Diversity and structure in California’s urban forest: What over six million data points tell us about one of the world's largest urban forests

Urban street trees provide many benefits to surrounding communities, but our ability to assess such benefits relies on the availability of high-quality urban tree data. While these data are numerous, they are not available in an easily accessible, centralized place. To fill this gap, we aggregated public and private data into a single, comprehensive inventory of urban trees in California called the California Urban Forest (CUF) Inventory. These data are offered to the public (aggregated to ZIP code) via an online data portal, which at the time of publication contained over 6.6 million urban tree records. In this study, we first describe the assembly and utility of the inventory. Then, we conduct the most comprehensive assessment of the diversity and structure of California’s urban forest to date at statewide, regional, and local spatial scales. These analyses demonstrate that California’s urban forests are highly diverse and among the most diverse urban forests in the world. We present a new and intuitive metric of species diversity, the top diversity or TD-50 index, which represents the cumulative number of species accounting for the top 50 % abundance of trees in an urban forest. We used species abundance data from 81 well-inventoried cities to demonstrate that the TD-50 index was a robust metric of diversity and a good predictor of comprehensive metrics like the Shannon Index. We also found that small-statured trees, such as crape myrtles (Lagerstroemia cv.) dominate California’s urban forests. This aggregated inventory of one of the world's largest urban forests provides the data necessary to assess the structure, diversity, and value of California’s urban forests at multiple spatial scales. The inventory’s presentation to the public and the information that can be gained from its analysis can be a model for urban forest management worldwide.     

Increased home size and hardscape decreases urban forest cover in Los Angeles County’s single-family residential neighborhoods

Single-family residential neighborhoods make up large areas within cities and are undergoing change as residences are renovated and redeveloped. We investigated the effects of such residential redevelopment on land cover (trees/shrubs, grass, building, and hardscape) in the 20 largest cities in the Los Angeles Basin from 2000 to 2009. We identified spatially stratified samples of single-family home lots for which additional square footage was recorded and for which additional construction was not recorded by the tax assessor. We then digitized land cover on high-resolution color imagery for two points in time to measure land cover change. Redevelopment of single-family homes in Los Angeles County resulted in a significant decrease in tree/shrub and grass cover and a significant increase in building and hardscape area. Over 10 years, urban green cover (trees/shrubs and grass) declined 14–55% of green cover in 2000 on lots with additional recorded development and 2–22% of green cover in 2000 for single-family lots for which new permits were not recorded. Extrapolating the results to all single-family home lots in these cities indicate a 1.2 percentage point annual decrease in tree/shrub cover (5.6% of existing tree/shrub cover) and a 0.1 percentage point annual decrease in grass cover (2.3% of existing grass cover). The results suggest that protection of existing green cover in neighborhoods is necessary to meet urban forest goals, a factor that is overlooked in existing programs that focus solely on tree planting. Also, changing social views on the preferred size of single-family homes is driving loss of tree cover and increasing impervious surfaces, with potentially significant ramifications for the functioning of urban ecosystems.     

Constructing community gardens? Residents’ attitude and behaviour towards edible landscapes in emerging urban communities of China

Community gardens are very popular in developed countries, providing multiple benefits to inhabitants. In developing China, residents in many emerging urban communities of China have been appropriating and reclaiming public open spaces intentionally as a leisure opportunity and transforming their entertainment functions into vegetable plots, which has caused a series of conflicts and disputes. However, this issue of informal community gardening has rarely been discussed formally at community level. Therefore, this study aims to learn and better understand what factors motivate residents to reclaim existing public open spaces for gardening and cultivating plants. The approach was to select and study informal community gardens in three urbanizing communities in Hangzhou, China. These emerging communities consist, to a significant extent, of people with farming experience, who have relocated here from previously rural areas during the urban expansion from the year 2000 to the current day. The informal community gardening takes place in the context of lack of community management, neglected public infrastructure and a disregard for resident’s living needs such as their personal sentiment, social activity, food quality and saving expenses. While most people are willing to participate in community gardening and those who do not want to contribute are not substantially against the activity. In the conclusions, suggestions are made about how to fulfil resident’s requirements and are presented at both community and city levels so that they may inform to the growth of emerging communities in other cities and countries undergoing rapid urbanization.     

