Quantifying urban forest structure,function, and value: the Chicago Urban Forest Climate Project

This paper is a review of research in Chicago that linked analyses of vegetation structure with forest functions and values. During 1991, the regions trees removed an estimated 5575 metric tons of air pollutants, providing air cleansing worth 9.2 million. Each year they sequester an estimated 315 800 metric tons of carbon. Increasing tree cover 10% or planting about three trees per building lot saves annual heating and cooling costs by an estimated 50 to 90 per dwelling unit because of increased shade, lower summertime air temperatures, and reduced neighborhood wind speeds once the trees mature. The net present value of the services trees provide is estimated as 402 per planted tree. The present value of long-term benefits is more than twice the present value of costs.     

A time series of urban forestry in Los Angeles

There has been an increasing interest in the evolution of urban forests. This research uses historic and digital aerial photography to quantify changes in tree density in Los Angeles, California since the 1920’s. High-resolution geographic information system analysis (4 to 6 time periods) of three regions (San Fernando Valley, Hollywood, Los Angeles Basin) of Los Angeles reveals that there has not always been an increase in tree density with time. Tree densities on public and private land were highest in the 1940’s in Hollywood, while the San Fernando Valley and Los Angeles Basin experienced a near linear increase in tree density on both private and public land since the 1920’s. When historic tree density reconstructions were examined for the 15 Los Angeles city council districts from the 1920’s, 1950’s and 2006, most districts in Los Angeles have experienced a significant increase in tree density, however, there has been wide variation in tree densities among city council districts. Trees densities have generally been higher on private land since the 1920’s and currently tree densities on private land are significantly higher than on public land. Results suggest the evolution of urban forests in Los Angeles mirrors the dynamics of urban forests in desert and grassland cities. It is possible to reconstruct the development of urban forests in sections of cities using historic and contemporary aerial photography. We estimated that Los Angeles averages approximately 104 trees per hectare (82 private land, 22 public land) based on 2006 imagery at 0.3 m resolution, however, field validation suggests that we identified only 73% of trees. Although there is still space to plant trees on public land, private land owners will need to be heavily involved in order to achieve the goals of Los Angeles’ Million Tree Initiative.     

Composition and conservation value of bird assemblages of urban ‘habitat islands’: Do pedestrian traffic and landscape variables exert an influence?

Urban forest fragments can potentially be ‘habitat islands’ for native birds, but pedestrian traffic could influence the composition and conservation value of their bird assemblages by reducing the representation of disturbance-sensitive species. Winter bird assemblages and pedestrian traffic rates were documented in twelve forested parks in suburban Melbourne, Australia. Native birds comprised 87% of sightings, but two exotic species were common. Bird species' distribution among the parks was significantly nested. However, park rank orders for bird assemblage nestedness and mean pedestrian traffic rate were not correlated and only one species' distribution was nested with respect to this variable. The observed correlation between park area and bird assemblage nestedness may have been partly due to passive sampling. Degree of isolation of parks influenced nestedness less than park area. Forested parks provided habitat for species that occur at intermediate to low densities in other suburban habitats and for ecological specialists otherwise rare in suburbia. Larger parks contained more species than, and many of the native species found in, smaller parks. However, smaller parks each had 25% of the native bird species inhabiting the suite of fragments and thus had both aesthetic value and some potential to enhance city-dwellers' awareness about biodiversity conservation.     

Government Sanctioned “Tight” and “Loose” Slot Machines: How Having Multiple Versions of the Same Slot Machine Game May Impact Problem Gambling

In Ontario, Canada, the regulator approves identical looking slot machine games with different payback percentages. We gained access to the design documents (called PAR Sheets) used to program these different versions of the same slots game and ran Gambler’s Ruin simulations of 2,000 first-time players who each arrived with a $100 bankroll and played either the 85 or 98% version of the same game until broke. Simulations revealed that the typical (median) player’s experience did not differ significantly between versions. However the payback percentage affected the experience of players in the upper tails of the distributions with those in the 98% version having dramatically more total spins, winning spins, entries into the “bonus mode”, and “hand pays” (a win of $100 bankroll and played either the 85 or 98% version of the same game until broke. Simulations revealed that the typical (median) player’s experience did not differ significantly between versions. However the payback percentage affected the experience of players in the upper tails of the distributions with those in the 98% version having dramatically more total spins, winning spins, entries into the “bonus mode”, and “hand pays” (a win of 125 or more on a given spin). Most importantly, the number of simulated players who had a maximum peak balance in excess of $1,000 rose tenfold—from 5 in the 85% version to 54 in the 98% version. The results are discussed in terms of the Pathways Model of Problem and Pathological Gambling especially in terms of behavioural conditioning, cognitive beliefs, and early big wins. It may well be that those machines that are on the surface the “fairest” to the gambler, actually pose the most risk for ensuing gambling problems.     

