A heatmap for the cool fall days

Hey, it’s Rose! I write for the blog at Datawrapper. In last week’s Weekly Chart, Lisa showed us how to chart the seasons on a very abstract level. This week, I’m bringing it down to earth…

For three seasons of the year, all trees are pretty much the same to me. I’m glad to have them around, but I just don’t think about them as individuals.

Then, almost overnight, everything changes. The maple on the corner starts to blush in red and orange. A brilliant yellow leaf on the sidewalk makes me look up and notice the only linden tree on the block. A cluster of oaks in the park suddenly stand out from the evergreens around them. For one season, you don’t need to know very much or look very hard to see the beauty and diversity that was there all year.

I’m willing to bet that the scientists of the Vermont Forest Ecosystem Monitoring Collective know a bit more about trees than I do. And they definitely know more than almost anyone about fall colors — because for almost thirty years, they’ve gone out every single day from early September to early November to record the progress of each tree from green to color to bare branches. There can’t be many places with a more beautiful palette than they see there, from the deeply colored red maples to the fiery sugar maples to the golden birches.

These “charts” are nothing but Datawrapper tables with the heatmap option turned on. Every day, for each species of tree, this study records the average percentage of leaves that have turned their fall color. In the beginning of the season, most trees have 0% fall color — because they’re still entirely green. By end of the season, most trees have 0% fall color again — because they’ve gone entirely bare or brown. On their peak, most colorful day of the year, the trees might be 85% covered in color. To show that double gradient, from green to color and from color to bare, these tables use relative values: I set each year’s peak day to zero, with the days leading up to it on a negative scale and the days following it on a positive one.

These weeks, and the transformation they bring even in the middle of the city, are magical to me. But it really is just a few weeks. Pretty soon the leaves will fall, or a good storm will come along to strip them from their branches. The trees will go back to their anonymous browns and greens — until next year.

That’s all for this week! I’ll be back next Thursday with another seasonal Weekly Chart — see you then.