Effects of roads on fruit crop and removal rate from rowanberry trees (Sorbus aucuparia) by birds in urban areas of Finland

Roads destroy natural habitats. To reduce erosion, support wildlife and decorate surroundings, ornamental trees are planted near the roadside. However, it is inadequately understood how roads influence fruit production of trees and birds that consume their fruits, within urban landscapes. During the autumn and winter of 2012–2013, we studied the extent to which birds used the fruit from rowanberry trees (Sorbus aucuparia), in two cities along a 700 km latitudinal gradient in Finland. In matched pair design (total of 35 pairs), we compared roadside trees (approximately 8 m from main roads) with trees grown away from roads (control trees; approximately >80 m from the roads). During the autumn, each rowanberry tree pair was photographed, and frugivorous birds were surveyed twice per month until all of the rowanberry fruit-crop was consumed. There was no difference in fruit crop size between roadside trees and control trees. A total of eight frugivorous bird species and 960 individuals were observed foraging in roadside trees. The three most abundant species were Bohemian waxwing (Bombycilla garrulus, 56.4%), Pine Grosbeak (Pinicola enucleator, 28.9%) and Fieldfare (Turdus pilaris, 10.5%). Total abundance and species richness of frugivorous birds were lower around roadside trees than control trees during most of the study period. Fruits were consumed later from roadside trees than from control trees, probably due to human-caused disturbance. Therefore, roadside rowanberry trees extended the period when frugivorous birds stayed in urban habitats. Later consumption of fruits in northern areas than in southern areas was related to earlier peak abundance of frugivorous birds in south than in north. Our results indicated that rowanberry is a suitable ornamental tree for urban and roadside landscaping and may additionally benefit birds and other frugivorous wildlife.     

Defect-disorder and risk assessment of heritage trees in urban Hong Kong

Heritage trees in a city, echoing factors conducive to outstanding performance, deserve special care and conservation. To understand their structural and health conditions in urban Hong Kong, 30 defect-disorder (DD) symptoms (physical and physiological) subsumed under four tree-position groups (soil-root, trunk, branching, and crown-foliage) and tree hazard rating were evaluated. The surveyed 352 trees included 70 species; 14 species with 233 trees were native. More trees had medium height (10–15 m), medium DBH (1–1.5 m) and large crown (>15 m). In ten habitats, public park and garden (PPG) accommodated the most trees, and roadside traffic island (RTI) and public housing estate (PH) had the least. Tree dimensions and tree habitats were significantly associated. The associations between the 2831 DD and tree-position groups, tree habitats and tree hazard rating were analyzed. Fourteen trees from Ficus microcarpa, Ficus virens and Gleditsia fera had high hazard rating, 179 trees from 22 species moderate rating, and 159 trees from 55 species low rating. RTI, roadside tree strip (RTS), roadside tree pit (RTP), roadside planter (RP) and stone wall (SW) had more moderate hazard rating, and PPG, roadside slope (RS) and government, institutional and community land (GIC) more low rating. Redundancy analysis showed that DD were positively correlated with RTS, RTP, RP and SW, but negatively correlated with PPG, RS and GIC (p < 0.05). The DD significantly increased tree hazard rating and failure potential. Future management implications for heritage-tree conservation and enhancement focusing squarely on critical tree defect-disorder in urban Hong Kong were explored, with application to other compact cities.     

The influence of increasing tree cover on mean radiant temperature across a mixed development suburb in Adelaide,Australia