The influence of small urban parks characteristics on bird diversity: A case study of Petaling Jaya,Malaysia

The capacity of small urban park to serve as urban habitats are rarely explored. This study analyses the characteristics of small urban parks and their potential to support urban biodiversity and ecological functions. Nine small urban parks were studied in Malaysia in August and September 2014 using the combined field survey method of structured observation and field measurements. The measured variables were divided into three broad categories of physical characteristics, species richness and human factors. Bird species richness and abundance were used as the indicators for assessing biodiversity. Pearson correlations and multiple regressions were conducted to analyse the relationships between variables and to identify which variables had a significant effect on bird species richness and abundance. The results demonstrated that park area and vegetation variables ( e.g. the percentage of tree canopy cover, open grass/ground, native-exotic plants) are the important predictors of bird species richness and abundance. The percentage of canopy covers (negative relation) and park area (positive relation) are the best predictors of bird species richness in small urban parks. Meanwhile, the best predictors for bird abundance are the percentage of canopy covers (negative relation) and native vegetation species (positive relation). Human activities and park surroundings have a marginal effect on the presence of bird species in small parks. Based on the findings, we provide two general recommendations that could probably increase bird diversity in small urban parks: (1) the park development and management plan should incorporate a social-ecological approach that can benefit both city-dwellers and bird species, and (2) findings from the study should be used to rethink the planting design and composition of especially newly established small urban parks.     

The replacement principle for the provision of multiple public goods on tree networks

This article considers the provision of two public goods on tree networks where each agent has a single-peaked preference. We show that if there are at least four agents, then no social choice rule exists that satisfies efficiency and replacement-domination. In fact, these properties are incompatible, even if agents’ preferences are restricted to a smaller domain of symmetric single-peaked preferences. However, for rules on an interval, we prove that Miyagawa’s (Soc Choice Welf 18:527–541, 2001) characterization that only the left-peaks rule and the right-peaks rule satisfy both of these properties also holds on the domain of symmetric single-peaked preferences. Moreover, if agents’ peak locations are restricted to either the nodes or the endpoints of trees, rules exist on a subclass of trees. We provide a characterization of a family of such rules for this tree subclass.     

Comparing the relative abilities of tree species to cool the urban environment

Increasing urbanisation poses numerous challenges to human quality of life. Cities are particularly vulnerable to the urban heat-island effect, which will be amplified by climate change. Increasing tree cover may be one of the most cost-effective ways of moderating urban temperatures. Trees cool their surroundings by casting shade, reflecting solar radiation, transpiring, and intercepting rainfall that subsequently evaporates. However, the potential of trees to reduce the urban heat-island effect is underutilised. The aim of this study was to synthesise understanding of the relative abilities of different tree species to provide urban cooling in temperate regions of the world and thereby develop a pragmatic approach for choosing those trees that have greatest potential in that regard. Based on a literature review and semi-structured interviews with leading experts, we developed a series of scenarios to illustrate the impacts of a tree’s cooling mechanisms and tree species’ attributes on components of the surface-energy balance equation. This enabled us to select parameters and propose simple equations that can be used to compare the relative abilities of tree species in relation to each of the cooling mechanisms. The parameters selected were for: transpiration – crown diameter, Leaf Area Index (LAI), canopy aspect ratio, and stomatal conductance or growth rate; reflection – albedo, crown diameter and LAI; shading – canopy aspect ratio, crown diameter, LAI and tree height. The approach is intended for use by urban planners and managers who wish to make informed decisions about which tree species to select for planting to counter the urban heat-island effect.     

