Spatial patterns of a subtropical,coastal urban forest: Implications for land tenure,hurricanes, and invasives

Spatial patterns of tree structure and composition were studied to assess the effects of land tenure, management regimes, and the environment on a coastal, subtropical urban forest. A total of 229 plots in remnant natural areas, private residential, public non-residential, and private non-residential land tenures were analyzed in a 1273 km² study area encompassing the urbanized portion of Miami-Dade County, USA. Statistical mixed models of structure, composition, location, and land tenure data were used to analyze spatial patterns across the study area. A total of 1200 trees were measured of which 593 trees (49%) were located in residential areas, 67 (6%) in public non-residential areas, 135 trees (11%) in private non-residential areas, and 405 (34%) in remnant, natural areas. A total of 107 different tree species belonging to 90 genera were sampled. Basal area in residential land tenures increased towards the coast while private residential land tenures and natural areas had higher species diversity than non-residential areas. Tree height, crown light exposure, and crown area might indicate the effects of past hurricane impacts on urban forest structure. Land tenure, soil types, and urban morphology influenced composition and structure. Broadleaf evergreen trees are the most common growth form, followed by broadleaf deciduous, palms, and conifers. Exotic tree species originated mainly from Asia and 15% of all trees measured were considered exotic-highly invasive species. We discuss the use of these results as an ecological basis for management and resilience towards hurricane damage and identifying occurrence of invasive, exotic trees.     

Effects of urbanization on ground-dwelling spiders in forest patches,in Hungary

Effects of urbanization on ground-dwelling spiders (Araneae) were studied using pitfall traps along an urban-suburban–rural forest gradient in Debrecen (Hungary). We found that overall spider species richness was significantly higher in the urban sites compared to the suburban and rural ones. The increased diversity was due to the significantly more open-habitat species in the assemblages at the urban sites. This suggests that species from the surrounding matrix (grasslands and arable lands) penetrated the disturbed urban sites. The ratio of forest species was significantly higher in the rural sites than in the suburban and urban ones, suggesting that forest species are indeed sensitive to the disturbance caused by urbanization. Canonical correspondence analysis revealed that the species composition changed remarkably along the urbanization gradient. Open-habitat spiders were associated with the urban sites of higher ground and air temperature. Forest spiders were characteristic of the rural sites with higher amount of decaying woods. Our findings suggest that the overall diversity was not the most appropriate indicator of disturbance; species with different habitat affinity should be analyzed separately to get an ecologically relevant picture of the effect of urbanization.     

Exotic trees contribute to urban forest diversity and ecosystem services in inner-city Cleveland,OH

Vacant land, a product of population and economic decline resulting in abandonment of infrastructure, has increased substantially in shrinking cities around the world. In Cleveland, Ohio, vacant lots are minimally managed, concentrated within low-income neighborhoods, and support a large proportion of the city’s urban forest. We quantified abundance, richness, diversity, and size class of native and exotic tree species on inner-city vacant lots, inner-city residential lots, and suburban residential lots, and used i-Tree Eco to model the quantity and economic value of regulating ecosystem services provided by their respective forest assemblages. Inner-city vacant lots supported three times as many trees, more exotic than native trees, and greater tree diversity than inner-city and suburban residential lots, with the plurality of trees being naturally-regenerated saplings. The urban forest on inner-city vacant lots also had two times as much leaf area and leaf biomass, and more tree canopy cover. The quantity and monetary value of ecosystem services provided by the urban forest was greatest on inner-city vacant lots, with exotic species contributing most of that value, while native taxa provided more monetary value on residential lots. The predominately naturally-regenerated, minimally managed exotic species on vacant land provide valuable ecosystem services to inner-city neighborhoods of Cleveland, OH.     