The implementation of trees in urban environments can mitigate outdoor thermal stress. Growing global urban population and the risk of heatwaves, compounded by development driven urban warmth (the urban heat island), means more people are at risk of heat stress in our cities. Effective planning of urban environments must minimise heat-health risks through a variety of active and passive design measures at an affordable cost. Using the Solar and Longwave Environmental Irradiance Geometry (SOLWEIG) model and working within the bounds of current urban design, this study aimed to quantify changes in mean radiant temperature (T_mrt) from increased tree cover at five different 200 × 200 m urban forms (including compact mid-rise development, residential and open grassy areas) within a suburb of Adelaide, Australia during summer. Following a successful validation of SOLWEIG, street trees were strategically distributed throughout each of the five urban forms and the model run over five warm sunny days (13–17 February 2011). Results showed spatially averaged daytime (7:30–20:00) T_mrt reduced by between 1.7 °C and 5.1 °C at each site, while under peak heating conditions (16 February, 14:00) T_mrt reduced by between 2.0 °C and 7.1 °C. The largest reduction in T_mrt under peak warming conditions was at the residential site, despite having the fewest number of trees added. Directly below clusters of trees, T_mrt could be reduced by between 14.1 °C and 18.7 °C. SOLWEIG also highlighted that more built-up sites showed higher T_mrt under peak warming conditions due to increased radiation loading from 3D urban surfaces, but over the course of the day, open sites were exposed to greater and more uniform T_mrt. This study clearly demonstrates the capacity of street trees to mitigate outdoor thermal stress and provides guidance for urban planners on strategic street tree implementation.     

Estimation of broad-leaved canopy growth in the urban forested area using multi-temporal airborne LiDAR datasets

Inter-annual canopy growth is one of the key indicators for assessing forest conditions, but the measurements require laborious field surveys. Up-to-date LiDAR remote sensing provides sufficient three-dimensional morphological information of the ground to monitor canopy heights on a broad scale. Thus, we attempted to use multi-temporal airborne LiDAR datasets in the estimation of vertical canopy growth, across various types of broad-leaved trees in a large urban park.The growth of broad-leaved canopies in the EXPO '70 urban forest in Osaka, Japan was assessed with 19 plots at the stand level and 39 selected trees at the individual-tree level. Airborne LiDAR campaigns repeatedly observed the park in the summers of 2004, 2008, and 2010. We acquired canopy height models (CHMs) for each year from the height values of the uppermost laser returns at every 0.5 m grid. The annual canopy growth was calculated by the differences in CHMs and validated with the annual changes in field-measured basal areas and tree heights.LiDAR estimations revealed that the average annual canopy growth from 2004 to 2010 was 0.26 ± 0.11 m m⁻² yr⁻¹ at the plot level and 0.26 ± 0.10 m m⁻² yr⁻¹ at the individual-tree level. This result showed that growing trends were consistent at different scales through 2004 to 2010 despite uncertainty in estimating short-term growth for small crown areas at the individual-tree level. This LiDAR-estimated canopy growth shows a moderate relation to field-measured increase of basal areas and average heights. The estimation uncertainties seem to result from the complex canopy structure and irregular crown shape of broad-leaved trees. Challenges still remain on how to incorporate the growth of understory trees, growth in the lateral direction, and gap dynamics inside the canopy, particularly in applying multi-temporal LiDAR datasets to the large-scale growth assessment.     

The feasibility of remotely sensed data to estimate urban tree dimensions and biomass

Accurately measuring the biophysical dimensions of urban trees, such as crown diameter, stem diameter, height, and biomass, is essential for quantifying their collective benefits as an urban forest. However, the cost of directly measuring thousands or millions of individual trees through field surveys can be prohibitive. Supplementing field surveys with remotely sensed data can reduce costs if measurements derived from remotely sensed data are accurate. This study identifies and measures the errors incurred in estimating key tree dimensions from two types of remotely sensed data: high-resolution aerial imagery and LiDAR (Light Detection and Ranging). Using Sacramento, CA, as the study site, we obtained field-measured dimensions of 20 predominant species of street trees, including 30–60 randomly selected trees of each species. For each of the 802 trees crown diameter was estimated from the aerial photo and compared with the field-measured crown diameter. Three curve-fitting equations were tested using field measurements to derive diameter at breast height (DBH) (r² = 0.883, RMSE = 10.32 cm) from the crown diameter. The accuracy of tree height extracted from the LiDAR-based surface model was compared with the field-measured height (RMSE = 1.64 m). We found that the DBH and tree height extracted from the remotely sensed data were lower than their respective field-measured values without adjustment. The magnitude of differences in these measures tended to be larger for smaller-stature trees than for larger stature species. Using DBH and tree height calculated from remotely sensed data, aboveground biomass (r² = 0.881, RMSE = 799.2 kg) was calculated for individual tree and compared with results from field-measured DBH and height. We present guidelines for identifying potential errors in each step of data processing. These findings inform the development of procedures for monitoring tree growth with remote sensing and for calculating single tree level carbon storage using DBH from crown diameter and tree height in the urban forest.     