Ultraviolet radiation in urban ecosystems with consideration of effects on human health

Excess exposure to ultraviolet radiation (UV) from the sun, particularly the ultraviolet B (UVB), is cited as a cause or contributing factor for deleterious effects on human health, including skin cancers and cataracts. Rates of skin cancer have increased greatly in recent years, and increased UVB caused by reductions in stratospheric ozone may be responsible for some of the increase in rates, though quantified estimates of the effect of the UVB changes on health have low certainty. UVB exposure also affects the function of the immune system, and the potential resulting effects on infectious diseases and immunizations are a concern. Epidemiological considerations suggest that peoples' routine exposure to UV in urban areas can be significant in adverse health effects, particularly for young children. Projected trends of ozone indicate that agreements to limit ozone-depleting substances are slowing the UVB increase, but high levels will continue and apparently impact health to the middle of the current century. Urban trees greatly reduce ultraviolet irradiance in their shade when they obscure both the sun and sky. Where trees or other structures obscure only the sun, leaving much of the sky in view, UVB irradiance will be greater than suggested by the visible shade. Since air pollutants influence the UVB above the canopy, and the overlying atmosphere is usually more polluted in urban than rural areas, additional above-canopy monitoring of UV in urban areas is needed for comparison to existing rural monitoring sites. Such monitoring would facilitate the development of computer models of urban effects on UV, which are needed for epidemiological investigations, public education, and urban planning.     

Distribution and activity of bats at local and landscape scales within a rural–urban gradient

We examined the relationship between bat species activity and composition and the extent of forest cover and urbanization in and adjacent to 11 U.S. National Park Service, National Capital Region Parks in Maryland, Virginia, West Virginia, and Washington, D.C., from 2003–2004, using mist nets, harp traps, acoustical detectors, and visual observations in a variety of habitats. Our efforts included 363 trap nights across 74 sites along with acoustical sampling at 362 sites. We captured 383 bats and identified 6,380 echolocation passes of 6 species. Both overall and species-specific activities were affected more by forest fragmentation within parks than by urbanization adjacent to parks. With an ability to exploit anthropogenic structures for day-roosts, big brown bats (Eptesicus fuscus) were the most ubiquitous and probably the most abundant species in NCR Parks, particularly in forested, urban parks. Northern myotis (Myotis septentrionalis), and to a lesser extent, little brown myotis (Myotis lucifugus) were more prevalent in forested, rural parks of the Ridge and Valley and Blue Ridge than in eastern, less forested urban parks of the Piedmont and Coastal Plain physiographic provinces. Retention of larger, residual forest tracts and day-roosting habitat (i.e., trees and snags) would be beneficial to most species, as urban expansion continues throughout the region.     

Robert K. Merton as postwar prophet

Within the context of a discussion of Robert K. Merton’s ideas on leadership in postwar America, the article examines the nature and impact of Merton’s “sociological parables.” This term refers to short tales from social life from which sociological lessons with moral implications can be drawn. These parables, such as the bank insolvency story told in “The Self-Fulfilling Prophecy,” illustrate the manner in which Merton merged moral and sociological messages in his writings. Suggestions are made along the lines that these parables, or at least the moral messages they contain, contributed to Merton’s postwar fame. His most recent publications are “Simmel’s Contribution to Parsons’ Action Theory and Its Fate,” in Michael Kaern, ed.Georg Simmel and Contempory Sociology (Kluwer, 1990); and “Robert K. Merton’s Extension of Simmel’sUbersehbar” inSociological Theory, Spring 1990.     

Poverty measurement: the critical comparison value

The Foster–Greer–Thorbecke (FGT) family of poverty-measures is commonly used when comparing income distributions with respect to poverty. Within this framework, the poverty ranking will be sensitive to the choice of poverty aversion parameter (defining a particular FGT poverty-measure). If we content ourselves with applying a few specific parameter values, then we may demand too little in order to claim robustness in our poverty comparisons. On the other hand, we may demand too much if we only work with FGT poverty-measure quasi orderings established by considering every possible parameter value. An alternative approach may be to report the number of parameter values representing possible reversal points in our poverty ranking—what we call critical comparison values—and leave the final evaluative step to the relevant decision-makers. By applying a generalized version of Descartes’ Rule of Signs, we show that the number of critical comparison values depends on the number of times the cumulative distribution functions intersect.

