Why Are Tamarack Trees Dying in Northern Wisconsin?

Jun 3, 2019

Tamarack trees, like many of us, could live anywhere in Wisconsin but prefer the Northwoods.

Recently a listener from Harshaw submitted this question to our Curious North series: What's up with the tamarack trees? They seem to be dying. Is it the rising water levels, or something else?

In today’s Wildlife Matters the Masked Biologist sheds some light on what might be causing tamarack tree mortality.

One of the questions that came in to Curious North caught my interest, so I thought I would try to provide an answer. There has been a fair amount of tamarack dying off in the last year or two, and the question was about the cause.

The question asker submitted this photo of tamarack trees on County Hwy J.

Tamarack is a rather unique tree. Native to Wisconsin, it can be found across the state. It is a member of the larch family, which is known for being a deciduous conifer. That means it is a cone-bearing tree that sheds its needles every fall. If you have driven any direction in or out of Rhinelander, Minocqua, Park Falls, pretty much every population center in the Northwoods, you have driven past tag alder stands. You probably don’t pay much attention to them until fall, when their needles turn a brilliant burnished gold color. These trees can grow quite large on drier sites, up to 60 feet tall, but rarely exceeding 30 feet tall or so in wetter areas. Tamarack is truly a northern swamp tree, usually found in leatherleaf or peat bogs that also grow balsam fir, white cedar and black spruce. It actually can be found scattered in most counties of Wisconsin, but further south it typically only holds on in the coldest swamps.

In areas where you see tamarack growing, you always see taller trees along the fringes of a bog and the closer they get to the center of the bog, the smaller they are. However, these trees could all be the same age, the trees in the wetter areas growing far slower. The trees that grow larger faster are usually also available for harvest sooner. The trees in the center of the wetland grow so slowly that they may never reach merchantable age, or they might not be accessible with equipment due to the nature of swamps. So they grow old and die. That is one possible explanation of why you see more dead tamarack trees, especially in the middle of the wetland.

A second explanation, probably the most likely, is changes in hydrologic regimes. For most of the last decade, we were in a drier trend, with below average precipitation. I remember people extending their docks to try and reach the water and mowing the dry lakebed. Then a couple of years ago, things changed and we started getting wetter again. As the water came up, trees that were growing along the edge of the lakes stayed wet year-round, started to stress and die. The same is true in the wetlands. Water levels in marshes came up, and trees that were barely able to hang on began to drown. If you tack on the possibility that within the last ten years there may have been a culvert replaced downstream, or beaver dams built in low water years you magnify the impact of increasing precipitation.

Finally there are documented ongoing changes in our climate that will directly and indirectly impact these trees.  Our precipitation comes in higher intensity and lower frequency events, which changes how wetlands work. Additionally, hotter summers and colder winters can have a significant impact on tree species that are not adapted to them. Add to that the change in the life activity and presence of insects, and you have a pretty complex set of impacts that a tree has to overcome to stay healthy. Our state saw a significant die-off of tamarack years ago due to larch sawfly, so we have very few if any legacy trees. I saw an article from Minnesota where they are experiencing a large die-off of tamarack due to larch beetle. These insects used to breed once a year and overwinter as non-flying juveniles, but due to moderating winters the larvae are now able to fly and breed before winter allowing them to spread more quickly than ever before. While I don’t know of any significant die-off event due to larch beetles here, I would not be surprised to hear at some point that insects are having a greater impact on tree mortality than they did in years past.

Managing a healthy forest is more complex than some might think. Active management and forward thinking are crucial to ensuring we keep the tamarack and other at-risk tree species as a part of our northern landscape.

Striving to make new things familiar and familiar things new, this is the Masked Biologist coming to you from the heart of Wisconsin’s great Northwoods.

The above photo can be viewed online here.

Do you have a question for the Masked Biologist? Submit it below to our Curious North series and it could be featured in an upcoming commentary.

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