The status of natural succession in lowland secondary forests of Hong Kong

Abstract

Hong Kong has undergone a long history of deforestation for more than 1, 000 years. No primary forest can now be found in Hong Kong and most of the secondary forests have been restored through natural succession after the Second World War. By knowing the most updated secondary forest succession status in Hong Kong, a more proactive management plan can be worked out to have a better forest restoration strategy.

Forest Dynamic Plots are large forest plots which can provide information about species composition, changes in the species spatial arrangement over time and population growth. In this study, the successional status of two local natural lowland secondary forests of different ages are evaluated by using Forest Dynamic Plot data. These two 1 hectare size plots are located at Shek Kong and Tai Po Kau Nature Reserve respectively. The data collected is analyzed and compared with another Forest Dynamic Plot in Dinghushan National Nature Reserve in Guangdong, China which is an old-growth lowland forest. It is within the same biogeographic region with Hong Kong. Tree surveys were conducted in these plots. All the trees and shrubs with diameter at breast height equal or larger than 10mm were tagged, measured, identified and mapped.

In the 20-year old Shek Kong Plot, a total of 10378 individuals of 62 native species of woody shrubs or trees were recorded. The dominant species are Litsea rotundifolia var. oblongifolia, Psychotria asiatica and Aporusa dioica with an importance value of 20.463, 11.725 and 6.574 respectively. The Shek Kong Plot is dominated by shade-intolerant shrub or pioneer species. The Shek Kong Plot is still in early secondary stage or entering the stem exclusion stage.

The 60-year old Tai Po Kau Plot has a total of 5172 individuals of 77 species. The Tai Po Kau Plot has much lower stem density than the Shek Kong Plot but with higher species diversity. The top three dominant species in Tai Po Kau Plot are Machilus chekiangensis, Psychotria asiatica and Diospyros morrisiana, with an importance value of 23.538, 15.321 and 7.652 respectively. Although the Tai Po Kau Plot is more dominated by tree species, when it is compared with the Dinghushan Plot, the shade-tolerant climax species are still in low intensity. Thus, Tai Po Kau is not yet an old-growth or mature forest. It is now in understory reintiaition stage or late secondary stage and more shade-tolerant species are needed to move to the mature forest stage.

To facilitate the forest succession process, it is recommended to have more studies on the distribution pattern and seed dispersal mechanism of shade-tolerant species. Feasibility study of reintroduction of relevant seed dispersal agents such as rodents from Southern China could be a more proactive management to facilitate the process.