Resettlement residential areas (RRAs) are a unique product of China’s urbanisation process. Their... more Resettlement residential areas (RRAs) are a unique product of China’s urbanisation process. Their greening environment is critical to the quality of life and liveable green neighbourhood of the displaced farmers. Our study aimed to (1) interpret the species composition of the landscape trees and their contributions to urban biodiversity in RRAs, and (2) elucidate the structural changes in the tree composition in the last 20 years. Twenty selected RRAs in Changzhou, Jiangsu Province, China, were divided into three categories by completion year. We assessed tree species composition, floristic diversity, tree dimensions, importance value, RRA characteristics, and greening management. The sampled sites accommodated 741 stems and 52 species belonging to 25 families. The three most abundant species were Cinnamomum camphora, Osmanthus fragrans, and Magnolia grandiflora, constituting 45.75% of all trees. The importance values revealed a changing tree planting pattern over time, with persist...
ABSTRACT Heritage trees play special ecological, historical and landscape roles in cities. The of... more ABSTRACT Heritage trees play special ecological, historical and landscape roles in cities. The officially designated old-valuable trees (OVTs) in Hong Kong, threatened by urban intensification and improper care, demand deep understanding to inform management and conservation. This study evaluated their floristic diversity, biomass structure and importance value, and spatial pattern and differentiation by districts and tree-habitats. Data analysis was assisted by detrended correspondence analysis (DCA), similarity percentage analysis (SIMPER) and other statistical tests. New indices, namely district dissimilarity index (DDI), district heterogeneity index (DHI), habitat dissimilarity index (HDI) and habitat heterogeneity index (HHI) helped to assess spatial differentiation. The 352 OVTs belonged to 70 species, 56 genera and 36 families. Ficus microcarpa dominated with maximum importance value, accompanied by only three common species. Some 22 rare and 44 solitary species denote diverse origins due to inheritance and cultivation. Moraceae and Ficus were the dominant family and genus. The oldest districts accommodated more species, trees, and unique species, whereas newer districts had notably less. DCA showed higher floristic fidelity in old districts, and three common Ficus species were ubiquitous in districts. SIMPER results showed the highest DDI and lowest DHI in the newer district. Public park and garden (PPG) habitat harbours most species, trees, and botanical uniqueness. Three Ficus species were also ubiquitous in habitats. Public housing and PPG had the highest HDI. District and habitat dissimilarities were mainly contributed by dominant and common species. Management implications with reference to preservation and enhancement of OVTs were explored, with applications for other cities.
Context Quantitative information regarding tree species-specific size is an essential tool for la... more Context Quantitative information regarding tree species-specific size is an essential tool for landscape planning. It reflects tree-environment and human–environment interactions in the urban landscape. The effects of habitat types on tree allometry have seldom been evaluated. Objectives Firstly, to derive size-related information of common urban tree species in Hong Kong. Secondly, to evaluate the effects of habitat types on tree allometry. Methods A database of 28,622 trees was established by a field assessment. The allometric relationships (DBH-height and DBH-crown width relationships), by both OLS regression and quantile regression, and maximum size of 30 common urban tree species, and the effects of five main habitat types on tree allometry were determined. Species were assigned to groups according to dimensional traits by cluster analysis. Results In general, the allometric relationships of height and crown width to DBH were significant and varied among species. The wide prediction intervals of the OLS regression indicated the high uncertainty of allometric relationships in our region. The 99th percentile crown width of most species reached 10 m, hinting the general failure of most habitats to meet the planting space requirement. Only two large-stature species have narrow crowns. Habitat types posed significant but small species-specific effects on tree allometry. Roadside tree pit was a particularly stressful environment. Conclusions Our findings can act as a reference for landscape planning and management in Hong Kong and nearby cities, including species growth space requirement and habitat limitations. However, prediction of height or crown width from DBH must be carefully interpreted in our city.
