How Do Trees Help Us?

I’ve written up my research project from environmental science class. It’s about the ecosystem services that trees provide, addressing rapid deforestation.

 
National canopy presence is declining. The US lost 3.8 million hectares of tree cover in 2019. But they’re necessary: we know trees provide building material and are essential for the cycle between O2 and CO2 for life. I wanted to explore the other benefits that trees could provide: cleaning Particulate Matter (PM) from the air, reducing heat impact, and providing essential habitat for animals, especially Endangered/Threatened species.

 

The data supports these relations. Trees improve measurable air quality, by up to 16% in the short-term, by intaking PM through the stomata during respiration. By providing physical shade, cooling via evapotranspiration, and absorbing sunlight through photosynthesis, canopy cover reduces peak temperatures by 1-5 °C, reducing heat islands. And trees provide food, shelter, and a reproduction site for animals, so their presence is especially important for Threatened/Endangered animals, which are sensitive to changes.

 

I wanted to explore these correlations spatially using Geographic Information System (GIS) mapping. So, I created my hypothesis: tree presence correlates to improved air quality and Threatened/Endangered species’ habitat presence, and lack of tree presence correlates to poor air quality and heat islands.

 

I used ArcGIS for this project, a platform developed by Esri that allows users to make or select maps, analyze data across locations and time, and share the information in an understandable format.

 

I used a simple basemap and a visual representation of national canopy cover using the National Land Cover Dataset (NLCD) from the US Geological Survey (USGS). I created four different maps with layers using different criteria: clean air, using locations with EPA Particulate Matter (PM) Air Quality Index Cleaner than 5; polluted air, with EPA PM AQI more polluted than 70; heat island locations, using temperature data from NASA; and critical habitat for threatened and endangered species, according to the US Fish and Wildlife Service (USFWS).

 

My results agreed:

Figure 1: Spatial correlation between tree presence, via canopy cover through the National Land Cover Dataset (NLCD), and locations with an EPA Particulate Matter (PM) Air Quality Index (AQI) cleaner than 5.
Figure 2: Spatial correlation between tree presence, via NLCD canopy cover, and locations with an EPA Particulate Matter (PM) AQI more polluted than 70.
Figure 3: Spatial correlation between tree presence, via NLCD canopy cover, and locations considered heat islands by temperature data from NASA
Figure 4: Spatial correlation between tree presence, via NLCD canopy cover, and critical habitat for endangered species

Regions with the most present tree cover, like the western coast and mid-southeast, are the most dense with clean air quality locations. 86.5% of locations with an AQI more clean than 5 had > 75% canopy cover within a 10 mile radius: Trees are correlated with clean air.


Regions with minimal tree cover, like the south-west border and upper-midwestern United States, are the most dense with poor air quality locations. 83.3% of locations with an AQI more polluted than 70 had < 1% canopy cover within a 10 mile radius:  A lack of trees is correlated with poor air quality.


And those same regions with minimal tree cover had the most heat islands: a lack of trees is correlated with heat islands.


Finally, regions critical for endangered and threatened species, such as the Northwest, Yellowstone, and Northern Maine for Threatened species, and the Midwest, Southern Florida, and Southern Maine for Endangered Species, all contain significant canopy cover: Trees are present in Endangered Species’ habitat.

Takeaways

By intaking PM through stomata during respiration, tree presence provides measurable benefits to improve air quality, and their lack reduces it, both in theory and in practice. By utilizing sunlight for photosynthesis, trees capture heat energy, spatially reducing the presence of heat islands. For animals, trees are necessary habitat composition, especially for those Threatened or Endangered.


Climate trends are worsening: since 1900, global temperatures have risen 1°C, 25% of assessed species are now deemed Threatened, and PM pollution has rebounded, increasing 5.5% from 2016 to 2018. With these trends, trees provide protection for humans against climate change.


These climate changes disproportionately impact environmental justice groups, with PM disproportionately  increasing COVID-19 complication risk and heat island presence disproportionately in historically redlined neighborhoods. By reducing these disparities, trees promote equity.


So trees are essential to maintaining livable temperatures, air quality, and habitat, especially as it relates to climate change and historically marginalized populations. With 3.8 million hectares of canopy cover lost in 2019, trees are being lost at an alarming rate due to deforestation. This study provides a call to preserve trees and forests for a sustainable and equitable future.


Overall, I’m happy with this project. To improve the data, I’ll quantitatively map tree cover instead of a graphic representation, explore mechanisms of causation instead of just spatial correlations, and search for ways to cut down on deforestation: these efforts protect both us and the environment.


References

1. “AirNow Air Quality Monitoring Site Data.” ArcGIS, US EPA, 8 June 2022, services.arcgis.com/cJ9YHowT8TU7DUyn/arcgis/rest/services/Air%20Now%20Current%20Monitor%20Data%20Public/FeatureServer. Accessed 9 June 2022.


2. “Center for International Earth Science Information Network.” Global Urban Heat Island (UHI) Data Set, Columbia University, 2016, sedac.ciesin.columbia.edu/data/set/sdei-global-uhi-2013. Accessed 9 June 2022.


3. “Forest Ecosystem Products and Services.” Natural Resources Canada, www.nrcan.gc.ca/our-natural-resources/forests-and-forestry/sustainable-forest-management/forest-ecosystem-products-services/13177. Accessed 9 June 2022.


4. Lindsey, Rebecca. “Climate Change: Global Temperature.” National Oceanic and Atmospheric Administration, NOAA, 15 Mar. 2021, www.climate.gov/news-features/understanding-climate/climate-change-global-temperature. Accessed 9 June 2022.


5. Lopez, Jose Chen. “Basics of Plant Respiration.” American Horticulture, 28 Apr. 2021, www.pthorticulture.com/en/training-center/basics-of-plant-respiration. Accessed 9 June 2022.


6. Nowak, David J., et al. “Tree and Forest Effects on Air Quality and Human Health in the United States.” Environmental Pollution, vol. 193, Oct. 2014, pp. 119-29, http://doi.org/10.1016/j.envpol.2014.05.028. Accessed 9 June 2022.


7. Our Endangered World. “IUCN Red List.” IUCN, 20 Oct. 2021, www.iucnredlist.org/resources/summary-statistics. Accessed 9 June 2022.


8. Popovich, Nadja. “America’s Air Quality Worsens, Ending Years of Gains, Study Says.” The New York Times, 24 Oct. 2019, www.nytimes.com/interactive/2019/10/24/climate/air-pollution-increase.html. Accessed 9 June 2022.


9. “Primary Forest Loss.” Global Forest Review, World Resources Institute, research.wri.org/gfr/forest-extent-indicators/primary-forest-loss. Accessed 9 June 2022.


10. Traverso, Vittoria. “The best trees to reduce air pollution.” Future Planet, BBC, 4 May 2020, 10. www.bbc.com/future/article/20200504-which-trees-reduce-air-pollution-best. Accessed 9 June 2022.