Saturday, November 29, 2008

The Brown Season: November in the Arb

The Carleton arboretum was raucous with crows but otherwise peaceful in the early afternoon on this partly cloudy but relatively mild November day. The crows were congregating near the river. Several flew from the far side of the river to treetops above us as we walked. I happened to catch one just about to land on a branch in the shot below. As the path we were following curved away from the river, we left their constant cawing behind us.

While the sky was mostly blue overhead and to the north, looking south toward Carleton's Skinner Chapel (visible in the photo below) there was quite an accumulation of pearl gray cloud. With the sun quite low in the southern sky three weeks from the winter solstice, even when we had clear sky above us we were never in direct sun.

A burst milkweed pod displayed its silky contents as we approached the savanna restoration area.
The sign below describes the oak savanna ecosystem that was prevalent in the area until settlers interfered with the normal pattern of natural burning that is necessary to keep the floor of the savanna clear. Invasive, non-native buckthorn is now one of the principal plants interfering with the restoration of the savanna. (Click on the photo to read the information on savanna restoration.)

An area of restored savanna is below.

The path rejoined the river at a sharp bend; below is the view looking back to the south, with a skim of ice at the water's edge holding some of the recent snow dusting that did not last long on the ground.

Despite some light snows earlier in the month, we are still in the brown season, before the arrival of the snow cover that typically lasts two or three months or more in southern Minnesota, providing plant roots a protective mulch against the bitter subzero cold that usually visits us at some point each winter. When we first moved here in 1990, we were told that there was typically snow on the ground from Thanksgiving until March. Our winters have tended to be shorter and less snowy more recently, with white Christmases less certain.

This Thanksgiving I am thankful to live so near to places like this, where in a matter of moments town life fades away and a quiet trail beckons onward.


Jim H. said...

Why is it a good thing to restore the savanna? Just because we can? I have absolutely no reason to to oppose the restoration of the savanna, but I honestly don't see why it should be done, either. If the environment supports buckthorn, I say good for the buckthorn!

Penelope said...

Hi Jim,

Good questions, and I certainly think there's value in considering the reasons for efforts such as this.

I'm no expert, but I think a major reason would relate to preserving plant and animal biodiversity by maintaining a unique and severely dwindling ecosystem. Why preserve a greater variety of species? If for no other reason, I'd say out of a sense of humility, in the recognition that we can't know all the implications of losing species and ecosystems forever. (Though now we seem to have the prospect of cloning extinct life forms from preserved remains...) Here is an overview of savanna restoration that talks not only about species diversity but also about the systems value of different habitats as they may relate to such processes as water management and carbon retention.

The Carleton arb website mentions that the arb's restoration site is a good one because original oaks still remain on the site.

And why fight buckthorn? The Minnesota DNR says the species "aggressively invades oak forests, savannas, prairies and riparian woods, completely eliminating native plant diversity in the understory over time." That can't be good news for birds and other animals. (Not only that, but there's evidence that the berries give birds and mammals the trots.) Here's an article from the Minnesota Conservation Volunteer with reasons to control buckthorn and tips on how to go about it.

Thanks for writing... and reading!

MojoMan said...

Thanks for the interesting information on savanna restoration. I didn't read the sign yet, but I imagine it tells an interesting tale about the interaction of native Americans and their use of fire to manage the landscape.

Jim's comments reflect an attitude that is all too common. Perhaps some people know instinctively that the destruction and modification of the natural environment by modern human activity is something to be aware of and to worry about. Others just don't get it, or don't care. Maybe it's simply a matter of education, but I wonder. Maybe many people don't understand the risk of invasive species. I've been thinking about this lately in the context of cats, both pets and feral cats. Many people get all worked up about saving feral cats, or think it's cute the way Puddy catches and plays with that chipmunk. Few pause to wonder what all those cats are doing to populations of native small wildlife. It's the same with plants like buckthorn. If folks don't understand that it's a non-native invader that out-competes native plants and is eaten by wildlife that didn't evolve with it, they think it's just another tree, so what's the big deal? I suppose the same even goes for starlings and house sparrows that decimate bluebird populations. They're all birds, right? So what?

Penelope said...

MojoMan - Good to hear from you again, and thanks for some additional insights on species displacement. Some of these effects of non-native species aren't widely known, and it's not surprising that people like Jim, whom I know via the blogosphere to be a thoughtful guy, may query why we shouldn't just let nature take its course in most cases -- and in some cases we probably should, or have little choice. And we've learned over the years that sometimes our reluctance to let nature take its course (Smokey the Bear and forest-fire prevention efforts, for example) has been ecologically counterproductive. I delight in receiving comments, welcome honest questions from all perspectives, and will do my best to provide factual support for any answers I venture to offer.

Penelope said...

Here's a little more information on non-native species and why we might draw a distinction between, say, buckthorn and the ring-necked pheasant:

"Many non-native species have a positive impact on the country’s economy, such as wheat in agriculture, Sitka spruce in forestry or the pheasant in the game industry. A small minority of non-native species become invasive[;] this can be due to one or several factors including;
• the non-native species losing their natural predators, competitors, pests and diseases during translocation,
• the biology of the invasive species making them a better competitor than native species,
• the site where the species becomes invasive being disturbed (often by human activity) decreasing the population numbers of native species and giving space to new invasive species,
• the non-native species being introduced so many times that by chance it arrives in the perfect location at the correct time to become invasive.

"These factors can allow non-native species populations to increase to a level where they become invasive, affecting other species, habitats or economic interests by carrying disease, predating native species, becoming pests on economically or ecologically important species, blocking waterways or damaging built structures."

The above is from a British government site, but the principles remain the same.

marcea5 said...

Good info on buckthorn, I have one small tree in my back yard and I'm pretty sure it is a buckthorn, we mow so it's not taking over the yard.

Penelope said...

Hi Marcea -- I had some by a fence at my old house: tenacious, prickly stuff! I'd cut it back and cut it back, but I wasn't able to pull it up and it always came back. But it's not unattractive; you can see why it was something that people planted on purpose. Thanks for writing; I enjoy your blog, which I just rediscovered recently.