Saturday, February 6, 2010

Oak Savannah, St. Michael's Preserve

Imagine your favorite open-grown white oak, long branches meandering towards ground and sky in equal measure. Now, imagine a dozen versions of it scattered within five acres or so. Between them, open glades. On the ground, picture a collage of mosses, native grasses, and annual wildflowers.

Now pepper in a few enormous chestnut oaks, several stands of shagbark hickories, widely branched in the abundant sunshine. Of native shrubs and small trees, distribute witch hazel, hophornbeam saplings, enormous serviceberries, lowbush blueberry, huckleberries, and others in little stands, throughout.

We stumbled upon this fantastic oak savannah while exploring St. Michael's, the new 337 acre preserve in Hopewell, NJ. It is on a gentle slope leading to short shale bluffs over the Bedens Brook. This small area seems like it is partially the result of human management (or mismanagement), perhaps 100 or more years ago. However, unlike almost any other place in our area, after being (presumably) opened by tree-cutting and possibly grazing, it has subsequently remained open and hardly succeeded at all. Of late, deer seem to be limiting tree recruitment. But, more importantly, the soil seems so thin, dry, acidic or poor (or all of the above) that mosses are still the dominant vegetation in many places.

 Shagbark hickories
How to reconcile the poverty of soil and the arrested forest succession with the presence of the enormous oaks I am unsure - this type of ecology is relatively unfamiliar to me, and reminds me most of the dry ridgetop forests of the highlands, Catskills, and the barrens of Maine. Are the oaks sited in the richest soil, are they just very old, or are they better able to eke out fertility from these barren soils than I'd assume? Maybe they are dipping their feet into the Bedens Brook and the small intermittent rills which grid off the savannah into half-acre segments?

I'm really excited to see this place in spring, summer and fall and find out what else grows here. For now, here are some photographs and field notes, some of them conjecture.

 Two native annuals - blue curls and American pennyroyal. Thanks to Rachel for finding the former in Lauren Brown's Weeds In Winter while I futzed with my photos. The latter has a great minty smell.

The glades seem to have had woody vegetation removed erratically, probably by hunters maintaining them. Great mosses!

 Native grasses like this little bluestem grew in clumps here and there.

 This glade had a lot of little bluestem.

Shale outcropping at the edge of the Bedens Brook

An extremely old, gnarled Amelanchier. The main stem was hollow and full of holes, and the bark was no longer smooth but furrowed in deep ridges.

 Enigmatic debris from collapsing huntstand

I'm not sure whose feather this was, it was one of three interesting feathers I found in the oak savannah. The first day I visited, we saw a cooper's hawk circling overhead. It seems like a great place for turkeys and owls too.

Maybe in the summer I'll find this plant and be able to identify it. Its dried stems were abundant in several places.

In the woods adjacent to the glades were a number of interesting old trees, including this hop hornbeam with a "window."



Red cedars were peppered throughout. This one, and several others, appear to have died young– maybe from the droughtiness of the soil?



At first I assumed that there were many browsed flowering dogwoods in the shade of other trees. One had so many suckers at 12" to 18" high that it caught my eye. There was no cut main stem, just all of these short stems. On the ground, the stems turned and rhizome-like, rooting at the nodes. Maybe this is Cornus rugosa, roundleaf dogwood? If so, it will be the first time I've met it.

This little azalea caught my eye as I was leaving from my second visit to the savannah. It was cowering next to a stand of huckleberries at the top of a 20 foot high shale bluff over the brook. It was browsed by deer, but did have two flowerbuds. I'm assuming it is pinxter azalea, but I'll check on it in early May to be sure. Nearby it was a very enigmatic blueberry, too tall to be lowbush (even pallidum), but growing on a very dry outcropping over the brook, and branching like mad.



Ancient Oak.

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