Restoring the Witch Hazel Collection and Surrounding Hillside at Slayton Arboretum

In 2015, Hillsdale College adopted a new ten-year master plan for the Slayton Arboretum.  In the plan, one of the goals was to, “restore the historical collections of the Slayton Arboretum, including the witch hazel collection, the lilac collection, and the magnolia collection.”  Of the three collections, the witch hazel collection was chosen to concentrate on first.  The collection is located in an area that presents many opportunities for visitors and Hillsdale College students to access and learn from the restoration, as well as enjoy the new landscaping.  Concurrently, the College began offering an environmental stewardship class which included having students participate in projects at the Arboretum as part of their hands-on learning.  The initial class chose to focus on what was needed to restore the area around the witch hazel collection for their Arboretum projects.  More about the class can be found by clicking on this link.

With regards to stewardship, we use Aldo Leopold’s environmental ethic as an overarching principle to evaluate our efforts.  His ethic provides the link between what we learn as scientists and what we do as stewards to apply our scientific understandings.  Leopold states, “A thing is right when it tends to preserve the integrity, stability and beauty of the biotic community.”

Together, the two goals merge into an approach that includes restoring the witch hazel collection and the hillside community around it.  Simply stated, we seek “to create a landscape that enhances and compliments the growth of witch hazels and facilitates the long term beauty, maintenance and sustainability of the site.”

As we began to plan the restoration, we noted that the site provides several challenges:

1. Naturally thin soil due to mixing of glacial till from moraine.
2. Disturbed area due to gravel mining.
3. Sloped area prone to erosion.
4. Presence of fill material including crushed concrete and asphalt left over from heavy machinery brought in to erect telephone poles.
5. Rainwater and salty meltwater running off of adjacent service road.
6. The presence of a large number of invasive species, several of which create conditions that are detrimental to the growth of other plant species.
7. Problems with deer getting into the Arboretum and heavily browsing on the plant collections.

We developed a strategy plan to meet the challenges.  It includes:

1. Finding a reference site to serve as a role model
2. Removing and controlling invasive species (and repairing damage they have caused)
3. Mapping the restoration area and surveying existing vegetation.  Monitoring vegetation installation and health.
4. Monitoring soil health.
5. Controlling erosion.
6. Managing deer.

Our reference site

Stewardship Class on trail through Lost Nation State Game Area

Lost Nation State Game Area, located south of Hillsdale about ten miles away, provides a perfect role model for our restoration efforts at the Slayton Arboretum at Hillsdale College.  The trails around “Lake Number Eight” in the preserve have many of the same qualities of the Arboretum, including hills created by glacial till, and adjacent wetlands.  The forest community along the lake is home to many native witch hazel plants.  The relatively undisturbed character of the natural community provides us with a reference model of what an ecologically intact and stable landscape might look like.  

In our study of this reference site, we used two scientific concepts to guide our understanding.  One was the idea that certain plants naturally associate together in communities, based on common ecological needs.  Resources in these communities are partitioning into niches that the various plants fill.  These plant associations have been given the name “guild” by advocates of permaculture, a landscape design philosophy based on creating man-made environments that retain the functions of a natural community. 

The second concept we used to help us evaluate the quality of our reference site, was doing a “floristic inventory” and diversity assessment.  Based on the work of pioneering botanists Gerould Wilhelm and Floyd Swink, this method of evaluating “ecological integrity” relies on the idea that plants are excellent indicators of environmental quality since they are totally dependent for survival upon the characteristics of the environment in which they are found.  They can’t move.  So the presence of certain environmentally sensitive plants indicates a pristine environment.  Plants are given “coefficients of conservation” by knowledgeable botanists--a numerical score based on whether they are sensitive or not to environmental degradation.  The stewardship class surveyed the site near Lake Number Eight and recorded the plant species found living near witch hazels.  We used this list to develop the plant list for restoring our witch hazel area at the Arboretum, seeking to create guilds similar to the ones we found at the State Game Area.  Using the floristic inventory, we discovered that most of the plants associated with witch hazel are moderately sensitive to environmental disturbance, so recreating an environment where they can thrive is a modest and hopefully achievable goal for our restoration effort. 

