Kali Katerberg/Daily Mining Gazette Now-dead alder trees dot the Nara Nature Park after Lake Superior water levels led to a die-off.

HOUGHTON — The alder trees of Lake Superior wetlands are having problems, dying off en masse since around 2015.

Walkers along the Nara Nature Park boardwalk may have guessed insects or invasives were to blame for the groves of dead shrubs. However, as it turns out, water levels are at fault.

The sustained high water levels on Lake Superior are making their habitat too wet and leading to the die off.

Though more dramatic than usual, the sudden loss of the alders is a normal part of a wetland life cycle.

“This is a natural process, I’m not alarmed. It’s just changing,” said Michigan Tech ecologist and wetland researcher Rodney Chimner.

He says he’s never seen such a dramatic die-off before.

“When the Great Lakes go up and down, the Great Lakes expand and contract,” he said.

Though the alders may have died off, for now, this is the cycle wetlands are adapted for. The changing levels even help maintain species diversity by not making the region consistently advantageous for one variety.

The scenario that led to the slew of dead alder trees began in 2007 with historically low lake levels that created new wetlands.

“Areas that were too wet before became suddenly good habitat,” Chimner said.

That is until the water later began returning to the normal levels and began nearing historic highs.

Unfortunately for the alders, they couldn’t survive the sustained high water levels that began in 2014. Chimner noticed the die-off beginning in 2015.

The dead alder can now be seen all around Lake Superior and connected bodies of water like Portage Lake. Unlike wetland plants like cattails, many wetland trees have a more limited habitat window and more limited niche.

Though a natural process, the loss of the alder isn’t without problems in some areas. In the Nara area, the die-off of the groves of alder has led to a return of invasive species like purple loosestrife and reed canary grass in the areas no longer shaded. Traditionally native grasses took the alder’s place after a die off.

As the invasives were not present when the alder grew, Chimner will be watching if the alder return once water levels are more suitable for them again.

“It might come back on their own no problem or maybe we’ll have to go back and plant one day,” he said.