A Treehouse for All

The Adele and Dean Bowden Treehouse Village is for visitors of all ages and abilities. With an accessible playground, several treehouses, a suspension bridge, and miles of trails, there is so much to explore! This space was imagined as the first stage in our master plan to engage families and children in nature. Tucked within our native woodland, this outdoor area gives access to 160 acres of woodland, prairie, and ravine slopes. The oak-hickory woodland over head is being actively managed by staff and volunteers, ensuring an ecologically productive and sense stimulating experience for decades into the future.

By 2020, most of the arboretum’s woodland had reach near 100% closed canopy. While this isn’t necessarily an indication of an unhealthy woodland, it did not match our goals of keeping our woods oak-hickory dominated. Both oaks and hickories require open ground and areas where sunlight reaches the understory in order to germinate, so a woodland closer to 50% canopy cover was desired. Emerald Ash Borer had taken its toll on the ash species, and Dutch Elm Disease had already killedmost of the mature elms. So when the 2020 derecho hit, vast areas of trees that were weak wooded, already dead, or too close together were blown down. Now the work has begun to select and keep big mature oaks and hickories while allowing for the next generation to sprout.

This graphic demonstrates what the woodland looked like prior to the 2020 derecho, with dense canopy coverage and little understory diversity. The future woodland will be rich with forbs, grasses, and saplings of long-lived tree species. Each tree has been individually assessed for their ecosystem services, lifespan, and likelihood to be resilient to climate change.

Our management goals are all about succession. A dense stand of trees prevents sunlight from reaching the lower canopy, drastically reducing the understory diversity of shrubs, forbs, grasses, and wildlife. By managing the canopy at 50-60% coverage, we are able to increase the abundance of species and provide sought after wildlife habitat. This is closer to what would have existed here 150-200 years ago before fire suppression and habitat destruction took hold. The densely growing woodland that existed prior to 2020 also contained a majority of short-lived, weak-wooded tree species that aren’t climate resilient. This type of woodland composition perpetuates a succession that doesn’t allow for oaks or hickories to regenerate and decreases the species diversity over time. The native tree species here prior to management are still important to keep, but they are restricted to growing on ravine slopes and bottomlands as they would have historically, when low-intensity fire put pressure on the uplands.

Ephemerals

One of the most delightful parts of native Iowa woodlands are spring ephemerals. Ephemerals are plants that grow, flower, and then complete their lifecycle in a short period, usually during a time that conditions are favorable. In our woodland, spring before trees have leafed out allows ephemerals to take advantage of sunlight while weather is still cool and wet. The understory in April and May is carpeted with these little jewels, each only lasting a few days. These plants are an indicator of undisturbed soil, as our woodlands were logged but never tilled. The best place to spot these plants are along the trail as it gets close to ravine edges, down the Herrick Memorial Trail, and near the suspension bridge.

Traditionally built using non-harvestable timber or low-value wood, these walls form a barrier to exclude deer. The first decade or so of woodland succession and rejuvenation are the most important, so using slash walls to keep deer from eating or damaging young trees is a low cost and effective tool to protect young trees. The exclusion of deer, even just for a few years also greatly increases the diversity of forbs growing in the understory, making the woodland more beautiful and productive over time. The slash walls also help us with several other goals:

-prevent humans from getting too close to ravine edges
-decrease soil erosion by protecting ravine stabilizing plant species
-provide habitat/shelter for small mammals, birds, and insects
-ethically dispose of non-native plant debris
-keep organic material and carbon from leaving the woodlands
-prevent the spread of disease from ticks and mosquitoes by excluding deer

Research from Cornell University about using slash walls has proved promising for its use as a long-term woodland management technique. Our own preliminary observations after a few years of slash wall usage indicate a great success, and we will likely be adopting the technique more broadly as we continue to manage our woodland. The prevalence of Emerald Ash Borer, Dutch Elm Disease, Oak Wilt, and other emerging pest issues in Iowa’s woodlands will also create a need for efficient and ethical disposal of low-quality wood. Slash walls are one way for woodland managers to address these issues and keep natural resources from becoming too strained over time.

The Wetland

A native wetland can be found along the north border of the Treehouse Village playground. This area floods seasonally, filling with water during the spring and early summer, then drying out as hotter weather arrives. This is a great spot to observe frogs, tadpoles, insects, and birds while also searching for orchids and other rare plants. The water is shallow, making it easy to see the bottom on clear days.