Private trees contribute uniquely to urban forest diversity,structure and service-based traits

The urban forest provides our communities with a host of benefits through the delivery of ecosystem services. To properly quantify and sustain these benefits, we require a strong baseline understanding of forest structure and diversity. To date, fine-scale work considering urban forest diversity and ecosystem services has often been limited to trees on public land, considering only one or two green space types. However, the governance of urban green spaces means tree species composition is influenced by management decisions at various levels, including by institutions, municipalities, and individual landowners responsible for their care. Using a mixed-method approach combining a traditional field-inventory and community science project, we inventoried urban trees in the residential neighbourhood of Notre-Dame-de-Grȃce, Montreal. We assessed how tree diversity, composition and structure varies across multiple green space types in the public and private domain (parks, institutions, street rights of way and private yards) at multiple scales. We assessed how service-based traits – traits capturing aspects of plant form and functions that urban residents find beneficial – differed across green space types, with implications for the distribution of ecosystem services across the urban landscape. Green space types displayed meaningful differences in tree diversity, structure, and service-based traits. For example, the inclusion of private trees contributed an additional 52 species (>30% of total species) not found in the local public tree inventory. Trees on private land also tended to be smaller than those in the public domain. Beyond patterns of tree richness, size, and abundance we also observed differences in the composition of tree species and service-based traits at site-scales, particularly between street rights-of way and private yards. While species composition varied considerably across street blocks, blocks were very similar to one another in terms of mean service-based traits. Contrastingly, while species composition was similar from yard to yard, yards differed significantly in mean service-based trait values. Our work emphasises that public tree inventories are unlikely to be fully representative of urban forest composition, structure, and benefits, with implications for urban forest management at larger spatial scales.     

Plant species response to urbanization: comparison of isolated woodland patches in two cities of North-Western France

The effect of urbanization on species distribution has been extensively documented, but a main challenge in urban ecology is to better understand the factors causing different distributions among species in response to urbanization. Hence, this paper aims to compare the effects of urbanization on woodland plant assemblages in two cities and to describe species responses by using several indicators. The study was carried out in the cities of Angers and Rennes (North-Western France) where 11 isolated woodlands were surveyed along an urban–rural gradient in each city. Abundance data of spontaneous species were collected from 220 quadrats. The effect of land cover (within a 500 m buffer around each woodland) on species assemblages was investigated by Canonical Correspondence Analysis. Buildings and pavement areas were the most significant predictors of species composition, and the effect of location in Angers or Rennes appeared on the second axis. More than 60% of the most frequent plant species were indicator of urban or rural location and their preferences were similar in the two cities. These lists of urban and rural indicator species were compared with Ellenberg’s indicator values and two other indicators specific to forest environment. The species which grow preferentially in urban woodlands are species which are already known to be associated with recent forests rather than ancient forests; with hedgerows rather than woodlands. The opposite pattern was observed concerning rural species. Moreover, urban indicator species have higher optima for soil pH and soil nitrogen content than rural indicator species. Different characteristics and history of forest habitat—continuity of the forest land cover, linearity of the habitat, change in adjacent land cover and land use—could select the same species, and the responses of the latter might involve different preferences concerning soil alkalinity and nutrient status.     

Preferences of urban dwellers on urban forest recreational services in South Korea

This paper aims to investigate the preferences of urban dwellers for various attributes of urban forests, with an emphasis on forest recreational services. A choice experiment was conducted using face-to-face interviews with 823 urban dwellers in 2010. Urban forest attributes such as trails, slope, biodiversity, environmental education programs and entrance fees were found to influence Korean citizens’ preferences regarding urban forests. Among the six urban forest attributes, biodiversity was the most influential among Korean urban dwellers in their choice of urban forest recreation. Three latent groups with relatively homogeneous preferences over various urban forest attributes were identified. Residential area, family composition and the purpose of their visit determined group membership. It was notable that the preferences of urban forest recreationists differ from the general preferences of visitors to forests located in remote areas. Urban forest planning and management should consider the attributes of urban forests and the preferences of citizens visiting urban forests to improve urban dwellers’ welfare.     