Urban woodland understory characteristics in relation to aesthetic and recreational preference

Urban woodlands provide aesthetic experiences and recreational opportunities for people. The characteristics of vegetation are closely linked to these benefits. However, previous research has primarily focused on the effects of trees on aesthetic preference, while less research has involved the understory. This paper explored the relationship between understory characteristics and aesthetic or recreational preference. Twenty one images were rated for preference by participants (n = 184) on a five-point scale. Except for the original picture, these images were created using the photomontage method that manipulated understory height, the flowers and the path of the original picture. Results indicated that: (1) concerning aesthetic preference, all vegetated images were preferred more than the paved image, but for recreational preference, the paved image was preferred over the vegetated images; (2) the height of understory vegetation had a significant influence on aesthetic and recreational preference; (3) flowers and path increased aesthetic and recreational preference significantly. These results suggest that, in management of woodland, (1) maintaining the understory vegetation in middle height (0.5–1.0 m) or in full-mixed heights (low + middle + tall) (2) increasing shade-tolerance flowers and constructing a winding path in woodland would be preferred by the public.     

Seasonal variations in the cooling effect of urban green areas on surrounding urban areas

We measured air temperature in an urban green area that includes forest and grassland and in the surrounding urban area for a full year in Nagoya, central Japan, to elucidate seasonal variations of the difference in air temperature between urban and green areas. We determined the range of the “cool-island” effect as well as the relationship between vegetation cover and air temperature throughout the year. The temperature difference between urban and green areas was large in summer and small in winter. The maximum air temperature difference was 1.9 °C in July 2007, and the minimum was ?0.3 °C in March 2004. The difference was larger during the day than during the night in summer, whereas in winter the opposite relationship was true. However, winter diurnal variation was not particularly noticeable, a behaviour thought to be related to reduced shading by deciduous trees in the green area. During the night, the cooling effect of the green area reached 200–300  m into the urban area. During the day, the cooling effect between August and October 2006 exceeded 300 m and varied widely, although there was no correlation beyond 500 m. The correlation between air temperature and forest-cover ratio within a radius of 200 m from each measurement site was significant from 16:00 to 19:00. There was also a correlation during the night; this correlation was weakest in the early morning. The effect of the forest-cover ratio on air temperature was most pronounced in August 2006 and June 2007.     

The influence of sidewalk replacement on urban street tree growth

Interactions between tree roots and sidewalks can result in damage to sidewalks and when sidewalk damage is repaired adjacent tree roots are often severed. The objective of this study was to quantify the growth response of urban trees in restricted planting spaces pre- and post-sidewalk construction. The research included four trees species commonly planted along streets in Minneapolis and Saint Paul, Minnesota, USA. Species included were: Acer platanoides, Celtis occidentalis, Gleditsia triacanthos, and Tilia spp. Two street tree populations were sampled: trees adjacent to replaced sidewalk panels (<1.75 m) and trees on streets with sidewalk construction that were greater than 3 m from replaced sidewalk sections. In total, increment core samples from 292 trees were analyzed. Annual rings from each tree were measured and converted to basal area increment (BAI) for analysis. Comparisons of BAI were conducted between the two sample populations to assess differences in tree growth patterns. Pre- and post-sidewalk construction BAI was also evaluated to determine the influence of construction on growth trajectory. Growth response was quantified using resistance, resilience, and recovery indices. Species were found to differ in their response to construction disturbance. Planting space width was also found to influence post-construction growth. Tilia spp. had the highest resilience and fastest overall growth recovery post-sidewalk construction and A. platanoides exhibited the lowest resistance, resilience, and recovery post-sidewalk construction.     

