The overlooked carbon loss due to decayed wood in urban trees

Decayed wood is a common issue in urban trees that deteriorates tree vitality over time, yet its effect on biomass yield therefore stored carbon has been overlooked. We mapped the occurrence and calculated the extent of decayed wood in standing Ulmus procera, Platanus × acerifolia and Corymbia maculata trees. The main stem of 43 trees was measured every metre from the ground to the top by two skilled arborists. All trees were micro-drilled in two to four axes at three points along the stem (0.3 m, 1.3 m, 2.3 m), and at the tree’s live crown. A total of 300 drilling profiles were assessed for decay. Simple linear regression analysis tested the correlation of decayed wood (cm²) against a vitality index and stem DBH. Decay was more frequent and extensive in U. procera, than P. acerifolia and least in C. maculata. Decay was found to be distributed in three different ways in the three different genera. For U. procera, decay did appear to be distributed as a column from the base to the live crown; whereas, decay was distributed as a cone-shape in P. acerifolia and was less likely to be located beyond 2.3 m. In C. maculata decay was distributed as pockets of variable shape and size. The vitality index showed a weak but not significant correlation with the proportion of decayed wood for P. acerifolia and C. maculata but not for U. procera. However, in U. procera, a strong and significant relationship was found between DBH and stem volume loss (R² = 0.8006, P = 0.0046, n = 15). The actual volume loss ranged from 0.17 to 0.75 m³, equivalent to 5%–25% of the stem volume. The carbon loss due to decayed wood for all species ranged between 69–110 kg per tree. Based on model’s calculation, the stem volume of U. procera trees with DBH ≥ 40 cm needs to be discounted by a factor of 13% due to decayed wood regardless of the vitality index. Decayed wood reduces significantly the tree’s standing volume and needs to be considered to better assess the carbon storage potential of urban forests.     

Density,diversity and richness of woody plants in urban green spaces: A case study in Chennai metropolitan city

A tree diversity inventory was carried out in urban green spaces (UGSs) of Chennai metropolitan city, India. This inventory aims to study the diversity, density and richness of trees in UGSs of Chennai. A total of one hundred 10 m × 10 m (total 1 ha) plots were laid to reveal tree diversity and richness of UGSs. Trees with ≥10 cm girths at breast height (gbh) were inventoried. We recorded 45 species in 42 genera and 21 families. Caesalpiniaceae and Fabaceae each with 6 species dominated the study area followed by Arecaceae (3). Density and stand basal area of the present study were 500 stems ha^?1 and 64.16 m², respectively. Most of the inventoried trees were native (31 species) and deciduous (28 species). Fabaceae and Caesalpiniaceae dominated the present study area in terms of stand basal area and density. The Shannon diversity index and evenness of study area were 2.79 and 0.73, respectively. The most important species and families based on species important value index (IVI) and family important value index were Albizia saman, Polyalthia longifolia and Azadirachta indica; Fabaceae, Caesalpiniaceae and Annonaceae respectively. We find Chennai's urban forest is relatively superior to many urban forests of the world in terms of stand basal area and species richness. Results emphasize the importance of enhancement of urban green spaces in Chennai metropolitan city.     

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.     

Relationships between bole and crown size for young urban trees in the northeastern USA

Knowledge of allometric equations can enable urban forest managers to meet desired economic, social, and ecological goals. However, there remains limited regional data on young tree growth within the urban landscape. The objective of this study is to address this research gap and examine interactions between age, bole size and crown dimensions of young urban trees in New Haven, CT, USA to identify allometric relationships and generate predictive growth equations useful for the region. This study examines the 10 most common species from a census of 1474 community planted trees (ages 4–16). Regressions were applied to relate diameter at breast height (dbh), age (years since transplanting), tree height, crown diameter and crown volume. Across all ten species each allometric relationship was statistically (p < 0.001) significant at an α-level of 0.05. Consistently, shade trees demonstrated stronger relationships than ornamental trees. Crown diameter and dbh displayed the strongest fit with eight of the ten species having an R² > 0.70. Crown volume exhibited a good fit for each of the shade tree species (R² > 0.85), while the coefficients of determination for the ornamentals varied (0.38 < R² < 0.73). In the model predicting height from dbh, ornamentals displayed the lowest R² (0.33 < R² < 0.55) while shade trees represented a much better fit (R² > 0.66). Allometric relationships can be used to develop spacing guidelines for commonly planted urban trees. These correlations will better equip forest managers to predict the growth of urban trees, thereby improving the management and maintenance of New England's urban forests.     

