I posted re this idea to HK Birdwatching Society forum, and sparked some discussion there, at http://www.hkbws.org.hk/BBS/viewthread.php?tid=5827&extra=page%3D1

Just added this post, following responses there:

Glad this has prompted some discussion, and there is some similar thinking from folk who know re birds etc.

As I understand it, paper barks planted in several places as they can grow in damp areas (even places that are flooded at times).
But, to me, they’re too extensive already; I’d be up for retaining, say, the paper barks that grow right by Shing Mun Reservoir, and have bases underwater when the reservoir is very high. But those in northwest of the area are on what could be prime site.

Wider biodiversity is impacted.
Tai Po Kau, say, is tiny by forest standards; and within this, the area of good tree diversity is tinier still (if other tree species could use some thinning, to give more diversity a chance, would seem good too). Plus, typical to get biodiversity higher in lower areas, and closer to streams – so paper barks here, and at Shing Mun, "hogging" what should be one of richer parts of the forest. With better trees here, will get wider benefits.
Hong Kong has close to 400 native tree species; not at all a place where it’s remotely natural to have single species stands dominating sectors of prime areas. In moist tropics, a tendency for tree species to be well spread, so an individual here, another there. This in turn leads to greater diversity overall; and surely more attractive to human visitors, even if they don’t care too much about finding certain birds, butterflies or whatever.

Intersting re having them killed and left to stand, rot. Some, anyway.

Should be possible to find expert advice on such matters, inc from overseas.
I reckon Hong Kong should serve as strong example of forest regeneration in the tropics. (Reached this conclusion partly after reading some research on forests and conservation in Borneo: plenty of info there on forests that had been felled to varying extents, but not on planted/regenerated forests that were some decades old.)
But this example is based on far-sightedness in the past: what a superb idea to make Tai Po Kau a special area, with species diversity!
Nowadays, some more far-sightedness – and even courage(!) – could be helpful.

Already, Hong Kong’s forests are immensely impoverished compared to their original state: can only guess what we have lost. (No breeding woodpeckers shows the terrible effecitiveness of past deforestation: should be several species here, based on sub-tropical forest in region)
Holding back biodiversity not so good, now, unless for strong reason.