Air pollution removal by urban forests in Canada and its effect on air quality and human health

Urban trees perform a number of ecosystem services including air pollution removal, carbon sequestration, cooling air temperatures and providing aesthetic beauty to the urban landscape. Trees remove air pollution by intercepting particulate matter on plant surfaces and absorbing gaseous pollutants through the leaf stomata. Computer simulations with local environmental data reveal that trees in 86 Canadian cities removed 16,500 tonnes (t) of air pollution in 2010 (range: 7500–21,100 t), with human health effects valued at 227.2 million Canadian dollars (range: $52.5–402.6 million). Annual pollution removal varied among cities and ranged up to 1740 t in Vancouver, British Columbia. Overall health impacts included the avoidance of 30 incidences of human mortality (range: 7–54) and 22,000 incidences of acute respiratory symptoms (range: 7900–31,100) across these cities.     

Street trees in Bangalore: Density,diversity, composition and distribution

Once renowned as India’s “garden city”, the fast growing southern Indian city of Bangalore is rapidly losing tree cover in public spaces including on roads. This study aims to study the distribution of street trees in Bangalore, to assess differences in tree density, size and species composition across roads of different widths, and to investigate changes in planting practices over time. A spatially stratified approach was used for sampling with 152 transects of 200 m length distributed across wide roads (with a width of 24 m or greater), medium sized roads (12–24 m) and narrow roads (less than 12 m). We find the density of street trees in Bangalore to be lower than many other Asian cities. Species diversity is high, with the most dominant species accounting for less than 10% of the overall population. Narrow roads, usually in congested residential neighborhoods, have fewer trees, smaller sized tree species, and a lower species diversity compared to wide roads. Since wide roads are being felled of trees across the city for road widening, this implies that Bangalore’s street tree population is being selectively denuded of its largest trees. Older trees have a more diverse distribution with several large sized species, while young trees come from a less diverse species set, largely dominated by small statured species with narrow canopies, which have a lower capacity to absorb atmospheric pollutants, mitigate urban heat island effects, stabilize soil, prevent ground water runoff, and sequester carbon. This has serious implications for the city’s environmental and ecological health. These results highlight the need to protect large street trees on wide roads from tree felling, and to select an appropriate and diverse mix of large and small sized tree species for new planting.     

Normalized difference vegetation index (NDVI) as a marker of surrounding greenness in epidemiological studies: The case of Barcelona city

The normalized difference vegetation index (NDVI) is often used as a marker of surrounding greenness in epidemiological studies aiming to evaluate the health effects of green space in urban settings. However, it is not clear the relationship between built environment characteristics, including green space, and NDVI. We aimed to evaluate the relationship between built environment characteristics, based on land-use and land-cover maps, and NDVI as a marker of surrounding greenness in the city of Barcelona. We used data from an already existing cohort of pregnant women in Barcelona (N = 8402). NDVI was derived and averaged within buffers of 100 m and 300 m for each participant, and categories of the built environment (m²) were derived from land-use and land-cover maps of Barcelona. We conducted ANOVA models to calculate the contribution (R²) of each land-use (or land-cover) category. The variability in NDVI in Barcelona was mainly explained by urban green (R² between 0.32 and 0.53) and natural green areas (R² between 0.19 and 0.52), although for the latter less than 4% of the participants were exposed to this. Both land-use and land-cover maps explained NDVI at 300 m better (full models explaining 76% and 78%, respectively) than at 100 m buffers (full models explaining 55% and 54%, respectively). Results of the present study indicate that NDVI can be a useful greenness metric depending on the hypothesis and area of study. However, for certain sizes of study areas (buffers smaller than 100 m), NDVI might have a lower predictive value. Results of the present study should be replicated in studies from other cities with different urban characteristics and climate conditions.     

