It is found across much of southeast Asia, while a similar relative found in Hong Kong, the Red Ring Skirt, has a more northerly distribution. Bonebrake assigned a student, Tom Au Tsun-fung, to study whether the two species are indeed adapted to different climes.

Using an environmental chamber within a university laboratory, Au discovered that Red Ring Skirts are more cold tolerant, remaining active at temperatures up to 2°C lower than Courtesans. “Maybe this is why Red Ring Skirt could withstand Hong Kong’s winter, and Courtesan has recently arrived because Hong Kong is more and more like the tropics,” he suggested via email. 

            Both Guénard and Bonebrake advocated safeguarding habitats as a key way to help species survive climate change – particularly if there are “corridors” such as strips of forest that allow them to move to more suitable places.  

            David Dudgeon, Chair Professor in Ecology & Biodiversity at the University of Hong Kong, primarily studies freshwater ecosystems, including the stream in Tai Po Kau Forest Reserve. “I’ve been sampling bugs in the stream for about 30 years, and the diversity is down a bit, and the stream has warmed up,” he says. “While we’re not losing many species, the community is different, with some species like mayflies becoming much less abundant, while there are more generalists, such as midges. A couple of caddis flies that have disappeared were on the southern margins of their range in Hong Kong, so maybe they don’t like when it’s hot.”

            With no other major changes, such as in vegetation, Dudgeon believes the reason for the ongoing transformation is the rising temperature. “The rate of change has been fastest in last few years; as has the rate of change in air temperature,” he notes.

            One species that Dudgeon believes could be particularly threatened by climate change is the Giant Spiny Frog, which is found only in south China and Vietnam, and globally endangered. “It’s a real upland species, found on Tai Mo Shan and Sunset Peak,” he says. “With greater heat, they can’t move up and breed in cooler streams, so they will become extinct.”

            As yet, there is not enough information on Giant Spiny Frog to indicate such an upwards shift, but this would correlate with research on amphibians in other parts of Asia. 

Short-legged Toad

“One of the things we should worry about is endemic species in Hong Kong,” says Dudgeon. “We don’t know to what extent they will do well, or badly, under climate change – such as Romer’s Frog, Short-legged Toad, and Hong Kong Paradise Fish. 

 Dudgeon is also concerned about the Hong Kong Newt, which was thought to be endemic but has also been found in Guangdong province. “It breeds during the colder months, and newts are temperate animals, with only one species found further south,” he says. “So it’s probably just hanging on here; if the climate becomes too warm, it may perish.”

Given the threat of extinction, Dudgeon thinks we should consider helping species that could become “trapped” in place, by translocating them to places where they have more chance of survival. “This is pretty controversial, with some conservation biologists,” he says. “But I take view, we are messing up the planet so much, we should do so. If we don’t do anything, these creatures will go extinct.”

Do Hong Kong Dragonflies Indicate Climate Change Impacts? … It’s Complicated 

Seeing information such as the US National Oceanic and Atmospheric Association reporting, in March 2021, that earth’s temperature has risen by 0.08°C per decade since 1880, and 0.18°C per decade since 1981, it may be easy to assume that there’s a steady process underway, with similarly steady impacts on plants and animals.

            In reality, however, climate change is not incremental and predictable from day to day, year to year. Some years prove unusually hot, others cooler than the trend indicates. Plus, parts of the planet may experience weather events such as heatwaves, droughts, and prolonged rainfall – which may in turn have relatively sudden effects on wildlife.

            For instance, the Hong Kong Observatory reports that from March to May 2021, Hong Kong experienced the warmest spring on record. Plus, the first five months of the year were the second driest on record, with just 163.1 millimetres of rain, 72 percent less than the normal of 590.9 millimetres.

            Dr Ken So Ying-kin, a Postdoctoral Fellow at The University of Hong Kong’s  School of Biological Sciences, was conducting dragonfly surveys on behalf of several green groups, and noticed that in the streams that were far drier than usual, the adults of various dragonfly species emerged about two weeks early than average. So refers to a paper on drought affecting stream life, which notes that aquatic insects may emerge early during droughts, thus avoiding the streams drying out even more, yet this may affect their ability to survive and reproduce as adults. 