Diversity of street tree populations in larger Danish municipalities

Healthy and sustainable tree populations require a high diversity of genera and species. This study examined the occurrence and contents of tree inventories in Denmark's 30 largest municipalities. 59% of the municipalities had a tree inventory for street trees, but only about half of these were complete and updated. Only one municipality had a registration for trees other than street trees. Based on data from the tree inventories, the diversity of road side trees was analyzed at genus level and species level. A total of 82,072 street trees are part of the study. 11 different genera account for 92% of the total street tree stock, and 2–6 genera account for 40–80% of the street tree stock in the individual municipalities. Tilia was the most dominating genera (26%). 12 species account for 73% of the total street tree stock. The 6 most common species account for almost 50% of the total tree population. The species representing the largest numbers were Tilia × europaea (12%), Acer platanoides (10.9%), Platanus × acerifolia (7.2%), Tilia cordata (7.2%), Fraxinus excelsior (6.2%) and Sorbus intermedia (5.9%). The four most urbanized municipalities had a surplus of non-native species, but all municipalities apart from one had most street trees belonging to native species. The concluding recommendation of this study is that tree managers need to start working more strategic with their tree stock, in order to reduce the vulnerability, due to potential attacks from pests or diseases and climate change effects. A risk spreading system for the urban tree population is proposed, suggesting that no genera should account for more than 10% and no species for more than 5% of the tree population.     

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.     

An index to identify suitable species in urban green areas

This paper presents a method that allows sorting of tree and shrub species according to their suitability for planting in urban areas of Madrid (Spain). Suitability was determined from a weighted index for each species according to the severity of damage (biotic, abiotic, and anthropogenic; stem wounds are the main problem in trees, while dead plants are the most important problem in shrubs, seasonal flowers, and vines) and to risk, which was obtained from a new measure, observed Species per Green Area per Year (SAYs). The greater the number of damaged SAYs, the less suitable a species was considered for outdoor planting. For this purpose, 49 green areas corresponding to 141 ha were sampled during 2005–2008. The tree species least recommended for planting include Robinia pseudoacacia, Ulmus sp., Acer negundo, Platanus × hybrid, Populus Boolleana. The shrubs least recommended for planting are Nerium oleander, Cotoneaster sp., Euonymus europaeus, Pyracantha coccinea, and Pittosporum tobira. Statistical analysis reveals that native species have a lower percentage of damaged SAYs than non-native species.     

Contrasting natural regeneration and tree planting in fourteen North American cities

Field data from randomly located plots in 12 cities in the United States and Canada were used to estimate the proportion of the existing tree population that was planted or occurred via natural regeneration. In addition, two cities (Baltimore and Syracuse) were recently re-sampled to estimate the proportion of newly established trees that were planted. Results for the existing tree populations reveal that, on average, about 1 in 3 trees are planted in cities. Land uses and tree species with the highest proportion of trees planted were residential (74.8 percent of trees planted) and commercial/industrial (61.2 percent) lands, and Gleditsia triacanthos (95.1 percent) and Pinus nigra (91.8 percent). The percentage of the tree population planted is greater in cities developed in grassland areas as compared to cities developed in forests and tends to increase with increased population density and percent impervious cover in cities. New tree influx rates ranged from 4.0 trees/ha/yr in Baltimore to 8.6 trees/ha/yr in Syracuse. About 1 in 20 trees (Baltimore) and 1 in 12 trees (Syracuse) were planted in newly established tree populations. In Syracuse, the recent tree influx has been dominated by Rhamnus cathartica, an exotic invasive species. Without tree planting and management, the urban forest composition in some cities will likely shift to more pioneer or invasive tree species in the near term. As these species typically are smaller and have shorter life-spans, the ability of city systems to sustain more large, long-lived tree species may require human intervention through tree planting and maintenance. Data on tree regeneration and planting proportions and rates can be used to help determine tree planting rates necessary to attain desired tree cover and species composition goals.     

