E. Gregory Mcpherson

• PhD Forestry
• United States Department of Agriculture

The aim of this study was to quantify street tree population dynamics in the city of Claremont, CA. A repeated measures survey (2000 and 2014) based on a stratified random sampling approach across size classes and for the most abundant 21 species was analyzed to calculate removal, growth, and replacement planting rates. Demographic rates were estim...

Urban forests produce ecosystem services that can benefit city dwellers, but are especially vulnerable to climate change stressors such as heat, drought, extreme winds and pests. Tree selection is an important decision point for managers wanting to transition to a more stable and resilient urban forest structure. This study describes a five-step pr...

This study used tree data from field plots in urban areas to describe forest structure in urban areas throughout California. The plot data were used with numerical models to calculate several ecosystem services produced by trees. A series of transfer functions were calculated to scale-up results from the plots to the landscape using urban tree cano...

This study evaluated the effectiveness of two bioswales eight years after construction in Davis, California. The treatment bioswale measured 9 m × 1 m × 1 m (L × W × D). Engineered soil mix (75% native lava rock and 25% loam soil) replaced the native loam soil. Four Red Tip Photinia (Photinia × fraseri Dress) trees and two Blueberry Muffin Hawthorn...

This data publication contains urban tree inventory data for 929,823 street trees that were collected from 2006 to 2013 in 49 California cities. Fifty six urban tree inventories were obtained from various sources for California cities across five climate zones. The five climate zones were based largely on aggregation of Sunset National Garden Book’...

Rainfall interception research in forest ecosystems usually focuses on interception by either tree crown or leaf litter, although the two components interact when rainfall occurs. A process-based study was conducted to jointly measure rainfall interception by crown and litter and the interaction between the two interception processes for four tree...

Ulmus americana (American elm) was an important urban tree in North America prior to the introduction of the Dutch elm disease pathogen in 1930. Subsequently, urban and community forests were devastated by the loss of large canopies. Tree improvement programs produced disease tolerant American and Eurasian elm cultivars and introduced them into the...

This article updates tree growth and mortality data for six drought tolerant tree species previously presented in Western Arborist (McPherson & Albers, 2014). It extends the scope of the earlier paper by assessing the vulnerability of each species to climate change stressors, as well as their potential for use in plantings to store carbon, reduce r...

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...

Information on urban tree growth underpins models used to calculate the effects of trees on the environment and human well-being. Maximum tree size and other growth data are used by urban forest managers, landscape architects, and planners to select trees most suitable to the amount of growing space, thereby reducing costly future conflicts between...

The past decade could be called a renaissance of urban forestry, driven by mayoral tree planting initiatives and increased attention on city trees as green infrastructure. The political support for urban greening has been fueled by research that quantifies and projects the ecosystem services of planting initiatives (Young and McPherson 2013). Major...

This study compiled recent inventory data from 929,823 street trees in 50 cities to determine trends in tree number and density, identify priority investments and create baseline data against which the efficacy of future practices can be evaluated. The number of street trees increased from 5.9 million in 1988 to 9.1 million in 2014, about one for e...

This data publication contains urban tree growth data collected over a period of 14 years (1998-2012) in 17 cities from 13 states across the United States: Arizona, California, Colorado, Florida, Hawaii, Idaho, Indiana, Minnesota, New Mexico, New York, North Carolina, Oregon, and South Carolina. Measurements were taken on over 14,000 urban street a...

An experiment was conducted to concentrate on the rainfall interception process of individual trees for four common species in Beijing, China, which included needle species ( Platycladus orientalis and Pinus tabulaeformis ) and broadleaf species ( Quercus variabilis and Acer truncatum ). Two types of interception storages, the maximum ( Cmax ) and...

Long-term survival and growth of urban forests are critical to achieve the targeted benefits of urban tree planting programs, such as building energy savings from tree shade. However, little is known about how trees perform in the long-term, especially in residential areas. Given this gap in the literature, we monitored 22-years of post-planting su...

As well as being planted for wind breaks, landscape trees, and fuel wood, eucalypts are also widely used as urban street trees in California. They now are besieged by exotic insect herbivores of four different feeding guilds. The objective of the current analysis was to determine the return on investment from biological control programs that have t...