The influence of small green space type and structure at the street level on urban heat island mitigation

The purpose of this study was to determine the types and structures of small green spaces (SGs) that effectively reduce air temperature in urban blocks. Six highly developed blocks in Seoul, South Korea served as the research sites for this study. Air temperature was measured at the street level with mobile loggers on clear summer days from August to September in 2012. The measurements were repeated three times a day for three days. By analyzing the spatial characteristics, SGs within the six blocks were categorized into the four major types: polygonal, linear, single, and mixed. The result revealed that the polygonal and mixed types of SGs showed simple linear regression at a significant level (p < 0.01). It indicated that the blocks’ urban heat island (UHI) mitigation (ΔT_Rmn) increased in a linear fashion when the area and volume of these two types of green spaces increased. The area and volume of a polygonal SG with mixed vegetation, over 300 m² and 2300 m³, respectively, lowered the ΔT_Rmn by 1 °C; SG with an area and volume of larger than 650 m² and 5000 m³, respectively, lowered the ΔT_Rmn by 2 °C. The results of this study will be useful to urban planners and designers for determine the types and structures of urban green spaces to optimize the cooling effect, as well as how such green spaces should be designed and distributed.     

Urban vegetation phenology analysis using high spatio-temporal NDVI time series

Most of current products can partially reach the requirement of high spatial and temporal resolution needed in urban applications. Fortunately, the new generation of satellite in a form of constellation, e.g. Europe’s Sentinel-2, China’s HJ-1A/B and GF-1/6, is expected to provide more frequent observations (<1 week) with a higher spatial resolution (<30 m). Consequently, a proper method should be selected to construct high spatio-temporal time-series NDVI and to derive phenological features for urban applications. In this study, a high spatio-temporal NDVI product for urban scale vegetation time series is conducted based on HJ-1A/B data. Three related issues, i.e. the optimal filter, time series decomposition, phenological features derivation are addressed. In addition, the effect of spatial and temporal resolution on the phenological features extraction is also discussed according to the comparison between the derived NDVI product and that extracted from MODIS. The results show that the Savitzky-Golay (S-G) filter is the best filter for the reconstruction of HJ NDVI time series. There is some difference for phenology derivation using “season” and “season + trend” depending on the absence/presence of breakpoints in the curve. The spatial details of phenological features can be built by the high-spatial time-series NDVI, showing a great potential in urban applications. Compared with the MODIS NDVI time series, HJ NDVI time series can get more detail information than overall phenological features because of its high spatio-temporal resolution.     

Preliminary data on low aerial plankton in a large city center,Paris

Some organisms are able to disperse by air through passive or active flying and can colonize highly isolated habitat. We can hypothesis than aerial dispersions could be a process of biodiversity development even in isolated town habitats such as some building roofs.The urban aerial plankton has been poorly studied and we analyzed here the arthropods and seeds trapping small species limited to 0.5–5 mm sizes and to a low part of the atmosphere (traps on roofs below 50 meters) in Paris, a center of a very large agglomeration. Using plates of wire meshes with fat, we observed that insects are dominant (Diptera and Hemiptera) when spiders and seeds appeared underrepresented.At high heights of buildings (and not at low heights), the Landscape Greening Index seems to have a strong positive effect on abundances for spiders, insects and seeds stressing the role of sources and the effect of building barriers on aerial dispersion. These preliminary data encourage research on this process.     

Comparison of non-destructive LAI determination methods and optimization of sampling schemes in an open Populus euphratica ecosystem