Effects of surrounding urbanization on non-native flora in small forest patches

The purpose of our study was to compare the number, proportion, and species composition of introduced plant species in forest patches situated within predominantly forested, agricultural, and urban landscapes. A previous study suggested that agricultural landscape context does not have a large effect on the proportion of introduced species in forest patches. Therefore, our main goal was to test the hypothesis that forest patches in an urban landscape context contain larger numbers and proportions of non-native plant species. We surveyed the vegetation in 44 small remnant forest fragments (3–7.5 ha) in the Ottawa region; 15 were situated within forested landscapes, 18 within agricultural landscapes, and 11 within urban landscapes. Forest fragments in urban landscapes had about 40% more introduced plant species and a 50% greater proportion of introduced plant species than fragments found in the other two types of landscape. There was no significant difference in the number or proportion of introduced species in forest fragments within forested vs. agricultural landscapes. However, the species composition of introduced species differed among the forest patches in the three landscape types. Our results support the hypothesis that urban and suburban areas are important foci for spread of introduced plant species.     

The effects of land tenure and land use on the urban forest structure and composition of Melbourne

The urban forest provides valuable ecosystem services for enhancing human well-being. Its structure and composition determine the quantity and quality of these services. There has been little research on the heterogeneity in structure and composition of urban forests in the Australasian region, especially in the centre of a highly dynamic and rapidly urbanizing city. This paper quantifies the structure and the composition of the urban forest of Melbourne, Australia's city centre. The effects of land tenure and land use on the heterogeneity of canopy cover, tree density and canopy size were explored. Species and family composition by land use, land ownership and street type were also analysed using the Shannon–Wiener and Jaccard similarity indices. Most of the canopy cover in the city centre is located on public land and is unevenly distributed across the municipality. The mean canopy cover (12.3%) is similar to that found for whole city studies around the world, which often include peri-urban forests. Similarly to other cities, structure varied across different land uses, and tree size, density and cover varied with land tenure and street type. The diversity index shows that the urban forest is rich in species (H′ = 2.9) and is dominated by native species. Improving the distribution, and increasing tree cover and variety of species will result in a more resilient urban centre, able to provide multiple ecosystem services to their residents and its large population of visitors and workers. The study of the urban centre provides further understanding of compact city morphologies, and allows inter-city comparison independent of the size.     

Changes in carabid beetle assemblages along an urbanisation gradient in the city of Debrecen,Hungary

Responses of carabid beetles (Coleoptera: Carabidae) to urbanisation were studied along an urban-suburban-rural gradient representing decreasing intensities of humandisturbance. Carabids were collected by pitfall trapping during their activity period in lowland oak forest patches in the city of Debrecen, Eastern Hungary. The average number of carabid species was significantly higher in the rural and urban areas compared to the suburban one. The high overall species richness in the urban area was due to the presence of species preferring open habitats. The species richness of forest specialist carabids significantly increased along the urban-rural gradient. The overall carabid abundance was significantly higher in the rural than the other two areas. The results did not support the hypothesis that overall diversity should decrease in response to habitat disturbance. They also contradicted the intermediate disturbance hypothesis: species richness was not the highest in the moderately disturbed suburban area. In the urban area, opportunistic species dominated. The average carabid body size was significantly larger in the rural and suburban areas than in the more disturbed urban area. Multivariate methods detected changes in species composition and abundance structure along the urban-rural gradient. Significant proportion of the variation in abundance and species richness was explained by the heterogeneity of environmental variables (ground temperature, surface temperature, humidity, cover of decaying wood material, herbs, canopy layer, and by the amount of prey).     

