Having read the discussion above, I have a few opinions on the issue.
Thinning has been widely practiced as a silvicuture tool to accelerate the growth of trees.
A few studies suggested using thinning of exotic trees as a restoration tool to improve plant diversity.
I think whether to chop down exotic trees need scientific evidence to support, yet, NO research has been done in HK
on the effect of thinning exotic plantation to plants/animals.
There is a study in Taiwan (Yuen et al., 2005) study the effect of thinning on short term response of animals communities.
Yuen, H.W., Ding, T.S. & Hsieg, H., 2005. Short-term Responses of Animal Communities to Thinning in a Cryptomeria japonica (Taxodiaceae) Plantation in Taiwan. Zoological Studies 44(3): 393-402.
They suggested that different thinning levels did not show significant effect on abudance and species of small mammals and non-breeding birds. But affect the abundance of ground invertebrate. Opening up forest canopy may increase plant diversity to colonize new niche.
I think all these should be considered carefully. Clear felling must not be possible as it affect microclimate condition and may introduce invasive species like Mikania in the forest. The effect of thinning on birds may not be reflected in short term, say within 5-10 years, as there are other factors affecting species richness and abundance, like food availability.
Ideally, native trees may able to grow larger if a few exotic trees are chopped down, but it takes long time for succession to take place and replace all of the exotic forest.
I think this is worth for discussion and to brainstorm what we can do to improve the biodiversity.
