Thursday, August 31, 2023

Birchbank Deer Exclosure Removed After Completing Its Mission


June 2015 Birchbank Trail - a sea of invasive Japanese Knotweed
This is story about Birchbank Deer Exclosure #1, which was located near the trailhead parking area off Indian Well Road. A deer exclosure is a fence designed to keep deer out (an enclosure would keep them in). Back in 2015, a vast sea of invasive Japanese Knotweed would block the hiking trail each summer until crews could get to it with a brush cutter. The Knotweed patch was 250 to 300 feet long and maybe 100 feet wide. With help from a summer intern, the Knotweed was cut back repeatedly all summer. 

June 2015 - The knotweed is cut repeatedly all summer
Later in the summer, we decided to install two deer exclosures along the trail to see what impacts the deer might be having on the native vegetation.  The first exclosure was placed right on the edge of where the Knotweed had been growing, at the toe of the river slope. The second was further down the trail, beyond where the Knotweed had been growing, but both exclosures were in areas that had blankets of Dutchman's Breeches and Red Trillium every April. 

August 2015 - Deer Exclosure #1 to the left of the trail

Upon identifying some of the unusual plants and looking at the geology, it became apparent that this spot was a "Rich Mesic" forest with unusual growing conditions for our area. There is a lime seam in the bedrock, sandy, well-drained subsoil with rich topsoil, and water seeping out of the 350-foot slope. Bladdernut is a shrub that only grows under these conditions. Over the next few years, the shrub began to thrive within the exclosure. But as soon as a portion of the shrub grew through the fencing, it would be nipped off. Turns out that Bladdernut is a deer favorite.

June 2017 - lots more growth inside the deer exclosure

Over the next few years, the battle with Japanese Knotweed continued with lots of digging and pulling. The plants within the deer exclosure grew quickly. Red Trillium plants grew larger each year, blooming and setting seeds, as did the Dutchman's Breeches. Outside the fencing, these plants became more stunted each year, failing to set seeds as deer nipped off their blooms. The annual wildflower hike was even canceled because the vast blankets of blooming Dutchman's Breeches carpeting the forest floor were a no-show. But inside the deer fencing, the Breeches were blooming fine.

June 2022, second year of using deer repellent
Outside the deer fencing, invasive plants quickly overtook the area where Knotweed had been removed. Mugwort, Garlic Mustard, and Japanese Stiltgrass were impossible to keep up with, and the Japanese Knotweed continued to resprout. In 2021, after six years of this losing battle, it was noted that there were no invasive plants inside the deer fencing. The lush native plants were outcompeting the invasive plants. A decision was made to start spraying deer repellent throughout the area where the Japanese Knotweed has been, and to transplant a few vigorous native species where mugwort was a problem. The invasive plants continued to be removed, while the deer repellent gave protection to the native plants. 

August 2023 after removing the deer fencing
After a few years of using deer repellent, the deer exclosure became surrounded by lush native plants.  Goldenrod, asters, grasses, Jewelweed, Horsebalm, Clearweed, and others took over.  In August of 2023, with a large dead ash hung up and ready to crash through the exclosure at any time, it was time to remove the deer fencing. 

The deer exclosure had served its purpose. It not only demonstrated the degree to which an excessive deer population was damaging our native plants, but showed also how the lack of competition from native plants then created an opportunity for invasive species to take over. 

The second exclosure remains in place. It's located in an area that is shadier and not so lush, and to the untrained eye it might not look much different inside the fence than outside. However, if you look closure, you'll see that the wildflower plants like Trillium and False Solomon Seal inside are larger, bloom successfully, and set seeds, while the ones outside do not. 

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