Assessing the species diversity and vulnerability of urban tree populations in the London borough of Westminster

The level of tree species diversity in urban tree populations can have serious implications for urban forest resilience and has a direct impact on ecosystem functioning at the local level. Few studies have measured the relationship between tree species diversity and vulnerability in UK urban forests. This study analysed the species composition, species diversity and the vulnerability to pests and diseases of 10,149 public trees in the London borough of Westminster across three land use types: housing, parks, and highways. Tree species diversity was significantly different across these land use types (Shannon’s diversity index (H) was 2.47 for housing sites, 1.63 for parks and 0.83 for highways) and we found that higher diversity appears to result in reduced vulnerability, evidenced by negative correlations between tree species diversity and susceptibility to pests and diseases. A stronger negative correlation was found between vulnerability and species richness than between vulnerability and Gini-Simpson’s diversity index. Our study reinforces the role of biodiversity indices in establishing and monitoring baseline levels of UK urban tree diversity. Our findings may inform future tree planting projects, help to ensure that development does not negatively affect urban tree diversity and inform proactive strategies for urban trees to contribute to wider biodiversity conservation.     

Geospatial methods provide timely and comprehensive urban forest information

Urban forests are unique and highly valued resources. However, trees in urban forests are often under greater stress than those in rural or undeveloped areas due to soil compaction, restricted growing spaces, high temperatures, and exposure to air and water pollution. In addition, conditions change more quickly in urban as opposed to rural and undeveloped settings. Subsequently, proactive management of urban forests can be challenging and requires the availability of current and comprehensive information. Geospatial tools, such as, geographic information systems (GIS), global positioning systems (GPS) and remote sensing, work extremely well together for gathering, analyzing, and reporting information. Many urban forest management questions could be quickly and effectively addressed using geospatial methods and tools. The geospatial tools can provide timely and extensive spatial data from which urban forest attributes can be derived, such as land cover, forest structure, species composition and condition, heat island effects, and carbon storage. Emerging geospatial tools that could be adapted for urban forest applications include data fusion, virtual reality, three-dimensional visualization, Internet delivery, modeling, and emergency response.     

A multiscale assessment of the diversity of New Zealand’s nursery trees

Nurseries play an important role providing trees for a variety of managed environments including urban forests. The diversity of urban forests and forest restoration projects are influenced by nursery species availability, and as such, there is a need to better understand tree species diversity at nurseries. We collected tree species lists from 75 nurseries throughout New Zealand, which were used to describe species richness (alpha diversity) and to examine similarity in the composition of native and non-native species assemblages among nurseries (beta diversity) at three spatial scales: island, region, city. Together, the nurseries grew 863 species, 174 of which were native to New Zealand, from 312 genera and 130 families. Nurseries grew significantly more non-native species (μ = 63.5, σ = 60.6) than native species on average (μ = 31.7, σ = 22.7) (t = 2.99, df = 48.45, p = 0.004). Beta diversity for native and non-native tree species were only significantly different at the scale of cities or regions, not at the larger scale of islands. Few species were grown in all cities or all regions and the majority of those that were common were native species. In contrast, non-native species dominated the unique species at all spatial scales, (i.e., species uniquely grown in one city, region, or island). By quantifying tree species diversity in New Zealand’s nurseries, this research provides a basis to better understand the influence that nurseries have on urban and peri-urban tree diversity, and ultimately how that diversity impacts resilience and the provision of ecosystem services.     

Species diversity of urban forests in China

A good knowledge of species diversity is essential for urban forest planning and management. In this study, we analyzed species diversity of urban forests in China using data synthesized through a systematic review. Our analysis showed that 3740 taxa of woody plants at species level and below have been reported in urban forests in 257 cities. Merging to the species level, there were 2640 species, including 1671 trees, 743 shrubs, and 226 lianas. Salix babylonica L. was the most widely distributed urban tree species in China. Overall, native species accounted for 76.02% of the observed species while the rest were exotic species. Inside cities, parks contained more species than other types of land use. Among cities, composition similarity of urban forests decreased as spatial distances among them increased. Besides, there was a latitudinal pattern in compositional similarity of urban forests in China. The relatively low ratio of the number of woody plant species in urban forests to these naturally distributed in China indicates that there is plenty of room for increasing species diversity of urban forests in China. However, cautions must be taken to avoid increasing compositional similarity of urban forests in China at the same time.     

