WWF Mai Po

致各觀鳥者 / 攝影師：

自1985年起，世界自然基金會每年均於觀鳥屋前的潮澗帶泥灘，進行清除紅樹樹苗的工作。此項工作對維持泥灘作為水鳥覓食地、生態研究、教育及觀鳥地點，尤其重要。

本會職員及外判承辦商會於2013年8月至10月其間進行清除紅樹樹苗的工作。此項管理工作由漁護署監察，並連同地政署，就基金會每年提交的影響評估報告，批准進行。

本會職員及外判承辦商將會於后海灣退潮時，亦即觀鳥屋前的水鳥數目較少時進行工作。他們會把紅樹樹苗踩進泥中，有別於非法漁民。如欲查詢進一步資料，請聯絡米埔自然保護區洪敦熹或張家駿，電話：2471-6212。

Dear Birdwatchers/Photographers,
  
Every year since 1985, WWF has cleared mangrove seedlings from the area of inter tidal mudflat in front of the floating bird-watching hides. This is necessary to maintain the area as a valuable feeding habitat for waterbirds as well as to promote ecological research, education and birdwatching.

WWF staff and contractors commenced the 2013 clearance works in August and will continue through to October. Our work is monitored by AFCD, who together with Districts Lands Office, give us their consent each year upon approval of a WWF impact assessment report.

WWF staff and contractors will only work during periods of low tide with less waterbirds in front of the hides. You will see our staff and contractors stepping seedlings into the mud, and behave differently from illegal fishermen. For further information please contact Mr. Tony Hung or Mr. Tommy Cheung (Tel 2471-6212).

irsychan

Plesae consider not to fell this particular mangrove just in front of the middle floating bird hide on the mudflats.  It is liked by birds and during my short visits to the bird hide at two Sunday mornings, I have already seen long-tailed shrike, zitting cisticola, yellow bittern, etc on the tree. This provided good opportunities for taking photos of these birds at reasonable distance from the bird hide.
Just one tree shouldn't worsen the sedimentation rate of the mudflats?

WWF Mai Po

Thank you for your comment. I understand that this tree may provide some opportunities for photographers, however there are other factors that need consideration:
- This tree is a Sonneratia species. This species is not native in Hong Kong, is very fast-growing (despite it's size, this individual is probably less than one year old) and is spreading rapidly in Deep Bay, potentially causing a problem for the mangrove ecology. This is therefore a priority species for removal. Leaving this individual may allow further spread of the species into the bay.
- Shorebirds generally avoid areas of tall vegetation because there is a risk that these may contain predators. Leaving this one tree will cause lower use of this part of the mudflats by shorebirds, especially as the tree grows larger.
- The location of the tree outside the hides will block the view of shorebirds and other birds in front of the hides; this will be worse because of the rapid growth rate of this species. One reason for the mangrove clearance is to ensure that visitors to the reserve (including birdwatchers, photographers and school groups) are able to enjoy the views of birds on the mudflats.

Based on these considerations, I don't think it will be appropriate to retain this one tree. I apologise that this would mean you lose the tree as a perch for birds, but I hope you understand that in the longer term this decision is for the benefit of the important populations of shorebirds in the bay, as well as for the benefit of visitors to the hides wanting to see these shorebirds. Hopefully the birds you mention will be able to find another perch nearby where they can be observed from the hide.

In fact, the control of mangroves is not really to prevent sedimentation but to retain an open area of mudflat suitable for the internationally important populations of waterbirds. By carrying out work in front of the hides, this also provides views of the birds for the benefit of bird watchers, photographers, researchers, school groups and other visitors. The long term impact of the work can be seen on aerial views of the mudflat, which show that the mangrove has encroached significantly onto the mudflat in much of Deep Bay, but not in the area where mangrove seedlings have been cleared.

John Allcock
Manager, Habitat Management and Monitoring, Mai Po Nature Reserve

irsychan

Dear John,
Thank you very much for your detailed explanation and I agree to your decision.
I am a bit surprised, though, to learn that sedimentation is not WWF's concern. The once inter-tidal Gei Wais are now relying on dredged inlet channels to maintain their function, as a result of the fact that the once inter-tidal zone at the Gei Wai location has moved far away toward the river, due to sedimentation.  I would have thought that the mangrove forest has played a part in slowing down the water current and causing siltation around the mangrove forest and raising the mudflat level.
Best regards,
SY Chan

WWF Mai Po

Dear SY Chan

Thank you for your understanding.
Perhaps I was not entirely clear; WWF are concerned about continued sedimentation in the bay. You are correct that we rely on the channels through the mangrove for water exchange in the gei wai, and that these channels are affected both by sedimentation and the spread of mangroves. This affects not only sedimentation rate but also water quality because it is harder to exchange water from the gei wai with that from the bay, meaning that it can be difficult to lose poor quality water from the gei wai (for example during algal blooms). We do sometimes trim mangroves along the channels to help with water flow for this reason.

However, the sedimentation of the bay is not the main reason for the annual mangrove removal exercise on the mudflat, which is intended to maintain an area clear of mangroves for birds and visitors.

I hope this helps to explain the situation.
John Allcock

irsychan

Dear John,
Thank you again for your further detailed explanation.
Best regards,
SY Chan

[ Last edited by irsychan at 24/09/2013 15:48 ]