Category: Ecology

During the past year or so I’ve talked with a number of botanists, ecologists, ornithologists, and wildlife biologists to learn how overabundant deer affect the forest ecosystem.  I’ve also talked with foresters.  True, their goals are different from those of botanists or ecologists, and their solutions may not always fit a less managed, industrial forest.  That passage of Deerland, in fact, makes a nice transition as I move from ecological to agricultural impacts.

But just like botanists, foresters are learning about deer impacts through careful study and analysis.  The difference is that their experimental plots are a bit larger, they can’t build an exclosure big enough to exclude deer from an entire forest, and their paychecks depend on their ability to defeat deer.  When deer, for example, move into a recently harvested plantation and devour every single pine seedling that’s just been planted, that’s not what foresters would call a good day at the office.

One I talked with is Craig Golembiewski, whose job is to manage 73,000 acres of county forest in northwestern Wisconsin for recreation, wildlife, and a profitable but sustainable yield of timber.  And when he uses the word sustainable, he’s doesn’t mean it in a tree-hugging kind of way.  He simply means the county is planning to sustain annual timber harvests at these same levels for at least the next century or two.

Here, however, he’s showing me what happens when ferns and sedges take over after deer have preferentially browsed everything else.  Deer don’t eat them, they get established once there’s no longer competition from other plants, and then nothing else has a chance to get started.

One solution is to “scarify” the ground before planting a new stand.  This involves using a bulldozer with a giant plow-like implement to rip a swath of two-foot furrows across the entire surface of a pine plantation that’s just been harvested. This would not be an ideal solution for most forests, and perhaps not even for the park down the street from your home in the suburbs.  Even out in a pine plantation, why resort to such extreme measures?

“Around here,” Craig told me that day, “It’s mainly Pennsylvania sedge that takes over. This stuff right here. Looks like grass, but its root system is incredible. Watch this.”  With that, he began rapidly stomping and scraping the ground with his heavy work boots.  Next, he slammed one heel into the ground as hard as he could. And again. And then the other, as hard and as fast as he could. This demented dance continued for several seconds. Even forewarned, I found it a bit alarming.

When Craig finally stopped, he’d barely made a dent. The wet ground was soft, and he’d managed to completely scrape away the above-ground portion of the sedges. But then he pointed to the thick, fibrous root mat he’d just revealed. “See that? That’s not going to let any other plant get a start. Here, we’re in a pine plantation. We can use bulldozers and scarifiers to tear all this up when we replant. But way out in the woods somewhere? If there are too many deer, then that forest is going to be changed for a long time.”

© 2012 Al Cambronne

Lately I’ve been learning a lot from botanists and ecologists about the effects of overabundant deer on the forest ecosystem.  For a different perspective, I’ve also talked with foresters.  It’s their job to grow trees for harvest, and sometimes it’s a fine line between forestry and agriculture.  But since deer enjoy browsing on seedlings and saplings, foresters and botanists have a lot in common when it comes to deer.

Last summer I spent a day out in the field with county forester Craig Golembiewski so he could show me what he’s up against.  The photo above is from just one of our many stops that day.  This tree is trying to tell us something about the recreational feeding of deer. 

Although it’s on county land, several lake homes are just over the hill.  Every winter a few of these homeowners feed the deer.  Craig explained that their feeding, probably in amounts well over Wisconsin’s two-gallon legal limit, keeps the deer concentrated in this small area all winter long.  They bed down somewhere near here, head over to the feeders every night, and then return to browse on whatever they find.  “Basically,” he told me, “they come for the corn and stay for the salad.”  Any tender green pine seedlings poking through the snow are in big trouble.  So is any tender new growth on medium-sized trees.

Craig told me the same thing happens with baiting out on public land.  Even though it only continues for a few weeks, or at most a couple months, it’s at just the wrong time of year.  In late fall and early winter, tender pine seedlings are the only tasty green browse remaining.  Deer are concentrated by the bait, and they get tired of the corn after a while.  It’s kind of like us polishing off a bag of Doritos and still craving a little salad.

