Nathan Phillips

Boston University | BU

The BosWash corridor is a megalopolis, or large urbanized region composed of interconnected transportation, infrastructure, physiography, and sociopolitical systems. Previous work has not considered the BosWash corridor as an integrated, holistic ecosystem. Building on the emerging field of infrastructure ecology, the region is conceptualized here...

The presence of volatile organic compounds (VOCs) in unprocessed natural gas (NG) is well documented; however, the degree to which VOCs are present in NG at the point of end use is largely uncharacterized. We collected 234 whole NG samples across 69 unique residential locations across the Greater Boston metropolitan area, Massachusetts. NG samples...

Unleakable carbon, or the uncombusted methane and carbon dioxide associated with fossil fuel systems, constitutes a potentially large and heretofore unrecognized factor in determining use of Earth’s remaining fossil fuel reserves. Advances in extraction technology have encouraged a shift to natural gas, but the advantage of fuel switching depends s...

Fugitive emissions from natural gas systems are the largest anthropogenic source of the greenhouse gas methane (CH4) in the U.S. and contribute to the risk of explosions in urban environments. Here, we report on a survey of CH4 emissions from 100 natural gas leaks in cast iron distribution mains in Metro Boston, MA. Direct measures of CH4 flux from...

From production through distribution, oil and gas infrastructure provides the largest source of anthropogenic methane in the United States and the second largest globally. Using a Picarro G2132i Cavity Ring-Down spectrometer, we mapped natural gas leaks across the streets of three United States cities—Durham, NC, Cincinnati, OH, and Manhattan, NY—a...

Significance Most recent analyses of the environmental impact of natural gas have focused on production, with very sparse information on emissions from distribution and end use. This study quantifies the full seasonal cycle of methane emissions and the fractional contribution of natural gas for the urbanized region centered on Boston. Emissions fro...

Background/Question/Methods Methane is a potent greenhouse gas and the primary constituent of the fossil fuel, natural gas. As the US develops its sizeable shale gas reserves, it is important to characterize the social and environmental ramifications of the expanding natural gas industry. Recent studies have begun to characterize the impacts of u...

Pipeline safety in the United States has increased in recent decades, but incidents involving natural gas pipelines still cause an average of 17 fatalities and $133 M in property damage annually. Natural gas leaks are also the largest anthropogenic source of the greenhouse gas methane (CH4) in the U.S. To reduce pipeline leakage and increase consum...

Background/Question/Methods Natural gas use is expanding rapidly in the United States, developed through the combination of horizontal drilling and hydraulic fracturing. Concerns over the net greenhouse gas balance and other environmental impacts have accompanied the natural gas boom. One of the biggest uncertainties for understanding greenhouse...

Due to advances in technology allowing observations of low flow rates, we now have abundant evidence of nocturnal sap flow occurring in a range of species, ecosystems, and under various microclimatic conditions. This paper synthesises the conditions that facilitate nocturnal sap flow and evaluates possible mechanisms. The microclimatic variables wh...

Climate change may alter forest composition by differentially affecting the responses of faster- and slower-growing tree species to drought. However, the combined effects of rising atmospheric CO2 concentration ([CO2]) and temperature on drought responses of trees are poorly understood. Here, we examined interactive effects of temperature (ambient,...

In this response, we address the criticisms put forth by Tomlinson and Quinn (American Journal of Botany 100: 461-464) about our original publication on secondary stem lengthening in Iriartea deltoidea palms (American Journal of Botany 99: 607-613) and find areas on which we may agree. We address our figure of a typical palm vascular bundle; the lo...

Palms are an important component of tropical ecosystems, living alongside dicotyledonous trees, even though they have a very different growth pattern and vascular system. As monocots, vessels in palms are located within vascular bundles and, without a vascular cambium that many dicotyledonous trees possess, palms cannot add additional vessels to th...

It is not known whether global warming will affect winning times in endurance events, and counterbalance improvements in race performances that have occurred over the past century. We examined a time series (1933-2004) from the Boston Marathon to test for an effect of warming on winning times by men and women. We found that warmer temperatures and...

Infection by eastern dwarf mistletoe (Arceuthobium pusillum) modifies needle and branch morphology and hastens white spruce (Picea glauca) mortality. We examined potential causal mechanisms and assessed the impacts of infection-induced alterations to host development and performance across scales ranging from needle hormone contents to bole expansi...

