C.Y. Jim

Comprehensive greenspace planning based on landscape ecology principles in compact Nanjing city, China

Urban greenspaces are universally valued as amenity-recreation venues, wildlife refuges and essential livable-city ingredients. Western strategies of urban greenspace provision are difficult to implement or retrofit in most Asian cities, commonly constrained by a high-density compact form. With recent rapid urbanization and associated brown and green field developments, ample opportunities arise to overhaul greenspace standards and patterns. The case study of the ancient city of Nanjing in China permits planning for an integrated greenspace network, aiming at flexibility for future urban expansion, green field acquisition, recreational functions, wildlife habitats and environmental benefits. It consists of green wedges, greenways and green extensions that incorporate urban green areas at three landscape scales. At the metropolis scale, through normative and substantive analyses of urban form and urban expansion, and assessment of suburban uplands, five green wedges are demarcated to generate a star urban form. The green wedges link the extensive countryside to the central city, and define elongated finger-like spaces between them for urban expansion to avoid conflicts with green fields. At the city scale, three major greenways, including city-wall circular greenway, Inner-Qinhuai River greenway, and canopy-road greenway, are designed as a permeating framework to guide new greenspace location, configuration and continuity, and to link existing parks. These greenways are equipped with a comprehensive trail system to foster pedestrian and cycling movements that are preferred by the public and the government. At the neighborhood scale, a greenspace organization, consisting of residential public open spaces, shaded sidewalks and riparian strips, conforms to the network geometry. As well-connected entities, these small proximate enclaves provide opportunities for residents to have day-to-day contact with nature. They also serve to resist undue urban influences and intrusions. Overall, the three-tiered greenspace system provides an alternative mode for urban development to the conventional transport-dominated one, to usher substantial improvement in landscape-environmental quality and to augment the sustainable-city notion.

Urban soil characteristics and limitations for landscape planting in Hong Kong

Soils in urban areas have not received adequate attention in relation to landscape planting. Recent urban tree surveys in Hong Kong identified many arboricultural problems related to stressful habitat conditions including edaphic ones. Soil constraints in the crowded city are acute and yet relevant data are lacking. This project evaluated in the field and laboratory 100 soil samples obtained from sites of varied natural and disturbance history at difficult roadside tree-pit sites in urban Hong Kong. An extensive range of physical and chemical properties were assessed to establish baseline information on soil limitations to amenity-vegetation growth. Most soils have lost natural soil horizons with morphological features of fill materials such as poor structure and artificial layering. They are excessively stony and coarse-textured, with abundance of building rubble and other foreign substances. The extensive soil compaction, associated with structural degradation and loss of porosity, is inimical to aeration, drainage, storage of plant-available moisture, and root growth. Release of carbonate from the calcareous construction waste has induced alkaline pH, with consequences on micronutrient and phosphorus deficiency. Organic matter contents, and the related supply of essential nitrogen and phosphorus, are all meager. The capacity to hold nutrient bases and the amount held in available forms are both inadequate for vigorous plant performance. There are signs of pollution by heavy metals, especially lead, which are derived from air-borne sources related to vehicular traffic. The results help to ascertain the need for soil tests in landscaping endeavors, to reinforce a weak link in landscaping programs, to establish a package of recommendations to improve urban soil management, to enhance the cost-effectiveness of greening programs, and to augment urban-tree performance so as to reduce recurrent management liability and burden.

Physical and chemical properties of a Hong Kong roadside soil in relation to urban tree growth

Tree planting in urban areas faces many limitations that suppress performance and increase management burdens. Soil problems are increasingly recognized as an important cause of establishment failures and declines. Recent city-greening programs in Hong Kong necessitate a better understanding of soil difficulties, but relevant information is lacking. A detailed study of physical and chemical properties of a representative roadside soil provides baseline data on edaphic restrictions and hints for correction and amelioration. The soil depth is inadequate for normal root expansion of trees, is excessively stony and sandy, and is beset by poor structure and heavy compaction. Root growth is likely to be restricted by the low levels of porosity and high shear strength. The densely packed surface layer reduces aeration and water movement into the lower layers. The nutrient stock is meager, and the ability to hold available moisture and nutrients is very limited. Soil reaction comparing with local natural soil is uncharacteristically alkaline with pH reaching 8.5 which may induce iron and manganese deficiency. Heavy metals register elevated concentrations especially for lead and zinc, but do not attain phytotoxic levels. The common multiple substrate problems need to be addressed properly before trees are planted. Evaluation of selected soil attributes is advocated for all planting sites.

