A Pleasant Surprise in the Walnut Woods

Puddock Hill Journal #66: Native white avens makes its statement.

Jul 12, 2024

I recently undertook a cursory examination of a part of Puddock Hill that I rarely mention, the black walnut woods, and saw something astonishing.

When I refer to this area—about half an acre—as “the walnut woods,” I am probably being overly grand. It is simply a collection of fewer than fifty mature walnut trees just northwest of the barn. But it’s bigger than a copse, and I have little doubt that these native Eastern black walnut trees (Juglans nigra) settled in this place naturally.

Let me give you a better picture. To the west lies the fenced property line, which once opened to corn and hay fields that were part of the property when it was a farm. Before we bought the original house that once went with the larger property (before being subdivided, it had been 100 acres), that area became the dedicated open space of a neighboring housing development, constructed on a majority of the former acreage.

A long time ago, on the south and east perimeter of the walnut woods, someone planted several stately Chinese chestnut trees, a large flowering shrub, native to the Mediterranean, called a chaste tree (Vitex agnus-castus), and a number of American holly trees, several of which have died on my watch and been left to decay in place. The preponderance of trees in this area, however, are black walnuts.

In order to help screen out the neighbors, over time we planted a few tall evergreens in the corner, a line of bottlebrush buckeyes to the west along the post-and-board fence we erected, and a few redbuds to the east. Despite claims that black walnuts inhibit the growth of many other plants, all of these introductions have performed well.

So have certain invasive plants under the trees, in particular garlic mustard, multiflora rose, and—on a nearby brush pile—mile-a-minute vine.

Having moved to the Brandywine Valley of Pennsylvania from New York’s Hudson Valley, I have continually been surprised and, to be honest, a bit distressed to find that much of the forest in these parts has a paucity of leaf litter and a great deal of herbaceous vegetation.

The frequency of herbaceous plants might derive from heavy deer pressure, which has devastated the shrub layer and understory trees, reducing shade, but the same should apply where we once lived in New York, and one does not look into a forest there and see a sea of green. I don’t know what to make of the lack of leaf litter—voracious worms? Characteristics of the soil might also be a factor, or the mix of trees in the canopy. In fact, a lot of light seems to reach the floor of the walnut woods at Puddock Hill. In any case, I don’t have a definitive explanation for these phenomena in the region as a whole. It also could be the opposite of a problem; it could be that the soil is just particularly fertile here for everything—trees, herbaceous natives, and invasive plants alike.

To manage invasives, for a number of years we would brush hog the walnut woods annually, but I leave fallen branches to replenish the soil and promote woodsiness, so brush hogging became more difficult over time. Also, we had transplanted several volunteer walnut saplings from other parts of the property and needed to give them a chance to show themselves. And perhaps other volunteers would rise just where we needed them, replenishing the woods. Therefore, instead of brush hogging, we transitioned to selective string trimming—more like random string trimming, to be honest.

Because while all of this may seem like a lot of fussing, the main strategy in the walnut woods over the past few years has mostly amounted to benign neglect.

In short, I don’t spend a lot of time in there, but a couple weeks ago, when we were over by the brush pile after an afternoon weeding, I did a double-take when I peered into the woods. Instead of the invasive plants I’d expected to find (and soon admonish myself about), I found a carpet of native white avens (Geum canadense) with few interlopers about.

This time of year, when it’s in bloom, much white avens reveals itself around the property in dribs and drabs (I’ve shared pictures of it in this newsletter), but I’d never noticed it in this density:

Here’s a close-up of one plant with its whorling seed heads:

This pleasant surprise caused me to educate myself a bit better about white avens, which is present in 39 U.S. states and four Canadian provinces. From a good write-up on the Illinois Wildflower website I learned that the “root system consists of a taproot and rhizomes; from the latter, vegetative offsets can be produced. This plant occasionally forms loose colonies.” Aha! Furthermore, the website notes that white avens is known to tolerate the phytotoxic chemicals present in the fallen leaves and roots of black walnut!

The Lady Bird Johnson Wildflower Center seems to think that white avens can be mowed as a low ground cover. I couldn’t say (although maybe the brush hogging we used to do contributed to its vigor). Here the plants are growing 1 ¹/₂ to 2 ¹/₂ feet tall in a forest of 80-foot trees.

White avens is not a superstar when it comes to supporting native wildlife, but it certainly provides more services than the invasives it seems to be outcompeting in parts of our walnut woods. From Illinois Wildflower:

The flowers attract various insects, including bees, wasps, flies, and beetles. These insects suck nectar; some bees also collect pollen, while Syrphid flies often feed on the pollen. Insects that feed on the foliage of White Avens and other Aven species (Geum spp.) consist primarily of aphids, including Acyrthosiphon pseudodirhodum, Amphorophora rossi (White Avens is the preferred host plant), Macrosiphum gei, Macrosiphum pallidum, and Macrosiphon pseudorosae. In addition, the larvae of a moth, Tinagma obscurofasciella, mine the leaves.

Before you get your rose hips out of joint, remember that the aphids cited above are native to North America. As such, they have their own role to play in our ecology.

Of course, I still see bad guys growing in the walnut woods. When I went out to snap the above pictures, I had a clipper in hand and used it to beat back a few canes of multiflora rose, as well as some dreaded porcelain berry.

But this is a story of a native plant holding its own and even thriving in the face of competition. If you learn to identify white avens and choose to leave it alone, it may thrive for you, too.

A fallen sassafras leaf glows on the ground in the east woods: