The Tree Removal grant project in the Arboretum is already well underway. Three of four sites have already been cleared of non-native trees and invasive brush. However, some arboretum visitors have wondered why the trees and bramble were removed in the first place.
One very important consideration is that much of the pine forests are already dying. In recent years trees have been weakening due to insect infestation, overcrowding and age. The Jack Pines were approaching the end of their life cycle, and as their structure weakens they’re susceptible to wind damage. This causes limbs fall on the trail and in extreme cases whole trees come tumbling down. As a result many worker hours are lost in trail maintenance, behind chainsaws and around heavy equipment. The pine forests also serve as massive reservoirs for invasive species known to choke off native forests, particularly Buckthorn and Honeysuckle. As a result huge tracts of invasive plants spring up, making the forests impassable, and serve as deep seed banks to invade the surrounding native forests.
Perhaps the most important reason to remove pine populations in the Arb is because they’re non-native: Arb long term goals are to restore native plant communities. They aren’t old growth forests in need of protection; the pine plantations exist because their human planters hoped to sell them and turn a profit. Before European settlement there were no pines south of the Twin Cities. If a core goal of the Arboretum is conservation we must always look to restore native habitats that once existed. For the purposes of primary academic research, as well as the education of our students we must present as accurate a picture of these ecosystems as possible.
Following the winter tree removal Arb staff will monitor for resurgence of non-native plants and control them as needed. Once the site is free of competition from problem plants, the areas will be replanted with native forest trees, grasses and wildflowers.
It’s a long road, and only hard work and a lot of effort can make this kind of transformation possible. But watching the pine forests slowly degrade and fill with buckthorn wasn’t an option. Quite a bit of thought went into the issue of the pine plantations, and how best to address it. In the end it was obvious that replacing them with native forests is the option most consistent with the values and goals of the Cowling Arboretum.