Urban tree survival is essential to sustain the ecosystem services of urban forests and monitoring is needed to accurately assess benefits. While some urban forestry studies have reported street tree survival, little is known about the factors influencing residential yard tree survival, especially over the long-term. We assessed residential shade t...

Urban forestry is an important green infrastructure strategy because healthy trees can intercept rainfall, reducing stormwater runoff and pollutant loading. Surface saturation storage capacity, defined as the thin film of water that must wet tree surfaces before flow begins, is the most important variable influencing rainfall interception processes...

This study seeks to answer the question, "Will the Million Trees LA (Million Trees Los Angeles, MTLA) program be a carbon dioxide (CO2) sink or source?" Because there has never been a full accounting of CO2 emissions, it is unclear if urban tree planting initiatives (TPIs) are likely to be effective means for reaching local reduction targets. Using...

Million Trees LA (MTLA) is one of several large-scale mayoral tree planting initiatives in the United States, striving to create more livable cities through urban forestry. This study combined field sampling of tree survival and growth with numerical modeling of future benefits to assess performance of MTLA plantings. From 2006 to 2010 MTLA planted...

This paper describes the use of field surveys, biometric information for urban tree species and remote sensing to quantify and map carbon (C) storage, sequestration and avoided emissions from energy savings. Its primary contribution is methodological; the derivation and application of urban tree canopy (UTC) based transfer functions (t C ha−1 UTC)....

Urban forest monitoring data are essential to assess the impacts of tree planting campaigns and management programs. Local practitioners have monitoring projects that have not been well documented in the urban forestry literature. To learn more about practitioner-driven monitoring efforts, the authors surveyed 32 local urban forestry organizations...

In this paper we explore whether the enhancement of urban ecosystem services through large-scale, metropolitan tree-planting initiatives is being planned and executed as a component of traditional municipal government or represents new, transdisciplinary strategies in environmental governance. Drawing on qualitative interviews with stakeholders in...

This paper addresses the development of a practical physicsbased model for fires in the wildland-urban intermix. These fires arise when wildland burning invades the built environment. Fire models for ignition and spread must consider individual fuel elements of both vegetation and structures in order to assess fire risk of developed properties. The...

Selecting, locating, and managing trees to provide ecosystem services are becoming increasingly important facets of municipal and consulting forestry. The science of urban tree growth modeling is fundamental to quantifying these services. This paper describes three long-term tree growth studies conducted to evaluate tree performance because repeate...

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 th...

Purpose This study provides a detailed, process-based life cycle greenhouse gas (GHG) inventory of an ornamental tree production system for urban forestry. The success of large-scale tree planting initiatives for climate protection depends on projects being net sinks for CO2 over their entire life cycle. However, previous assessments of urban tree...

Given the increasing demand for carbon dioxide storage estimates in urban areas and the high cost for ground-based inventories, there is need for more efficient approaches. Limited open-grown urban tree species biomass equations have necessitated use of forest-derived equations with diverse conclusions on the accuracy of these equations to estimate...

A rainfall interception study was conducted in Oakland, California to determine the partitioning of rainfall and the chemical composition of precipitation, throughfall, and stemflow. Rainfall interception measurements were conducted on a gingko (Ginkgo biloba) (13.5 m tall deciduous tree), sweet gum (Liquidambar styraciflua) (8.8 m tall deciduous),...

A bioswale integrating an engineered soil and trees was installed in a parking lot to evaluate its ability to reduce storm runoff, pollutant loading, and support tree growth. The adjacent control and treatment sites each received runoff from eight parking spaces and were identical except that there was no bioswale for the control site. A tree was p...

The Million Trees LA initiative intends to improve Los Angeles's environment through planting and stewardship of 1 million trees. The purpose of this study was to measure Los Angeles's existing tree canopy cover (TCC), determine if space exists for 1 million additional trees, and estimate future benefits from the planting. High-resolution QuickBird...

A multidisciplinary group of researchers and policy-makers met to discuss the state-of-the-science regarding the potential of roadside vegetation to mitigate near-road air quality impacts in April 2010. Scientists discussed several studies that have measured and modeled the impacts of vegetative barriers on near-road air quality. Workshop participa...