Many cities advocate retrofitting green roofs and green walls (GRGW) to create additional green a... more Many cities advocate retrofitting green roofs and green walls (GRGW) to create additional green areas, especially in cramped urban areas. Yet, worldwide, only a handful of studies have evaluated the public views towards the benefits and negative issues and promotion policies of this innovative greening option. To address this gap in the literature, we conducted a survey (N = 500) of residents’ opinions towards GRGW in Tokyo, a city with mandatory installation of GRGW for almost two decades. Respondents mostly agreed with the contribution of GRGW to thermal comfort, air quality, and cityscape but weakly endorsed other potential benefits. High costs as well as mosquitoes and plant litter nuisances were the most recognized negative issues. Mandatory installation was the least preferred promotion policy. Instead, respondents expected installation on public buildings and provision of installation guidance. Respondents predominantly held a “moderate” view towards both the benefits and negative issues, showing indifferent attitudes towards GRGW. Income level and housing type shaped the overall perceptions, whereas age, sex, and current living environment influenced perceptions of individual aspects. Our findings signified a need for a bottom-up strategy to heighten public awareness for the advanced development of GRGW to complement and prime the top-down mandatory installation policy.
Abstract. Trees on buildings sites are routinely damaged or felled in Hong Kong due to negligence... more Abstract. Trees on buildings sites are routinely damaged or felled in Hong Kong due to negligence and lax control. In an unprecidented move, the government required the developer of a large well-wooded lot to retain one large Chinese Banyan (Fiscus microcarpa) tree and take necessary measures to en-sure its long-term survival. The size, fine condition, species rarity, longevity and setting justify its preservation. Great costs (about US$120,000) was needed mainly to construct a 18 m diameter and 10m deep reinforced concrete planter in site above five stories of shops and carparks. Routine ar-boricultural inputs, such as phased pruning of crown and roots, installation of aeration and irrigation facilities, and fer-tilization, are prescribed. Special precautions, including regular monitoring of watering and fertilization to minimize risks of physiological stresses, are justified in view of the costly
Recent rapid urbanization has rendered outdoor space a key quality-of-life factor, yet walkabilit... more Recent rapid urbanization has rendered outdoor space a key quality-of-life factor, yet walkability studies especially in hot-humid climates have seldom considered human biometeorology. This site-level study investigated microclimatic functions of an overhead structure in improving walkability, and identified biometeorology-related factors influencing pedestrian behaviour. A walkway with overhead tinted glass cover, demarcated into sunny zone and shaded zone, was equipped with hanging aluminium fins. Human thermal sensation was approximated by physiologically equivalent temperature (PET) and universal thermal climate index (UTCI), both closely related to global solar radiation and black-globe temperature. Pedestrian flow was tallied by demographic factors to assess the choice between shaded or sunny zones. Compared with sunny zone, shaded zone slashed maximum global solar radiation by 432 W/m 2 in full effect to achieve 90% solar radiation reduction. The maximum cooling in air and black-globe temperatures reached 0.8 °C and 6.1 °C respectively. The overhead structure imposed minimal effect on wind field in both zones. Contrast in maximum PET and UTCI between the two zones reached 8.2 °C and 5.3 °C respectively. In shaded zone, the dominant biometeorological condition was moderate heat stress or slightly warm sensation in contrast to strong heat stress or warm sensation in sunny zone. An overall preference for shaded zone was detected. Pedestrian gender and age, namely female and elderly, were significantly associated with shaded zone preference. The findings could inspire a biometeorological perspective in understanding walking behaviour and pedestrian-friendly facilities. Biometeorological-sensitive design of artificial shade could improve walkability in urban environment that increasingly demands climate change proofing.
Selecting suitable species to enhance ecological functions is crucial for improvements in the pla... more Selecting suitable species to enhance ecological functions is crucial for improvements in the planning and design of roof greening and in maintaining sustainable urban development, especially in rapidly urbanized areas. Assisted by field trips to enhance studies, the present project assessed the ecological functions of 207 plant species used for roof greening in Beijing based on their key functional traits. The results indicate that regulating, cultural, supplying, and supporting functions differed significantly among species and families in the study area. Rosaceae species have higher levels of overall ecological functions than other species, and a large number of Compositae species have lower-level functions. Compared to other families, Araliaceae and Nyctaginaceae have higher mean values of cultural and supporting functions and the highest mean overall function value of 37. Ulmaceae, Sapindaceae, Ginkgoaceae, Berberidaceae, and Aceraceae have higher mean regulating, cultural, sup...
