A recent SUNY-ESF research study found that the sugar maple tree has been experiencing negative growth rates over the last few decades despite conditions that favored their growth and regeneration.

The study, which was published on Oct. 21 in the open-access journal “Ecosphere,” involved analysis of growth rings from trees in the Adirondack Mountains in northern New York. It’s unclear exactly why the trees are in decline.

Daniel Bishop, who is currently a research assistant at Harvard Forests, had been a graduate student at the State University of New York College of Environmental Science and Forestry when he began working on the sugar maple tree project as part of his master thesis.

The project was created by a few of the co-authors of the study, but Bishop said he extended the project and increased the sample size, which is what led to the realization that the growth rate was in decline. The team then began to investigate the impacts of climate, insect defoliation and acid rain on the growth of sugar maple trees in the Adirondack Mountains, Bishop said.

He added that they started the project by measuring tree rings to quantify growth — given the width of each ring and the diameter of the tree they were able to calculate annual growth rate for the trees.

Bishop said it was a shock to him and everyone involved in the project that the majority of the sugar maple trees sampled experienced declining growth rates and only a small percentage experienced no change or a positive trend.

“These reduced growth rates were unexpected given the competitive status, relatively young age and seemingly advantageous climatic conditions for this species,” Bishop said.

The sugar maple is one of the first trees people who grow up in rural central New York and spend much time in the Adirondacks learn about when they’re young, said Neil Pederson, a co-author of the study and an ecologist at Harvard Forest in Massachusetts, as well as an expert on tree rings and climate change, in an email.

“We learn about this tree first because it produces maple syrup — shouldn’t that be enough of a reason to like a particular tree species?” Pederson said.

It is not clear exactly why the sugar maple trees are in decline. Pederson said there are a few hypotheses as to why the trees are in decline: tree size, tree age, soil quality, acid rain and climate change are just a few.

Pederson added that it is also important to look at factors that affect tree growth such as competition from neighboring trees, insect outbreaks and fungal pathogens.

The research team was able to examine tree size, age and soil quality and did not find evidence so far that any of those factors were triggers for the decline in population, Pederson said.

The team did find that the sugar maple trees have a need for moisture, but since daily rainfall has increased over the last few decades, moisture availability was also ruled out as a factor of the decline. The team also ruled out global temperature increase as a trigger since summers in the Adirondacks are not particularly hot.

“The decline is likely an interaction of many factors — some we tested and some that we were not able to test,” he said.

Pederson said it is important to understand that this might be a temporary phenomenon, and that the red spruce tree had a similar decline in the 1970s and 80s but seems to have recovered.

He added that the research needs to continue and the many factors behind the decline need to be sorted out before anything can be done, but he said he believes there is hope to restore the sugar maple tree population.

“We had six in the front yard of the house I grew up in and spent much time under them on hot days,” Pederson said. “We got all the leaf-pile jumping each fall from these trees.”

Published on November 1, 2015 at 7:40 pm

Contact Anjali: acalwis@syr.edu