Planning for the conservation and sustainable use of urban forestry in Addis Ababa,Ethiopia

The planning and management of urban forest has become increasingly important as a focus of urban environmental management. The objectives of this study were to analyze the landuse/land cover and to map functional zones of the urban forest in the upper catchment area of Addis Ababa. This study identifies five landuse/land cover types: (i) Eucalyptus–Juniperus dominated forest, (ii) mixed native forest, (iii) built-up areas, (iv) Eucalyptus plantation (v) crop/grazing lands. The vegetation analysis shows 44 woody plant species representing 31 families, out of which 13 tree species, 29 shrubs and two species of lianas. The woody species diversity was 1.35 with the species richness and evenness of 44 and 0.80, respectively. This indicates that the forest has poor species diversity which is attributed to high anthropogenic pressure and monoculture plantation development strategies in the last decades. The density of plants ranged from 25 for Olea europea to 825 individuals per hectare for Eucalyptus globules from the tree layers and from 50 for Dombeya torrida and Erica arborea to 900 individuals per hectare for Myrsine africana from shrub layers. Based on importance value index (IVI), Eucalyptus globulus and Juniperus procera showed the highest IVI of 96.37 and 54.80, respectively as compared to other species. The forest structure showed higher contagious distribution where out of the recorded 44 species, 37 species showed contagious distribution. The result also showed poor regeneration potential in all studied forest layers. Based on the landuse/cover analysis, the phytosociological study and field observation, this study recommends six urban forest zoning. These include: (i) conservation zone, (ii) recreation zone, (iii) production zone, (iv) agroforestry zone, (v) reforestation zone, (vi) buffer zone between the green area and the built-up environment. The green area in the upper catchment has no definite boundaries and needs re-demarcation activities.     

Twelve-year change in tree diversity and spatial segregation in the Mediterranean city of Santiago,Chile

Tree diversity is one of the most important components of urban ecosystems, because it provides multiple ecological benefits and contributes to human well-being. However, the distribution of urban trees may be spatially segregated and change over time. To provide insights for a better distribution of tree diversity in a socially segregated city, we evaluated spatial segregation in the abundance and diversity of trees by socioeconomic group and their change over a 12-year period in Santiago, Chile. Two hundred vegetation plots were sampled across Santiago in 2002 and 2014. We found that overall abundance and diversity of urban trees for the entire city were stable over 12 years, whereas species richness and abundance of native tree species increased. There was segregation in tree species richness and abundance by socioeconomic group, with wealthier areas having more species and greater abundance of trees (for all tree species and native species) than poorer ones. Tree community composition and structure varied with socioeconomic group, but we found no evidence of increased homogenization of the urban forest in that 12 years. Our findings revealed that although tree diversity and abundance for the entire city did not change in our 12-year period, there were important inequities in abundance and diversity of urban trees by socioeconomic group. Given that 43% of homes in Santiago are in the lower socioeconomic areas, our study highlights the importance of targeting tree planting, maintenance and educational programs in these areas to reduce inequalities in the distribution of trees.     

Multi-scaled habitat considerations for conserving urban biodiversity: native reptiles and small mammals in Brisbane,Australia