Abstract A census of all existing roadside trees in urban Hong Kong was implemented to collect co... more Abstract A census of all existing roadside trees in urban Hong Kong was implemented to collect comprehensive information on site characteristics, growing space, tree structure, and tree defects and disorders. The survey methodology, emphasizing data quality, uniformity, ...
The changing mode of urban development through time can bring a varied landscape mosaic accompani... more The changing mode of urban development through time can bring a varied landscape mosaic accompanied by spatial-temporal differentiation of urban vegetation. Hong Kong as an ultra-compact city generates intense interactions between trees and urban fabric to highlight urbanization effects on tree communities. The study areas cover public housing estates which accommodate about half of the 7.26 million population. Thirteen site factors related to estate, landform and habitat traits were measured or computed as surrogate urbanization effects. Species composition and diversity of tree communities in 102 estates were assessed by field surveys, including four estate groups: older or newer ones situated respectively in urban core or new towns. They contain 48,823 trees belonging to 232 species with heavy exotic representation. Total tree density and native tree density in newer estates were significantly higher than older ones. Differences in species richness and diversity and native species richness between older and newer estates were not significant, expressing to a certain extent the floristic-homogenization phenomenon. Multi-response Permutation Procedures (MRPP) results showed significant difference in species composition between older and newer estates, which could be explained by variations in development age, density, town plan and pre-urbanization land cover. Nonmetric Multidimensional Scaling (NMDS) results found tree distribution patterns in four estate groups strongly associated with estate area, open space area, estate population, estate age, Shannon index (H′) at planting strip and tree pit, and tree site quality index. Urban-forest management could be improved by adopting more native species and providing high-quality and spacious planting sites to accommodate more and larger trees. The research methods and findings could be used by policy makers and planners in similar large and developing cities to evaluate, design, maintain and enhance urban biodiversity.
Urban trees, as prominent and pertinent landscape elements of cities, are increasingly studied by... more Urban trees, as prominent and pertinent landscape elements of cities, are increasingly studied by both practitioners and academics. Trees in Chinese cities have hitherto received little detailed analysis from the viewpoint of urban forestry or landscape analysis. This study attempts a comprehensive evaluation of the tree population in Nanjing, focusing on the association between urban development and treescape attributes. Six
Resettlement residential areas (RRAs) are a unique product of China’s urbanisation process. Their... more Resettlement residential areas (RRAs) are a unique product of China’s urbanisation process. Their greening environment is critical to the quality of life and liveable green neighbourhood of the displaced farmers. Our study aimed to (1) interpret the species composition of the landscape trees and their contributions to urban biodiversity in RRAs, and (2) elucidate the structural changes in the tree composition in the last 20 years. Twenty selected RRAs in Changzhou, Jiangsu Province, China, were divided into three categories by completion year. We assessed tree species composition, floristic diversity, tree dimensions, importance value, RRA characteristics, and greening management. The sampled sites accommodated 741 stems and 52 species belonging to 25 families. The three most abundant species were Cinnamomum camphora, Osmanthus fragrans, and Magnolia grandiflora, constituting 45.75% of all trees. The importance values revealed a changing tree planting pattern over time, with persist...
ABSTRACT Heritage trees play special ecological, historical and landscape roles in cities. The of... more ABSTRACT Heritage trees play special ecological, historical and landscape roles in cities. The officially designated old-valuable trees (OVTs) in Hong Kong, threatened by urban intensification and improper care, demand deep understanding to inform management and conservation. This study evaluated their floristic diversity, biomass structure and importance value, and spatial pattern and differentiation by districts and tree-habitats. Data analysis was assisted by detrended correspondence analysis (DCA), similarity percentage analysis (SIMPER) and other statistical tests. New indices, namely district dissimilarity index (DDI), district heterogeneity index (DHI), habitat dissimilarity index (HDI) and habitat heterogeneity index (HHI) helped to assess spatial differentiation. The 352 OVTs belonged to 70 species, 56 genera and 36 families. Ficus microcarpa dominated with maximum importance value, accompanied by only three common species. Some 22 rare and 44 solitary species denote diverse origins due to inheritance and cultivation. Moraceae and Ficus were the dominant family and genus. The oldest districts accommodated more species, trees, and unique species, whereas newer districts had notably less. DCA showed higher floristic fidelity in old districts, and three common Ficus species were ubiquitous in districts. SIMPER results showed the highest DDI and lowest DHI in the newer district. Public park and garden (PPG) habitat harbours most species, trees, and botanical uniqueness. Three Ficus species were also ubiquitous in habitats. Public housing and PPG had the highest HDI. District and habitat dissimilarities were mainly contributed by dominant and common species. Management implications with reference to preservation and enhancement of OVTs were explored, with applications for other cities.