Fragmentation of China’s landscape by roads and urban areas

China’s major paved road-ways (national roads, provincial roads, and county roads), railways and urban development are rapidly expanding. A likely consequence of this fast-paced growth is landscape fragmentation and disruption of ecological flows. In order to provide ecological information to infrastructure planners and environmental managers for use in landscape conservation, land-division from development must be measured. We used the effective-mesh-size (M_eff) method to provide the first evaluation of the degree of landscape division in China, caused by paved roads, railways, and urban areas. Using M_eff, we found that fragmentation by major transportation systems and urban areas in China varied widely, from the least-impacted west to the most impacted south and east of China. Almost all eastern provinces and counties, especially areas near big cities, have high levels of fragmentation. Several eastern-Chinese provinces and biogeographic regions have among the most severe landscape fragmentation in the world, while others are comparable to the least-developed areas of Europe and California. Threatened plant hotspots and areas with high mammal species diversity occurred in both highly fragmented and less fragmented areas, though future road development threatens already moderately divided landscapes. To conserve threatened biodiversity and landscapes, we recommend that national and regional planners in China consider existing land division before making decisions about further road development and improvement.     

Increases in heat-induced tree mortality could drive reductions of biomass resources in Canada’s managed boreal forest

Landscape Ecology - The Canadian boreal forest provides valuable ecosystem services that are regionally and globally significant. Despite its importance, the future of the Canadian boreal forest is...     

How many people should be in the urban forest? A comparison of trail preferences of Vienna and Sapporo forest visitor segments

Differences in trail preferences for social conditions of visitors to forests in Vienna and Sapporo were investigated in 2006 using a standardised image-based stated choice approach. On-site visitors to two comparable peri-urban forests – the Lobau Forest in Vienna, Austria (n=373), and the Nopporo Forest in Sapporo, Japan (n=256) – evaluated the same sets of computer manipulated images depicting 128 trail scenarios with different levels of social stimulation. Latent class segmentations, in three sub-segments of similar sizes, differentiated by partly opposite preferences for social conditions, were derived for both samples. A positive contribution of social stimulation to preferences was found for about 17% of Nopporo and 9% of Lobau respondents, while for close to 50% of Lobau respondents and 38% of Nopporo respondents very low levels of social stimulation were preferred. The results indicate that urban forests should be managed for users with a desire for low social densities as well as a denser social setting providing some levels of social stimulation.     

Towards social arboriculture: Arborists’ perspectives on urban forest labour in Southern Ontario,Canada

This paper explores how arborists negotiate their work environment, including the pressures of policies, the labour market, technologies, government regulations and lack thereof, and the non-human agencies with which they are confronted. The political climate surrounding urban forestry in Southern Ontario influences and governs operations and physical labour. There are many (f)actors and conditions (both external and internal) surrounding fieldwork in urban forestry and that these affect work and personal lives. The questions guiding this paper include: (a) How do various political and labour conditions impact arborists’ sense of pride, independence and skill?; (b) What are the social and labour divisions within the culture of arboriculture?; and (c) What is the lived experience of urban forest workers, their employment, and what is it like to be a frontline worker? This paper provides a closer look at licensing, work conditions, subcultures and social dynamics in urban arboriculture. Using accounts from semi-structured interviews with arborists across Southern Ontario and by examining field arborists’ activities, relationships with co-workers and working conditions through participant observation and ethnographic field notes, I explore and reveal how arborists feel about their working environment and the labour processes and people who oversee and surround them. Findings reveal that despite dehumanizing (f)actors within the field, there are elements of resistance and negotiation, and potential for an alternative future.     

Elevational treeline and forest line dynamics in Norwegian mountain areas – a review

Purpose

Treelines and forest lines (TFLs) have received growing interest in recent decades, due to their potential role as indicators of climate change. However, the understanding of TFL dynamics is challenged by the complex interactions of factors that control TFLs. The review aims to provide an overview over the trends in the elevational dynamics of TFLs in Norway since the beginning of the 20th century, to identify main challenges to explain temporal and spatial patterns in TFL dynamics, and to identify important domains for future research.

Method

A systematic search was performed using international and Norwegian search engines for peer-reviewed articles, scientific reports, and MA and PhD theses concerning TFL changes.

Results

Most articles indicate TFL rise, but with high variability. Single factors that have an impact on TFL dynamics are well understood, but knowledge gaps exist with regard to interactions and feedbacks, especially those leading to distributional time lags. Extracting the most relevant factors for TFL changes, especially with regard to climate versus land-use changes, requires more research.

