Good Fences Make Good Natives

Puddock Hill Journal #8: Deer Fences and Consequences

A couple months ago, I came across an article published by the Yale School of the Environment on “How the Boom in Fences Is Harming Wildlife.” While the article focused mostly on expansive fences disrupting large landscapes such as the desert at our southern border, the Mongolian steppes, and the Greater Mara region of East Africa, it struck home because we installed a deer fence two autumns ago around most of our property.

The Yale article references a 2020 study that found both expected and unexpected effects of fencing, from disrupted migration of large mammals such as wildebeests and mule deer to the conclusion that fences lead to decreased insect abundance.

That impact on insects caught me by surprise. It turns out fences create more places for spiders to build their webs, and more webs means fewer flying insects. Another, perhaps more predicable, impact involves increased disease transmission resulting from “concentrating animals more closely together than they might be in the wild.” As usual, beware unintended consequences.

When Robert Frost, in his poem “Mending Wall,” famously wrote that “Good fences make good neighbors,” he had in mind people neighbors, of course, but the narrator also teasingly wonders:

Before I built a wall I'd ask to know
What I was walling in or walling out,
And to whom I was like to give offense.

This is profound. Fences may or may not please the neighbors, but their greatest offense is against that which they fence in or fence out, and these are likely creatures who have their own sense of territorial ownership.

That is one of the reasons we agonized before erecting our deer fence. We also wondered whether the fence would be too ugly. And we fretted the expense.

But in the fence’s favor weighed the negative impact of deer on the native plants we wanted to cultivate.

For more than a decade, we watched with trepidation as the local herd of about fifteen deer daily worked its way from west to east across our landscape in the morning and from east to west every evening. Along their journey, destruction ensued: They devastated non-native hostas planted right beside the house; they imposed a five-foot browse line on trees and older shrubs; and bucks deformed the trunks of young trees when rubbing their antlers.

While we had some success planting larger trees with branches beyond the deers’ reach and wrapping wire mesh around tree trunks to discourage rubbing, we also experienced deer pushing down light fencing around shrubs to get at their morsels. They completely destroyed several witch hazels in this manner.

It’s worth noting that there are more white-tailed deer (Odocoileus virginianus) in the northeast than there were when the colonists arrived. There are several reasons for that. In the suburbs and exurbs we have eliminated natural predators, but as significantly we have created a landscape that is conducive to their eating and breeding habits—woodlots where they hide that transition to open spaces for browsing, which yield to the accidental smorgasbord presented by ambitious gardeners.

We came to the reluctant conclusion that in order to plant for the birds and other critters, not to mention for ourselves, we would have to bar the deer that would otherwise eat us out of house and home.

In doing so, we faced several decisions. First, should we fence off every inch? We decided not to—not quite—in order to leave a corridor for the herd to continue moving through in their usual pattern (almost!) without being forced into the road.

Second, what kind of posts to use? In areas where the fence builders (a hard-working Amish crew) could not get a big enough machine to drive piles, we had to resort to coated steel posts. But where we wanted to use wood posts we had to choose between treated and untreated. As readers of this newsletter know, I try hard not to put chemicals into the environment, so I shy away from pressure-treated lumber, but a back-of-the-envelope analysis led me to conclude that the environmental impact of more often having to replace untreated posts would exceed the impact of longer-lasting pressure-treated posts.

Third, how tall should the fence be? Here we had to weigh the effectiveness of the fence against its obtrusiveness to the eye. We settled on about seven and a half feet, which consists of six feet of fencing plus a six-inch gap below, protected with two high-tension wires, plus two more high-tension wires extending about a foot above.

Finally, what kind of mesh should we choose? This is perhaps the most important decision regarding other wildlife that could be inadvertently impacted—for example, foxes, possums, turtles, and rabbits. We decided upon metal wire fencing with six-inch-square gaps.

Here’s the finished product in its most obvious spot, but in real life the eye tends to be drawn away from the fence posts, and the mesh virtually disappears.

As an aside, there seems to be a trend lately of people deploying, on the perimeter of their property, the kind of fencing that was made to keep “pests” such as rabbits out of small gardens. The holes in this mesh can be so small that it is highly disruptive to wildlife such as those critters mentioned above. Please don’t do this. Habitat fragmentation is habitat destruction.

To return to our fence… We began with a six-inch gap underneath in order to make it easy to string trim and prevent invasive vines from grabbing hold, as well as to facilitate the movement of non-deer critters. Unfortunately, we soon learned that small deer can splay their legs and work their way through that six-inch gap with remarkable agility. That’s how we ended up with the wires underneath, but we dug narrow swales in a few places for larger foxes and opossums to find.

I can’t emphasize enough that we do not want to create the unintended consequence of barring foxes and opossums. While red foxes are not native, they have completely supplanted the native gray fox in these parts, and they fill an important ecosystem niche, keeping wild rabbit, groundhog, and rodent populations under control. Similarly, the Virginia opossum (Didelphis virginiana) checks insects.

The impact of our deer fence on native plant populations has gone beyond our greatest expectations. We anticipated protecting native plants that we would introduce to the landscape after a long absence, and we have accomplished that so far. What we had not deeply considered was how well—and how quickly—existing natives would recover from deer browse when given the chance.

I’ll talk about many of these plants in future posts. One to note briefly here is the native sassafras tree (Sassafras albidum). This is a first succession tree; that is, it is among the first to populate open space such as an abandoned field or a forest leveled by fire. Before we installed our deer fence, we had only seen them growing very close to the driveway and road, but after less than a year of deer banishment, more than two dozen sassafras saplings have sprung up on the property.

Here’s one just in its second spring, already about seven feet tall:

Where were they before? Eaten down to the ground by deer before we set eyes on them.

It’s a shame we have so disrupted the balance of nature that we require fencing to rectify things, but in our current reality, good deer fences make good natives!

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This old native azalea has an umbrella shape due to deer browse. The spring after our fence went up, it had already begun to grow bushier, but an over-ambitious garden helper took his pruner to it. By next year, we expect a more natural look. See the green growth by the base?

Here is the same azalea up close in peak bloom:

This tuliptree flower fell to the ground. Pictured on top of a chest:

Strict blue-eyed grass (Sysyrinchium montanum) grows near the deer fence in the small pond field:

In other news, the eggs in the fountain pool are now tadpoles. Here’s a small sampling (sorry for the glare):

Do you know a gardener or environmentalist who wants to change the world? Gift away!