Growth and climate sensitivity of native and non-native urban trees under varying soil conditions in Santiago, Chile

This special issue of Arboriculture & Urban Forestry contains a series of papers related to urban tree growth and longevity. Research and new information on urban tree growth and longevity is important for improved management of our urban trees and forests, as well as assessing their function and value. The papers in this issue were presented at the Urban Tree Growth & Longevity Conference held on September 12–13, 2011 at The Morton Arboretum (Lisle, Illinois, U.S.). This international conference brought together researchers and practitioners to discuss the current state of knowledge concerning urban tree growth and longevity. The conference covered four topic areas: 1) Descriptive studies of tree growth, longevity, and mortality, 2) Roles of tree production and sales on tree growth and longevity, 3) Roles of site design and tree selection on tree growth and longevity, and 4) Roles of tree and site management on tree growth and longevity. The objectives of the conference and these papers are to: develop collaboration among professionals and researchers to help identify important gaps in our knowledge, foster discussions about promising new methodologies, prioritize research and education needs, and outline a course of action for future research and outreach on urban tree growth and longevity. A few additional papers from the conference will be published in a special section of a future issue of this journal.

城市林木生物量对硬化地表和种植密度的响应

Ground-level ozone pollution(O3) and climate change have become key global problems threatening the environment and sustainable development of urban forests. At present, various studies have assessed the O3 impacts on trees; however, it is difficult to accurately evaluate the complex ecological effects caused by multiple factors on the natural urban environment. In this paper, the interactions between O3 and carbon dioxide(CO2), drought, nitrogen deposition, and warming, as well as the effects of the physiology, biochemistry, and growth of urban trees in China were reviewed. Elevated CO2 could alleviate the negative effects of elevated O3 on the photosynthetic metabolism, antioxidant system, and growth of trees. There is a complex interaction between O3 and drought, which may synergistically aggravate, alleviate, or have no effect on trees. However, there was no correlation between O3 and N deposition, only a significant interaction between elevated temperatures and O3, which slowed down the adverse effects of O3 on tree growth and photosynthesis. Finally, suggestions are put forward to manage and sustainable develop urban forests in China under future climate change and air pollution.

The effects of urban conditions on tree growth have been investigated in an increasing number of studies over the last decades, emphasizing the harsh environment of cities. Urban trees often grow in highly paved, compacted sites with consequently less soil moisture, higher soil temperatures, and greater vapor pressure deficits. However, there is still a knowledge gap regarding the impact of harsh paved environments on urban tree growth during drought years on the growth patterns of urban trees. The present study investigated the structure and growth of the common urban tree species small-leaved lime (Tilia cordata) at a highly paved public square (CPS) compared with a contrasting more open, greener square (OGS). Continuously, measured high precision dendrometer data along with meteorological data of the extreme dry and warm summer 2015 as well as dendrochronological data of the sampled trees were investigated to analyze tree growth during a drought year. The results highlight different tree dimensions and growth patterns of the trees at both sites, influenced by tree age and distinct site conditions. While the trees at OGS grew up to 2.5mm from July until mid of August, the trees at CPS had only 0.4-mm diameter increment. After the initial expansion at CPS, tree diameter contracted again during summer to the point of shrinkage (up to 0.8mm) at the end of our investigation. Further drought year analysis confirmed the patterns of significant stem growth reductions in the consecutive two years following the drought. A correlation analysis revealed that transpiration, air temperature, and vapor pressure deficit were negatively correlated with the daily diameter growth, whereas precipitation had a strong positive effect. Due to high transpiration rates associated with anisohydric water use behavior, T. cordata was able to provide evaporative cooling even during drought. However, this anisohydric behavior resulted in substantial growth decline afterwards especially at paved sites like CPS. Our results suggest selection of tree species, such as those with isohydric water use behavior, which may achieve a better balance between growth, transpiration, and hence evaporative cooling.