Conclusions

Existing data on TFL dynamics provide a broad overview of past and current changes, but estimations of reliable TFL changes for Norway as a whole is impossible. The main challenges in future empirically-based predictions of TFLs are to understand causes of time lags, separate effects of contemporary processes, and make progress on the impacts of feedback and interactions. Remapping needs to be continued, but combined with both the establishment of representative TFL monitoring sites and field experiments.

     

Contact with urban forests greatly enhances children’s knowledge of faunal diversity

The replacement of natural environments with urban centers has increased the distance between people and nature, which generates an indifference and apathy towards natural areas. Such a phenomenon is particularly concerning when children are involved because they represent future generations. In the present study, we investigated the effect of ‘contact with a forest’ versus ‘no contact with a forest’ on the knowledge of biodiversity in children under the same socioeconomic and educational conditions. We recruited 267 children for our study; 110 children maintained contact with a forest, while 157 had no contact with an urban forest. We encouraged the children to express their knowledge of the natural environment through drawings. Our results showed that contact with a forest granted children greater knowledge of the native animals, but it did not seem to affect their knowledge of the vegetation. However, the lack of contact with a forest caused the children to give greater importance to human components as part of the forest. Proximity to a natural area, even in an urban environment, seems to help draw attention to its components and sets the groundwork for knowledge construction. Hence, it is highly important to encourage contact between urban children and natural environments, as it enables future generations to have a better connection with nature, which is essential for biodiversity conservation.     

Biotic homogenization of China’s urban greening: A meta-analysis on woody species

Human preferences for the species in urban greening have greatly facilitated the spread of non-native species, resulting in the homogenization of urban plant communities across spatial scales. We selected 11 major cities along the Yangtze River in China and examined the species composition in their urban plant communities. We found that China’s urban plant communities are becoming homogenized, as urban communities of different cities are highly similar to each other despite the geographical separation. Meanwhile, these artificial communities we investigated have diverged greatly from the natural communities at both the city and the geographic scale. We recorded a total of 91 woody species that have been used in urban greening in all 11 cities. Of those species, 27% were cultivars and introduced species, and 25% were being used outside of their native distribution ranges in China. This may be explained by the market and urban planners who tend to favor greening plants that are highly profitable and have aesthetic ornamental traits, rather than spending time introducing and acclimatizing the native species in each city. Given the current trend of homogenization, measures that recognize the importance of native species should be emphasized with comprehensive urban planning strategies.     

How can forest fragments support protected areas connectivity in an urban landscape in Brazil?

Cities continue to grow worldwide, and the highly modified urban landscape becomes an inhospitable environment for many species because the natural vegetation cover is commonly fragmented, and the remnants are often isolated. Protected Areas (PAs) located surrounding or within urban areas may not achieve their goal of protecting local or regional biodiversity. Thus, an urban ecological network is essential to support their PAs. Thus, this study aimed at assessing the PAs connectivity in an urban landscape in Brazil and understanding whether urban forest fragments can support an urban ecological network. Besides spatial models based on functional connectivity and graph theory, we used participatory techniques to design the resistance surface and the least-cost paths (LCPs) for Atlantic Forest birds. The results showed critical paths (LCPs), important areas for restoration programs for improving PAs connectivity, and essential forest fragments for conservation and restoration. Although the landscape has a forest structure with 1873 forest fragments and 516 links through which the LCPs were structured, most forest fragments and LCPs cannot provide the necessary support for the PAs connectivity. The current ecological network is dependent on forest fragments neighboring (outside PAs) and the flux dispersions occurred mainly in the peri-urban areas. Riparian zones and anthropic grasslands also showed importance for the PAs connectivity. We identified only 28 forest fragments spatially connected, presenting several sizes, and located near large forest areas, relevant PAs, and riparian zones. Six of these forest fragments, smaller than ten hectares and strategically located in the urban matrix, were indicated for restoration actions. The current low connectivity among PAs brings the importance of native vegetation restoration in the riparian zone and anthropic grassland and the importance of the periurban areas to promote biodiversity connectivity in the urban landscape.     

Deforestation scenarios show the importance of secondary forest for meeting Panama’s carbon goals

Landscape Ecology - Tropical forest loss has a major impact on climate change. Secondary forest growth has potential to mitigate these impacts, but uncertainty regarding future land use, remote...     

