ALBERT

Description: The ever-increasing demands for outdoor recreation have caused widespread ecological damages in many parts of the world, so that methods to contain deleterious impacts and maintain the quality of recreational experience must be earnestly sought. Besides the commonlyprescribed preventive and ameliorative actions on the resource-base, visitor management which can provide cost-effective and long-term solutions deserves more attention than hitherto. This paper evaluates a spectrum of relevant options including the subtle (influencing userbehaviour), through the intermediate (redistributing use), to the regulatory (rationing use).The reduction of per caput impact can, naturally, raise the capacity of an area to accommodate continuing use. Minimum impact techniques can substantially curtail the largely inadvertent damage due to ignorance rather than malice, while recreational planning and management can take into account the changing user preference. Appropriate data to guide management decisions can be acquired through innovative non-contact approaches, including visitor observation, to solicit candid and spontaneous responses. Good-quality information, conveyed through different channels in ample time before a visit, can effectively modify user behaviour and perception. Formal and informal education, to inculcate a responsible attitude towards the natural environment, can bring long-range benefits. Citizen participation can furnish diversified and useroriented perspectives that are important for successful programmes.

Description: The Country Parks programme in Hong Kong has been overwhelmingly successful in generating outdoor recreational demands. Most visitors concentrate in designated barbeque-picnic sites of which many have been badly damaged by intensive recreational use. The conditions in 60 sites in a popular Country Park were evaluated by allocating ordinal ratings to 20 soil-erosion and site-attractiveness indicators. Index sites representing three levels of impacts were studied in detail for specific changes in vegetation and soil that had been induced by trampling. The magnitude of site degradation was indicated by the relative proportions of vegetation, organic litter, and bare ground, covers. The conversion from vegetation to litter was faster than that of litter to bare soil initially, but the converse is true at advanced stages of degradation. Seven out of fourteen site-attractiveness attributes, including accessibility, facility provision, shape, stocking rate and distribution pattern of facilities, on-site naturalness, and scenic diversity, were associated with erosion–in most cases positively.

Description: Trees in cities face a severe limitation of plantable space and an exceptionally stressful growing environment. In Hong Kong, shortage of developable land has relegated trees to a lower priority and intensified urban impacts on them, relative to other cities. The vicissitudes of urban growth and trees since the founding of Hong Kong are reviewed, and eleven specific conflicts between urbanization and trees in Hong Kong are described. Redevelopment of existing buildings has raised site coverage by impervious surface and taken away ground-level planting space within and around affected lots. Infilling of relatively low-density areas mainly for government and institutional land-uses has increased development density and removed existing greenery and planting spaces. Road construction and improvement has widely damaged roadside trees and removed valuable and conspicuous greenery. Proliferation of underground utilities has fuelled the contest for usable space and precluded planting in many places. Widespread and frequent roadside trenching, associated with utilities and the laying of cable television and telecommunication networks has incurred massive root damage at roadsides. Poor soil quality commonly beset by chemical and physical constraints has caused chronic poor tree performance. Intrusion into urban parks and other green enclaves by buildings and roads has usurped the limited stock of green spaces. Encroachment into peri-urban woodlands has deprived the city of fringing mature greenery with conservation, landscape and amenity worth. Plantable space in reclaimed lands has been intensively used with inadequate allocation for trees. Protection and preservation of champion specimens has lacked statutory means and a coordinated policy. Reinforcement and demolition of stone walls has destroyed many large trees on unique mural habitats. Quality of arboricultural practice is poor, particularly in the private sector. Possible solutions to these limitations in Hong Kong are suggested, and have implications for other cities facing similar problems.