The role of air pollution and climate on the growth of urban trees

ABSTRACTClimate change has a negative impact on the vitality of forests, and drought and heatwaves are the most influential abiotic stressors that contribute to tree health decline and mortality. Urban trees are not only vulnerable to climate change, but they also face harsh environmental conditions, including the urban heat island effect, limited soil volume and water availability. Therefore, the long‐term sustainability of urban forests relies on healthy and thriving trees and the identification of species that are resilient to climate change. Thus, it is fundamental to understand how urban trees respond to environmental conditions, including climate. This study investigates how urban trees respond to both long‐term climatic conditions and episodic extreme climate events. We evaluated variation in urban tree growth across differing climates by reconstructing growth histories and developing drought response indices. We selected 10 tree species planted in seven cities distributed along temperature and precipitation gradients across the Australian continent. We determined spatial and temporal patterns of tree‐ring growth in relation to extreme climate events. We found significant differences among cities, suggesting that local environmental conditions significantly influence tree growth. While some species showed fast annual growth in cool and wet cities, other species had similar growth across all cities or even faster growth in hot and dry cities. Urban trees generally responded positively to wetter conditions during the warmest month, which might be related to longer growing seasons and water availability. We found a positive effect of extreme hot conditions on growth, suggesting that urban trees might be well adapted to warm urban environments. Species climate‐growth relationships can help guide species selection to maximize benefits delivered by urban forests and minimize environmental and socio‐economic losses under current and future climates.

Background: Urban tree growth may be reduced due to poor urban soil conditions. Soil management to alleviate poor urban soil conditions often includes organic amendments, fertilization, and/or tillage. A 3-year experiment was conducted in an urban landscape in Bolingbrook, Illinois, USA, to test whether an arboriculture treatment with biochar, fertilization, and tillage could improve soil quality and tree growth. Methods: The urban landscape included 75 street trees (Gleditsia triacanthos, Ulmus parvifolia, and Acer rubrum) growing in compacted, fine-textured soils. Results: The results of this experiment suggest that the arboricultural treatment of biochar, fertilization, and tillage (BFT) may improve soil quality and urban tree growth. Relative height growth was significantly greater (P ≤ 0.05) for Acer rubrum trees with BFT treatment (+ 28.9%) compared to tillage alone (+ 13.3%). Total soil organic matter (SOM), particulate soil organic matter (POM), and a soil quality index (SQI) were significantly (P ≤ 0.05) greater in the BFT treatment (total SOM = 6.00%, POM = 9.73%, and SQI = 70.2) compared to the tillage treatment (total SOM = 5.29%, POM = 7.23%, and SQI = 60.8). The SOM responses to the BFT treatment appear to be relatively short-lived but correlated with measures of tree growth. Conclusion: This arboricultural treatment of biochar, fertilization, and tillage has potential to be used to improve soil quality and promote growth for trees growing in compacted, fine-textured soils in suburban street tree landscapes.

Urban trees and the services they provide (e.g., evapotranspirational cooling, shading, recreation, carbon storage, air pollution filtering) can have major effects on the microclimate of a city, although the growth conditions are often inadequate to ensure tree vitality and growth, negatively affecting their beneficial effects. In a worldwide dendrochronological study on ten urban tree species in four climatic zones, the growth and impacts of common urban tree species were assessed. This paper focuses on the results for Robinia pseudoacacia L. in the Mediterranean climate city of Santiago de Chile, highlighting the faster growth of the studied black locust trees since 1960 than its growth in the years before 1960. Furthermore, black locust displayed the best growth when situated closer to the city center than the city periphery and when in the northern and western parts of Santiago de Chile. The species characteristics of black locust also revealed an immediate negative growth reaction to drought events, followed by a rapid recovery, which was similarly influenced by the direction from and distance to the city center of the growing site. The results underline the overall worldwide findings on urban tree growth that indicate that a city climate with an extended growing season and increased temperatures can lead to improved growth of urban trees in the Mediterranean climatic zone. However, with increased growth, more rapid ageing and tree death might follow, leading to increased costs for new plantings and tree management.

Nine tree species in four central New Jersey communities were studied to determine the relationship of site factors with the growth of trees in urban areas. The four site variables included: house setback from the road; the presence of competing vegetation; the width of the tree lawn; and the amount of permeable surface beneath the tree crown, Tree growth was measured using a growth ratio index, the ratio of DBH to age for a given tree. The results indicated that although for several species there is a significant linear relationship between growth ratio index and these site factors, the R2 values for the nine species ranged between less than 0.01 and 0.14, indicating that a maximum of 14% of the variation in growth of these species can be explained by the linear models chosen.

