New look at national patterns in leaf out and leaf color change

Credits: Ellen G. Denny
Sugar maple with colored leaves
Fri, May 14, 2021

In a nutshell

We have a decade of data on over a thousand species – thanks to your efforts! We are starting to be able to ask and answer the big questions, like: What causes spring leaf out and fall leaf color change across the nation? Authors of this study took a crack at this question, using new statistical methods to leverage the many species and locations in the Nature’s Notebook dataset. The answer? Leaf out in spring comes earlier in response to longer days, spring warmth and overwinter cold, while frosts delay leaf out. Patterns of fall phenology are less clear, but leaves tend to change color earlier with shorter days and colder temperatures.

Researchers also asked: Is how a plant responds to temperature or precipitation more a result of what species it is or the region where it’s located? Both had an effect, but plants in the same region tended to respond more similarly than plants of the same species.

What is special about this study?

Few studies examine such large regions or numbers of species. This is made possible by our standardized data collection across the country, as well as our long-standing partnership with the National Ecological Observatory Network (NEON). NEON and the USA-NPN use the same approach for tracking phenology, enabling the data to be readily used together.

The study also tries out a new statistical approach, perfect for datasets like ours, that have information on the presence and absence of a phenophase, and where we know there are likely to be similar patterns within species and regions.

What does this mean for YOU?

Does what you are noticing in plants near you line up with the overall patterns we are seeing across the country? You might see the delaying effects of a spring freeze or warming winters, for example. A delayed start may limit the time plants have to gain energy and reproduce through the season, or cause a mismatch with their pollinators. However, if delayed activity is protecting plants from the impacts of false springs (when early warmth prompts plants to leaf or bloom, followed by frost damage), it may be a good thing!

If, like us, you are curious about what is going on with fall – you can track trees and shrubs in the fall, with particular attention to the date of the first yes for colored leaves.

Citation:  Elmendorf, S.C., Crimmins, T.M., Gerst, K.L. and Weltzin, J.F., 2019. Time to branch out? Application of hierarchical survival models in plant phenology. Agricultural and Forest Meteorology.