Sugar maples should be doing well; here are theories on why they're not

Nov 27, 2015

Maple sugar operators, scientists and forest managers have known for years that the sugar maple is very sensitive to acid rain. So when the federal acid rain levels dropped levels dramatically after federal regulation, it could only mean good news for one iconic tree that found living with acid rain difficult -- right? A recent study published by the SUNY School of Environmental Science and Forestry (SUNY ESF) in Syracuse shows that hypothesis doesn’t hold water.

SUNY ESF scientists wanted to know how the decline in acid rain affected sugar maple trees in the Adirondacks. These trees don’t like an acidic soil, says ecology professor Colin Beier, so the study of growth rings should have brought good news. But it didn’t.

Credit SUNY ESF

"We quite unexpectedly found the majority of trees that we looked at -- which are kind of in the prime of their lives -- are growing much more slowly than they used to,” Beier says.

The study found the region-wide downturn started after 1970. That’s when concern escalated about acid rain, which happens when sulfur dioxide pollution spewing from coal-fired power plants in the Midwest drifts east and damages marine life and forests in its wake. Government regulators eventually stepped in and sulfur emissions dropped dramatically. That’s why scientists like Beier were optimistic when they started studying tree rings from a wide swath of the Adirondacks.

"The long and short of this is, we have less acid inputs in the system, so we would expect the trees to be growing better, but they’re not,” Beier says.

"One of the possibilities is we may have short periods where the trees are moisture stressed and that could be playing a role here too."

At this point researchers don’t know why the maples aren’t thriving. Beier says climate change could have an impact, although that doesn’t make sense, because these trees should love a wetter climate.  He does have a theory though.

"One of my hunches is that we have more hot dry periods in the summer than we used to. And so even when we look at precipitation data, and it’s wetter than it used to be, it’s coming in fewer storms,” says Beier. “One of the possibilities is we may have short periods where the trees are moisture stressed and that could be playing a role here too.”

Beier expects more studies into the depth and scope of the problem, forcing scientists and forest managers to take steps to ensure their longevity. Measures could be taken to add calcium to the soil or more closely monitor maple syrup production, he says. And when more research is in the books, Beier suspects there won’t be just one culprit making life tougher for the sugar maple.

“For organisms that live this long and deal with so many different types of stresses and stimuli in their environment, because they can’t run away from things they don’t like, when you see declines like this it’s rare they’re attributable to any single cause,” Beier says.