Old lessons for new science: How sacred-tree metaphors can inform studies of the public-health benefits of the natural environment.

Many studies have identified an association between exposure to the natural environment and improved public-health outcomes. However, much of this observational work lacks a theoretical foundation, so we look to the humanities for a stronger basis for green-health research, examining how trees have been used as religious metaphors and symbols for health and wellbeing. In particular, the tree of life, sacred trees, and other religious symbols provide a promising theoretical basis for green-health research. Based on this review, we propose the value of incorporating attributes such as vegetation species and size in exposure metrics, and considering the interactions between exposure attributes (e.g., species) and individual attributes (e.g., culture).

Public nature and health for homeless populations: Professionals' perceptions of contingent human benefits and harms.

This article investigates relationships between public nature and health for unsheltered homeless populations. It examines perceptions of health benefits and harms for people living in public natural areas including local, state, and national forests and parks in the Seattle metropolitan area (USA). Interviews with environmental, social service, and law enforcement professionals who regularly interact with this vulnerable population were conducted and thematically analyzed to understand perceptions of physical and mental health outcomes. Results show professionals' perspectives on the health benefits and detriments of time spent in natural environments and the contextual factors perceived to influence health. Interviewees' observations about the variability of personal circumstances and biophysical, social, and weather conditions encourage the nuanced consideration of how contingent therapeutic landscapes provide deeply needed benefits, but for a population with a diminished capacity to adapt when conditions change. We conclude with insights for future research that directly assesses homeless populations' exposures and health outcomes of living in public natural areas.

Shortcomings of the normalized difference vegetation index as an exposure metric.

The health benefits of exposure to trees and plants is a rapidly expanding field of study. Research has shown that exposure is associated with improvements in a wide range of health outcomes including cardiovascular disease, birth outcomes, respiratory disease, cancer, mental health and all-cause mortality1. One of the challenges that these studies face is characterizing participants' exposure to trees and plants. A common approach is to use the normalized difference vegetation index, a greenness index typically derived from satellite imagery. Reliance on the normalized difference vegetation index is understandable; for decades, the imagery required to calculate the normalized difference vegetation index has been available for the entire Earth's surface and is updated at regular intervals. However, the normalized difference vegetation index may do a poor job of fully characterizing the human experience of being exposed to trees and plants, because scenes with the same normalized difference vegetation index value can appear different to the human eye. We demonstrate this phenomenon by identifying sites in Portland, Oregon that have the same normalized difference vegetation index value as a large, culturally significant elm tree. These sites are strikingly different aesthetically, suggesting that use of the normalized difference vegetation index may lead to exposure misclassification. Where possible, the normalized difference vegetation index should be supplemented with other exposure metrics.

Spatial predictors of heavy metal concentrations in epiphytic moss samples in Seattle, WA.

The use of bio-indicators is an emerging, cost-effective alternative approach to identifying air pollution and assessing the need for additional air monitoring. This community science project explores the use of moss samples as bio-indicators of the distribution of metal air particulates in two residential neighborhoods of the industrial Duwamish Valley located in Seattle, WA (USA). We applied geographically weighted regression to data from 61 youth-collected samples to assess the location-specific area-level spatial predictors of the concentrations of 25 elements with focus on five heavy metals of concern due to health and environmental considerations. Spatial predictors included traffic volume, industrial land uses, major roadways, the airport, dirt roads, the Duwamish River, impervious surfaces, tree canopy cover, and sociodemographics. Traffic volume surrounding sample locations was the most consistent positive predictor of increasing heavy metal concentration. Greater distance from the heavy-industry corridor surrounding the Duwamish River predicted lower concentrations of all metals, with statistically significant associations for chromium and lead in some areas. As the distance from dirt roads increased, the concentration of arsenic and chromium decreased significantly. Percent tree canopy within 200 m of sample locations was a significant protective factor for cadmium concentrations. In addition, percent people of color was significantly positively associated with increasing lead, chromium and nickel concentrations. Our findings underscore the potential influence of heavy industry and mobile sources on heavy metal concentrations, the buffering potential of trees in local environments, and persistent opportunity to improve environmental justice.

Therapeutic landscapes, outdoor programs for veterans, and public lands.

In recent decades, scholars have developed ideas about therapeutic landscapes that explore how social processes, symbolism, and physical features generate diverse meanings. We examine here how therapeutic landscapes are produced and utilized for outdoor programs for military veterans, particularly veterans experiencing post-traumatic stress. Outdoor programs for veterans (OPVs) provide restorative opportunities through nature immersion and outdoor recreation. OPVs involve diverse social settings, activity types, durations, geographic and land management contexts, and degrees of therapeutic intervention. In many combinations they can generate therapeutic landscapes conducive to some degree of recovery. Our analysis relies on qualitative data gathered through semi-structured interviews with OPV providers and participants, mental health specialists, and public land officials. Arguing against a reductionistic approach, we suggest that the diversity of OPVs and disparate character of activities, locations, and dosages may contribute in important ways to the efficacy of these programs. Ironically, the very qualities that present challenges for measuring and evaluating the benefits of OPVs may prove to be advantageous with respect to therapeutic outcomes. We highlight how public lands present a distinctive set of attributes that make them particularly well-suited to provide therapeutic opportunities, and that agency policies can shape the development of therapeutic landscapes.

Toward Environmental Justice in Civic Science: Youth Performance and Experience Measuring Air Pollution Using Moss as a Bio-Indicator in Industrial-Adjacent Neighborhoods.

This article reports on an interdisciplinary evaluation of the pilot phase of a community-driven civic science project. The project investigates the distribution of heavy metals in air pollution using moss growing on street trees as a bio-indicator in two industrial-adjacent neighborhoods in Seattle, Washington (USA). One goal of the ongoing project is to meaningfully engage local urban youths (eighth to twelfth grade) in the scientific process as civic scientists, and teach them about environmental health, environmental justice, and urban forestry concepts in a place-based, urban-oriented environmental research project. We describe the collaborative context in which our project developed, evaluate the quality of youth-collected data through analysis of replicate samples, and assess participants' learning, career interests, and overall appraisal of the pilot. Our results indicate that youth scientists collected usable samples (with acceptable precision among repeated samples), learned project content (with statistically significant increases in scores of test-style survey questions; p = 0.002), and appraised their engagement favorably (with 69% of participants reporting they liked the project). We observed few changes in career interests, however. We discuss our intention to use these preliminary insights to further our community-driven education, research, and action model to address environmental injustices.