Most of the mapped lowland forest patches are relatively intact and confirmed to be of high ecological value, except for a few sites where ecological value was downgraded because of disturbance due to pollution (eg rubbish dumping), development (eg slope stabilisation) and/or low structural complexity and species abundance of the habitat. The majority of the forest habitats surveyed were generally well-preserved and subject to little or no human disturbance. Some of the forest patches, such as those at Tai Lam Chung, though small in size (about 0.4 ha), support a closed, highly stratified canopy and dense under-storey vegetation. Large patches (> 3 ha) of well-preserved lowland forest were observed within various Country Park areas (eg Pat Sin Leng) or located next to villages (eg Wong Chuk Yeung Village). However, a few of the small lowland forests appear to have been disturbed by (regular) clearance of their under-storey vegetation. Such clearance of vegetation serves to either provide sufficient space for recreational activities (eg near picnic areas) or landscape purposes (particularly those established on slopes).

Plantations were first established in Hong Kong in the 1870s and just prior to World War II covered 70% of Hong Kong Island. Due to cutting for firewood and other uses, most plantation forest was removed during the Japanese Occupation from 1942 to 1945 (Corlett 1997). Although plantations are artificial habitats, they may be invaded over time by other species of vegetation and may thus support moderate ecological diversity. Corlett (1999) reports that the purposes of afforestation schemes in Hong Kong have changed with time, and that whilst controlling soil erosion and improving water supplies has been important for much of the 20th Century, current concerns are largely ecological. Following the second world war, planting predominantly used Pinus massoniana (which has subsequently been lost to pests such as the Pinewood Nematode) along with exotics such as Acacia confusa, Lophostemon confertus and Pinus elliottii as well as broad leaved native species such as Castanopsis fissa, Liquidambar formosana and Schima superba. The ecological value of more recent plantings has been increased through the use of mixed plantings and native species and it is reported (Zhuang and Corlett 1997) that efforts to contain hill fires in the last 30 years have resulted in a great expansion of spontaneous secondary forest dominated by Persea spp. such that forest now covers approximately 15,000 ha in Hong Kong of which around 5,000 ha is recognisably plantation. Whilst there is evidence that plantations can act as "nurse crops" or "foster ecosystems", Corlett (1999) notes that it may be difficult to separate the direct influence of tree planting from the effects of long term protection from fire since fire-protected grasslands can develop rapidly into shrubland and secondary forest, even in the absence of planting.

Some patches of plantation surveyed were considered to be of high ecological value (ie upgraded from their indicative medium habitat value) because of their apparent old age and the observed structural complexity and species diversity which has made them resemble a native secondary forest. In contrast, one of the "plantation" habitats at Sau Mau Ping had their ecological value downgraded from medium to low. The adjustment was based on the disturbance the habitat has been subject to as a result of its proximity to a rubbish collecting station. One of the surveyed plantation patches was found to be used by AFCD as an experimental site for planting native species on hill-sides and an asterisk "*" (1) was assigned to the habitat.

(1) In addition to the classifications of high, medium, low and negligible ecological value, the habitat map has also included an asterisk ("*") to indicate that the area has one or more unique features which distinguish it from other areas in the same habitat category. For details, please refer to SUSDEV 21 Environmental Baseline Survey on Terrestrial Habitat Mapping and Ranking based on Conservation Value - Topic Report 1 or Draft Final Report.

Shrubland represents an intermediate successional stage and can vary widely in habitat structure from a mixture of low shrubs and grasses to tall shrubs approaching the height and structure of secondary forests. For the purposes of this discussion on habitat value, shrublands have been classified as either mixed shrubland or Baeckia shrubland. In general, shrubland habitat has a higher potential to support biodiversity than grassland habitat, but a lower potential than most forest types. Those areas which are covered with more than 50% shrubs as the major woody life form are considered to be mixed shrubland. If such habitat is dominated by Baeckia frutescens (Myrtaceae), which occurs mainly on dry, coarse substrates, the habitat is considered to be Baeckia shrubland. Although Baeckia shrubland is a natural element of the flora of Hong Kong, it has been demonstrated to support lower plant and animal diversity than other mixed shrubland (RT Corlett, pers comm).