published_or_final_version / Architecture / Master / Master of Landscape Architecture

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

After 8-19 years of restoration, therefore, there were improvements in the quality of the restored sites in terms of vegetation structure, soil productivity and nutrient cycling. While the degree of improvement increases with age of the plantations, the qualities of the restored sites still lag behind that of the mature forest. / Based on the above findings, an assessment system is developed for the evaluation of restoration progress in the subtropical region. It includes a set of ecological indicators including: species diversity, timber transaction areas, standard deviation of tree height, total crown area, sapling density, species invasion, soil bulk density, soil water-holding capacity, organic carbon content, TKN, pH, seed bank, soil mineralization rate and litter decomposition rate. These findings have, therefore, filled the knowledge gap that there is virtually no study on the ecological assessment of restored subtropical forests in the literature. In addition, the goals and strategy of ecological restoration in Hong Kong are also discussed in the thesis. / Ecological rehabilitation with exotic species, particularly nitrogen-fixing legumes, is capable of ameliorating the degraded soils. While there is no change in the soil texture, ecological rehabilitation lowered pH and bulk density, increased organic carbon (OC) and total Kjeldahl nitrogen (TKN) contents, and elevated field capacity and available water contents of the soil. Intra-layer differences in OC and TKN were widened in R89, a trend comparable to TO. Ammonification and nitrification were detected in the restored soils, where NH4-N predominated over NO3-N and net N mineralization was higher in R89 than R95 and R00. In contrast, TO is dominated by NO3-N and net N mineralization is higher than the restored soils. / Ecological succession is happening in all the restored sites and the evidence of proof include: stem exclusion (declining density); steady increase of tall trees (>12m); invasion of grass, fern, vine and climber though few; increase in species diversity; canopy closure; decreasing standing litter but a simultaneous increase in fruits and seeds; increase of DBH, transaction areas and crown area, etc. Overall, the restored forests are inferior to the mature forest in terms of biodiversity and stand complexity. / Keywords: ecological assessment, forest rehabilitation, soil destruction sites, subtropical area / Litterfall production was characterized by bimodal peaks in TTEBA and by a single peak in TO. Peak production in August through September in Tai Tong was caused by mechanical breakage during the passage of tropical cyclones. In contrast, litterfall in TO was less easily affected by cyclones. Total litterfall production was in the order of TO ≥ R00 > R89 ≥ R95. Litterfall production was only positively correlated with canopy closure of the forests. Nutrient return was higher in the dry season than the wet season, which is governed by the quantity of litterfall. / The decomposition constants (k) for Acacia mangium and Schima superba foliage litter decreased in the order of TO > R89 > R00 > R95. It is positively correlated with SOC, TKN, TP, clay percentage and FC water of the soils but negatively with soil bulk density (p<0.05). Among the restored sites, the half life (T50) of leaf litter was shortest for Acacia mangium (92.4 days) and Schima superba (105.0 days) in R89. Overall, litter decomposition is faster in TO than any of the restored sites. / The present study investigates the successional development of three restored subtropical forests in Hong Kong, with special emphasis on the development of an assessment system suitable for the evaluation of restoration progress. The restored forests, aged 8 (R00), 13 (R95) and 19 (R89) years, were established on severely degraded lands in Tai Tong East Borrow Area (TTEBA) depleted of vegetation and top soil cover. The vegetation, soil and nutrient cycling processes of these restored forests were benchmarked against a mature forest (TO), aged 300+ years, characterized by high biodiversity and undisturbed soil. The restored forests are dominated by exotic species, mostly nitrogen-fixing legumes, and the mature forest by broad-leaved native species. The objectives of this thesis are threefold: (a) to assess the ecological development of the restored forests; (b) to develop an assessment system that can be employed to assess restoration progress; and (c) to revisit the goals and strategy of ecological restoration in Hong Kong. / Zheng, Hailong. / "October 2009." / Source: Dissertation Abstracts International, Volume: 72-01, Section: A, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 187-209). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.