Compensation: If it is too difficult or expensive to manage problematic vegetation in a particular site, restoration or creation of tidal flats or saltmarshes elsewhere (ideally nearby) could be considered. If restored/created sites are near a site with problematic vegetation, consider how invasion of the new site will be prevented or managed.
Case Study: Mangrove seedling removal from intertidal flats at Mai Po Marshes
Removal of mangrove seedlings, and patches of grasses and sedges, from tidal flats at Mai Po Nature Reserve (Hong Kong) is carried out annually (in autumn) by World Wide Fund for Nature (WWF) Hong Kong. The aim is to maintain an area of open tidal flat, free of seedlings, for waterbirds to roost and feed, and to keep a clear open view for birdwatchers to observe the birds. The area being managed in this way (at least since 2001, when 5 ha was cleared) has increased over the years and is now some 43 ha. Mangroves on the tidal flats in front of the floating bird hides at Mai Po Nature Reserve have been managed in this way since 1986. Each August – October, permission is obtained from the District Land Office (Yuen Long) to remove a pre-agreed number of mangrove seedlings over a set area of tidal flat (WWF Hong Kong, 2006). Removal of mangrove seedlings is achieved by pushing the seedlings into the mud, causing them to die. For the removal in 2007, a team of six people required a total of 65 person-days to clear approximately 31,000 mangrove seedlings from a 43-ha area of tidal flat. The removed seedlings consisted mainly of Kandelia obovata (75%) and Aegiceras corniculatum (22%), with the rest (3%) of Acanthus ilicifolius and Sonneratia sp. (an exotic species).
Source: WWF Hong Kong (2021)
5. Other sources of information
Guidance on managing mangrove expansion: Lundquist C., Carter K., Hailes S. & Bulmer R. (2017) Guidelines for Managing Mangroves (Mānawa) Expansion in New Zealand . NIWA Information Series No. 85. National Institute of Water & Atmospheric Research Ltd.: New Zealand. Available at: http://www.niwa.co.nz/managingmangroveguide
References
Beeston M., Cameron C., Hagger V., Howard J., Lovelock C., et al . (eds.) (2023) Best Practice Guidelines for Mangrove Restoration . Global Mangrove Alliance: Washington DC. Available at: https://www.mangrovealliance.org/wp-content/uploads/2023/10/Best-Practice-for-Mangrove-Restoration- Guidelines-v2.pdf
Besterman A.F., Karpanty S.M. & Pace M.L. (2020) Impact of exotic macroalga on shorebirds varies with foraging specialization and spatial scale. PLoS ONE, 15 , e0231337. https://doi.org/10.1371/journal.pone.0231337
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