Background/Question/Methods Methane has substantial greenhouse warming potential and is the principle component of natural gas. Fugitive natural gas emissions could be a significant source of methane to the atmosphere. However, the cumulative magnitude of natural gas leaks is not yet well constrained. We use a combination of mobile and stationary...

Background/Question/Methods: We investigated the impacts of natural gas leaks from an urban distribution pipeline system on soil processes. We conducted this study in Boston, Massachusetts, one of the oldest cities in the United States. Boston has an aging natural gas distribution infrastructure, which provides an ideal environment in which to in...

Although foliar reflectance in the visible wavelengths is largely understood, species-specific relations between leaf spectral properties, pigment content and carbon exchange, and interdependence of these fundamental drivers that ultimately produce large-scale signals complicate understanding of and upscaling in remote sensing applications. We reco...

Premise of the study: Although traditionally assumed that all height growth in trees occurs at apical meristems, sequential measurement of internode lengths in the palm Iriartea deltoidea suggested that stems were lengthening long after the differentiation of tissues and far below the apical meristem. This observation is difficult to reconcile wit...

To identify and quantify major methane sources in Boston and Indianapolis, measurements of CH4 concentrations were made using a vehicle mounted cavity ringdown analyzer with Global Positioning Device capabilities along with plume transport models.

Trees adapted to mesic and xeric habits may differ in a suite of physiological responses that affect leaf-level carbon balance, including the relationship between photosynthesis (A) and respiration at night (R(n)). Understanding the factors that regulate physiological function in mesic and xeric species is critical for predicting changes in growth...

Background/Question/Methods Climate change may alter forest composition by differentially affecting the responses of tree species to drought, which limits primary production of most terrestrial ecosystems for part or most of the year. However, the interactive effect of rising [CO2] and temperature on tree responses to drought is a key unresolved i...

Nearly 30 years ago, Whitehead and Jarvis and Whitehead et al. postulated an elegant mechanistic explanation for the observed relationship between tree hydraulic structure and function, hypothesizing that structural adjustments promote physiological homeostasis. To date, this framework has been nearly completely overlooked with regard to varying at...

Because palms grow in highly varying climates and reach considerable heights, they present a unique opportunity to evaluate how environment and plant size impact hydraulic function. We studied hydraulic properties of petioles from palms of varying height from three species: Iriartea deltoidea, a tropical rainforest species; Mauritia flexuosa, a tro...

Components of the tree water transport pathway; roots, trunks, branches and leaves; can also serve as water storage compartments and therefore act transiently as intermediate sources of water for transpiring leaves. However, most previous work has focused on gradual depletion and recharge of tree internal water reserves as soil water availability v...

Nocturnal water flux has been observed in trees under a variety of environmental conditions and can be a significant contributor to diel canopy water flux. Elevated atmospheric CO(2) (elevated [CO(2)]) can have an important effect on day-time plant water fluxes, but it is not known whether it also affects nocturnal water fluxes. We examined the eff...

Soil moisture is a critical regulator of C, water, and nutrients flowing through forests (Kozlowski 1982; Aber et al. 1995; Granier et al. 1999; Kljun et al. 2007; Nepstad et al. 2007; Penuelas et al. 2007; Welp et al. 2007; Johnson et al. 2008; Borken and Matzner 2009), and shortages of moisture thus can have a dramatic influence on forest functio...

Unlabelled: Premise of the study: This study seeks to determine how hydraulic factors vary with ontogeny and whether they begin to limit further height growth in palms. Palms are an attractive group for physiological research because their columnar trunks and simple leaf habit allow key intrinsic and extrinsic hydraulic variables to be estimated...

The unabated rise in atmospheric [CO(2)] is associated with increased air temperature. Yet, few CO(2)-enrichment studies have considered pre-industrial [CO(2)] or warming. Consequently, we quantified the interactive effects of growth [CO(2)] and temperature on photosynthesis of faster-growing Eucalyptus saligna and slower-growing E. sideroxylon. We...

The wet and dry seasons in tropical rain forests can differ in precipitation, soil moisture and irradiance more significantly than often assumed. This could potentially affect the water relations of many tree species that may exhibit either increased transpiration in the dry season as a response to the increased irradiance or decreased transpiratio...

To identify environmental and biological drivers of nocturnal vapour exchange, we quantified intra-annual, intra- and inter-specific variation in nocturnal water transport among ecologically diverse Eucalyptus species. We measured sap flux (Js) and leaf physiology (leaf surface conductance (gs), transpiration (E) and water potential (Ψl)) in three...

To investigate if Eucalyptus species have responded to industrial-age climate change, and how they may respond to a future climate, we measured growth and physiology of fast- (E. saligna) and slow-growing (E. sideroxylon) seedlings exposed to preindustrial (290), current (400) or projected (650 μL L−1) CO2 concentration ([CO2]) and to current or pr...

The unabated rise in atmospheric [CO2] is associated with increased air temperature. Yet, few CO2-enrichment studies have considered pre-industrial [CO2] or warming. Consequently , we quantified the interactive effects of growth [CO2] and temperature on photosynthesis of faster-growing Eucalyptus saligna and slower-growing E. sideroxylon. Well-wate...

To investigate if Eucalyptus species have responded to industrial-age climate change, and how they may respond to a future climate, we measured growth and physiology of fast-(E. saligna) and slow-growing (E. sideroxylon) seedlings exposed to preindustrial (290), current (400) or projected (650 lL L À1) CO 2 concentration ([CO 2 ]) and to current or...

As trees grow taller, the energetic cost of moving water to the leaves becomes higher and could begin to limit carbon gain and subsequent growth. The hydraulic limitation hypothesis states that as trees grow taller, the path length and therefore frictional resistance of water flow increases, leading to stomatal closure, reduced photosynthesis and d...

Background/Question/Methods As trees grow taller, the path length for water flow increases and could begin to limit stomatal conductance, subsequent carbon gain and further height growth. This study seeks to determine how hydraulic properties of fronds from Washingtonia robusta palms change along a height gradient. Fronds were measured from palms...

While it is well established that stomata close during moisture stress, strong correlations among environmental (e.g., vapor pressure deficit, soil moisture, air temperature, radiation) and internal (e.g., leaf water potential, sap flow, root-shoot signaling) variables obscure the identification of causal mechanisms from field experiments. Models o...

Sap flow sensors are uniquely able to continuously monitor whole tree physiology. Recently, Burgess and Dawson (Burgess SSO, Dawson TE, Plant Soil 305:5-13, 2008) urged caution in using sap flow probes to estimate water storage use in trees. Here we respond to three criticisms raised there: (1) Sampling: that tree water storage, estimated from bran...

Transient responses of sap flow to step changes in wind speed were experimentally investigated in a wind tunnel. A Granier-type sap flow sensor was calibrated and tested in a cylindrical tube for analysis of its transient time response. Then the sensor was used to measure the transient response of a well-watered Pachira macrocarpa plant to wind spe...

Atmospheric carbon dioxide [CO2] has increased dramatically within the current life spans of long-lived trees and old forests. Consider that a 500-year-old tree in the early twenty-first century has spent 70% of its life growing under pre-industrial levels of [CO2], which were 30% lower than current levels. Here we address the question of whether o...

Transient responses of sap flow to step changes in wind speed were experimentally investigated in a wind tunnel. A Granier-type sap flow sensor was calibrated and tested in a cylindrical tube for analysis of its transient time response. Then the sensor was used to measure the transient response of a well-watered Pachira macrocarpa plant to wind spe...

Eastern hemlock (Tsuga canadensis (L). Carr.) is a late-successional species found across the northeastern United States of America that is currently threatened by the exotic pest, hemlock woolly adelgid (Adelges tsugae Annand). Because whole-tree physiological characteristics may scale to influence ecosystem processes, we considered whole-tree hyd...

Water use and carbon exchange of a red oak-dominated (Quercus rubra L.) forest and an eastern hemlock-dominated (Tsuga canadensis L.) forest, each located within the Harvard Forest in north-central Massachusetts, were measured for 2 years by the eddy flux method. Water use by the red oak forest reached 4 mm day(-1), compared to a maximum of 2 mm da...

Measurements of variation in the diameter of tree stems provide a rapid response, high resolution tool for detecting changes in water tension inside the xylem. Water movement inside the xylem is caused by changes in the water tension and theoretically, the sap flow rate should be directly proportional to the water tension gradient and, therefore, a...

