This is the first of my fall color reports for 2021. Of course, starting off in August there isn’t a lot of color development yet, but there are some isolated cases among urban trees, which always begin changing color before trees in the woods. In particular, urban red maples, dogwoods and sourwoods, as well as some stressed sugar maples are coloring up now, but don’t panic, as the major fall color display will still occur in mid-October.
My graduate student, Claire Martin, is studying how urban red maples, including the Armstrong and Autumn Blaze cultivars, develop their fall colors, especially with regard to where in the canopy colors first appear. For the Armstrong cultivar, past years indicate that color develops all over the canopy at approximately the same time, whereas for the Autumn Blaze cultivar, there is distinct development in the upper canopy first, with lower leaves coloring up afterwards. We are trying to figure out why this cultivar does that and whether it is because the weather is different in the upper crown, or the leaves differ there, or both. In the attached photograph, you can see Claire taking measurements of photosynthesis in a bucket truck some 25 feet up a red maple. The Autumn Blaze cultivar started showing red leaves the first week in August, which is somewhat early, if I recall past years correctly.
I’ve seen sourwood trees starting to turn color this week, and dogwoods have been turning since mid-July. They develop their fall colors slowly and incrementally over a 6-8 week period. I’ve included a progression of color development for the dogwood trees that are growing across the road from my house.
Another of my students, Bubba Pfeffer, who recently graduated from Appalachian State University, has been digitizing images of trees to learn more about their phenology (the science of when organisms go through distinct phases of their life cycle, such as leafing out, coloring, and dropping leaves). We have a camera that takes digital images of the same forest every day and we have now accumulated five years of data. Bubba is in the process of analyzing when the trees green up and when they lose leaves, and how long the fall color periods last. We have found some differences among the years in the timing of these events and we are now trying to figure out what aspects of the weather have the most influence on them. Once we’re done we’ll post our results for you to see.
Finally, a New York Times article allows readers to find out how many days of the year the temperature gets above 90 degrees Fahrenheit, from 1960 to 2018. In 1960, Boone averaged only 3 days over 90 degrees, but the trend over the past 58 years has been inexorably upward to the point that we now average 9 days over 90 degrees each year, a three-fold increase. That is alarming, but goes along with the dire predictions just released this week by the International Governmental Panel on Climate Change (IPCC), which unequivocally states that human activities have warmed the Earth and that unless actions are taken immediately, we will have no chance to avoid significant warming in the future, often to levels that will have catastrophic effects on countries. It is definitely a wake-up call. I mention this because warming is the single most important variable affecting fall leaf color displays, both with regards to timing and intensity. Warmer years result in delayed onset of color, as well as a reduced intensity of color, particularly the reds, and will diminish the quality of the display compared to past years. Last year was a throwback to earlier years in that the colors were back on time (mid-October) and they were vibrant and quite beautiful.
So far this year, the weather in the High Country has been fairly mild, with no long-term dry periods and there is lush tree growth everywhere. The first week of August this year we had morning temperatures in the low 50s and highs only in the mid-70s, which is quite remarkable. It will be warmer this week, but if this trend continues into the fall, we should be setting up for a good fall color season. What happens in September will be crucial!
So, welcome back. I hope everyone has had a good summer. Schools have already started and others will be back in the next few weeks. It’s super busy here in Boone as the students are now moving into the dorms and off-campus apartments. Classes start here on Monday, August 16th. If you’re coming to the High Country, most trails and roads are fully open. To avoid the crowds, get out early or come during the middle of the week. If you want to go to Grandfather Mountain (https://grandfather.com/), be aware that you need to make reservations online first.