Populus euphratica (P. euphratica) grows in the water-limited Tarim River Basin in spatially heterogeneous open ecosystems; thus, efforts to quantify the leaf area index (LAI) with optical instruments developed for homogeneous closed canopies have a high probability of failure. In this study, we explored methods for designing an acceptable sampling scheme to quantify the tree LAI for open P. euphratica canopies in arid areas. Field data were collected from three 30 m × 30 m plots and one 100 m × 100 m plot. We compared three indirect methods, i.e. i) allometry, ii) LAI-2000 canopy analyser, iii) Tracing Radiation and Architecture of Canopies (TRAC), and a new semi-direct method combining leaf density and crown volume (SDDV) method for quantifying the isolated tree and canopy LAI of a P. euphratica forest. We also analysed the effects of random and grid sampling designs on the accuracy of the LAI estimates obtained with the LAI-2000. The results showed that the allometric method is applicable to isolated trees with regular shapes; however, because the LAI of P. euphratica was calculated from an allometric equation based on the basal area (at 1.3 m), the allometric equation is prone to failure if the basal area is beyond a specific range. Because there are no significant differences in the plot size between the allometric and the SDDV method predictions, the proposed SDDV method can be used as an alternative for field measurements. The combination of LAI-2000 and TRAC is found to be more reliable than TRAC only, and the field view of the LAI-2000 sensor and the clumping index are important factors for sparse vegetation LAI retrieval. The results from sampling optimization showed that for the LAI-2000 instrument, the best sampling method is grid sampling, and the sampling interval should not be less than 20 m. For random sampling scheme, the number of sampling points in a 100 m × 100 m plot should be greater than 86 with a coefficients of variation of 15% and an allowable error (AE) of 0.15 m² m⁻², respectively.     

Mapping leaf area of urban greenery using aerial LiDAR and ground-based measurements in Gothenburg,Sweden

Leaf area of urban vegetation is an important ecological characteristic, influencing urban climate through shading and transpiration cooling and air quality through air pollutant deposition. Accurate estimates of leaf area over large areas are fundamental to model such processes. The aim of this study was to explore if an aerial LiDAR dataset acquired to create a high resolution digital terrain model could be used to map effective leaf area index (L_e) and to assess the L_e variation in a high latitude urban area, here represented by the city of Gothenburg, Sweden. L_e was estimated from LiDAR data using a Beer-Lambert law based approach and compared to ground-based measurements with hemispherical photography and the Plant Canopy Analyser LAI-2200. Even though the LiDAR dataset was not optimized for L_e mapping, the comparison with hemispherical photography showed good agreement (r² = 0.72, RMSE = 0.97) for urban parks and woodlands. Leaf area density of single trees, estimated from LiDAR and LAI-2200, did not show as good agreement (r² = 0.53, RMSE = 0.49). L_e in 10 m resolution covering most of Gothenburg municipality ranged from 0 to 14 (0.3% of the values >7) with an average L_e of 3.5 in deciduous forests and 1.2 in urban built-up areas. When L_e was averaged over larger scales there was a high correlation with canopy cover (r² = 0.97 in 1 × 1 km² scale) implying that at this scale L_e is rather homogenous. However, when L_e was averaged only over the vegetated parts, differences in L_e became clear. Detailed study of L_e in seven urban green areas with different amount and type of greenery showed a large variation in L_e, ranging from average L_e of 0.9 in a residential area to 4.1 in an urban woodland. The use of LiDAR data has the potential to considerably increase information of forest structure in the urban environment.     

Long-term impact of road salt (NaCl) on soil and urban trees in Edmonton,Canada

The application of de-icing salts for winter road maintenance is recognized as a major contributor to the decline of urban trees. We conducted a long-term monitoring program across several locations in the City of Edmonton (Alberta, Canada) to evaluate the impact of roadway salt application on tree species widely planted in boulevards and right-of-ways: Ulmus americana, Fraxinus pennsylvanica, Pinus contorta, and Picea glauca. Soil and leaf samples were collected from a total of 16 sites over six years. There were four sites selected for each tree species: three mid- to high- traffic roadside sites that received regular winter maintenance and one non-serviced site (control). Sampling was performed three times per year from late spring to late summer. Airborne salinity was assessed in four locations at different distances from the road. In 50% of the roadside sites, soil electrical conductivity (EC) values exceeded 2 dS m⁻¹. Soil pH in all of the roadside sites was also significantly higher than in the control sites, with values ranging from 7.6 to 8.5. In all four species, trees growing in sites with high soil EC had increased leaf Na concentrations and reduced leaf chlorophyll concentrations. Among the airborne monitoring sites, Na deposition in high traffic locations was over four-fold higher than those measured in the control location. Furthermore, Na levels remained relatively high at 20–50 m from the main road. Our data suggest that while soil salinity is among the main stressors affecting roadside trees in Edmonton, salt spray deposition may also have a significant impact on trees located close to high vehicle traffic areas and dense road networks. Our study highlights the importance of collecting data over several years and from multiple locations to account for the spatial and temporal heterogeneity of the urban environments in order to better evaluate the impact of road salt application on urban trees.     