Current and potential carbon stocks of trees in urban parking lots in towns of the Eastern Cape,South Africa

Greening of shopping centre parking lots is a potentially important strategy that can contribute to urban carbon mitigation efforts, improve aesthetics and the shopping experience of consumers, whilst adding to urban biodiversity. Twenty-eight shopping centre parking lots in six Eastern Cape urban centres, South Africa, were sampled to determine tree species composition, density and annual carbon sequestration potential. The best case parking lot found during the study was used as a benchmark to display the difference between current tree density and above-ground carbon stocks relative to the potential optimum. The highest tree density was 66 trees ha^?1, whereas the average density across all sampled parking lots was less than half that (27.2 ± 22.6 trees ha^?1). The average annual carbon sequestration potential per parking lot was 1390 ± 2503 kg ha^?1. Planting density was positively related to annual sequestration rates, whilst parking lot age and the mean annual rainfall of the town had no influence. Mean tree species richness per parking lot was 2.3 ± 1.8 species, with a positive relationship to parking lot size, but not to mean annual rainfall of the site. The majority of trees (62.5%) in parking lots were alien species, although newer parking lots had significantly greater proportions of indigenous species. There was no difference in mean annual carbon sequestration rate per tree between indigenous and alien trees species. Low tree densities and small parking lot areas constrained the potential for earning carbon credits from trees in parking lots. Nonetheless, planners and designers need to be more aware of the potential contribution of trees towards urban sustainability.     

Rainfall interception and stem flow by eucalypt street trees – The impacts of canopy density and bark type

Understanding how trees influence water movement in an urban landscape is important because in an ‘engineered xeriscape’ small changes in rainfall frequency or magnitude have significant implications to plant water availability and mortality at one extreme, and stormwater runoff and flooding at the other. This study relates direct measures of tree canopy interception and discusses their implication for catchment hydrology in different urban landscape contexts. We measured canopy throughfall and stemflow under two eucalypt tree species in an urban street setting over a continuous five month period. Eucalyptus nicholii has a dense canopy and rough bark, whereas Eucalyptus saligna has a less-dense canopy and smooth bark. E. nicholii, with the greater plant area index, intercepted more of the smaller rainfall events, such that 44% of annual rainfall was intercepted as compared to 29% for the less dense E. saligna canopy (2010). Stemflow was less in amount and frequency for the rough barked E. nicholii as compared to the smooth barked E. saligna. However, annual estimates of stemflow to the ground surface for even the smooth barked E. saligna would only offset approximately 10 mm of the 200 mm intercepted by its canopy (2010).Tree canopy and bark characteristics should be considered when planting in pervious green space, or impervious streetscapes, because of their profound impact upon tree and surrounding water availability, soil water recharge or runoff. This study provides an evidence base for tree canopy impacts upon urban catchment hydrology, and suggests that rainfall and runoff reductions of up to 20% are quite possible in impervious streetscapes. Street tree canopies can function as a cost-effective compliment to water sensitive urban design for stormwater reduction benefits.     

