Dr. Craig Harper and his students at the University of Tennessee seem to love fact-checking untested but long-held assumptions about deer habitat. Their scientific work confirmed some popular theories and crushed many others. The latest lore on trial: whether hinge-cut bedding blocks attract significant use by deer.
Had they known of this latest experiment, many a hinge-cutting promoter might have been nervously awaiting results. The University of Tennessee has previously discredited a lot of habitat doctrine. We now know fertilizing mature oak trees has no benefit for acorn production. Mowing clover does not make it more productive or nutritious. Frost does not significantly change the sugars in brassicas.
This time, hinge-cutting fans can rest easy. The technique can remain in your toolbox, unlike clover-mowing and oak-fertilizing. Craig’s master’s degree candidate Thomas Rovery presented surprising preliminary findings on February 18 at the Southeast Deer Study Group Meeting. Before I share those results, it’s important for you to know the experimental design and the methods used.
The Hinge-Cut Study Design
Earlier students of Craig’s helped design and select sites for this experiment, and it was already underway in winter 2023 when Thomas earned a spot as Craig’s latest master’s student.
“My first interview with Dr. Harper was in the field, hinge-cutting one of the treatment areas,” said Thomas. “So he was carrying a chainsaw the whole time, and I was trying to make a good impression.”
Three states hosted study sites: Mississippi, Pennsylvania and Tennessee. At each site, researchers chose a 10-acre block of hardwoods. They treated half the block with hinge-cutting and Forest Stand Improvement. The other 5 acres would remain unmanaged, serving as the “control” of the experiment for later comparison.
“We were looking for areas that were open but being used by deer,” said Thomas. “We selected areas that had enough mid-story stems that were less than 10 inches DBH (diameter at breast height) to hinge-cut and reduce visibility in the stand. And we wanted to make sure the two 5-acre areas would be similar before we created the bedding block.”
Next, they divided each half of the study site into quadrants and placed a trail-camera at the center of each quadrant – eight cameras at each of the three study sites. The cameras operated throughout 2022 to collect pre-treatment deer activity levels while researchers collected vegetation data. In winter 2023, they filled squirt bottles with Craig Harper Cocktail and cranked their chainsaws.
The Bedding-Block Method
“People believe that hinge-cutting works. They use it all the time,” said Thomas. “But Dr. Harper wanted to create a reliable method to test and see if you could increase deer use.”
To ensure similar treatments in all three states, the bedding-block designs followed the same recipe. In the treatment areas, researchers hinge-cut every mid-story tree under 10 inches DBH. They chose species that can hinge without breaking and that would be likely to continue to live, including hickories, red maples, hackberry, American beech, sweetgum and even some oaks. They hinged the trees about 4½ feet above the ground by cutting about 60% through the trunk and directing them down with a push-pole. The use of a push-pole, said Craig, is critical to lean the tree while cutting through as little of the stem as possible, which increases odds of survival.
“You put one tree down, and then you can back up 5 or 10 yards and start hinge-cutting around that point, laying additional trees on top of the first tree you felled, so they are resting on the hinge or the trunk of the first tree you cut,” said Thomas. “As you start moving on to additional trees, you can repeatedly lay trees on top of each other and on the hinges you created. However, you need to create open trails to allow deer to move through the bedding block.”
Hinging the trees about 4½ feet high creates a visual barrier at a deer’s eye level, but the hinged trees are high enough that deer can walk under them. The method is not random like a tornado, and the open paths and trails throughout the block are important, said Thomas.
But wait, there’s an important second part to the method: girdle-and-spray. Researchers selectively killed mature trees of undesirable species greater than 10 inches DBH with girdle-and-spray herbicide injection to increase sunlight into the bedding block. Sunlight drives the response of the understory that provides forage and cover and increases the survival rate of hinge-cut trees.
“We were shooting for at least 50% sunlight,” said Thomas. “We girdled species that do not provide hard or soft mast for deer. We also felled some trees that were selected browse species, such as elms, blackgum, and hackberry, without spraying the stump to allow them to sprout.”
It takes a significantly open forest canopy to allow at least 50% sunlight to the understory. So, the study method is not just testing hinge-cutting. It’s testing it in combination with Forest Stand Improvement. If you hinge-cut smaller mid-story trees without admitting sunlight, you aren’t creating the same type of bedding block and likely won’t get the same results.
“I want to point out that this method does not degrade forest stand quality,” said Dr. Craig Harper. “High-value trees for deer are left standing while undesirable species or desirable species with poor form are hinged, cut, or killed.”
With treatments installed on all three study sites, researchers kept the trail-cameras running for the remainder of 2023, including fawning and hunting seasons.
Deer Response, and Predators Too
Thomas tracked deer use of the sites by calculating “average daily detections” of deer by the cameras. He didn’t have to wait long to see a change. In January 2023, the last month before hinge-cutting took place, cameras in the treatment units averaged 1.4 daily detections of deer. The first month after treatment, daily detections leaped to 7.5, a 435% increase.
Across the entire study period through December 2023, average daily detections jumped from 5.1 to 9.0 in the treated bedding blocks, an increase of 76% compared to the year before treatment. Interestingly, detections dropped 12% in the control areas, from 6.8 to 6.0. Not only were the bedding blocks more attractive, they seemed to pull normal use away from the surrounding forest.
Two shorter periods saw notable increases in use compared to other months. In fawning season from May to July, average daily detections exploded by 146% in the bedding blocks while they fell 6% in the unmanaged forest. In hunting season, activity climbed 78% in the bedding blocks while falling a significant 24% next door.
That’s not all of the good news. Predator detections fell 41% in the bedding blocks! Anyone who has ever hinge-cut trees for deer knew this study would probably find positive results for deer, but I did not expect the predator effect. This mostly involved coyotes, as few bobcats were caught on camera at any study site. Coyotes generally move swiftly through open areas, hunting both visually and using scent. It may be that their hunting efficiency is greater when they cover more ground faster, so they don’t prefer to meander through hinge-cut bedding blocks. Whatever the explanation, it’s a positive finding since does and fawns preferred the bedding blocks to open woods.
Creating and Maintaining Your Own Bedding Block
If you want to replicate this success in your own bedding blocks, Thomas said the combination of hinge-cutting and canopy reduction is the key. He found 72% of the hinge-cut trees survived the first year.
“I think the most important thing is the combination of hinge-cutting and girdling, because sunlight is what is causing the understory growth and causing the hinge-cut trees to continue to live,” he said. “The hinge-cut trees remain alive, and vegetation underneath and around them is growing. It’s likely if we didn’t have that sunlight, fewer trees would have survived treatment.”
As for size, Thomas said the 5-acre bedding blocks obviously worked well. But if you aren’t sure you have the right area to create a bedding block of that size, he said smaller bedding blocks would attract deer but not as many as a larger block. “The more acreage, it’s likely the more deer use you’ll see,” he said. “It doesn’t take long. A team of three people can create a 5-acre hinge-cut bedding block in a day.”
Finally, Thomas recommends you visit bedding blocks at least every two years to evaluate and maintain. If hinged trees have died, you can rebuild the structures by hinging additional trees. You also may need to girdle more overstory trees if sunlight is limiting survival of the hinged trees.
This study isn’t finished. Cameras are still running, and this year Craig Harper’s students will work on identifying and measuring forage and cover species growing in the bedding blocks. There’s more to learn, but you don’t have to wait for an update to create your own bedding block now using the University of Tennessee model.
