Urban Silviculture
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Research
Urban Silviculture research consists of six components:
- literature review
- analysis of archival weather data
- model simulation
- small-scale wind tunnel experiments with small portions of tree canopy
- "natural" experiments utilizing existing in-ground trees, and
- new demonstration plantings that can be used to test site-specific hypotheses addressing planting arrangement on air-quality improvement at the human scale.
1. Literature Review
(Click here for a summary)
Using both online databases and traditional library work, literature review is an ongoing activity both to keep abreast of current research and to follow lines of inquiry that necessary to address questions arising from our experiments. Topics we follow include (1) the effects of air pollution on human respiratory health, (2) the effects of vegetation on air pollution, (3) the effects of vegetation on human health, (4) tree species' tolerance of urban conditions, (5) technologies for monitoring airborne particulates, (6) static charge on surfaces, (7) resuspension of particles. There is surprisingly little interchange among researchers contributing to these related topics, much less a cogent synthesis.
2. Archival Data Analysis
This pertains to weather and air quality data collected by state and federal government agencies and readily available in the public domain. Accessing data from the past 30 years has yielded an analysis of seasonal and spatial variation in weather patterns and air pollution transport. This analysis is useful for determining the relative contributions of regional and local sources to the particulate load and will be useful for evaluating the effectiveness of trees in filtering air at various spatial scales.
- For educational purposes only - please do not distribute: DeGaetano, A. T. and O. M. Doherty, 2003. Temporal, Spatial and Meteorological Variations in Hourly PM 2.5 Concentration Extremes in New York City. Atmospheric Environment.
Click here for a copy of the report (pdf). - Click here for an interview with Owen Doherty (Cornell '03), who discusses the project's meteorological and climatological research.
3. Models and Simulation
Empirical scaling from leaf to an entire tree is feasible, though extremely consumptive of time and labor. Scaling from the level of a tree to a stand or landscape, however, is impossible unless numerical simulations are used. At the landscape scale, the UFORE model developed by Nowak and colleagues at the US Forest Service addresses questions of mass fluxes of gasses and particles between trees and the urban atmosphere. The model was designed to account for the PM 10 fraction, not the smaller particles now recognized to be the most deleterious to respiratory function.
- Click here to access the U.S. Forest Service's Web page on Urban Forests Effects on Environmental Quality.
- Click here to access maps created by the UFORE model. (Urban Silviculture maps are at bottom of page)
4. Small Scale Wind Tunnel Experiments
Wind Tunnels were designed and constructed to aid in experimentation.
Whereas UFORE is a numerical model, wind tunnel experiments are a physical model for studying deposition at the scale of single leaves and aggregates of leaves. These experiments may be thought of as "dose-response" trials consisting of applying pulses of particles with known sizes to leaf samples while controlling wind speed, dose size, leaf characteristics and total leaf surface. These experiments complement numerical models and also add a scale dimension that is pertinent regardless of other sources of variation, an advantage if one wishes to answer questions about variation among species. Results from these experiments will allow UFORE to be extended to PM 2.5, to recognize interspecific differences, and to account for re-suspension and wash-off. We are using two kinds of particles: Arizona Test Dust to characterize gross filtration through groups of leaves, while fluorescent particles are used to visualize spatial patterns on leaves and how they change over time.
5. Natural Experiments
A "natural experiment" refers to an investigation of a pre-existing situation, not originally intended as an experiment, but which has systematic variation in factors of interest. Examples include sampling trees along distance gradients from pollutant sources such as roadways. Natural experiments are especially useful to ecologists because they allow trends to be studied at much larger scales than controlled experiments can typically accommodate. Too, they necessarily incorporate "reality" into the picture. We are using natural experiments to compare the performance of free-growing city trees in our demonstration experiments (see below) with our wind tunnel experiments and to evaluate effects of distance from roads on concentration of suspended particulates. Extensive use of natural experiments as originally envisioned has been deemed premature in light of the extreme naturally occurring variation in atmospheric particulate concentrations in comparison with the small effect of leaves we have been able to detect in the lab.
6. Demonstration Plantings
An oft-cited shortcoming of scientific research is the real or apparent lack of relevance to society as a whole. Demonstration tree plantings in the communities most likely to benefit from the presence of trees will establish a tangible connection between research and the local communities while at the same time providing additional opportunities for observing tree performance under real-life conditions. In addition, demonstration plantings will be natural foci for outreach activities.