Context Quantitative information regarding tree species-specific size is an essential tool for la... more Context Quantitative information regarding tree species-specific size is an essential tool for landscape planning. It reflects tree-environment and human–environment interactions in the urban landscape. The effects of habitat types on tree allometry have seldom been evaluated. Objectives Firstly, to derive size-related information of common urban tree species in Hong Kong. Secondly, to evaluate the effects of habitat types on tree allometry. Methods A database of 28,622 trees was established by a field assessment. The allometric relationships (DBH-height and DBH-crown width relationships), by both OLS regression and quantile regression, and maximum size of 30 common urban tree species, and the effects of five main habitat types on tree allometry were determined. Species were assigned to groups according to dimensional traits by cluster analysis. Results In general, the allometric relationships of height and crown width to DBH were significant and varied among species. The wide prediction intervals of the OLS regression indicated the high uncertainty of allometric relationships in our region. The 99th percentile crown width of most species reached 10 m, hinting the general failure of most habitats to meet the planting space requirement. Only two large-stature species have narrow crowns. Habitat types posed significant but small species-specific effects on tree allometry. Roadside tree pit was a particularly stressful environment. Conclusions Our findings can act as a reference for landscape planning and management in Hong Kong and nearby cities, including species growth space requirement and habitat limitations. However, prediction of height or crown width from DBH must be carefully interpreted in our city.
Many cities advocate retrofitting green roofs and green walls (GRGW) to create additional green a... more Many cities advocate retrofitting green roofs and green walls (GRGW) to create additional green areas, especially in cramped urban areas. Yet, worldwide, only a handful of studies have evaluated the public views towards the benefits and negative issues and promotion policies of this innovative greening option. To address this gap in the literature, we conducted a survey (N = 500) of residents’ opinions towards GRGW in Tokyo, a city with mandatory installation of GRGW for almost two decades. Respondents mostly agreed with the contribution of GRGW to thermal comfort, air quality, and cityscape but weakly endorsed other potential benefits. High costs as well as mosquitoes and plant litter nuisances were the most recognized negative issues. Mandatory installation was the least preferred promotion policy. Instead, respondents expected installation on public buildings and provision of installation guidance. Respondents predominantly held a “moderate” view towards both the benefits and negative issues, showing indifferent attitudes towards GRGW. Income level and housing type shaped the overall perceptions, whereas age, sex, and current living environment influenced perceptions of individual aspects. Our findings signified a need for a bottom-up strategy to heighten public awareness for the advanced development of GRGW to complement and prime the top-down mandatory installation policy.
Abstract. Trees on buildings sites are routinely damaged or felled in Hong Kong due to negligence... more Abstract. Trees on buildings sites are routinely damaged or felled in Hong Kong due to negligence and lax control. In an unprecidented move, the government required the developer of a large well-wooded lot to retain one large Chinese Banyan (Fiscus microcarpa) tree and take necessary measures to en-sure its long-term survival. The size, fine condition, species rarity, longevity and setting justify its preservation. Great costs (about US$120,000) was needed mainly to construct a 18 m diameter and 10m deep reinforced concrete planter in site above five stories of shops and carparks. Routine ar-boricultural inputs, such as phased pruning of crown and roots, installation of aeration and irrigation facilities, and fer-tilization, are prescribed. Special precautions, including regular monitoring of watering and fertilization to minimize risks of physiological stresses, are justified in view of the costly
Recent rapid urbanization has rendered outdoor space a key quality-of-life factor, yet walkabilit... more Recent rapid urbanization has rendered outdoor space a key quality-of-life factor, yet walkability studies especially in hot-humid climates have seldom considered human biometeorology. This site-level study investigated microclimatic functions of an overhead structure in improving walkability, and identified biometeorology-related factors influencing pedestrian behaviour. A walkway with overhead tinted glass cover, demarcated into sunny zone and shaded zone, was equipped with hanging aluminium fins. Human thermal sensation was approximated by physiologically equivalent temperature (PET) and universal thermal climate index (UTCI), both closely related to global solar radiation and black-globe temperature. Pedestrian flow was tallied by demographic factors to assess the choice between shaded or sunny zones. Compared with sunny zone, shaded zone slashed maximum global solar radiation by 432 W/m 2 in full effect to achieve 90% solar radiation reduction. The maximum cooling in air and black-globe temperatures reached 0.8 °C and 6.1 °C respectively. The overhead structure imposed minimal effect on wind field in both zones. Contrast in maximum PET and UTCI between the two zones reached 8.2 °C and 5.3 °C respectively. In shaded zone, the dominant biometeorological condition was moderate heat stress or slightly warm sensation in contrast to strong heat stress or warm sensation in sunny zone. An overall preference for shaded zone was detected. Pedestrian gender and age, namely female and elderly, were significantly associated with shaded zone preference. The findings could inspire a biometeorological perspective in understanding walking behaviour and pedestrian-friendly facilities. Biometeorological-sensitive design of artificial shade could improve walkability in urban environment that increasingly demands climate change proofing.
