Sha Lo Tung, an eighty-hectare valley sitting at an altitude of about two hundred metres in Tai Po District, is the most important dragonfly habitat in Hong Kong. The freshwater wetland is home to over 70 dragonfly species, including Spangled Shadow-emerald (Macromidia ellenae), which was new to science when first discovered here. However, the dragonfly paradise has been trapped in the perpetual controversy over development versus conservation between the developer, villagers, government and environmental groups for over four decades. A breakthrough was seen before the end of term of the last government. In June this year, the government finally opted for a non-in-situ land exchange for the conservation of Sha Lo Tung. This will hopefully end the days when the environment was assaulted by local villagers out of their frustration over land development issues. The next challenging step is to work on the revival and even enhancement of ecology at Sha Lo Tung.
Sha Lo Tung is akin to an upland basin in a high valley between Cloudy Hill and Wong Leng in Tai Po District. At an altitude of about 200 metres, the basin receives water from several streams with abundant flows year-round. The soil is rich, and the surrounding mountains form a natural protective screen. The ideal farming place attracted three Hakka villages to settle here more than three hundred years ago. The villagers made the best use of the local geographical features. They built ditches and practiced paddyfield farming, turning the highland valley into a freshwater wetland. This is particularly rare in Hong Kong, as most of the important wetlands are located by lowland estuaries where freshwater and sea water meet.
The paddyfield wetlands, in addition to the clear and flowing streams and the dense forest in the area, were home to numerous dragonfly species as well as butterflies and fireflies. There were also a variety of freshwater fish, amphibians, reptiles, mammals and birds, including rare species such as Chinese Pangolin (Manis pentadactyla), Chinese Tiger [a dragonfly] (Gomphidia kelloggi) and Hance’s Viburnum (Viburnum hanceanum). Sha Lo Tung was once full of greenery, with an abundance of plants and animals.
However, the 1970s was the time of change. Earlier, in the 1960s, emigration of local villagers began and more and more farmlands were abandoned. A developer came in and started purchasing land and houses from the villagers during the 1970s and 1980s. An application was submitted to the government for the construction of a golf course and low-density residential development. By that time, almost all villagers had already moved out. Although there were few people and no farming activities, the irrigation ditches and water fields remained in good condition, continuing to nurture the wetland ecology
In the early 1990s, experts discovered a substantial dragonfly population at Sha Lo Tung, including a species that was new to science when first discovered here. Botanists also confirmed the presence of at least 100 rare plant species at the valley. This finding of the high ecological value of Sha Lo Tung was thrilling. At the same time, this was where the controversy began.
The Halting of Development and Conservation
The original development plan for a golf course and low-density housing was fiercely opposed by green groups and a judicial review was conducted. The development plan was eventually suspended. In the mid 1990s, some villagers, out of anger over the failure to develop the land, launched an assault on the farmlands and irrigation ditches with machines including bulldozers, all in the name of “farming action”. The farmlands and wetlands later dried up, allowing grasses and invasive plants such as Mikania (Mikania micrantha) to thrive and threaten the ecology of Sha Lo Tung.
There were other activities that caused damage to Sha Lo Tung. The deserted village houses and large area of farmlands attracted many war game players and off-road vehicles, ruining even the natural streams. The consequences were profound. Besides, illegal catching of wild animals was rampant and animal traps, particularly those targeting turtles, could be seen all around in the area.
The drastic dwindling of the wetland area posed serious threats to the local ecosystem. In 1997, the government designated the river channels and river banks at Sha Lo Tung as a Site of Specific Scientific Interest. Yet protection by the legislation was limited and artificial damage persisted. The government was unable to stop activities on private land. Habitats at Sha Lo Tung continued to deteriorate.
In 2004, the government launched the New Nature Conservation Policy in an attempt to resolve the conflict between private land ownership and conservation of high ecologically valuable land. Twelve conservation sites were prioritised, and Sha Lo Tung ranked second. The developer of Sha Lo Tung participated in the Public-Private Partnership scheme under the new policy and submitted a new application to the government, still waiting for approval after more than a decade. In 2015-2016, some villagers embarked on a rapeseed saga as a way to express fury—they cleared massive areas of vegetation to make a rapeseed field blossom, bright yellow, which attracted wide public attention. The cruel fact behind the apparently pretty scenery was, planting of rapeseed would further dry up the wetland, accelerating the damage to the precious wetland at Sha Lo Tung.