It is well known that urban trees produce various types of benefits and costs. The computer tool i-Tree STRATUM helps quantify tree structure and function, as well as the value of some of these tree services in different municipalities. This study describes one of the first applications of STRATUM outside the U.S. Lisbon's street trees are dominate...

CHAPTER TWO—METHODOLOGY AND PROCEDURES............................................. 10

The i-Tree Streets (formerly STRATUM) computer program quantifies municipal forest structure, function, and value using tree growth and geographic data from sixteen U.S. reference cities, one for each of sixteen climate zones. Selecting the reference city that best matches a subject city is problematic when the subject city is outside the U.S., lay...

Many studies have analyzed the benefits, costs, and carbon storage capacity associated with urban trees. These studies have been limited by a lack of research on urban tree biomass, such that estimates of carbon storage in urban systems have relied upon allometric relationships developed in traditional forests. As urbanization increases globally, i...

Given a set of global (natural) tree parameters measured for many specimens of different ages for a range of species, we have developed a tool that visualizes these parameters over time. The parameters include measures of tree dimensions such as heights, diameters, and crown shape, and measures of costs and benefits for growing the tree. We visuali...

Given a set of global (natural) tree parameters measured for many specimens of different ages for a range of species, we have developed a tool that visualizes these parameters over time. The parameters include measures of tree dimensions such as heights, diameters, and crown shape, and measures of costs and benefits for growing the tree. We visuali...

A GIS-based method for locating potential tree-planting sites based on land cover data is introduced. Criteria were developed to identify locations that are spatially available for potential tree planting based on land cover, sufficient distance from impervious surfaces, a minimum amount of pervious surface, and no crown overlap with other trees. I...

In the face of increasing urbanization, there is growing interest in application of microscale hydrologic solutions to minimize storm runoff and conserve water at the source. In this study, a physically based numerical model was developed to understand hydrologic processes better at the urban residential scale and the interaction of these processes...

Emission trading is considered to be an economically sensitive method for reducing the concentrations of greenhouse gases, particularly carbon dioxide, in the atmosphere. There has been debate about the viability of using urban tree plantings in these markets. The main concern is whether or not urban planting projects can be cost effective options...

For city planning purposes, animations of growing trees of several species can be used to deduce which species may best fit a particular environment. The models used for the animation must conform to real measured data. We present an approach for inverse modeling to fit global growth parameters. The model comprises local production rules, which are...

Given a set of global (natural) tree parame- ters measured for many specimens of different ages for a range of species, we have developed a tool that visualizes these parameters over time. The parameters include mea- sures of tree dimensions like heights, diameters, and crown shape, and measures of costs and benefits for growing the tree. We visual...

Benefit-based tree valuation provides alternative estimates of the fair and reasonable value of trees while illustrating the relative contribution of different benefit types. This study compared estimates of tree value obtained using cost- and benefit-based approaches. The cost-based approach used the Council of Landscape and Tree Appraisers trunk...

Approximately 75-80% of the population of North America currently lives in urban areas as defined by national census bureaus, and urbanization is continuing to increase. Future trajectories of fossil fuel emissions are associated with a high degree of uncertainty; however, if the activities of urban residents and the rate of urban land conversion c...

Tree health is a critical parameter for evaluating urban ecosystem health and sustainability. Traditionally, this parameter has been derived from field surveys. We used multispectral remote sensing data and GIS techniques to determine tree health at the University of California, Davis. The study area (363 ha) contained 8,962 trees of 215 species. T...

Forty-eight street segments were paired into 24 high- and low-shade pairs in Modesto, California, U.S. Field data were collected to calculate a Pavement Condition Index (PCI) and Tree Shade Index (TSI) for each segment. Statistical analyses found that greater PCI was associated with greater TSI, indicating that tree shade was partially responsible...

Trees are now part of urban planning. They are now recognized for their health benefits, increasing property values, attracting business, conserve energy, improve air quality, reduce storm water runoff and many others. Since the Clean Water Act regulations require municipalities to manage storm water runoff, trees have been a healthy, environment-f...

In computer graphics, models describing the fractal branching structure of trees typically exploit the modularity of tree structures. The models are based on local production rules, which are applied iteratively and simultaneously to create a complex branching system. The objective is to generate three-dimensional scenes of often many realistic- lo...

