Monday, October 26, 2009

Belle Isle tree trip

Belle Isle is one of my favorite places to go birding, and I've promoted the value of this place in my book, A Birder's Guide to Michigan (now out of print), as well as in a recent Birders World article, Hotspots Near You, and have led many birding field trips for local Audubon chapters and conducted bird surveys here in 2005. But there's so much more to Belle Isle, and this blog entry will turn away from the birds for a moment to focus on some of the interesting plant life here, particularly the trees.

On Sunday, October 25, a field trip was scheduled for 1:00 - 3:00 p.m. by the Huron Valley Chapter of the Michigan Botanical Club, and co-sponsored by the Essex County Field Naturalists' Club, the Lakeplain Cluster of the Stewardship Network, and the Friends of Belle Isle (and possibly others). The purpose was to see some of the rare trees and shrubs on the island, and talk about ways to improve the habitat in broad ecological terms by removing invasives and enhancing the area's hydrology, and improving (or maintaining) the value to breeding and migratory birds. At least 50 people showed up (perhaps more than 60), much to our surprise!

The main leader of the trip (though several of us co-led) was Suzan Campbell, currently with the Michigan Natural Features Inventory (MNFI), and formerly a naturalist at Belle Isle. After a brief orientation at the Nature Center, we stepped outside to have a look at one of the rare trees on Belle Isle, the Pumpkin Ash (Fraxinus profunda). This is a species of the Atlantic coastal plain from Virginia to Florida, and in the Mississippi River valley. It is found only in a few small areas in southern Michigan, which is at the northernmost point of its world range, and it is a Threatened species in the state. Sadly, it is also being attacked by the Emerald Ash Borer (Agrilus planipennis).

In the photo below, Suzan explains to the group (only a few of which are in the photo) the botanical history of the Pumpkin Ash and shows the identification features on a sapling that was planted here maybe 7-8 years ago.

Ash trees have compound leaves, and identification of the various species can be tricky. Pumpkin Ash can be identified by the larger spaces between the pairs of leaflets, giving the tree a more airy appearance than other ashes. This is seen well in the photo below.

We then drove around to the other end of the ~350 acre patch of old-growth swamp woods to a trail where we spent the rest of the afternoon. One of the first patches of Pumpkin Ash we came to was, sadly, a small grove that had all been recently killed by Emerald Ash Borers.

Upon closer inspection we were able to see the numerous, characteristically D-shaped exit holes where the adults emerged after feeding on the tree as larvae.

But we did see some Pumpkin Ashes that were still alive, or struggling to survive. The most interesting was the State Champion (largest in Michigan) individual that Nancy is touching below.

I married a tree-hugger, and I'm proud of her! She would have hugged this one except that there were a couple of Poison Ivy vines climbing the trunk.

The dark bunches in the photo below are the dried flowers from earlier in the year. This champion individual is a male tree. Some trees have separate male and female individuals, making cross-pollination a bit more challenging. Also, there seems to be a shortage of female Pumpkin Ash trees on Belle Isle; yet one more hurdle to their survival in Michigan.

Another ash, though not actually in the ash family, was the Prickly Ash (Zanthoxylum americanum), which had beautiful yellow leaves hiding an abundance of sharp thorns.

We also enjoyed the fall color along the walk, and there were certainly several other species of oak, as well as the maples below.

Even the common Poison Ivy (Rhus radicans) in the photo below provided nice color, as well as an educational opportunity for many of the trip participants!

Unfortunately there were numerous invasive species seen, including at least two species of Asian honeysuckle (Lonicera maacki, Lonicera tatarica). One of the worst invasives in the state, though not as much a problem on Belle Isle, is the Japanese Knotweed (Polygonum cuspidatum), which can get quite shrubby but here seems to stay mostly low and herbaceous.

A species I was hoping to see, as it was a "lifer" plant, was the Wahoo (Euonymus atropurpurea), also called Burning-bush in some references; a rare plant in Michigan and one of only two native species in this genus (others are escaped from cultivation). None of them had any leaves on them this time of year, but I doubt I'd be able to recognize it by those anyway as the leaves (a few of which were on the ground) looked a lot like ash tree leaves! Luckily, Suzan and some of the other trip leaders had gone around and put signs on them!

But once we got closer we saw the odd berries that are very distinctive, and beautiful.

Another rare tree in Michigan, found at Belle Isle, is the Shumard Oak (Quercus shumardii). This oak is fairly common in the south, from Texas to Florida north to Missouri and Indiana.

It grows on the edges of swamps, and at Belle Isle it grows on hummocks in the swamp woods and is at the northernmost end of its world range. Identifying any tree can be tricky, and oaks are no different. The shape of the leaves put in field guides are often an "average", and on an actual tree the leaves at the bottom are often different from those at the top. In the two photos below, leaves from the bottom and near the top of the same Shumard Oak show these differences.

From one of the bridges over the stream and against the blue sky, we could see a very tall, stately Shumard Oak turning orange with the season. Suzan told us that it was the largest Shumard Oak on Belle Isle, and apparently a state champion as well.

So, of course we had to walk over to get close to, and touch this impressive tree. Many of the trees in this swamp woods on Belle Isle develop "buttressed" roots, which is a broadening of the trunk which allows them to gain a more firm footing in the wetlands (and clay soil here), much like trees in southern swamps do.

All of these trees can, of course, also be identified by their bark patterns by experts.

But we'll have to leave that lesson for another field trip, on another day.

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