Two Climate Change Studies of Trees and Wildflowers Yield Different Results

By Richard Primack

 

“An honest misunderstanding is often the ground of future intercourse.” Henry David Thoreau in his Journal.

 

Five years ago, our research group examined field observational records started by Henry David Thoreau in the 1850s in Concord, Massachusetts combined with modern observations and found that trees are responding more rapidly than wildflowers to climate change. This represented a surprising and important example of “phenological mismatch.” 

Photo 1: Bloodroot (Sanguinaria canadensis) is one of the wildflower species in the study (CREDIT Anna Funk, Holden Forests & Gardens).

Using thousands of herbarium specimens to cover a wider geographical area, we confirmed that trees across North America are indeed more responsive to a warming climate than wildflowers. 

However, another research group, using observations contributed by citizen scientists to the U.S. National Phenology Network, found that wildflowers were more responsive to climate change than trees, the opposite of our results. 

Photo 2: Native wildflowers, such as these Dutchman’s Breeches, leaf out and flower early in the spring before trees leaf out (© Andrew Cannizzaro and licensed for reuse under Creative Commons License CC-BY-2.0).

Instead of ignoring or criticizing these conflicting outcomes, our teams decided to work together to figure out why we got such different results.

As described in a recent article, our combined team found that even though we both started with the same question, we had used different data types, plant samples from slightly different geographic ranges, and data analysis based on different statistical models. Taking these factors into account, we were able to reduce, but not eliminate, differences between the two studies. 

In the end, both groups recognize that trees and wildflowers are responding to climate change, and are leafing and flowering earlier over time. But our seemingly conflicting study outcomes demonstrated how important it is for scientists investigating climate change to be aware of the peculiarities of their methods and data sets.

Here is a link to the article: LINK