Migration Flows Into Colorado and the Increasing Presence of Invasive Noxious Weeds
By Ainsley Cox
Since colonists came to America from Europe, invasive species have been an ever growing problem. A plants main function is to spread and reproduce, so they find many clever ways to make this happen. They produce seeds that can attach to clothing, equipment, vehicles, animals, and even other plants. Once these seeds are knocked off of these transportation vessels, they can germinate and begin a whole new ecosystem of plant. Unfortunately, a lot of the strongest and most resilient plants end up making homes in foreign places, stealing needed resources from native species and creating an ecological monopoly.
The first of many invasive species that are effecting Colorado and other Western states today originated in Europe, Western Asia, and Northern Africa due to the similar climates. Species like Russian Olive, Salt Cedar, Leafy Spurge, Canada Thistle, Common Mullein, and Downy Brome have taken over areas in Southwestern, Northwestern, and Central Western Colorado. Most likely brought to the United States by way of freighter ships, these plants have spread around the country in many different ways, most notably, by way of migration.
Invasive species take over an area by crowding out native species and taking advantage of communal resources such as water, sunlight, soil nutrients and clam weather conditions. While some only steal these resources so native plants begin to die off in a region, other begin to corrupt them so no plants can survive. The Salt Cedar, for example, has roots that grow so deep they take up salt into their leaves. When the leaves fall in the Autumn, the salt contaminates the soil, which then erodes into the water and effects plants and land downstream.
With not native predators to keep them in check, these plants take over local ecosystems and begin to decimate the biodiversity of the area. They can effect other plants, animals, land, and even local communities.
Plants like Russian Olive, Salt Cedar, and Leafy Spurge were introduced to Colorado as ornamental species but have spiraled so out of control that removal efforts could take at least 20 years. These plants seemingly begun to overpopulate the area in the 1990s.
As stated before, migration has had a big impact on the movement of these invasive species. Over the last 30 to 40 years, thousands have people have moved to Colorado from neighboring states, most notably, California and Texas. According to MoveBuddah, responses to a 2023 survey allowed them to determine that of Californians looking to relocate to different states, 4.17% set their eyes on Colorado. Additionally, according to Census data, 13.46% of new Colorado residents were from California in 2021. In 2021, nearly 7% of all Texans moving relocated to Colorado, making Colorado the 2nd most moved to state by Texans that year.
In a ProPublica article by Janet Wilson, Wilson wrote “Those fiefdoms exclude most of Imperial’s 180,000 residents. Agricultural operations — which in addition to historic farming families include universities, the Mormon Church, outside speculators and a Middle Eastern hay company — get 97% of the irrigation district’s river water, while every town, strip mall and other business combined get 3%. And the county ranks among the poorest in California, with a 2021 per capita income of $19,005. The U.S. per capita income that year was $70,480.” The article was about 20 farming families in the Imperial Valley in California that are granted nearly 386.5 billion gallons of water from the Colorado River every year. And while these families and organizations are thriving, these laws are doing tremendous harm to our local ecosystems in Colorado and other western states.
Having established that invasive species and water over-usage are intensely damaging our environment in Colorado, I wondered how much migration really impacts this. Using data from the Colorado Agricultural Department and the State Demography Office, I wanted to ask the question “Does increased migration from other states increase the rate of invasive species growth in Colorado?”
First to establish there is indeed a rising number of noxious invasive weeds in Colorado, I used two datasets, one documenting noxious weeds found on the side of the road in Colorado in 2010, and the other documenting noxious weeds found on the side of the road in Colorado in 2017. I grouped together these sightings by the primary weed that was found and created two bar charts to compare the growth.
As you can see from the bar graphs, Common Mullein sightings have shot through the roof, with Canada Thistle increasing slightly, and Johnsongrass increasing quite a bit. From this we can establish that the rate at which invasive noxious weed species are being found along Colorado roads is increasing at an alarming rate. Here is a line graph showing the observations of some noxious weeds in 2017.
To do the correlation analysis, I used the same data set documenting noxious weeds in Colorado in 2017 and an additional data set from the Colorado Demography Office documenting the amount of people moving from and moving too Colorado in 2016–2020 and the states to which they are going to and coming from. To do this correlation analysis, I created a new column counting up the total times the weed was found in the dataset and then reduced the number of duplicates so that each weed only presented itself once but the total number of weeds was still preserved in the additional column. I then compared this total weeds column to the total net migration column in the Colorado migration dataset.