The rapid expansion of the world’s urban population is a major driver of contemporary landscape change and ecosystem modification. Urbanisation destroys, degrades and fragments native ecosystems, replacing them with a heterogeneous matrix of urban development, parks, roads, and isolated remnant fragments of varying size and quality. This presents a major challenge for biodiversity conservation within urban areas. To make spatially explicit decisions about urban biodiversity conservation actions, urban planners and managers need to be able to separate the relative influence of landscape composition and configuration from patch and local (site)-scale variables for a range of fauna species. We address this problem using a hierarchical landscape approach for native, terrestrial reptiles and small mammals living in a fragmented semi-urban landscape of Brisbane, Australia. Generalised linear modelling and hierarchical partitioning analysis were applied to quantify the relative influence of landscape composition and configuration, patch size and shape, and local habitat composition and structure on the species’ richness of mammal and reptile assemblages. Landscape structure (composition and configuration) and local-scale habitat structure variables were found to be most important for influencing reptile and mammal assemblages, although the relative importance of specific variables differed between reptile and mammal assemblages. These findings highlight the importance of considering landscape composition and configuration in addition to local habitat elements when planning and/or managing for the conservation of native, terrestrial fauna diversity in urban landscapes.     

90 years of forest cover change in an urbanizing watershed: spatial and temporal dynamics

Landscape structure in the Eastern US experienced great changes in the last century with the expansion of forest cover into abandoned agricultural land and the clearing of secondary forest cover for urban development. In this paper, the spatial and temporal patterns of forest cover from 1914 to 2004 in the Gwynns Falls watershed in Baltimore, Maryland were quantified from historic maps and aerial photographs. Using a database of forest patches from six times—1914, 1938, 1957, 1971, 1999, and 2004—we found that forest cover changed, both temporally and spatially. While total forest area remained essentially constant, turnover in forest cover was very substantial. Less than 20% of initial forest cover remained unchanged. Forest cover became increasingly fragmented as the number, size, shape, and spatial distribution of forest patches within the watershed changed greatly. Forest patch change was also analyzed within 3-km distance bands extending from the urban core to the more suburban end of the watershed. This analysis showed that, over time, the location of high rates of forest cover change shifted from urban to suburban bands which coincides with the spatial shift of urbanization. Forest cover tended to be more stable in and near the urban center, whereas forest cover changed more in areas where urbanization was still in process. These results may have critical implications for the ecological functioning of forest patches and underscore the need to integrate multi-temporal data layers to investigate the spatial pattern of forest cover and the temporal variations of that spatial pattern.     

Urban plant species patterns are highly driven by density and function of built-up areas

This paper aims to assess the relative importance of the type of built-up area in structuring plant species composition and richness in urbanised environments. The study was carried out in the city of Brussels where all vascular plant species were recorded in 189 grid cells of 1 km² each. The effect of urban land use type on species composition was investigated using first Canonical Correspondence Analysis. Densely built-up area was the most powerful predictor for species composition, followed by industrial built-up areas, half open or open built-up areas with plantations, and open built-up areas with much natural vegetation in the surroundings. Indicator species were found for each type of built-up area and a response curve to the amount of built land was produced using Generalised Additive Modelling. Various types of built-up areas had different effects on environmental conditions as inferred by Ellenberg’s indicator values, as well as on the species richness, species rarity, number of exotic species and proportion of extinction-prone species. It is concluded that future ecological studies should not treat urban areas as homogeneous areas by combining all anthropogenic factors into one aggregated variable. Instead, the urban matrix should be categorised in subsystems as it is multidimensional and highly variable across space.     

Promoting and preserving biodiversity in the urban forest

Efforts at mitigating global biodiversity loss have often focused on preserving large, intact natural habitats. However, preserving biodiversity should also be an important goal in the urban environment, especially in highly urbanized areas where little natural habitat remains. Increasingly, research at the city/county scale as well as at the landscape scale reveals that urban areas can contain relatively high levels of biodiversity. Important percentages of species found in the surrounding natural habitat, including endangered species, have been found in the urban forest.

This contribution concisely highlights some examples of urban biodiversity research from various areas of the world. Key issues involved in understanding the patterns and processes that affect urban biodiversity, such as the urban–rural gradient and biotic homogenization, are addressed. The potential for urban areas to harbor considerable amounts of biodiversity needs to be recognized by city planners and urban foresters so that management practices that preserve and promote that diversity can be pursued. Management options should focus on increasing biodiversity in all aspects of the urban forest, from street trees to urban parks and woodlots.