Species diversity of three major urban forest types in Guangzhou City, China

Abstract Guangzhou city in South China was assessed to understand the associations between tree species diversity and urban development. The study area covers five urban districts which form the bulk of the built-up areas. Reconnaissance field trips and aerial photograph survey identified main green covers in three urban-forest types, namely roadside niches, urban parks, and institutional grounds. Trees at roadsides and 21 parks were censused, whereas 14 large institutional sites were sampled. A total of 115,140 trees were evaluated for species identification, dimensions and site-environs conditions, with 40.8% at roadsides, 38.2% in parks, and 21.0% in institutional grounds. The urban forests composed of 254 species in 62 botanical families led by Moraceae, Caesalpiniaceae and Myrtaceae. Institutional forest has the highest diversity, followed by park and roadside trees. Most trees are derived from a small group of dominant species. Broadleaf species are prominent, especially the evergreen, whereas conifers and palms are sparingly adopted, except palms in institutional areas. Exotic species, mainly originating from tropical Asia and Australia, are common but not as dominating as in other tropical cities. Native species include spontaneous invasion into ruderal habitats, especially in parks. Species composition was interpreted vis-a-vis the interplay of natural and cultural factors then and now. Changing site conditions (geometric vs. physiological attributes), decision-making and management regimes (official-public vs. individual-lot stewardship), funding constraint (straitjacketed vs. adequate), intended amenity functions, and evolving landscape fashion (traditional vs. innovative), have helped to mould respective species assemblages to define their identity. Implications for long-term tree planning and management in Guangzhou and other fast developing cities are explored.

Precipitation chemistry of Lhasa and other remote towns, Tibet

Abstract Precipitation event samples during 1987–1988 field expedition periods and 1997, 1998, 1999 and 2000 have been collected at Lhasa, Dingri, Dangxiong and Amdo, Tibet. The sampling and analysis were based on WMO recommendations for a background network with some modifications according to local conditions and environmental characteristics. The following precipitation constituents and related parameters were measured: pH, conductivity, CO2 partial pressure, total suspended particles, and the content of K+, Na+, Ca2+, Mg2+, Fe, Mn, NH4+, Cl−, NO2−, NO3−, SO 4 2− Br − , HCO3− and HPO42−. Some atmospheric dust samples have also been collected. Over 300 precipitation events have been measured for pH and conductivity. Among these, 60 have been analysed for their chemical components. The results show that Lhasas precipitation events were constantly alkaline with weighted averages of pH 8.36 in the 1987–1988 period, and 7.5 for 1997 to 1999. Only one event was weakly acidic during 1997–1999. Although CO2 partial pressure, a major producer of acidity in natural water on the Plateau, falls with increasing elevation, the lowest measured CO2 partial pressure can only raise pH value by 0.1 units in the sampling areas. Chemical analysis indicates that the major contributor to alkaline precipitation is the continental dust, which is rich in calcium. The analysis also shows that Tibet is still one of the cleanest areas in the world with little air pollution. However, the decline of pH from the 1980s to 1990s, which was reflected by an increase of NO3− and SO42− in precipitation, alerts us to the urgency of environmental protection in this fragile paradise.

Soil Compaction as a Constraint to Tree Growth in Tropical & Subtropical Urban Habitats

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 exerted via mechanical 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.

Climate change, social unrest and dynastic transition in ancient China

The evident connection between human evolution and climatic changes has been concurred by scientists. Although many people are trying to forecast the impacts of climatic changes on our future society, there are not any studies to quantitatively scrutinize the interrelation between climatic changes and social developments by using historical data. In line with this knowledge gap, this study adopted a scientific approach to compare the paleoclimatic records with the historical data of wars, social unrests, and dynastic transitions in China spanned from the late Tang to Qing Dynasties. Results showed that war frequency in cold phases was much higher than that in mild phases. Besides, 70%–80% of war peaks and most of the dynastic transitions and nationwide social unrests in China took place in cold phases. This phenomenon could be attributed to the diminishing thermal energy input in cold phases resulting in the fall of land-productivity and hence, the deficiency of livelihood resources across society. Accompanied with certain social circumstances, this kind of ecological stress was transformed into wars and social unrests, followed by dynastic transitions in most of the cases. By closer examination, it was even found that war frequency was negatively correlated with temperature anomaly series. As land carrying capacities vary from one climatic zone to another, the magnitude of war-temperature association also differed among different geographic regions. It is suggested that climatic change was one of the most important factors in determining the dynastic cycle and alternation of war and peace in ancient China.