Tree type and species information are critical parameters for urban forest management, benefit cost analysis and urban planning. However, traditionally, these parameters have been derived based on limited field samples in urban forest management practice. In this study we used high-resolution Airborne Visible Infrared Imaging Spectrometer (AVIRIS)...

Effects of urban forests on runoff reduction have been conceptualized in management practice, but not well quantified due to lack of practical application tools. In this study, a storm runoff reduction model was developed and applied in an urban watershed in Bismarck, North Dakota. Methods and analyses conducted in this model were based on research...

Tree canopy cover data from aerial photographs and building energy simulations were applied to estimate energy savings from existing trees and new plantings in California. There are approximately 177.3 million energy-conserving trees in California communities and 241.6 million empty planting sites. Existing trees are projected to reduce annual air...

The accurate modeling of the physiological and functional processes of urban forests requires information on the leaf area of urban tree species. Several non-destructive, indirect leaf area sampling methods have shown good performance for homogenous canopies. These methods have not been evaluated for use in urban settings where trees are typically...

Forestry and urban forestry have more in common than practitioners in either field may think. The two disciplines could each take better advantage of the other's expertise, such as foresters' impressive range of scientific theory and technological sophistication, and urban foresters' experience in working with diverse stakeholders in the public are...

This study demonstrates an approach to quantify the structure, benefits, and costs of street tree populations in resource-limited communities without tree inventories. Using the city of Davis, California, U.S., as a model, existing data on the benefits and costs of municipal trees were applied to the results of a sample inventory of the city's publ...

Tree work records for ten species were analyzed to estimate average annual management costs by dbh class for six activity areas. Average annual benefits were calcu- lated by dbh class for each species with computer modeling. Average annual net benefits per tree were greatest for London plane (Platanus acerifolia) ($178.57), hackberry (Celtis sinens...

This paper presents a comparison of the structure, function, and value of street and park tree populations in two California cities. Trees provided net annual benefits valued at $2.2 million in Modesto and $805,732 in Santa Monica. Benefit-cost ratios were 1.85:1 and 1.52:1 in Modesto and Santa Monica, respectively. Residents received $1.85 and $1....

Total canopy cover and canopy cover over street and sidewalk surfaces were estimated for street trees in Davis, California, U.S. Calculations were made using simple trigono- metric equations based on the results of a sample inventory. Canopy cover from public trees over streets and sidewalks varied between 4% and 46% by city zone, averaging 14% cit...

Effects of urban forests on rainfall interception and runoff reduction have been conceptualized, but not well quantified. In this study rainfall interception by street and park trees in Santa Monica, California is simulated. A mass and energy balance rainfall interception model is used to simulate rainfall interception processes (e.g., gross precip...

Western Forestry Leadership Coalition, Oregon State Department of Forestry Program, Portland General Electric, Pacific Power, Washington Department of Natural Resources, Urban and Community Forestry Program, Puget Sound Energy.

A survey of 15 Sacramento parking lots and computer modeling were used to evaluate parking capacity and compliance with the 1983 ordinance requiring 50% shade of paved areas (PA) 15 years after development. There were 6% more parking spaces than required by ordinance, and 36% were vacant during peak use periods. Current shade was 14% with 44% of th...

Literature relevant to tree root and urban infrastructure conflicts is reviewed. Although tree roots can conflict with many infrastructure elements, sidewalk and curb conflicts are the focus of this review. Construction protocols, urban soils, root growth, and causal factors (soil conditions, limited planting space, tree size, variation in root arc...

Concern about climate change has evoked interest in the potential for urban vegetation to help reduce the levels of atmospheric carbon. This study applied computer simulations to try to quantify the modifying effects of existing vegetation on the indirect reduction of atmospheric carbon for two residential neighborhoods in north-west Chicago. The e...

Interference between trees and sewer systems is likely to occur in old systems and in cracked pipes. Factors that contribute to damage include old pipes with joints, shallow pipes, small-dimension pipes, and fast-growing tree species. Because roots are reported to cause >50% of all sewer blockages, costs associated with root removal from sewers is...

Although the modeling of energy-use re- duction, air pollution uptake, rainfall interception, and microclimate modification associated with urban trees depends on data relating diameter at breast height (dbh), crown height, crown diameter, and leaf area to tree age or dbh, scant information is available for common municipal tree species. In this st...