Visitors’ and residents’ perceptions of urban forests for leisure in Washington D.C

While there is an increasing number of studies on the experience of urban forests, few have examined the similarities and differences between first time visitors, repeat visitors, and local residents in their perceptions of urban forests for leisure. This study fills this research gap using Analysis of Covariance (ANCOVA) and Structural Equation Modeling (SEM), based on data collected on-site from a year-long survey of 1090 participants in Washington D.C. Results indicate that participants are generally positive on urban forests’ value for leisure and are highly satisfied with their leisure experience in the city, with “beliefs in parks and gardens” and “beliefs in street trees” being assessed the highest and lowest, respectively. The study also finds that interaction effects do exist between gender, season, location, and past experience, suggesting respondents’ visiting experience with urban forests is multidimensional, contextual, and situational. Specifically, the older the respondents are, the more positive their responses would be. A location with diverse and dense urban forests is more likely to stimulate positive perceptions, particularly for first timers. In addition, residents tend to focus on recreational aspects of urban forests as opposed to visitors, especially repeaters who are more likely to value the visual and aesthetic aspects of urban forests. This is not only evidenced by the ANCOVA results whereas fall and summer, the best seasons for pursuing outdoor activities, are highly positively perceived by residents, but also by the SEM analyses which show that street trees significantly contribute to repeaters’ satisfaction via their perceptions of “leisure value of urban forests” while no such relationship exists for first timers and residents. Urban parks and gardens are found to significantly and positively contribute to respondents’ visiting experience, which, in turn, leads to satisfaction for each respondent group. Finally, research limitations and theoretical, methodological, and managerial implications are discussed.     

Where is environmental justice? A review of US urban forest management plans

The distribution of trees and access to nature is rarely equitable across urban neighborhoods. This injustice is present in many cities, and its origins are predominantly rooted in enduring procedural and recognitional injustices. The purpose of this research was to systematically investigate Urban Forest Management Plans (UFMPs) prepared by municipalities across the United States (107 total) for their mention and explanation of environmental justice themes relevant to urban forestry. UFMPs describe municipal urban tree-planting and stewardship goals as well as pathways for both implementation and monitoring. Using a mixed-method approach that combines qualitative content analysis and quantitative measurement, we interrogated UFMPs for reference to three specific environmental justice pillars: distribution, procedure, and recognition. Mentions and explanations of these concepts were identified and counted for all UFMPs. Summary counts were then investigated for association with a UFMP’s publication year, its municipal population, and its racial composition. The frequency of reference to environmental justice themes was greater in UFMPs published more recently and whose authoring municipalities have a larger population. A positive association exists between the proportion of Black residents in a city with an UFMP and the frequency of identified distributional justice explanations. While a positive association with procedural justice mentions was found with the proportion of white residents in UFMP authoring cities, environmental justice, overall, is not a central theme across most UFMPs published to date. More generally, we discovered that where UFMPs referenced environmental justice concepts, it was often brief and lacking in substance; recognitional justice themes were absent in almost all documents. Improving environmental justice goals and implementation strategies in UFMPs that validate the perspectives and experiences of residents can strengthen accountability between urban foresters and the communities they serve.     

How does forest fragmentation affect tree communities? A critical case study in the biodiversity hotspot of New Caledonia

Context

The biodiversity hotspot for conservation of New Caledonia has facing high levels of forest fragmentation. Remnant forests are critical for biodiversity conservation and can help in understanding how does forest fragmentation affect tree communities.

Objective

Determine the effect of habitat configuration and availability on tree communities.

Methods

We mapped forest in a 60 km² landscape and sampled 93 tree communities in 52 forest fragments following stratified random sampling. At each sampling point, we inventoried all trees with a diameter at breast height ≥10 cm within a radius of 10 m. We then analysed the response of the composition, the structure and the richness of tree communities to the fragment size and isolation, distance from the edge, as well as the topographical position.

Results

Our results showed that the distance from the forest edge was the variable that explained the greatest observed variance in tree assemblages. We observed a decrease in the abundance and richness of animal-dispersed trees as well as a decrease in the abundance of large trees with increasing proximity to forest edges. Near forest edges we found a shift in species composition with a dominance of stress-tolerant pioneer species.

Conclusions

Edge-effects are likely to be the main processes that affect remnant forest tree communities after about a century of forest fragmentation. It results in retrogressive successions at the edges leading to a dominance of stress-tolerant species. The vegetation surrounding fragments should be protected to promote the long process of forest extension and subsequently reduce edge-effects.

