Visualizing Red Maple Observations
One of the unexpected consequences of attending college in Connecticut has been experiencing autumn twice a year. I watch the trees of New Haven change color during late October and early November, then return home in Georgia for fall break and watch the leaves change color again.
I understood the basic principle behind my double-dipping of fall. But what would it look like actually to observe leaf color change across the whole continent? I decided to tackle this question over my winter break.I've been wanting to do something with iNatrualist data for a while now and decided that this could be it.
I had three qualifications choosing a tree species. It had to have a drastic fall color change, a large range, and many observations. After considering Sugar Maple, (Acer saccharum), Sassafras (Sassafras albidum), Trembling Aspen (Populus tremuloides), among other trees, I finally decided on Red Maple (Acer rubrum), which had the highest observation count.
Figure 1: 2019 research grade observations of A. rubrum with leaves. The color of each marker corresponds to the dominant color of the leaves in the respective observation. Each marker disappears 10 days (frames) after it first appears. At the end of April, observations get green as trees “green up,” and fall colors start appearing at the start of October and spread south.
Figure 2: 2016, 2017, 2018, and 2019 research grade observations of A. rubrum with leaves. 2015 omitted so that a nice square could be made for this graphic
Figure 2: Number of observations with “fall” colors in each week of the year for 2015-2019. “Fall” color was defined in an HSV color model as colors with a hue (0-360) > 300 or < 60, a saturation (0-1) > 0.09, and a value (0-255) > 150. Peaks are present at week 17, and weeks 41-44. Week 17 is overrepresented because of the number of total observations in that week, but early leaves can be reddish. Interestingly the 2018 fall colors appear to be about two weeks later as a whole compared to 2019. The late 2018 fall was observed by others, and was attributed to higher than average daily low temperatures.
Figure 3: Overview of process
For a more detailed writeup on the data and the process, check it out on my website