Factors influencing urban tree planting program growth and survival in Florida,United States

High levels of mortality after installation can limit the long-term benefits associated with urban tree planting initiatives. Past planting projects funded by the Florida Forest Service were revisited two to five years after installation to document tree survival and growth and assess program success. Additionally, various site (e.g., soil compaction, installed irrigation) and tree-related (e.g., species, nursery production method, initial size at planting) factors were noted to assess their impact on tree growth. Results show that the overall establishment rate for the 26 sites (n = 2354 trees) was high, with 93.6% of trees alive at the time of final inspection. On-site irrigation played a significant role in tree survival and growth, especially for Magnolia grandiflora (97.7% survival on irrigated sites; 73.8% survival on non-irrigated sites). Findings from this work validate the effectiveness of current program policies which include maintenance of tree quality within the first year after planting, and offer further insights regarding the impacts of season of planting and initial size of nursery stock on plant growth and development.     

Spatial distribution of saplings in heavily worn urban forests: Implications for regeneration and management

We studied the spatial distribution of saplings in the vicinity of other saplings and mature trees in heavily worn urban forests. Our aim was to identify favorable microsites for saplings to regenerate under different levels of wear. We hypothesized that these safe microsites were situated close to tree trunks that might offer shelter from trampling caused by humans and their pet dogs. The distribution of saplings was explored at 0.1–0.6 m to the nearest sapling and 0.1–2 m to the nearest mature tree. Sorbus aucuparia was the most abundant sapling species, followed by Populus tremula, Betula pubescens and Picea abies. These species all tended to cluster with their conspecific saplings and were generally randomly distributed with respect to mature trees. Saplings of S. aucuparia and P. tremula favored growing close to mature P. abies (already at 0.4–0.8 up to 2 m from the trunk base, respectively) and S. aucuparia trees (at 0.2–0.4 m up to 2 m). Betula sp. and Acer platanoides grew close to Pinus sylvestris trees. Furthermore, with increased levels of wear, saplings clustered more likely together and close to tree trunks. The results are contrary to the gap regeneration hypothesis known from rural unworn forests where saplings often grow in canopy gaps. We suggest the idea of a ‘sheltering group’, i.e. tree groups and thickets of densely growing conspecific saplings, for the maintenance of regeneration of saplings and other vegetation in heavily worn recreational forests. Since urban forestry may strongly affect the existence and spatial location of a high variety of microhabitats, small-scale spatial exploration is needed to identify microsites that offer opportunities for natural regeneration under heavy recreational use. To maintain natural regeneration and the survival of saplings in worn urban forests, we recommend microhabitat-level species-specific forest management.     

Ozone forming potential of tropical plant species of the Vidarbha region of Maharashtra state of India

Volatile organic compounds (VOC) are emitted by many plants. In this study, sixty common plant species of the Vidarbha region of Maharashtra, India were examined for VOC (isoprene and monoterpene) emissions. Plant species VOC emission rates ranged from undetectable to 75.2 μg g^?1 h^?1. Dalbergia sissoo exhibited a maximum VOC emission rate of 75.2 μg g^?1 h^?1. Ozone forming potentials (OFP) of the sixty plant species were also estimated using the method of Benjamin and Winer (1998). Maximum ozone forming potential of 77 g O₃ (tree)^?1 d^?1 was observed in the case of Mangifera indica. Out of 60 species, 26 species (43.3%) had low OFP (less than 1 g O₃ (tree)^?1 d^?1), 18 species (30%) had medium OFP (less than 1–10 g O₃ (tree)^?1 d^?1) and 16 species (26.7%) had high OFP (more than 10 g O₃ (tree)^?1 d^?1).     

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.     

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.     

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.     