The first correlation test I conducted, using a Pearson’s R test, resulted in a correlation coefficient and a p value. A correlation coefficient is used to asses the strength in the relationship between two variables and the p value is used to see if the relationship is statistically significant, meaning that you can be confident in saying x causes y, in this case the number of people migrating causes the number of invasive noxious weeds. In the case of this test, the correlation coefficient was 0.353 and the p value was 0.0236. Because of this preliminary test, we could consider the relationship between these two variables a moderately strong significant relationship, meaning as one increases, so does the other. Below is a scatterplot illustrating this relationship.
There are 40 values on the scatter plot, and generally, it looks like a weak positive relationship. However, a Pearson’s R test is only one way to test for a relationship and so I also ran and OLS Regression test to get more information on the relationship.
From this, we continue to see a strong p value indicating that there is a significant relationship between the two variables. However, the R squared value is 0.125 which is concerning. The R squared is the amount of variance in the variable y that can be explained by the variable x and is measured between 0 and 1. While the analysis suggests that there is a slight positive relationship between the two variables, there are likely unaccounted for variables that are causing the majority of the change that we see in the y variable.
Though the relationship may not be as strong as ideal, there is still a correlation between the migration of people from other states to Colorado and the rate of invasive noxious weeds sightings. The answer to solving this problem is not a simple one. Those who admire Colorado’s beauty should be able to come and go as they please without fear of killing the natural ecosystem, but that ecosystem needs to be protected.
Some small steps that can be taken to minimize the impact of tourism and increased migration in Colorado could be extra care with clothing, equipment, and vehicles to make sure that they are clean and not carrying any potentially dangerous seeds. On a larger scale, in order to protect native species in Colorado and fight against already rooted invasive species, we must continue to support restoration efforts and farmers in their effort to restore native biodiversity to their land. Tools like controlled burning, herbicides, and bio-controls like host bugs who only feed on one specified plant, are being implemented and continue to be developed to help restore native ecosystems.
Already, there are efforts in rural regions of Colorado to tackle their particular brands of invasive weeds and politicians are reaching out to the Federal Government to request funding for these efforts. Surprisingly, Republican Lauren Boebert is one of these such politicians, and contrary to what she’s been displaying of her capabilities, this is an admirable task that she has undertaken. Another thing we can continue to do is support climate change legislation protecting Colorado River Water from being over-used so that there is enough for native plant species back in Colorado.
This topic continues to be prevalent in our era of climate crisis so I believe it is important to understand how it is impacting us in our state and what we can do to support those fighting for sustainability and a healthy ecological future. More research understanding other contributing factors and solutions need to be conducted but I hope that this article can be informative to those looking for a place to start.
Work Cited
- Fleming, Margaret. Invasive Plants are Slurping up Precious Water in Drought — Stricken Southwest Colorado. The Colorado Sun, 2022. https://coloradosun.com/2022/05/05/invasive-species-water-contamination/
- Delay O’Connor, Amber. The Leafy Spurge Invasion: Group Aims to Combat Spread of Invasive Plant Species. Craig Press, 2022. https://www.craigdailypress.com/news/the-leafy-spurge-invasion-group-aims-to-combat-spread-of-invasive-plant-species/
- Colorado Demography Office. Colorado Migration Flows. https://demography.dola.colorado.gov/assets/html/migflow.html
- CalIPC. Salvinia Molesta. https://www.cal-ipc.org/plants/profile/salvinia-molesta-profile/
- Guevara, Christopher. Tiny Bugs Help Land Owners Against Past and Invasive Species. KKCO 11 News, 2022. https://www.kkco11news.com/2022/11/04/tiny-bugs-help-land-owners-against-pest-invasive-species/
- McKee, Spencer. ‘Californian Invasion’ Continues in Colorado. The Denver Gazette, 2023. https://denvergazette.com/outtherecolorado/news/californian-invasion-continues-in-colorado/article_2acbeba6-45ce-11ee-9656-b3dd2a952dcd.html#:~:text=Californians%20relocating%20to%20Colorado%20has,2021%2C%20based%20on%20census%20data.