            “In addition, I found that a significant proportion of a stream in Sha Lo Tung was dried out in May this year [2021],” So reported by email. “The males of a threatened dragonfly species – Gomphidia Kelloggi [commonly known as Chinese Tiger]; classified as Endangered in the IUCN Red List of Threatened Species, which can only be found in the Sha Lo Tung/ Hok Tau region – were apparently exhausted from guarding their territories, since their territories are restricted to the stream sections with open water, and the drying of the stream had reduced the territory area per individual and caused intensive fighting among individuals.”

          The Chinese Tiger was first described from a single specimen obtained in Fujian province in 1928. It was 64 years before the species was rediscovered, at Sha L Tung, by Keith Wilson. Though working as a senior fisheries officer with the Agriculture, Fisheries and Conservation Department, Wilson had a passion for dragonflies, and was a classic citizen scientist, devoting considerable free time and energy to surveying dragonflies, even discovering three species that were new to science and endemic to Hong Kong.

             Wilson was the main author of a Field Guide to the Dragonflies of Hong Kong, which was published in 2004, and notes that there had been no published records of Chinese Tiger in mainland China since 1928. Even so, the IUCN Red List website has a range map indicating it still occurs in Fujian, as well as Hong Kong, around 450km to the southwest.

            Only time will tell whether the hot, dry spring has an impact on the last known population of Chinese Tigers, at Sha Lo Tung and nearby. If so, this might be a result of the changing climate, though several years more data would be needed to reinforce this conclusion.

            A study of the distributions of 99 dragonfly species in Europe found that 55 had expanded their ranges, evidently in response to climate change making conditions more suitable for them. 

In Hong Kong, there are also indications of range expansions among dragonflies – and closely related damselflies. “Some species have apparently spread more widely in the last ten years,” ecologist Graham Reels noted via messaging. “Others have colonised (or re-colonised) from Guangdong.”

These locally increasing species include the Ruby Darter (Rhodothemis rufa), which appears in the Hong Kong field guide based on just one specimen found at Sha Lo Tung in 1992, but is now widespread. While this is a common Asian species, the Ruby Darter is mainly found in tropical regions, so it’s tempting to suggest that climate change is making Hong Kong more suited to its requirements. Reels – who has a master’s degree in Conservation Biology from the University of Hong Kong, and has conducted extensive dragonfly surveys here – is far from convinced.

            “Climate might be playing a role, but I think habitat change is a major factor,” Reels comments. “Many of the new dragonfly arrivals are forest species. Hong Kong was largely deforested as recently as 50 years ago. I don’t think it’s a coincidence that as Hong Kong’s secondary woodland has expanded and matured more woodland dragonfly and butterfly species are showing up.”

Wandering Gliders – highly migratory dragonflies, also known in Hong Kong as Typhoon Dragonflies

Moths Including Rampaging Red Peril as Marauding Muncher of Banyans

Several moth species have likewise arrived in Hong Kong and become resident, even relatively common, during the past decade, according to moth expert Dr Roger Kendrick. As they tend to be moths with more southerly, tropical distributions, it may be that climate change is spurring range expansions in the north of their distributions. They may be helped, too, by initially outpacing their parasites, which may follow and restrain their burgeoning populations.

One moth species exploded in numbers and visibility this spring – perhaps in response to the unusual weather, or reduced parasites and predators, or a combination of these factors. This is a day-flying red moth known mostly by its Latin name, Phauda flammans, and while the adults look attractive with their vermillion wings marked by black patches, the caterpillars feed on banyan tree leaves. In recent weeks, there have been so many of these caterpillars that banyans in a swathe of the New Territories have been almost completely defoliated – even prompting the creation of a Facebook group, with the English name “Against red moth Phauda flammans”.