Reliable models of urban tree growth over time are useful for selecting appropriate species for available planting sites, anticipating future tree maintenance and removal costs, and quantifying the benefits provided by trees. There is a need to develop growth models for multiple cities within the same climate region to understand the degree of variability for the same species in different cities. In this study, we developed tree growth models for 13 common street tree species in Cincinnati, Ohio, USA, based on field data and planting records. These models relate tree age to diameter at breast height. Then we compared the modeled tree growth curves for Cincinnati to analogous models from nearby Indianapolis, Indiana. To estimate how differences in modeled tree growth translate to differences in ecosystem services, we compared annual ecosystem service estimates from Cincinnati and Indianapolis using the i-Tree Eco model. The comparisons showed varying levels of difference between cities; for example, modeled growth curves for Acer platanoides were nearly identical, while models for Pyrus calleryana differed by > 47% over 35 years of growth. These results advance our understanding of urban tree growth rates by comparing models from two nearby cities, and by underscoring the inherent variability in urban tree growth that will drive attendant differences in the ecosystem services provided by trees.

Urban tree growth is often affected by reduced water availability, higher temperatures, small and compacted planting pits, as well as high nutrient and pollution inputs. Despite these hindering growth conditions, recent studies found a surprisingly better growth of urban trees compared to trees at rural sites, and an enhanced growth of trees in recent times. We compared urban versus rural growing Sakhalin fir (Abies sachalinensis (F. Schmidt) Mast.) trees in Sapporo, northern Japan and analyzed the growth differences between growing sites and the effects of environmental pollution (NO2, NOX, SO2 and OX) on tree growth. Tree growth was assessed by a dendrochronological study across a gradient from urban to rural sites and related to high detailed environmental pollution data with mixed model approaches and regression analyses. A higher growth of urban trees compared to rural trees was found, along with an overall accelerated growth rate of A. sachalinensis trees over time. Moreover, environmental pollution seems to positively affect tree growth, though with the exception of oxides OX which had strong negative correlations with growth. In conclusion, higher temperatures, changed soil nutrient status, higher risks of water-logging, increased oxide concentrations, as well as higher age negatively affected the growth of rural trees. The future growth of urban A. sachalinensis will provide more insights as to whether the results were induced by environmental pollution and climate or biased on a higher age of rural trees. Nevertheless, the results clearly indicate that environmental pollution, especially in terms of NO2 and NOX poses no threat to urban tree growth in Sapporo.

The growing conditions of urban trees differ substantially from forest sites and are mainly characterized by small planting pits with less water, nutrient and aeration availability, high temperatures and radiation inputs as well as pollution and soil compaction. Especially, global warming can amplify the negative effects of urban microclimates on tree growth, health and well-being of citizens. To quantify the growth of urban trees influenced by the urban climate, ten urban tree species in four climate zones were assessed in an overarching worldwide dendrochronological study. The focus of this analysis was the species water oak (Quercus nigra L.) in Houston, Texas, USA. Similar to the overall growth trend, we found in urban trees, water oaks displayed an accelerated growth during the last decades. Moreover, water oaks in the city center grew better than the water oaks growing in the rural surroundings of Houston, though this trend was reversed with high age. Growth habitat (urban, suburban, rural and forest) significantly affected tree growth (p < 0.001) with urban trees growing faster than rural growing trees and forest trees, though a younger age of urban trees might influence the found growth patterns. Growing site in terms of cardinal direction did not markedly influence tree growth, which was more influenced by the prevalent climatic conditions of Houston and the urban climate. Higher temperatures, an extended growing season and eutrophication can cause an accelerated growth of trees in urban regions across, across all climatic zones. However, an accelerated growth rate can have negative consequences like quicker ageing and tree death resulting in higher costs for new plantings and tree management as well as the decrease in ecosystem services due to a lack of old trees providing greatest benefits for mitigating the negative effects of the urban climate.