Selecting suitable species to enhance ecological functions is crucial for improvements in the pla... more Selecting suitable species to enhance ecological functions is crucial for improvements in the planning and design of roof greening and in maintaining sustainable urban development, especially in rapidly urbanized areas. Assisted by field trips to enhance studies, the present project assessed the ecological functions of 207 plant species used for roof greening in Beijing based on their key functional traits. The results indicate that regulating, cultural, supplying, and supporting functions differed significantly among species and families in the study area. Rosaceae species have higher levels of overall ecological functions than other species, and a large number of Compositae species have lower-level functions. Compared to other families, Araliaceae and Nyctaginaceae have higher mean values of cultural and supporting functions and the highest mean overall function value of 37. Ulmaceae, Sapindaceae, Ginkgoaceae, Berberidaceae, and Aceraceae have higher mean regulating, cultural, sup...
Abstract A census of all existing roadside trees in urban Hong Kong was implemented to collect co... more Abstract A census of all existing roadside trees in urban Hong Kong was implemented to collect comprehensive information on site characteristics, growing space, tree structure, and tree defects and disorders. The survey methodology, emphasizing data quality, uniformity, ...
The changing mode of urban development through time can bring a varied landscape mosaic accompani... more The changing mode of urban development through time can bring a varied landscape mosaic accompanied by spatial-temporal differentiation of urban vegetation. Hong Kong as an ultra-compact city generates intense interactions between trees and urban fabric to highlight urbanization effects on tree communities. The study areas cover public housing estates which accommodate about half of the 7.26 million population. Thirteen site factors related to estate, landform and habitat traits were measured or computed as surrogate urbanization effects. Species composition and diversity of tree communities in 102 estates were assessed by field surveys, including four estate groups: older or newer ones situated respectively in urban core or new towns. They contain 48,823 trees belonging to 232 species with heavy exotic representation. Total tree density and native tree density in newer estates were significantly higher than older ones. Differences in species richness and diversity and native species richness between older and newer estates were not significant, expressing to a certain extent the floristic-homogenization phenomenon. Multi-response Permutation Procedures (MRPP) results showed significant difference in species composition between older and newer estates, which could be explained by variations in development age, density, town plan and pre-urbanization land cover. Nonmetric Multidimensional Scaling (NMDS) results found tree distribution patterns in four estate groups strongly associated with estate area, open space area, estate population, estate age, Shannon index (H′) at planting strip and tree pit, and tree site quality index. Urban-forest management could be improved by adopting more native species and providing high-quality and spacious planting sites to accommodate more and larger trees. The research methods and findings could be used by policy makers and planners in similar large and developing cities to evaluate, design, maintain and enhance urban biodiversity.
Urban trees, as prominent and pertinent landscape elements of cities, are increasingly studied by... more Urban trees, as prominent and pertinent landscape elements of cities, are increasingly studied by both practitioners and academics. Trees in Chinese cities have hitherto received little detailed analysis from the viewpoint of urban forestry or landscape analysis. This study attempts a comprehensive evaluation of the tree population in Nanjing, focusing on the association between urban development and treescape attributes. Six
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