How Do Humans Influence Habitats?

By Shannon Christopher, WellKind Forestry Intern

Shannon Christopher was an intern for WellKind Forestry during our spring 2022 session, exploring habitat destruction and other environmental issues.

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Population growth and increased industrialization have allowed us to develop advanced societies. However, as our population grows and expands, we take up more and more space, impacting the habitat of wild animals and the health of ecosystems. The effects of anthropogenic (human) activities could permanently change the global climate. Are there ways to minimize our footprint?

Human Impacts on Habitats: Urban Sprawl

As humans continue to industrialize our societies, our population size increases, so we build infrastructure to keep up with demands. With increased populations comes increased urbanization. 

There are two ways in which humans can build: up or out. Human cities either build up, with taller buildings compacting everything and everyone into a small area of land, or we can build out, creating suburbs and road networks and continuous expansion, which is known as urban sprawl. In the United States, we typically do the latter, choosing to build out in order to support our consumerist lives. Urban sprawl results in humans continuously encroaching on habitats and forcing animals to leave destroyed ecosystems (Nechyba & Walsh, 2004).

Along with habitat encroachment, urban sprawl results in increased pollution. People have to travel further to work in the city, and they typically travel by personal cars, which emit CO2 and other greenhouse gasses. A study compared 86 metropolitan areas in the U.S. in order to determine the relationship between urban sprawl and pollution, and found that areas with higher levels of sprawl had higher levels of air pollution (Bereitschaft & Debbage, 2013). These findings can be linked to increased transportation and an increase in personal vehicles that people buy when they move into the suburbs and work in the city. 

In addition, increased populations result in increased food demand, and plants that have been cultivated for crops get introduced into new areas. In the U.S., most food crops are non-native plant species (Carthy, 2011). Although these crops are not naturally occurring in the local environment, they are not necessarily harmful. Other plants that have been introduced by humans do harm the ecosystem, and they are considered invasive plants. 

Native vs. Invasive Plants

Native plants are species that have developed and originated in a given habitat and adapted to live in that environment. Nonnative species are those that originated in a location that is different from the location they were introduced to. Invasive species are species that outcompete other species in an ecosystem, and by doing so cause harm to the ecosystem (Lilly Center for Lakes and Streams, 2021). Not all nonnative species are invasive, but the vast majority of invasive species are nonnative. Species that are native to some locations may be nonnative— and even invasive—in other locations. 

Invasive species are invasive because they cause harm to the ecosystem from their being not native to the ecosystem. Invasive species can be introduced to one ecosystem from another by ship ballast water, accidental release, or intentionally by people (National Ocean and Atmospheric Administration, 2021). These species haven’t developed relationships with the other organisms in the ecosystem, so they likely don’t have any predators to control their population. They may also have biological advantages that allow them to outcompete native plants for resources, including space, nutrients, water, and sunlight. When invasives outcompete natives, resources in the ecosystem can be drained, and native populations drop and can even go extinct, which decreases local and global biodiversity. 

There are many invasive species in the United States, including the Purple Loosestrife, Japanese Honeysuckle, and the English Ivy. The Purple Loosestrife originated in Europe and temperate Asia, and was introduced in the U.S. in the early 1800s for medicinal purposes. One plant can grow one foot in height annually and produce two million seeds annually. Today, it grows in most states and dominates wetlands.

Japanese Honeysuckle originated in Eastern Asia and was brought to the U.S. in 1806 to control erosion and for decoration. This plant adapts easily and it has dominated the East Coast, growing like an aggressive vine that outcompetes nearby vegetation.

The English Ivy originated in Europe and was brought to the U.S. by the colonists in the early 1700s for the purpose of evergreen ground cover. It is the most dominantly spread invasive plant in the country due to its adaptability and ability to outcompete other vegetation by restricting its access to light (Grebenstein, 2013).

Habitat Restoration

Humans have already harmed ecosystems all over the globe, but there are ways that we can mitigate our impacts. One thing we can do is restore our local habitats. Habitat restoration requires an understanding of the functioning of the ecosystem and involves rehabilitating an area into the ecosystem that it once was (Habitat Loss / Restoration, n.d.). Restoration can involve removing invasive species, planting native plants, and taking other steps to counteract anthropogenic damage.

Invasive species populations can be controlled by going out and literally pulling invasive weeds and chopping down invasive plants, and planting native plants in their place. Depending on other harm humans have caused to the ecosystem, such as pollution, soil erosion, or habitat encroachment, different steps can be taken.