Urban forests provide important ecosystem services to city residents, including pollution removal and carbon storage. Climate change and urbanization pose multiple threats to these services. However, how these threats combine to affect urban trees, and thus how to mitigate their effects, remains largely untested because multi‐factorial experiments on mature trees are impractical. We used a unique urban warming experiment paired with a laboratory chamber experiment to determine how three of the most potentially damaging factors associated with global change for urban and rural trees—warming, drought, and insect herbivory—affect growth of Quercus phellos (willow oak), the most commonly planted large shade tree in the southeastern US, which is known for its resilience to these potential stressors. In a previous study, we found that the urban heat island effect was associated with reduced growth of Q. phellos and higher abundance of Parthenolecanium scale insects, key pests of oaks in cities. Here, we tested the hypothesis that tree water stress is the mechanism for these effects of warming. We found evidence that water stress is a major, interactive factor reducing urban tree growth, but found no evidence that water stress is associated with Parthenolecanium survival or abundance. Warming and Parthenolecanium only reduced growth in Q. phellos saplings that were simultaneously water stressed. Synthesis and applications. Across many temperate cities worldwide, urban trees grow less than rural trees. Our results point to water stress as the most likely driver for this pattern. Importantly, we found that water stress both reduces tree growth on its own and exacerbates effects of warming and insect pests on tree growth. Therefore, management strategies targeted at increasing tree hydration in cities may reduce effects of these three key stressors that are expected to intensify with further urbanization and climate change.

Researchers from around the world gathered at The Morton Arboretum (Lisle, Illinois, U.S.) in September 2011 to share their experiences and knowledge on the topic of urban tree growth and longevity. A roundtable discussion was held at the end of the second day’s program, during which attendees discussed the state of current research in these areas and identified needs for future research. Four distinct subgroups were identified within the broader topic of urban tree growth and longevity: tree production; site design and tree selection; tree and site management; and the need for descriptive studies. Throughout the discussion, it became clear that there must be greater collaboration among researchers investigating tree growth, increased investment in long-term studies, the development of a clearing house for information, and the fostering of productive partnerships between the governmental, industry, and academic sectors. To strengthen the impact of urban tree growth research on the tree care industry, results and conclusions must be summarized and distributed through suitable means for a variety of audiences, which might include federal, state, and local governments; property owners and consumers; nurseries and growers; tree care and other green industry professionals; and urban planners, civil engineers, and landscape architects. To this end, the Urban Tree Growth &amp; Longevity Working Group has been established to support communication between researchers and professional practitioners, enrich scientific exchange, and enhance the quality, productivity, and timeliness of research on tree growth, longevity, and mortality.

BackgroundRecent projections expect that Vietnam will be affected most severely by climate change with higher temperatures, more precipitation and rising sea levels. Especially increased temperatures will worsen the situations in cities, amplifying the urban heat island effect. Green infrastructures, i.e. urban trees are a common tool to improve the urban micro-climate for humans. Vital and well growing trees provide greatest benefits such as evaporative cooling, shading, air filtering and carbon storage. However, urban tree growth is often negatively affected by urban growing conditions such as high soil sealing with compacted tree pits providing small growing spaces with limited water, nutrient and oxygen supply, further warm temperatures and high pollution emissions. This study analyzed the growth of urban and rural African mahogany (Khaya senegalensis (Desr.) A. Juss.) trees in the city of Hanoi, Vietnam and the effects of the surrounding climate conditions on tree growth.ResultsThe results showed that rural African mahogany trees grew better than trees situated in the city center, which is contrary to other results on tree growth of temperate and subtropical cities worldwide. Moreover tree growth was similar regardless of the time of growth. Other results regarding stem growth of African mahogany located in different areas of Hanoi (east, west, north, city center) revealed a better growth in the northern and western outskirts of the city compared to the growth of trees in the city center.ConclusionAfrican mahogany trees in the urban centers of Hanoi showed a decreased growth compared to rural trees, which was likely induced by a low ground-water level and high pollution rates. In view of climate change and global warming, the decreased tree growth in the city center may also affect tree service provision such as shading and cooling. Those climate mitigation solutions are strongly needed in areas severely affected by climate change and global warming such as Vietnam.