Private residential urban forest structure and carbon storage in a moderate-sized urban area in the Midwest,United States

In conjunction with urbanization and its importance as a major driver of land-use change, increased efforts have been placed on understanding urban forests and the provisioning of ecosystem services. However, very little research has been conducted on private property and little is known about the structure and function of privately owned urban forests. This research examines the structure of and carbon storage services provided by private residential urban forests in a moderate-sized Midwestern city. The primary research questions are as follows: What is the structure of private urban forests, and how does it vary across parcels? How much carbon is stored in tree and soil pools of private urban forests, and how does carbon vary across parcels? Ecological inventories were conducted on 100 residential parcels within 14 Neighborhood and Homeowners Associations of varying size and development age. Tree species richness, diversity, density, and diameter distribution were determined on a per parcel basis and for the entire tree population sampled. Further, tree and soil carbon storage were determined for each parcel. Results of this research demonstrated large variability in per-parcel tree metrics. Twelve of the parcels sampled had two or fewer trees, while eleven had greater than 50 trees. Further, tree carbon storage ranged from no carbon to 11.22 kg C m^?2. Alternatively, soil carbon storage was less variable and averaged 4.7 kg C m^?2, approximately 1.9 times higher than the average carbon stored in trees (2.5 kg C m^?2). Management efforts aimed at maintaining or enhancing carbon storage and other ecosystem services should focus on both soil protection and maximizing services in living biomass. Our results demonstrate that sustaining tree-produced ecosystem services requires maintenance of large old trees and species diversity, not only in terms of relative abundance, but also relative dominance, and in combination, species–specific size distributions.     

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.     

Contributions of landscape trees in public housing estates to urban biodiversity in Hong Kong

Public housing estates (PHEs) in Hong Kong, accommodating 3.3 million of the 7-million population, have generous landscape planting in their grounds. The independent tree management regime generates a tree stock that deviates from the general urban-tree population. This study evaluated species composition, floristic diversity, importance value, and spatial distribution of trees in 102 PHEs (half of the total) occupying 8.31 km² (territory land area of 1104 km²), assessed their contribution to urban biodiversity, and developed a species selection strategy to enrich urban biodiversity. 48,823 trees belonged to 232 species, 151 genera and 59 families. Natives contributed 69 species and 10,837 trees. Species profile was skewed toward exotic species and trees. The species were divided into six frequency groups. The signature group had 45 species each with >200 trees. The dominant, common and occasional groups had 20, 26 and 48 species, respectively. 59 species in the rare group and 34 in the solitary group denoted changing and diverse species selections, respectively. Nonmetric Multidimensional Scaling (NMDS) found that species distribution in PHEs was strongly associated with species diversity, estate area and estate age. However, district and region were not correlated with NMDS. Some 98 species were significantly correlated (Spearman) with one or both NMDS axes. Species groups were analyzed to inform a species selection strategy to improve future planting program and enrich urban biodiversity. The methods and findings could be applied to south-China and other cities to rationalize urban-forest programs with the help of objective research data.     

A rapid urban site index for assessing the quality of street tree planting sites

Urban trees experience site-induced stress and this leads to reduced growth and health. A site assessment tool would be useful for urban forest managers to better match species tolerances and site qualities, and to assess the efficacy of soil management actions. Toward this goal, a rapid urban site index (RUSI) model was created and tested for its ability to predict urban tree performance. The RUSI model is field-based assessment tool that scores 15 parameters in approximately five minutes. This research was conducted in eight cities throughout the Midwest and Northeast USA to test the efficacy of the RUSI model. The RUSI model accurately predicted urban tree health and growth metrics (P < 0.0001; R² 0.18–0.40). While the RUSI model did not accurately predict mean diameter growth, it was significantly correlated with recent diameter growth. Certain parameters in the RUSI model, such as estimated rooting area, soil structure and aggregate stability appeared to be more important than other parameters, such as growing degree days. Minimal improvements in the RUSI model were achieved by adding soil laboratory analyses. Field assessments in the RUSI model were significantly correlated with similar laboratory analyses. Other users may be able to use the RUSI model to assess urban tree planting sites (<5 min per site and no laboratory analyses fee), but training will be required to accurately utilize the model. Future work on the RUSI model will include developing training modules and testing across a wider geographic area with more urban tree species and urban sites.