If humans have caused pollution in an ecosystem, we could start by not continuing to pollute, and from there clean up substances if possible and take any and all measures possible to store pollutants and balance out the chemical (and nutrient) levels. In the case of soil erosion, humans can lay down erosion fabric on river/stream banks and plant native trees and grasses so their roots can hold the soil together. Habitat encroachment is trickier to find a fix for, as many people don't want to get up and leave their houses, but one method to lessen the consequences could potentially be to incentivize people to plant native plants on their property and limit their pollution. 

Restoration in Action

The Salmon Protection And Watershed Network (SPAWN) is a restoration organization in Marin County, California. The program is a branch of the Turtle Island Restoration Network. SPAWN’s focus is to protect endangered wild coho salmon. These salmon live their adult lives in the ocean but travel upstream into freshwater rivers in Marin County to lay eggs. The watersheds in Marin County have been increasingly threatened by urban sprawls—houses and human infrastructure are often built right next to the creeks—and invasive species. In order to protect the salmon, SPAWN works to repair the watershed habitat so the fish can effectively lay and hatch their eggs. 

SPAWN has been working at restoration locations in the San Geronimo floodplains, and one of their restoration sites is a retired golf course. A 100-year-old dam that used to block salmon migration was taken down, and the damaged stream banks around it are being restored (Staub et al., 2021). SPAWN brings out volunteer groups to pull invasive weeds and plant and nurture native species, among other things. 

Historical records of the coho salmon estimate spawning populations in the thousands, but in 2021 only 173 were reported. Previously, the dam had made it very hard for adult fish to move up the creek and for juvenile salmon to make their way out to the ocean. 

With SPAWN’s creek restoration, more salmon have been seen making their way upstream to spawn (Hayes, 2022). Increased restoration of the watersheds in Marin County will continue to help the coho salmon boost their dwindling population. 

In short, habitat restoration works. With continued efforts, humans can minimize our impacts on ecosystems globally. This restoration will not only be beneficial to wildlife and habitats, but it will also help humans who depend on these habitats for ecosystem services such as oxygen production from photosynthesis, maintained populations of species we hunt and eat, erosion prevention from plants roots holding the soil together, and much more. 

References

Nechyba, Thomas, J., and Randall P. Walsh. (2004). "Urban Sprawl." Journal of Economic Perspectives, 18 (4): 177-200. 

Bradley Bereitschaft & Keith Debbage (2013) “Urban Form, Air Pollution, and CO2 Emissions in Large U.S. Metropolitan Areas”. The Professional Geographer, 65:4, 612-635.

Carthy, N. (2011, March 24). “Invasive Species”. National Geographic Society. Retrieved April 19, 2022, from https://www.nationalgeographic.org/encyclopedia/invasive-species/

Lilly Center for Lakes and Streams. (2021, August 19). “Native, non-native and invasive species... what's the difference?”. Lilly Center for Lakes & Streams. Retrieved April 18, 2022, from https://lakes.grace.edu/native-non-native-invasive-species/ 

National Ocean and Atmospheric Administration. (2021, February 26). “What is an invasive species?” NOAA's National Ocean Service. Retrieved April 19, 2022, from https://oceanservice.noaa.gov/facts/invasive.html

Grebenstein, E. (2013, April 19). “Escape of the invasives: Top six invasive plant species in the United States”. Smithsonian Institution. Retrieved April 26, 2022, from https://www.si.edu/stories/escape-invasives 

University of California Museum of Paleontology. (n.d.). “Habitat loss / restoration”. Understanding Global Change. Retrieved April 18, 2022, from https://ugc.berkeley.edu/background-content/habitat-loss-restoration/ 

Staub, R., Steiner, T., & Belsky, E. (2021, April 15). “From Roy's Dam to Roy's Riffles: Removing the Top-Priority Barrier for Central California Coho Salmon.” Trees Foundation. Retrieved April 19, 2022, from https://treesfoundation.org/2021/04/from-roys-dam-to-roys-riffles/

Hayes, A. (2021, October 28). “Videos Show Salmon Returning to Marin County Creeks for Spawning Season.” Turtle Island Restoration Network. Retrieved April 19, 2022, from https://seaturtles.org/videos-show-salmon-returning-to-marin-county-creeks-for-spawning-season/