Description: Trees, as welcome and necessary components of Nature and functional landscape elements in cities, provide a worth-while theme for applied ecological study. Of the different approaches, the micro-scale evaluations of tree—habitat interactions can throw light on practical tree management. The roadside trees in Hong Kong, generally dwelling in a stressful physical and physiological environment, have been surveyed in detail in the field with regard to species composition, tree structure, tree defects, and habitat characteristics.Despite a diversified floristic composition, the street-tree population is dominated by a small number of common species, of which 12 have been chosen for in-depth evaluations. The recent emphasis on exotic and fast-growing species with limited final dimensions will modify the treescape in the long run. Many existing large specimens have been sacrificed to urban redevelopments. The differential performance of different species with reference to the occurrence of defects has been interpreted. Almost all the trees are inflicted by some structural or physiological problems, and large trees are practically collectors of diverse maladies.The urban tree habitats of Hong Kong are characterized by gravely cramped and stressful conditions from the soil-level upwards and especially as regards headroom. Tree-habitat correlations and associations suggest a need to plant rapid-growing, tall but narrow-canopied species that are able to resist a maximum proportion of the inevitable tree defects and diseases. The shortage of good-quality habitats with space for tree-growth, and the accompanying unfavourable ecological niches, are crucial factors for tree existence. The prospects of street trees in the long-term urban planning and upgrading for environmental quality, with special reference to the provision and preservation of proper habitats, are elaborated, with Hong Kong as a practical example.

Description: High-frequency monitoring of suspended particulate matter (SPM) concentration can improve water resource management. Missing high-resolution satellite images could hamper remote-sensing SPM monitoring. This study resolved the problem by applying spatiotemporal fusion technology to obtain high spatial resolution and dense time-series data to fill image-data gaps. Three data sources (MODIS, Landsat 8, and Sentinel 2) and two spatiotemporal fusion methods (the enhanced spatial and temporal adaptive reflectance fusion model (ESTARFM) and the flexible spatiotemporal data fusion (FSDAF)) were used to reconstruct missing satellite images. We compared their fusion accuracy and verified the consistency of fusion images between data sources. For the fusion images, we used random forest (RF) and XGBoost as inversion methods and set “fusion first” and “inversion first” strategies to test the method’s feasibility in Ebinur Lake, Xinjiang, arid northwestern China. Our results showed that (1) the blue, green, red, and NIR bands of ESTARFM fusion image were better than FSDAF, with a good consistency (R2 ≥ 0.54) between the fused Landsat 8, Sentinel 2 images, and their original images; (2) the original image and fusion image offered RF inversion effect better than XGBoost. The inversion accuracy based on Landsat 8 and Sentinel 2 were R2 0.67 and 0.73, respectively. The correlation of SPM distribution maps of the two data sources attained a good consistency of R2 0.51; (3) in retrieving SPM from fused images, the “fusion first” strategy had better accuracy. The optimal combination was ESTARFM (Landsat 8)_RF and ESTARFM (Sentinel 2)_RF, consistent with original SPM maps (R2 = 0.38, 0.41, respectively). Overall, the spatiotemporal fusion model provided effective SPM monitoring under the image-absence scenario, with good consistency in the inversion of SPM. The findings provided the research basis for long-term and high-frequency remote-sensing SPM monitoring and high-precision smart water resource management.

Description: Of the many forms of above- and below-ground stresses facing urban trees, physical soil limitations are generally among the most persistent and least amenable to amelioration. Soil compaction is a common soil malady that afflicts many planting-sites and causes tree decline. The concept of soil structure in terms of porosity and moisture-suction is reviewed, to provide a basis for the interpretation of compaction as structural degradation. The reorganization of solid and interstitial void constituents, which can result in increased dentity of packing, is related to some fundamental physical and physico-chemical soil properties.Compaction brings about changes in a wide spectrum of related geometric and other soil attributes, the consequences of which are often inimical to plant growth. Many deliberate and inadvertent actions in urban areas increase packing density, which can be diagnosed through some field and laboratory tests. The harmful effects of compaction is exertedviamechanical impediment and other indirect impacts on root growth. Excessively loose soils and soil crusts are discussed in the light of compaction concepts and in relation to tree growth.A wide range of measures could be adopted to alleviate the problems of soil compaction. Preventive actions taken before tree planting are preferred to post-planting remedies which are cumbersome, and injurious to roots. Soils at planting sites could be partially improved by various mechanical means to reduce packing density and enhance aggregation. Coarse-textured materials with inherently high strength and resistance to dense packing could provide a stable medium for tree growth. The installation of subsurface aeration and drainage pipes could alleviate the ill-effects of compaction. Care should be taken to avoid structural degradation in stockpiling and construction activities.