Wetland Conservation > Management and study of invasive mangroves Sonneratia sp. @Sham Wat, Lantau Island
In Hong Kong, there are two known invasive mangrove species from the genus Sonneratia - S. caseolaris and S. apetala. Both are fast-growing, tough pioneer species commonly used to restore mangrove forests along the coast. After being accidentally introduced into Hong Kong in 2000, they first took root in Deep Bay, then expanded to some of the mangrove forests on Lantau Island, including Sham Wat, via water. Sonneratia trees can reach up to 10-20m tall and form groves within 4 years, competing with local mangrove species for space and blocking out sunlight, which inhibits the growth of other mangroves beneath them. They favor open mudflats as well, and by colonizing these originally plantless lands, they have reduced the feeding grounds of migratory birds and habitats of other mudflat organisms, negatively impacting the local mangrove ecosystem. Therefore, it is necessary to manage and control invasive species with methods like prevention, monitoring, research, and removal.
As of 2022, there were approximately 200 Sonneratia apetala trees settled in the mangrove forest in Sham Wat, Lantau Island. CAHK is commissioned by the Civil Engineering and Development Department’s Sustainable Lantau Office to carry out management, research, and public education on Sonneratia sp. in the area. First, we organized a seminar to explain to the public the background information of the invasive plants, the situation in Hong Kong and their management on 17 December 2022. Then on 13-14 January 2023, we had 2 days of S. apetala removal activities with about 50 participants in total to help people understand the problem with invasive species and participate in the conservation of local mangrove forests. Some of the S. apetala trees cut down would be made into furniture or other wood products so they might live on in a new form. We will be hosting beach cleaning events as part of the programme in the future to improve the living condition of mangroves in Sham Wat.
Furthermore, our team has conducted various studies on the ecological impact of Sonneratia apetala on the local ecosystem, such as vegetation survey, mangrove organism survey, local mangrove growth study, resprouting of S. apetala stumps, accumulation of marine debris in the mangrove forest etc. for the past year.
The Sonneratia apetala trees in Sham Wat have an average height of 8-10m, dwarfing the 1m tall local mangroves. Not only does their canopy block out sunlight, they also compete with local mangroves for space and resources.
The grove of Sonneratia apetala is way taller than local mangroves and other plants, and rubbish is scattered around the area.
Our team conducting research on how Sonneratia apetala affects the local ecosystem, including mangrove growth study
Tree expert from CAHK leading the Sonneratia apetala removal effort
Volunteers working hard to cut down Sonneratia apetala trees
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| Volunteers moving the cut Sonneratia apetala trees to the roadside for temporary storage; part of the wood would be recycled, whereas the rest would be sent to Y·PARK for processing. | |
We covered the Sonneratia apetala stumps with soil to stop them from resprouting.
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| As the mangrove forest was littered with rubbish, our volunteers did more than chopping down Sonneratia apetala and helped with beach cleaning, all to improve growth conditions for local species. | |
