Regional Gardening Reports :: National Gardening Association

In the Garden:
Northern & Central Midwest
February, 2005
Regional Report

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Buckthorn leaves are quite attractive until you realize what the plants do to our natural habitats.

Alien Invaders Need to be Managed

I just found out that some of the plants I love have a dark side. I know about the negative attributes of Siberian elms, silver maples, green ash, and Tatarian honeysuckle, but Japanese tree lilac is on the Chicago Botanic Garden invasive species "watch" list as well. This means that it has not become a problem yet but may in the future. The same with black alder. Are these good trees gone bad? Have those characteristics I chose them for in my landscape suddenly changed to make them devious invaders to be feared?

Defining "Invasive"
Some of the plant characteristics that earn a plant a place on the invasive plant list are: no natural enemies, rapid growth and early maturity, production of many seeds, ability to reproduce by runners or stolons, seeds that are dispersed widely, seeds that germinate quickly, and seeds that are produced asexually.

Take buckthorn, for example. It's an imported plant that is tenacious enough to push out other desirable species. It is easily transported in bird droppings, and thus fills our woods, sometimes completely choking out the native plants.

It is a disheartening sight to see open oak forests where buckthorns form a thick understory to the mature oaks. These forests with distinct canopies will eventually become a dense forest of buckthorn, green ash, and elms, if not managed carefully.

My own woods are filled with buckthorn, multiflora roses, and grapevine. I'm working on managing them, but it takes time. From the invasive list, I've also found that in order to manage my land, I must remove wild crab apples, European euonymus, Japanese barberries, periwinkle, burning bush, honeysuckle, Amur maples, and European cranberry viburnums. I certainly knew about honeysuckle, but was shocked about the European viburnums.

Without management, invasive plants can eventually dominate the system, reducing the natural diversity by changing the environment and crowding out the native species. Diversity in a biologic community means stability, and changing one part of the system sends a ripple throughout the system.

Taking a Realistic Look
Many invasive species are not appropriate in the natural landscape, but we need to consider the situation of each invasive plant before doing whole-scale removal. What's the ecological impact on a plant's habitat if we sweep in with our chainsaws and herbicides?

For example, what about the tree of heaven (Ailanthus) that grows in the heart of the city between cracks in the sidewalk? Tree-of-heaven is a major weed species, but if it's the only thing that will grow in the harsh urban environment, I certainly wouldn't recommend taking it out.

What about the thicket of white poplars that graces one bank of the Des Plaines river near me and is home to an amazing number of bird species? Removal of these would not only mean loss of habitat for the birds, but also a serious erosion problem for the riverbanks.

I will keep reading the invasive plant lists and will do my part to rid my own land of these species. I also will spread the word as best I can about invasive plants. And I will support the horticultural institutions in their ever-expanding search for information about these plants. But can I please keep my Japanese tree lilac?

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