The hemlock woolly adelgid (HWA; Adelges tsugae Annand) is causing widespread decline and mortality of eastern hemlock (Tsuga canadensis (L.) Carr.) throughout most of the range of eastern hemlock. Stem injection of insecticide is widely used as a chemical control measure, but the effectiveness of this method depends on the hydraulic characteristic...

Eastern hemlock (Tsuga canadensis (L.) Carr.) is a coniferous evergreen species found across the northeastern United States that is currently threatened by the exotic pest hemlock woolly adelgid (HWA; Adelges tsugae Annand). As HWA kills eastern hemlock trees, black birch (Betula lenta L.) has been found to be a dominant replacement species in the...

Diurnal and seasonal tree water storage was studied in three large Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) trees at the Wind River Canopy Crane Research site. Changes in water storage were based on measurements of sap flow and changes in stem volume and tissue water content at different heights in the stem and branches. We measured sap f...

Feedbacks of vegetation on summertime climate variability over the North American Grasslands are analyzed using the statistical technique of Granger causality. Results indicate that normalized difference vegetation index (NDVI) anomalies early in the growing season have a statistically measurable effect on precipitation and surface temperature late...

Transpiration is generally assumed to be insignificant at night when stomata close in response to the lack of photosynthetically active radiation. However, there is increasing evidence that the stomata of some species remain open at night, which would allow for nighttime transpiration if there were a sufficient environmental driving force. We exami...

We proposed the hydraulic limitation hypothesis (HLH) as a mechanism to explain universal patterns in tree height, and tree and stand biomass growth: height growth slows down as trees grow taller, maximum height is lower for trees of the same species on resource-poor sites and annual wood production declines after canopy closure for even-aged fores...

Linking sap flow in tree boles to plant transpiration continues to be a fundamental and practical research problem in physiological ecology and forest hydrology. Many models have been proposed to describe water movement within trees with varying degrees of success. The prevailing resistance–capacitance (RC)-circuit models have the advantage of bein...

Ralph Lorenz's Perspective “Full steam ahead—probably” (7 Feb. 2003, p. [837][1]) on the recent groundbreaking work of Roderick Dewar ([1][2]) mentions the puzzle that “All else being equal, MEP [maximum entropy production] would predict a planet's meridional temperature contrast to be

An in vivo method for diagnosing hydraulic characteristics of branches and whole trees is described. The method imposes short-lived perturbations of transpiration and traces the propagation of the hydraulic response through trees. The water uptake response contains the integrated signature of hydraulic resistance and capacitance within trees. The m...

We report measurements of rates of sap flow in dominant trees, changes in soil moisture, and evaporation from coarse woody debris in an old-growth Douglas-fir–western hemlock ecosystem at Wind River, Washington, USA, during dry periods in summer. The measurements are compared with eddy-covariance measurements of water-vapor fluxes above the forest...

Large areas of forests in the Pacific Northwest are being transformed to younger forests, yet little is known about the impact this may have on hydrological cycles. Previous work suggests that old trees use less water per unit leaf area or sapwood area than young mature trees of the same species in similar environments. Do old forests, therefore, u...

Do branchlets within a branch have autonomous water supplies, or do they share a common water supply system? We hypothesized that if branchlets shared a common water supply, then stomatal conductance (gs) on sunlit foliage would increase with reduced transpiration of competing foliage on the branch. We reduced transpiration of other foliage on the...

Recent global-scale analyses indicate that climate variability affects net carbon storage but regard temperature and precipitation to be the main contributors. Seasonal and interannual variation in light availability may also limit CO(2) uptake. As an experimental test of light limitation by cloud cover during tropical rainy seasons and by the unus...

The hydraulic limitation hypothesis (Ryan and Yoder 1997) proposes that leaf-specific hydraulic conductance (kl) and stomatal conductance (gs) decline as trees grow taller, resulting in decreased carbon assimilation. We tested the hydraulic limitation hypothesis by comparison of canopy-dominant Douglas-fir (Pseudotsuga menziesii var. menziesii (Mir...

Water use by vegetation can be closely linked to streamflow patterns on a variety of time scales. However, many of the details of these linkages are poorly understood. We compared diel (24 h) patterns of transpirational water use with streamflow patterns in a small headwater basin that displays a marked diel variation during summer months. The stud...