It was last summer when I went out on my tour with Craig.  Later, as deer season was approaching, I had a great idea.  Clearly, this would be a perfect hunting spot.  I was certain this was a great idea.  It should have worked, but it didn’t.  Although I’m admittedly not an expert hunter, every morning I saw many fresh deer tracks revealing one more reason why my brilliant plan wasn’t working.

Deer naturally get nervous after all the shooting starts on opening morning, and as hunting pressure increases they tend to become nocturnal.  But since these deer had been visiting backyard feeders every night, they were already well on their way.  They’d eat corn at night, and then in the daytime bed down nearby in thick brush where it was hard to sneak up on them.  You might call them commuter deer.  Or maybe Dracula deer.  Anyway…  By the time I was out hunting every morning, I could tell from the tracks that these deer had just left.  They were already home in their beds.

The photo below is one I took a few days ago.  It shows a spot about forty miles from where I took the other one.  Notice the small, spindly saplings with no branches for the first four or five feet.  Umbrella trees.  Every winter they’ve been hit hard by hungry deer. 

This is a beautiful spot with lots of tall, towering pines.  But although there’s plenty of light filtering through them, there’s no understory like you’d see under similar pines only a mile away.  Nor are there many small pines getting ready to replace the tall ones.  Only these umbrella trees, which have probably taken several decades to reach this height. 

The reason?  This location is a very small deer refuge.  It’s on private land, out on a high, rocky peninsula in a neighborhood with several large lake homes.  Although snow had fallen the night before, fresh deer tracks were everywhere.  More than one set of tracks seemed to be headed to and from the back yard of a nearby home.  Commuters.

© 2012 Al Cambronne

Here in northern Wisconsin, it’s a cold, gray day in late January.  It’s time for some green leaves, blue skies, and bright sunshine.  For now, we’ll have to settle for these photos, which also happen to have great scientific value.  They’re part of an ingenious technique botanists have developed to measure canopy foliage density and leaf area indices.

Using a specialized digital camera with a ultra wide-angle lens that covers a full 180 degrees, they aim straight up from the forest floor and take hundreds of hemispheric canopy photos.  When captured on a cloudless day with bright sunlight filtering through the canopy, these photos can be quite beautiful.  But as much as one might enjoy their aesthetic value, they’re studied most closely by a piece of software that analyzes the light patterns and uses certain mathematical relationships to obtain a measure of foliage density at that particular location.  Average out the results for multiple photos, and you get a single foliage density value for each stand.

It’s just one of many tools ecologists use to measure the long-term impacts of overabundant deer on the forest ecosystem.  I recently talked with Dr. Timothy Nuttle to learn more about his latest research, which has to do with deer and birds.  “Short-term,” he told me, “we know that too many hungry deer can eliminate the habitat where ground-nesting and midstory birds eat, nest, and rest.  But here’s the question: How does herbivory by whitetails affect bird communities in the long term?  As whatever trees are left behind by deer eventually grow and mature, how do those effects extend to birds in the canopy?”

“The details are complicated,” he told me.  “But we found that one simple relationship seems key.  Both deer and caterpillars like to eat leaves from the same trees, and for the same reasons.  They’re more delicious and digestible than the leaves on other trees.  If deer eat those leaves first, before the seedling or saplings can even turn into trees, then caterpillars don’t get them.  Fewer caterpillars in the canopy, fewer birds.  So apart from deer eating the places where birds would nest and rest, the closest link between deer and birds is caterpillars.”

In one recent paper, Nuttle and his co-authors describe “a five-step trophic ricochet” that occurs in a forest with too many deer: “top-down release of ungulates has shifted forest tree communities to less palatable species that present a less dense food resource (foliage) for canopy herbivores (caterpillars) and their predators (insectivorous birds).  Furthermore, this browsing legacy persists long after ungulate density has been equalized and trees have escaped browsing by growing into the canopy.”

How long?  Decades, and in some cases even centuries.  It’s an ugly but inescapable conclusion.  Still, the photos are beautiful.

© 2012 Al Cambronne