            But the red moths are not new to Hong Kong, suddenly invading and wreaking havoc. “Please remember Phauda flammans is part of our native fauna,” notes Kendrick, who in 2002 obtained a PhD from the University of Hong Kong, with a thesis titled Moths (Insecta: Lepidoptera) of Hong Kong and now runs an ecological consultancy. Though well used to finding Phauda flammans, albeit at low, almost undetectable population levels, he adds, “I haven’t seen it in such a boom in nearly 30 years. It may be decades before we see such a boom again. The fig trees have dealt with these moths for many thousands of years. That will not change.”

            As to the question of whether this is an exceptional event, Kendrick adds, “Please note from a tropical ecology perspective, ‘predator-prey’ population cycles have long periodicity, usually measured in decades. Consequently there are very few studies published….. Mostly on mass flowering of tropical trees, events that trigger major population booms in pollinators and then the pollinators’ predators. So the cycle at the moment is a peak population of flammans. We don’t even fully know who its predators are. They will catch up over the next months, perhaps a few years, then the moth population will come back to low level. In the meantime, the fig trees have a year or two of slow growth. Nothing new there.”

            While it’s only possible to speculate about such events in the past, Kendrick does suspect there’s a human factor triggered the current boom in flammans. “My bet will be a human factor related to climate change, or possibly the general pollution loading has caused decline in predators.” Kendrick also wonders if the blanket use of pesticides has reduced the population of predators, and parasites.

This blanket use of pesticides has been especially high after dengue fever cases surged to 29 in 2018 – leading to a veritable blitz of pesticide spraying and fogging aimed at mosquitoes that may carry dengue. Pesticides included permethrin, which is toxic to a wide spectrum of insects, with moth predators and parasites surely among them. 

Pesticides might also seem useful for countering the rampant red moths, yet a team of researchers in Nanning, Guangxi province – describing the moth as “one of the notorious defoliators” of banyans and other Ficus trees – report that, “Widespread use of chemical insecticides in the control of this pest is no longer acceptable due to insecticide resistance, negative effects on biodiversity and environmental pollution.” They studied three wasp and one fly species that are parasitoids – with larvae that start life within and feed on caterpillars, and indicated that, after further studies, one of the wasps could be mass produced and released as a biological control agent.  

            Such a mass release might have other, unintended side effects – such as the wasps parasitising other, desirable species. Hence it might be best to follow Kendrick’s advice: don’t panic, and let nature take its course, while reducing the use of wide-spectrum pesticides.

            Plus, more generally, take note of Kendrick’s belief that, “We’ve been messing with the environment for a long time. Climate change, is one of the symptoms of our destruction of the planet. We need to address fossil fuel use, and habitat change.” 

Trees can help but get stressed too

More trees can help mitigate the impacts of climate change, such as by helping cool areas, as well as boosting carbon storage.

            Professor Joe Lee Shing-yip, of the Chinese University of Hong Kong’s Simon F.S. Li Marine Science Laboratory, has conducted research showing mangroves are especially efficient at storing carbon – at a rate that may be five to ten times that of forests on land. “They are productive systems, converting carbon to biomass in leaves, twigs and roots,” he says. “This is stored in sediment for a long time, as it’s low in oxygen so decomposition is very slow.” 

            Mangroves can also help safeguard coastal regions from extreme events such as storm surges and tsunamis, as their complex structures including trunks and roots form protective barriers.

tung chung bay eel grass n mangroves2013Mar04_3721800px
Tung Chung Bay eel grass and mangroves

            Climate change may even benefit Hong Kong’s mangroves, with warmer winters affording them a longer growing season – providing it does not become too hot in summer.

            “Hong Kong has sub-tropical vegetation, so the shade plus strong cooling effect resulting from transpiration means that, in general, urban greening with more trees is good for mitigating climate change,” says Amos Tai, Associate Professor in the Earth System Science Programme and Graduate Division of Earth and Atmospheric Sciences in the Faculty of Science at the Chinese University of Hong Kong. However, trees can also become stressed by heat and other changes.

            “My research includes large scale simulations of the impact of climate change on Hong Kong ecosystems,” says Tai. “While more CO2 may benefit plant growth, ozone levels will be higher, and the productivity of Hong Kong ecosystems will decline by up to ten percent, as warmer conditions make things tougher.”