Carbon sequestration of four urban parks in Rome

Urban parks form the largest proportion of public green spaces contributing to both physical and mental well-being of people living in urban areas. CO₂ sequestration capability of the vegetation developing in parks of four historical residences (Villa Pamphjli, Villa Ada Savoia, Villa Borghese and Villa Torlonia) in Rome and its economic value were analyzed. Villa Pamphjli and Villa Ada Savoia having a larger vegetation extension (165.04 ha and 134.33 ha, respectively), also had a larger total yearly CO₂ sequestration per hectare (CS) (780 MgCO₂ ha⁻¹ year⁻¹ and 998 MgCO₂ ha⁻¹ year⁻¹, respectively) than Villa Borghese (664 MgCO₂ ha⁻¹ year⁻¹) and Villa Torlonia (755 MgCO₂ ha⁻¹ year⁻¹), which had a lower vegetation extension (56.72 ha and 9.70 ha, respectively). CS was significantly correlated with leaf area index (LAI). The calculated CS for the four parks (3197 MgCO₂ ha⁻¹ year⁻¹), corresponding to 3.6% of the total greenhouse gas emissions of Rome for 2010, resulted in an annual economic value of $ 23537 /ha.     

Mapping of urban roadside trees – A case study in the tree register update process in Helsinki City

This case study describes a method for utilizing leaf-off airborne laser scanning (ALS) data for mapping characteristics of urban trees. ALS data were utilized to detect and update all street trees in the tree inventory of the City of Helsinki, Finland. The inventory consists of roughly 20,000 street trees with mean diameter at breast height (DBH) of 24 cm and mean height of 10.6 m. The large number of trees makes the manual updating process very laborious. The automatic mapping procedure presented in this paper detected 88.8% of all trees in the inventory. Tree height was predicted with root mean square error (RMSE) of 1.27 meters and tree DBH with RMSE of 6.9 cm. The presented method provides a practical and cost–effective tool for the mapping of urban tree characteristics. The cost–efficiency was further enhanced because the used ALS data were originally collected for other urban planning purposes.     

Comparing street tree assemblages and associated stormwater benefits among communities in metropolitan Cincinnati,Ohio, USA

Green infrastructure approaches leverage vegetation and soil to improve environmental quality. Municipal street trees are crucial components of urban green infrastructure because they provide stormwater interception benefits and other ecosystem services. Thus, it is important to understand the patterns and drivers of structural heterogeneity in urban street tree assemblages. In this study, we compared the forest structure of street trees across nine communities along both geographic and demographic gradients in metropolitan Cincinnati, Ohio, USA. Specifically, we used a two-part statistical model to compare both the proportion of sampled street segments containing zero trees, and basal area magnitude for street segments with trees. We made community-scale comparisons based on street tree management, socioeconomics, and geographic setting. Then, using modeled stormwater interception estimates from i-Tree Streets, we investigated the implications of heterogeneity in street tree assemblages for stormwater interception benefits. The forest structure of street trees varied across communities in relation to management practices, namely participation in the Tree City USA program. As a consequence of this structural difference, we observed a stark discrepancy in estimated stormwater interception between Tree City USA participants (128.7 m³/km street length) and non-participants (59.2 m³/km street length). While street tree assemblages did not vary by community poverty status, we did find differences according to community racial composition. In contrast to previous research, basal area was greater in predominantly black (i.e., African American) and racially mixed communities than in predominantly white communities. We did not observe structural differences across geographic strata. This research underscores the importance of proactive management practices for increasing the forest structure of street trees. Our findings regarding socioeconomics and geographic setting contrast previous studies, suggesting the need for continued research into the drivers of structural heterogeneity in street tree assemblages.