In mid 2017, the government finally opted for non-in-situ land exchange to preserve Sha Lo Tung. The developer swapped the land with a restored landfill plot at Shuen Wan, to be developed into a golf course. With the resolution of the land ownership problem, conservation of Sha Lo Tung has become possible.
Over a Decade of Environmental Damage
Since 2009, Green Power has carried out annual dragonfly surveys at Sha Lo Tung. In the early years, over 50 species were recorded on average. In July 2009, a new Hong Kong record was found –White-tipped Grappletail (Heliogomphus retroflexus). The species is designated as Class II in The List of Wildlife under Special State Protection. In recent years, however, only about 30 dragonfly species were recorded over the year.
The adults and nymphs (larvae) of dragonflies live in completely different habitats. The adults fly in the air while the nymphs spend their lives in water. Different species also require distinct breeding and feeding habitats. Diverse habitats, including dense woodlands, shrubs, open wetlands and channels, provide homes to different dragonfly species. As for the nymphs, diversity of the microhabitats—including sandy beds, rocky stream, deep pool or shallow flow—is important too. Some species dig under sand and gravel in the river bed, while some prefer to lay under the rocks. It makes a big difference to the nymphs whether there are aquatic plants and roots in the water or not.
At present, farmlands at Sha Lo Tung have gradually dried up and the original wetland vegetation has largely been reduced and replaced by terrestrial plants and even invasive weeds such as Mikania. In the days when there were active agricultural activities, villagers managed the ditches and streams well for irrigation needs, hence supporting a variety of aquatic microhabitats. Today, all these are left unattended and even ruined by off-road vehicles. The water channels are filled with grasses and weeds, deep pools have become shallow due to sedimentation. Rocky streams with aquatic plants are converted into sandy ones. The diversity of plants and microhabitats has been drastically depleted, threatening the survival of dragonfly adults and larvae.
Revival of Paddyfields
In the past, Sha Lo Tung attracted dragonflies with its paddy fields. Today, if we are to mitigate and reverse the damage done to the drained watershed, the best approach is to revive the paddy field cultivation to establish a healthy and sustainable ecosystem again. It is certainly not easy to work on a wasteland deserted for decades. The task will be challenging.
A few years ago, a farming revitalisation programme was initiated at Lai Chi Wo by several conservation groups and the university. From the programme, we learned that paddyfields that have been deserted for years will lose their water-holding capacity due to damage by weeds and tree roots. Restoring the water retention layer is the key to the successful creation of a wetland.
A simple way to create a water retention layer is to lay an impermeable membrane underground. Yet this may not work well in Sha Lo Tung. There is still no proven method to restore this water-holding capacity of soil. It will take much trial and error, even with reference to traditional Hakka wisdom, to rebuild the capacity. A few years of time may be needed to see the results.
During this period, organic farming may be practiced on the dry land. Cultivating crops that attract animals can enrich the ecology and prevent weeds and bushes from further damaging the water retention layer of the soil. The farming process allows nutrients to accumulate in the soil and improve soil properties. Whether there is dry-land organic farming or paddyfield farming, it will need long-term manpower on the site. Time, skills and experience are all essential.
Sha Lo Tung is ecologically significant as it nurtures rare dragonflies, particularly species in the families of Gomphidae and Corduliidae. The adults also inhabit the mature forest by the streams. Therefore conversation of the woodlands is important too. Rebuilding water pond habitats helps to increase dragonfly diversity. Orthetrum spp. and Trithemis spp. of the Libellulidae family, albeit common, have dwindled in population as such habitats have disappeared at Sha Lo Tung.
After decades of artificial damage and abandonment, it will take a long time and a lot of resources to rebuild the ecosystem. We have yet to fully understand the process of natural succession. We can only keep trying and learn from past experience to find out the most appropriate measures for establishing, conserving and enriching the ecosystem of Sha Lo Tung. The road of conservation is long. But it carries the hope of Hong Kong people to see the return of the dragonfly paradise and a dynamic ecological community at Sha Lo Tung.
Text ｜ Henry Lui & Dr. Cheng Luk-ki