What's In a Witch Hazel Guild?

Arrow-leaved Viburnum

Some of the ground cover plants associated with witch hazels include blue-stemmed goldenrod, various asters, and false solomon’s seal.  In the shrub layer of the forest, common witch hazel associates include blueberry, maple leaved and arrow leaved viburnum, small musclewood trees, wild currant, and alternate-leaved dogwood.  The forest canopy was dominated by red oaks and shagbark hickory, along with red maple and black cherry.

Invasive Species

Conservation Club Members vs Honeysuckle Shrubs

At the Slayton Arboretum, we have several “most wanted” weeds on our invasive species list.  Although there are many weeds, we are focusing on the weeds most likely to inhibit the growth of desirable plants.  These weeds include Norway maple, known for aggressively out competing other plants, Asian honeysuckles, which grow rapidly and exude chemicals into the soil which inhibit the   growth of other plants (if the thick tangle of honeysuckle shrubs wasn’t enough!), and garlic mustard, which spreads by root colonies and seeds, and also exudes toxins that inhibits the growth of other plants.  Additional problems include the prolific seedlings of smokebush and buckthorn trees.  We have ongoing help from the College’s Conservation Club and Tri Beta Biology Honor Society, who come out every fall and help us battle and remove the invasive plants on the Arboretum’s hillside.

Mapping the Restoration Site

The next step in restoring the witch hazel collection was to survey the remaining trees and shrubs on the site after the invasive species were removed.  Again, or intrepid Environmental Stewardship class undertook this project in the fall of 2015, going beyond the call of duty to survey the area during an early snowstorm.

Soil Monitoring and Deer Browsing

Two additional Environmental Stewardship student groups developed a soil monitoring protocol and a deer management plan for the witch hazel restoration site.  During the soil monitoring study, it was observed that hillside erosion from runoff coming off a recently widened adjacent service road was having a severe impact on the natural amphitheater next to the witch hazel collection area.  We realized that this runoff could be channeled into a rain garden.  This became the next step in the restoration.  The rain garden and additional soil remediation will address the problems of erosion and poor soil due to large amounts of fill and gravel left on site.

Deer browsing continues to be a problem and will be addressed in the future by using cameras to monitor the fence line around the Arboretum for potential deer intrusions.  Once the weak areas of the fence have been identified, we can shore up these areas.  Meanwhile, we use fencing and deer repellent to protect the plants in the collection.

The Rain Garden

The first step to creating the rain garden was the installation of a drain tiling system along the service road that channels runoff to the garden area.  This was completed in the fall of 2016.  The rain garden was excavated and compost from the City of Hillsdale was donated to improve the soil’s moisture retention capacity in the area of the garden.  During the grading and excavation of the rain garden, it was observed that the fill dirt remaining in the area created a significant problem for having plants grow and flourish.  We realized we needed to bring in a significant amount of compost and mulch in improve the soil.  Fortunately for the success of the project, the College purchased a large lot of compost, peat and tree and shrub soil at a soil auction, which will be used to amend the site.  We are in the process of moving six pallets of new soil and another pallet of peat to the site.

Here is a rough drawing of what the rain garden will look like. 

It will be framed on the left by two 

small trees—yellowood and ironwood.  In the back will be a mix of evergreen concolor firs and juniper trees, providing a fall contrast for the reds and yellows of the witch hazels and other shrubs.  The berms in front of the water absorption areas will be planted with wildflowers, and the garden will be accented with witch hazels and other forest understory shrubs including viburnums, sweetspire, dogwood and blueberry.

Future Directions

Once the rain garden has been installed, the Arboretum staff, along with volunteers and future environmental stewardship classes, are committed to:

1. Monitoring and continued control of invasive weeds.
2. Future plantings along other areas of the hillside.
3. Continued monitoring of the soil, including studying the bacterial composition of the soil, and continued improvements to the soil through the addition of compost.
4. Implementation of deer management strategies.
5. Extension of restoration efforts to the natural amphitheater and hillside across from the heart-shaped pond.
6. Continuing to educate public on restoration efforts and stewardship of the arboretum.