When one looks at the ecosystem of northern Michigan (along with the northern tier of US states and most of Canada), there is an unusual feature – on top of there being relatively few species compared to further south, there is a distinct lack of endemic species (species that live here and nowhere else). Practically everything that lives in this region belongs to widespread species with ranges that extend considerably south of here. This is in contrast to places like Florida, which has tens of thousands of species of invertebrates, and at least 1500 of them are considered endemic to Florida.

So why is that? Well, we can sum it up in one word: Glaciers.

(The Rise and Fall of the Great Lakes)

For the last 2.4 million years or so, the average condition of what is now Michigan and the Great Lakes was “Buried under about a mile of ice”. It wasn’t until about 10,000 years ago that the glaciers started melting back, and up until maybe 8000 years ago the Upper Peninsula was mostly either still under ice, or flooded by backed-up glacial melt.

On the scale of a human lifetime 8000 years seems like a long time[1], but on the scale of the time it takes for animals and plants to evolve into new species, it is the merest blink of an eye.

The terrain in northern Michigan and surrounding areas got pretty badly mauled by the glaciers, shoving and gouging and lifting and redepositing everything while they advanced, and then massively flooding everything when they finally melted. This left some pretty characteristic landforms that you only get as a result of glaciation [2], and once the glaciers melted the land was essentially sterile expanses of rounded rocks, gravel, sand, and mud. With big rocks scattered about at random, miles and miles away from their original source and nothing remaining to show how they got there. 

Which means that, relatively recently, there was nothing living here large enough to be visible to the naked eye, and the entire ecosystem had to be reconstituted from scratch. As the glaciers retreated, the organisms living in the land just south of  the maximum extent of the ice followed them back. However, they did not follow them back at a uniform rate. The first plants to colonize would be the ones with spores that can be easily carried by the wind like horsetails, ferns, club mosses, actual moss, and lichens, all of which are very plentiful here. These were accompanied by plants with parachute seeds (willows, poplars, cottonwoods, cattails, etc.) and winged seeds (maples, birch, pines, spruces, basswood and the like). And these are in fact still the dominant plants in the area. 

A bit slower are the ones whose seeds are carried by animals (burrs, nuts that get stashed and buried by squirrels, and seeds that pass through bird and mammal digestive tracts). These have to wait until there is enough vegetation in the area to attract animals, but once there, they spread seeds very effectively. And so we have oaks too, along with a lot of burr-bearing plants and small fruits like blueberries, wild strawberries, and blackberries.

And as far as the animal life goes (particularly insects) the ones that came back fastest were the ones that (a) could eat the early-colonizing plants, and (b) had wings so that they could fly into the area quickly. We therefore have the full complement of flies, bees/wasps, moths/butterflies, and beetles. Ants arrived as well, particularly the ant species where the new queens have wings and so can fly away from the parent nest to establish a new colony. 

This process never got completed on its own. In particular, earthworms and wingless arthropods (walking sticks, woodlice, pillbugs, and earwigs) didn’t have the capability to walk here on their own in the time available. So, when people arrived from Europe and started keeping records, the ecosystem that they encountered was not yet really at a steady state. So, when they started bringing in new species (either accidentally or on purpose), the ecosystem still had many vacant niches that they could move into.

There are a lot of new species that have made it up here to the Keweenaw Peninsula just in the 40 or so years that I have lived here. I have watched woodlice, pillbugs, two species of ticks, several species of weevils, snailcase bagworms, asian lady beetles, gypsy moths, and dozens of other new organisms all go through a similar cycle:

1. A few individuals reach the area, and manage to find an ecological niche that lets them survive through the winter.
2. They reproduce freely, without any local predators, parasites, or diseases.
3. There is a massive population explosion, and they get so plentiful that everyone notices, and in some cases panics, about them. 
4. After a variable amount of time (sometimes only a year or two, sometimes over a decade) something happens to knock back their population. This might be a local predator that develops a taste for them, or a disease or parasite that either was already present and jumped to a new host, or followed them from wherever they originally came from. 
5. Their population crashes. Sometimes this is a hard crash, going to practically nothing (like the snailcase bagworms, that I haven’t seen again after their big boom in 2008). Other times, they just drop back to populations comparable to the species that have been here longer, like what happened with earwigs and european paper wasps. 
6. Sometimes there are a series of boom-and-bust cycles before things steady down, but eventually they are no longer a particularly notable species and just kind of merge into the background. 

