Research Question | Is it better to have few large trees or many small trees in a given size lot, with respect to storm water uptake? |
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Predictions | A larger number of small trees will more effectively uptake storm water. This is because there are more root systems to uptake the water. |

Experimental Design | Find two equal size lots, one with a few large trees and one with a lot of small trees. Use the tree calculator to measure the storm water uptake of all the trees in each lot. Add the uptake values from each lot together and compare with the other lot. |

Conclusion | Dear City Manager, We’re three students from University Liggett School in Grosse Pointe Woods. In our current Environmental Science class, we were given the task of formulating an experiment that involves comparing trees and their various benefits given to us by entering data into an online tree calculator. Of the numerous categories we could’ve chosen, we decided to dive deeper into stormwater uptake among trees. This was somewhat of an obvious choice for us given the flooding of homes within our Grosse Pointe community over the summer. We wanted to figure out what some viable solutions were to stopping basements from flooding, and through our class, we were able to figure out that trees were the perfect solution. When we initially learned just how much stormwater trees took in, it was startling. This allowed us to attempt to discover which trees, how many trees, and how the diameter of trees affects stormwater uptake. As you could imagine, stormwater uptake is so important because it prevents areas from pooling up water, and could potentially save families from damages to their homes and belongings. Trees take up water to keep healthy by performing photosynthesis. Trees need plenty of water, along with sunlight and CO2 to produce oxygen vital for humans and animals, and energy in the form of sugar. This led us to think about how many trees, and how the size of the tree affects water uptake. So, our final question was how many smaller trees (diameter 15-24 inches) would be needed to match the stormwater uptake of five larger trees (diameter 20-56 inches)? To analyze the stormwater uptake of lots with different size trees we located two different lots, one with large trees and one with smaller trees. The large tree lot is at 180 Ridge Road in Grosse Pointe Farms. The smaller tree lot is behind University Liggett School in Grosse Pointe Woods. To measure trees we measure the circumference of the tree at 4.5 feet above the ground, then divide by pi to get the diameter of the tree. This value, and the species of tree can be entered into the National Tree Benefit Calculator. The calculator gives information about all the benefits of the tree, including stormwater uptake. We averaged the stormwater uptake of the trees in the Liggett lot to get the average stormwater uptake of a small tree. We added the water uptake values of all the trees in the Ridge road lot and divided this value by the average small tree uptake. This gave us the number of small trees that would be required to equal the stormwater uptake of large trees. The data showed that it would require 12 smaller trees to equal the stormwater uptake of the 5 large trees on the Ridge Road lot. The average stormwater uptake for a smaller tree was 2,432 gallons per year. This means that it takes 2.4 times the number of small trees to uptake the same amount of water as large trees. Trees also provide other benefits, these benefits can be measured as the amount of money they generate per year. The smaller trees generate an average of $210 per year. The large trees generate an average of $324 per year. This means that we need 1.5 times more small trees to gain the same monetary value as large trees. The largest source of error in our data is sample size. To more accurately measure the differences between large and small trees more lots would need to be analyzed and compared. We took the average amount of stormwater uptake from the two lots, five trees per lot, and found that five large trees take up an average of 27,430 gallons of stormwater. Because of the flooding throughout our community, we have concluded that when large trees are removed, new trees need to be planted to help prevent flooding. The removal of one large tree would require two smaller size trees to take up the same amount of water. |

Investigation Theme | TREE |

Grade Level | High School Students (Grades 9,10,11,12) |

Teacher Name | Elizabeth Dann |

School Name | University Liggett School |

Session | Fall 2021 |

About this Project | I consider this to be a star project since they managed to put together a comprehensive and compelling report in order to convince the city council about the benefit of urban trees. Not only they managed to explain nicely the obvious - that trees are beneficial - but they managed to tear apart and compare tree age/size in terms of what would be the most beneficial for storm water uptake, as well as how many smaller trees would need to be planted to cover up for the benefit of one large tree removed. |