Assessment and Valuation of the Ecosystem Services Provided by Urban Forests

Urban forests, composed of trees and other vegetation, are integral parts of urban ecosystems. Whether planted intentionally or left by default, urban forests appeared even in the earliest settlements. In urban areas, the constituent greenery provides a broad range of benefits, including opportunities for residents to have daily contact with nature, and to enjoy attractive landscapes and recreational activities (Grey and Deneke, 1986; Rowntree, 1986; Ulrich, 1986; Dwyer et al., 1992; Miller, 1997; Bolund and Hunhammar, 1999; Tyrvainen and Miettinen, 2000). In addition, vegetation in cities moderates microclimate extremes and reduces regional pollution (Botkin and Beveridge, 1997; Whitford et al., 2001). They contribute to an improved quality of urban life in many ways, even though these functions are often taken for granted by the public and some city authorities. The environmental benefits and natural functions provided by urban forests can be interpreted as ecosystem services, which are defined as benefits that the human population can derive, directly or indirectly, from ecosystem functions (Costanza et al., 1997). The urban population must rely mainly on services derived from external ecosystems, such as food and energy. However, the diversified benefits generated by urban forests, which are limited in comparison with the amount of imported ecosystem services, could be more instrumental in solving local environmental problems. They could significantly improve the quality of urban life, and play a paramount role in stabilizing and sustaining urban ecosystems (Daily, 1997; Bolund and Hunhammar, 1999; Jensen et al., 2000). Such ecosystem services, however, are not very tangible and generally not well understood or appreciated. Recent studies have generated a wealth of scientific information on the magnitude of their benefits. A more direct interpretation of these benefits for laypersons could promote their preservation and enhancement. A useful approach is to quantify these natural services, and then follow with a valuation of these nonmarket and noncommodity goods. The results could be translated into the universal language of monetary units, and be compared with alternatives to facilitate decision making related to natural resources or the environment. Valuation is inseparable from the choices and decisions humans have to make about ecosystems (Bingham et al., 1995; Costanza et al., 1997; Barbier et al., 1998; Costanza, 2000). Some studies have attempted to quantify the ecosystem services generated by urban

Sustainable urban greening strategies for compact cities in developing and developed economies

Urban greening contributes notably to quality of life and ecosystem services in cities. Compact cities in developing and developed countries are commonly beset by greenspace deficit. Based on literature review supplemented by field studies in different cities, a sustainable urban greening strategy is proposed. Urban renewal and new developments without a greening vision could miss the opportunities to bring relief. The public and private sectors can join hands to insert plantable spaces into the urban fabric. Urban greenspaces (UGS) with good connectivity forming a green network to permeate the city constitute the hallmarks of a naturalistic design. Preservation and creation of natural areas with rich biodiversity offer a new dimension to UGS design. Greening benefits could be expressed in economic terms to complement conventional ecological-environmental emphasis. Outstanding trees could receive high-order conservation efforts, and trees in construction sites warrant enhanced protection. Tree transplanting demands an overhaul in concepts and skills. Improving roadside tree planting and maintenance offers a cost-effective way to upgrade the townscape. Ameliorating widespread soil limitations could remove a major hindrance to tree growth. Innovative ideas of development right transfer, street pedestrianization, river and canal revitalization, green roofs and green walls could mobilize hitherto underused plantable resources. Lacking appropriate institutional setup and scientific capability pose intractable bottlenecks. Innovative public policies and greening technologies are needed for sustained improvements. Amalgamating natural and social sciences in a multidisciplinary approach and reinforcing the link between science and public policies could overhaul greening.

Impacts of intensive urbanization on trees in Hong Kong

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 insti