I conducted this project as part of Professor Pringle’s EEB321 class at Princeton University.

As I was walking around Princeton's campus looking for organisms that piqued my interest, I noticed that there were a whole cluster of maple trees by the Frick Chemistry Building that still had many yellow leaves attached even though it is already the beginning of December.


I thought this was quite odd, and so I wanted to investigate these trees more. With the help of the Seek app, I was able to identify these as Norway Maples (Acer platanoides). Although their leaves are beautiful, especially in the fall, they are unfortunately an invasive species in the U.S., originating from Europe and Asia. They outcompete other native plants such as the Sugar Maple (Acer saccarum). The Norway Maple tends to sprout much earlier in the spring than other trees, has its leaves drop in the fall later than other trees, has high germination rates, can grow in low lighting conditions, has dense cover to limit light in the understory, and has shallow roots that reduce moisture that other plants need to survive, all of which are traits that allow it to dominate the U.S. landscape. This tree tends to be found in higher latitudes in Europe and Asia, so its leaves would drop earlier in the fall over there than here in the U.S. This explains why I still saw many leaves attached to the tree even though it's already December.

Here is an example of what the leaf of the Norway Maple looks like


I put this leaf under the Foldscope to see its structure.

Here you can see the individual cells separated by cell walls, which is pretty cool! With the naked eye, the leaf looks like such a homogenous structure, but there are actually tiny clear spaces between the yellow-colored cells. These yellow-pigments are in the leaf all year round, but are masked by the green color of chlorophyll during the spring/summer. The chlorophyll breaks down in the leaf as the days become shorter. It's amazing to see how the tiny cells make up the whole leaf.

I also attempted to peel the leaf stem a bit to see what the inside of it looks like under the Foldscope. The image is unfortunately pretty blurry, but you can start to make out some of the individual white fibers that make up the leaf stem. Apparently, the Norway Maple has a characteristic white sap in the leaf stem.

I am definitely curious about how these specific trees ended up on Princeton's campus, and what the distribution of these trees looks like in the Princeton area versus other native trees such as the Sugar Maple. I also wonder if Princeton might replace these trees with native plants at some point in the future to foster a more sustainable habitat. When I walked around this area, I only saw the Norway Maple and Japanese Wineberry (Rubus phoenicolasius), a hearty, low-lying invasive vine which can grow in a wide variety of habitats. The biodiversity of this area could definitely be improved. I know that Princeton is working on introducing more native plants back to campus, so hopefully this area will look different in the future!