Now, sometimes they can be a real issue during the population explosion stage, particularly if they focus on a particular local food species. For example, the emerald ash borers spread a disease to the ash trees, and there is a good chance that they will drive the ash trees locally extinct before the beetle population crashes. But overall, I think that our big issue is just that our ecosystem never had a chance to be stable, and we are going to get these fluctuations and invasions over and over and over again until the number of species builds up to the point that the local niches are filled, and new invading species have a hard time getting a toehold. 

And, basically, I feel that we don’t have “native” versus “invasive” species up here. Instead, we have the early invaders that have gotten a head start, and the later invaders that are still trying to catch up. 

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[1] Even compared to a human lifespan, it isn’t that long, not really. There have always been people who lived for over 80 years, and so 8000 years could be covered by only 100 human lifespans. And considering that written records were starting to be kept by the Egyptians and the Sumerians almost 6000 years ago, it is almost recent enough for there to be written records of the melting of the ice!

[2] For example, I think this is a Drumlin field that is about 40 miles southeast of us, just south of Mount Arvon (the highest natural point in the state of Michigan). The drumlins are all of those little hills that were left behind by the glacier scraping away everything between them. 

Here’s a bit better of an example down at the Michigan/Wisconsin border, where the teardrop shape of the drumlins shows the direction the ice sheet was travelling when it made them.

There is also a Fjord just east of Keweenaw Bay. It is that long narrow bay that goes past Skanee and the Arvon Township Park (Huron_Bay). This was formed the same way as the better-known fjords in Norway (glaciers scraping out river beds), except that this one empties into Lake Superior instead of into the ocean.

Closer to home, we live at the top of the hills overlooking the Portage, an odd waterway which goes from the northwest side of the Keweenaw Peninsula, past Houghton into Portage Lake, and then back out the other side at the Portage Entry.

I was mystified about how this formed for a long time, because it cuts completely across the Keweenaw in a direction that I wouldn’t have expected the glaciers to flow, and it isn’t really a river because it goes from Lake Superior back into Lake Superior at the same elevation. But, it looks like a valley eroded out by a pretty brisk flow of water. After reading up on the glacial history of the area, I think the Portage valley probably formed like this:

When the glacier retreated, it went back along the line of the Keweenaw, which has a significant elevation running down the middle. Between the ice and the Keweenaw ridge, this trapped water in Glacial Lake Duluth. Currently it is part of Lake Superior, but at the time Lake Duluth was draining off to the southwest, where Duluth was later built. This is fairly high ground, and so the lake was backed up to a few hundred feet deeper than it is now. Meanwhile, to the southeast of the Keweenaw, the lake level was close to where it is now because it was draining off across lower terrain across Canada. So the Keweenaw was acting as a dam holding back Glacial Lake Duluth.

Apparently, the spot next to Houghton is where the ridge was a bit lower than elsewhere, so once the retreating glacier exposed it, that was where Glacial Lake Duluth overtopped the natural dam. And once it overtopped, the resulting fast-flowing river had a few hundred feet of drop, and turned into a raging torrent that quickly scoured out the Portage valley as Lake Duluth drained.

Then, once the ice finished melting and both ends of the Portage were at the same elevation, the water mostly stopped flowing. This left a slow, kind of boggy waterway that provided an easy way to canoe from one side of the Keweenaw to the other, with just some swampy areas where they had to “portage” the canoes. When the copper mining got going up here, they dredged the whole thing back out to make it into a navigable canal, and now here we are: with a landform that looks like a river, but no longer has an obvious way for it to have formed.