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Geometric models of consistent judgement aggregation

Given a set of propositions with unknown truth values, a ‘judgement aggregation function’ is a way to aggregate the personal truth-valuations of a group of voters into some ‘collective’ truth valuation. We introduce the class of ‘quasimajoritarian’ judgement aggregation functions, which includes majority vote, but also includes some functions which use different voting schemes to decide the truth of different propositions. We show that if the profile of individual beliefs satisfies a condition called ‘value restriction’, then the output of any quasimajoritarian function is logically consistent; this directly generalizes the recent work of Dietrich and List (Majority voting on restricted domains. Presented at SCW08; see , 2007b). We then provide two sufficient conditions for value-restriction, defined geometrically in terms of a lattice ordering or a metric structure on the set of individuals and propositions. Finally, we introduce another sufficient condition for consistent majoritarian judgement aggregation, called ‘convexity’. We show that convexity is not logically related to value-restriction.     

Factors related to tree growth across urban-rural gradients in the Midwest,USA

Several environmental factors influence tree growth at any site. The objective of this study was to examine the relationship between biotic and abiotic factors and tree growth rate (mean ring width averaged over the last 10 years) in settings ranging from urban to rural. Six clusters, each with five communities and two rural parks, were sampled in Illinois, Iowa, Minnesota, Missouri, and Wisconsin, for a total sample of 320 trees. Within each community, trees in parks, and along residential and commercial streets were sampled. Five species were sampled: silver maple (Acer saccharinum L.), honeylocust, (Gleditisia triacanthos L.), hackberry (Celtis occidentalis L.), black maple (Acer nigrum Michx F.), and basswood (Tilia americana L.). Factors were investigated for three scenarios: (i) all trees sampled in all clusters, (ii) a single species, all clusters, and (iii) all species, a single cluster.Baseline variables (cluster, place population, site, species, and age) accounted for 49–71% of observed variation in growth rate. Combined biotic factors accounted for 5 to 6% of observed variation. For all species in a single cluster, combined abiotic factors accounted for 11% of observed variation. Biotic factors related to growth rate detected using multivariate analyses included number of other trees within 9 m, presence of disease and insects, and human-induced mechanical injury. Abiotic factors that were related to tree growth included presence of pavement and core bulk density. For trees in rural parks, number of other trees within 20 m, and for trees in both rural and community parks, number of other trees within 9 m of sample trees were associated with decreased growth rate.     

Contrasting effects of urban habitat complexity on metabolic functional diversity and composition of litter and soil bacterial communities

Functional diversity and composition of soil bacterial communities affect important soil biogeochemical processes. In natural and semi-natural ecosystems, variations in habitat complexity have been shown to significantly impact both litter and soil bacterial communities. However, this remains largely untested in urban ecosystems, where human management can lead to habitat complexity combinations unobserved in rural ecosystems. We established 10 research plots in low-complexity park, high-complexity park, and high-complexity remnant habitat types (n = 30) in Melbourne, Australia. The use of organic carbon substrates by soil and litter bacteria was measured using EcoPlates to investigate the effects of habitat complexity upon metabolic functional diversity and functional composition of bacterial communities of i) soil and ii) one-year old litter. Direct and indirect effects of habitat complexity, microclimate and decomposition status upon litter microbial functional diversity and composition were also modelled using path analysis. Soil bacterial communities had significantly higher functional diversity compared to litter bacterial communities, but no significant effect of habitat complexity was apparent. The functional composition of soil bacterial communities was not affected by habitat complexity. In contrast, the functional composition of litter bacterial communities in high complexity parks and remnants was significantly different from that in low-complexity parks. The functional composition of litter bacterial communities, but not their diversity, was directly affected by habitat complexity and microclimate as well as their indirect effects upon the decomposition status of litter. Human management of urban habitat complexity can alter the functional composition of litter and soil bacterial communities without affecting their functional diversity. While this can have significant impacts on bacteria-regulated processes and ecosystem services, it also suggests that urban bacterial communities might be able to adjust to further environmental and climatic changes affecting urban ecosystems.     