Tree height, crown height, crown width, diameter at breast height (dbh), and leaf area were measured for 16 species of commonly planted street trees in the coastal southern California city of Santa Monica, USA. The randomly sampled trees were planted from 1 to 44 years ago. Using number of years after planting or dbh as explanatory variables, mean...

A three-dimensional physically based stochastic model was developed to describe canopy rainfall interception processes at desired spatial and temporal resolutions. Such model development is important to understand these processes because forest canopy interception may exceed 59% of annual precipitation in old growth trees. The model describes the i...

A rainfall interception measuring system was developed and tested for open-grown trees. The system includes direct measurements of gross precipitation, throughfall and stemflow, as well as continuous collection of micrometeorological data. The data were sampled every second and collected at 30-s time steps using pressure transducers monitoring wate...

A survey of 18 California cities indicated that approximately $70.7 million (se $11.1 million) was spent annually statewide due to conflicts between street tree root growth and sidewalks, curbs and gutters, and street pave- ment. The largest single expenditure was for sidewalk re- pair ($23 million, se $9.5 million), followed by curb and gutter rep...

Introduction Over 70% of the population in developed countries live in cities. World wide, the average urban population proportion is 42% (World population reference, 1993). Urbanization creates significant changes in land use and land cover, affecting the structure, pattern and function of the ecosystem. The public is increasingly concerned about...

This study answers the question: Do the accrued benefits from Modesto's urban forest justify an annual munici- pal budget that exceeds $2 million? Results indicate that the benefits residents obtain from Modesto's 91,179 public trees exceeded management costs by a factor of nearly 2. In fiscal year 1997-1998, Modesto spent $2.6 million for urban fo...

A pilot study was performed to measure the difference in parking lot microclimate resulting from the presence or absence of shade tree cover. Microclimate data from contrasting shade regimes were then used as input to a motor-vehicle emissions model. Model results were used to estimate the potential for regional increases in parking lot tree cover...

The urban forest of Sacramento County, California, contains approximately 6 million trees. Tree density and basal area decrease along an urban-rural gradient from city (73 trees/ha, 13.4 m2/ha), to suburban (64 trees/ha, 4.5 m2/ha), to rural (10 trees/ha, 0.9 m2/ha) sectors. Within the city and suburban sectors, where 90% of all residents live, app...

Concern about global climate change and the effects that increasing atmospheric carbon dioxide could have on the earth has risen in recent years. Methods for accurately and efficiently quantifying carbon storage and annual carbon fluxes are needed to determine what role urban forests may have in reducing levels of atmospheric CO2. This will require...

A one-dimensional mass and energy balance model was developed to simulate rainfall interception in Sacramento County, California. The model describes tree interception processes: gross precipitation, leaf drip, stem flow, and evaporation. Kriging was used to extend existing meteorological point data over the region. Regional land use/land cover and...

Over the course of 150 years, a combination of cultural and natural processes drove Sacramento's transition from City of the Plains to the City of Trees. This paper describes how the many authors of Sacramento's treescape have affected the health, management, and public perception of the city's trees. Local government directed early street and park...

Site surveys were conducted on residential properties in Sacramento, California, and residents were given questionnaires about whether they had added trees to their properties, their motivations for planting trees, and the extent and frequency of their maintenance of the trees on their properties. These surveys indicate that most residents (68% of...

We compared the accuracy of five methods used to estimate leaf area index (LAI) of eight open-grown deciduous trees, including six white mulberries (Moms alba) and two black cherries (Prunus serotina var. rufula). The methods included the use of four instruments (AccuPAR Ceptometer, CI-100 Plant Canopy Analyzer, image processing with the AgVision S...

Tree shade reduces summer air conditioning demand and increases winter heating load by intercepting solar energy that would otherwise heat the shaded structure. We evaluate the magnitude of these effects here for 254 residential properties participating in a utility sponsored tree planting program in Sacramento, California. Tree and building charac...

The Sacramento Municipal Utility District's (SMUD) shade tree program will result in the planting of 500,000 trees and has been found to produce net benefits from air conditioning savings. In this study we assume three scenarios (base, highest, and lowest benefits) based on the SMUD program and apply Best Available Control Technology (BACT) cost an...