     

Temporal variation of characteristic scales in urban landscapes: an insight into the evolving internal structures of China’s two largest cities

Urbanization has induced profound landscape changes. While the spatiotemporal patterns of urban landscapes have been extensively studied, the manner by which the internal structures of already urbanized areas change remains little understood. Characteristic scales are an important measure of landscape structure, and they represent the typical spatial extents of landscape elements in hierarchies. In this study, we quantified temporal variations of the characteristic scales in the central urban landscapes of Beijing and Shanghai over an 18?year period. Using transect data from Landsat images, characteristic scales were identified through wavelet analysis and then classified into several discrete domains using the k-means clustering method. These characteristic scale domains appeared to correspond with the typical extents of the blocks and block clusters in the study areas. Results showed that the number of the characteristic scale domains changed within a small range of 3?C5 while the mean values of the characteristic scales within the domains showed substantial temporal variation. Larger characteristic scales were more variable than smaller ones in both cities. Distinguishing relative change rates of building forms, land use and street layout of urban landscapes allowed us to interpret these differences. The street layout of urban landscapes usually reacts slowly to the force of change, acting as the skeleton of the urban landscape. As a result, block sizes can remain relatively stable and corresponding characteristic scales present inheritance features. Land use and building forms are more susceptible to changes. Block clusters with flexible extents could result in significant variation of characteristic scales.     

Diversity in mind: Towards a differentiated understanding of migrants’ recreational practices in urban forests

This paper presents results of a study investigating the relationship between migration and recreation in urban forests in two German cities. Research in this field is growing in Europe, yet in certain countries, such as Germany, it remains underdeveloped. Until now, it has revealed ambiguities and diverging results. Furthermore, it has been the subject of criticism and calls for more differentiation between and within migrant groups, as well as for more reflection on the categorisation of “migrant” or “ethnic group”. This paper builds on these claims and aims to shed new light on forest recreation and ethnicity through a context-sensitive research approach in the tradition of symbolic interactionism. It draws upon the analysis of 42 qualitative interviews conducted with people with a Turkish, Russian-German and no migration background. The analysis leads to the construction of five narratives, each of them regrouping respondents who share a similar perspective on a specific theme. The narratives show how personal life context and its interlinkages with migration influence the individual's perspectives on and uses of urban forest. They also show how lifestyle and gender shape recreational practices independently from migration background. Beyond the focus on individual experience, collective recreational practices attributed to some groups are expressed in the narratives. This paper addresses the social aspect of leisure and discusses how forest recreation affects the social construction of groups such as migrant groups.     

The role of green space in Chicago’s gentrification

Investment in park green space can improve the quality of life for urban residents but has also been linked to green gentrification. Investments in informal green space have been proposed as means for improving green access while minimizing the risk of displacement. Very little empirical research, however, has examined the differential impacts of park and non-park green space investments in the broader context of neighborhood greening. To further this understanding, we examine the association between park and non-park green space increases and the likelihood of gentrification in Chicago using satellite imagery, land use, and census data during two periods—1990–2000 and 2000–2010. We found that green space of any type did not have a statistically significant role in increasing the odds of gentrification, but the importance of green space variables in predicting gentrification increased with time. Neighborhood characteristics like the distance to downtown or the presence of gentrifying neighbors were most predictive, suggesting that green investment efforts should consider the pre-existing risk factors for gentrification. Our results do not dispute that green space has the potential to play a role in gentrification, simply that green gentrification may be strongly contingent upon timing and neighborhood characteristics.     

The role of greenspace deprivation in children’s decision-making

We explored the role of long-term greenspace deprivation in how children evaluate potential rewards and punishments and use this information to make decisions. We used data from the Millennium Cohort Study (MCS), a large population-based longitudinal birth cohort in the UK. Reward and punishment sensitivity was measured at the age 11 data wave with the Cambridge Gambling Task (CGT). Our sample (N = 1701; 51 % male) included children who, as at the age 11 wave, had lived in the same address in urban England since the beginning of MCS and had valid data on the CGT. Our analysis adjusted for families’ selection into neighbourhoods, children’s pubertal status, sex, ethnicity and cognitive ability but also several important aspects of the home’s and the neighbourhood’s physical and social environments. Even after full adjustment, children growing up in the least green neighbourhoods showed less aversion to risk (they scored higher on risk-taking), and the association was similar across sexes. However, long-term absence of local greenspace was not significantly associated with other aspects of reward and punishment sensitivity, including risk adjustment, deliberation time or delay aversion, even after minimal adjustment. Long-term greenspace deprivation seems uniquely predictive of fast decision strategies in children.