Consistency between tastes and values: A universalization approach

The object of this paper is to propose a consistency test for an individual involved in collective choice process. Collective choice processes considered in the paper are those that transform individuals ‘tastes’– which reflect the self-interested view point of the individuals – into (social) ranking of alternatives. In addition to her tastes, an individual has values about the way by which collective decision should be made. We distinguish two categories of such values. First, there are end-values that restrict the class of social rankings that the individual considers ethically acceptable. Second there are aggregation-values that specify the way by which the social ranking should depend upon the individuals tastes. The consistency test stands on an hypothetical operation of universalization of the individual tastes to everyone. Five illustrations of the potential usefulness of our approach for interpreting social choice theory and welfare economics are proposed. These illustrations deal with utilitarian aggregation in the presence of income inequality aversion, the so-called ‘ethics of responsibility’ and the aggregation of individual ranking of opportunity sets based on their freedom of choice. A discussion of the relevance of the consistency test for addressing the problem of ‘laundering’ individual preferences is also provided. Received: 25 June 1998/Accepted: 16 March 1999     

Computational application of the mathematical theory of democracy to Arrow’s Impossibility Theorem (how dictatorial are Arrow’s dictators?)

The article is based on three findings. The first one is the interrelation between Arrow’s (Social choice and individual values, Wiley, New York, 1951) social choice model and the mathematical theory of democracy discussed by Tangian (Aggregation and representation of preferences, Springer, Berlin, 1991; Soc Choice Welf 11(1):1–82, 1994), with the conclusion that Arrow’s dictators are less harmful than commonly supposed. The second finding is Quesada’s (Public Choice 130:395–400, 2007) estimate of their power as that of two voters, implying that Arrow’s dictators are not more powerful than a chairperson with an additional vote. The third is the model of Athenian democracy (Tangian, Soc Choice Welf 31:537–572, 2008), where indicators of popularity and universality are applied to representatives and representative bodies. In this article, these indicators are used to computationally evaluate the representativeness/non-representativeness of Arrow’s dictators. In particular, it is shown that there always exist Arrow’s dictators who on the average share opinions of a majority, being rather representatives. The same holds for dictators selected by lot, which conforms to the practice of selecting magistrates and presidents by lot in ancient democracies and medieval Italian republics. Computational formulas are derived for finding the optimal “dictator–representatives”.     

Marriage matching and gender satisfaction

The performance of the Gale–Shapley marriage matching algorithm (Am Math Mon 16:217–222, 1962) has been studied extensively in the special case of men’s and women’s preferences random. We drop the assumption that women’s preferences are random and show that , where R _n is the men’s expected level of satisfaction, that is, the expected sum of men’s rankings of their assigned mates, when the men-propose Gale–Shapley algorithm is used to match n men with n women. This is a step towards establishing a conjecture of Knuth (Mariages Stables et leurs relations avec d’ autres problémes combinatoires, 1976, CRM Proceedings and Lecture Notes, Vol 10, 1997) of 30 years standing. Under the same assumptions, we also establish bounds on the expected rankings by women of their assigned mates.     

Gray squirrel density,habitat suitability,and behavior in urban parks

Increased density, increased intraspecific aggression, and a reduced fear of humans have been suggested as the more observable and frequently described characteristics of wildlife species undergoing synurbization, the process of becoming urbanized. The relationship among these variables and how they may be related to environmental variables that change with urbanization is poorly understood. In this paper we explore the relationship between density, intraspecific aggression, and reduced fear of humans in urban populations of gray squirrel. In the summer and fall of 2003 and 2004, we studied a park with a documented high density of gray squirrels, Lafayette Park, Washington, DC, and six urban parks in Baltimore, MD with unknown squirrel densities. We used linear regression (SAS Institute, SAS/STAT user’s guide. SAS Institute, Cary, NC, 2005) to determine if there was a relationship (P < 0.05) between squirrel density and intraspecific aggression, squirrel density and reduced fear of humans (wariness), and squirrel density and habitat suitability. We found a positive association between density and intraspecific aggression (R ² = 0.81, P < 0.00). A negative relationship between density and wariness (, P < 0.00). However, no relationship was evident between habitat suitability and squirrel density (, P = 0.437).