Man-made barriers might protect Hong Kong

As Hong Kong contributes only around 0.13 per cent of carbon dioxide emissions, according to Worldometer, local actions can barely make a dent in global warming. However, there are possible measures for minimising the local impacts of climate change, perhaps including grand infrastructure projects.

            Robert Gibson, an Adjunct Professor in the Environment and Sustainability Division of the Hong Kong University of Science and Technology and a Fellow of Civic Exchange, is among people who are thinking big regarding ways Hong Kong might build defences against climate change threats. “Scientists know the rate of Greenland and Antarctica ice melt is increasing,” he says. “However, the International Panel on Climate Change reports include deep uncertainty regarding how fast the resulting sea level rise will be, and this could be greater that the projections on which the Hong Kong government has based its plans.”

            To Gibson, Hong Kong’s most vulnerable area to sea level rise is the northwest New Territories. “It’s a really flat area,” he notes. “Even with a one to two metre sea level rise, there will be extensive flooding – especially at times a typhoon creates a storm surge.”

In order to help counter the threat, Gibson advocates encouraging the growth of mangroves, in tandem with oyster beds at the month of Deep Bay. “This will help to protect northwest Hong Kong and Shenzhen,” he says. “Mangroves efficiently absorb carbon, creating a nature-based solution that self-repairs and grows with sea level rise, so costs are much lower than a concrete barrier.” 

            But Gibson believes it will also be necessary to have an earth bank running through the middle of mangroves protecting the mouth of Deep Bay, coupled with a structure like a small version of the Thames Barrier with gates than can be closed as typhoons approach. 

Gibson notes the ecological impacts of such a barrier will need careful planning.  “Starting growing a mangrove barrier at the mouth of Deep Bay now will give the mangroves time to keep up with the sea level rise,” he says.

Gibson also suggests additional, far more ambitious barriers – between Castle Peak and Lantau west of the airport; linking Lantau and Lamma; and from Lamma to Ocean Terminal, as well as a barrier spanning the narrow Lei Yu Mun gap. “The whole of the city would now be protected,” he says.

While a planned reclamation around islands east of Lantau – known as the East Lantau Metropolis, and rebranded Lantau Tomorrow Vision – is proving controversial, Gibson believes it could be within the area protected by barriers from sea level rise and storm surges, and hopes the government will ensure it is only accessed from the rest of Hong Kong by trains and ferries. “There should be no private cars on the island. Instead there should cycling and electric vehicles for goods and for on-demand taxis,” he says. 

            But will we get such long-term planning?  Gibson notes that, with few exceptions, business decisions depend on what may happen in 10 years or less years, rather than considering long term problems. So, we need the Government to take the lead on long-term planning for sea level rise.

Restrict coastal development, while using money to protect Hong Kong

Mostly, it appears Gibson’s wishes will not come true, at least in the near term. Hong Kong’s Climate Action Plan 2030+, published by the Environment Bureau in 2017, abounds with bright, cheerful colours and upbeat illustrations, yet features little that Gibson recommends other than ideas for reducing numbers of private cars. Sea level rise is mentioned almost as an aside, posing a generally low risk of coastal inundation by 2100 (without storm surges), with related studies underway but no countermeasures like barriers or mangrove forests planned. 

            And the experiences of Lam Chiu-ying suggest the Hong Kong government is relaxed, even blasé, about the potential threats from climate change. Unlike Gibson, however, Lam believes it is not practicable for Hong Kong to build Thames-style barriers. Instead, some areas prone to sea water flooding should be designated unsuitable for human habitation.

            Nor does Lam see any benefits in Lantau Tomorrow Vision. “It’s simply a silly idea, at a time when island nations are worrying about disappearing from the world,” he says. Instead, there is suitable land for development in the New Territories, like in and around existing villages; and the new island’s value could be short lived, given the sea might be five to six metres higher by the end of next century. “We should use the money to protect Hong Kong, and not waste it on a new problem for Hong Kong,” Lam says.

Written for the Croucher Foundation


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