A Subtle Invasion (So Far)

My younger daughter and I were able to enjoy the recently warm (and dry weather) earlier this week and did some nice local hikes. One of her favorite hikes a couple times each year is to visit JSOL (Janesville School Outdoor Laboratory) which is also known as the Robert O. Cook Arboretum (160 acres of woodlands owned by the Janesville School District). Our older daughter has been out there many times with various classes over the years and my younger daughter (now 11) and I have hiked this space since she was two. Highlights include lots of nice trails, a stream with a beaver dam, lots of frogs and some neat swampy areas that are loaded with skunk cabbage (Symplocarpus foetidus) that we see in late March each spring. The woods contain all sorts of nice oaks, hickories, basswoods, maples and other native understory trees. However, as is the case with most of our woodlands in the United States, the infiltration of unwanted visitors was apparent. While most of us are familiar with European buckthorn (Rhamnus cathartica) and garlic mustard (Alliaria petiolata), there are some other thugs starting to set a foothold in our woodlands and most would be overlooked by those not familiar with the native range of these plants. Ironically, most of these invasive plants were introduced as landscape plants before they were considered as potential threats to our woodlands and less managed landscapes. All the pictures here were taken at JSOL but could be taken in most of our Southern WI woodlands. For example, the top picture shows Oriental bittersweet (Celastrus orbiculatus) which was introduced from Asia back in 1736 which continues to be a vigorous vine that constricts and engulfs native vegetation in its efforts to spread. We have it at RBG and remove it on sight.

Directly above and to the below left are just a few of the many samples of burning bush or winged euonymus (Euonymus alatus) that I saw peppered throughout the woodlands. The specimen above has lots of red seeds that will be distributed by birds and the resulting seedlings (see pink to the lower right) will establish and continue this sequence of reproduction. The timing of our hike coincided with the pinkish/red fall color of this shrub so the infiltration was very evident. Burning bush has become quite invasive in woodlands along the east coast and is banned as a landscape plant in Massachusetts with other states soon to follow. Dr. Laura Jull from UW-Madison (Dept. of Horticulture) has been doing a study on the variable seed production of different varieties of burning bush to determine those that have either more (or less) of a risk for seed dispersal. She contacted us regarding our observations on our varieties out in the gardens. It is not unlikely that burning bush will be listed as invasive in other states including WI in the coming years. To the right are the glossy hips of the multiflora rose (Rosa multiflora) which was prevalent throughout JSOL and can be found throughout many Southern WI woodlands as well as further South and East. Ironically, again, this plant was introduced from Japan in 1886 as potential root stock for roses and was promoted in the 1930s thru 1960s as control for soil erosion, a great "living fence" and a food/cover source for wildlife. Well, wildlife has spread it near and far and this plant has enjoyed free range of woodlands in our area and is quite aggressive to say the least.

Of equal concern is the Japanese barberry (Berberis thunbergii) which could be seen throughout JSOL (see next two pictures below). The orange fall color of the barberry made it quite conspicuous this week and the number of fruits on this widely distributed plant was concerning. I recall a spring blog of mine regarding a visit to JSOL (April) in that the "haze" of emerging green foliage in the understory of the woodlands was entirely Japanese barberry, leafing out before the native vegetation had started. As with burning bush (Euonymus alatus), it is possible that barberry will be examined as a questionable landscape plant because of this spreading potential. There are currently many cultivars of Japanese barberry offered in the landscape industry and while fruiting volume is variable, this plant has already shown its thuggish tendencies in my mind. At the bottom are the fruits of the female European buckthorn (Rhamnus cathartica) awaiting consumption and subsequent dispersal by area birds. When I lived in MI (prior to coming to RBG), the buckthorn was "jail bar" thick thru woodlands that were not maintained. The entire understory of these woodlands was a shaded thicket of buckthorn that had edged almost everything else out (aside from garlic mustard). We are still removing buckthorn at RBG. If you have any buckthorn issues, you're headed in to the best season for control. As the rest of our native, deciduous woodland trees and shrubs turn a fall color and drop leaves, the buckthorn will retain glossy green leaves in to early November. This is a great way to locate all offenders. It is difficult to dig up the extensive roots and the wood is extremely hard and not easy to cut. However, we target late October for removal with a nice flush cut at ground level, followed by the focused and targeted painting of concentrated herbicide (Round-Up) directly on the cut trunk. We've seen very few "returnees" and this has been more effective than the daunting hand removal. Enjoy our woodlands but keep an eye out for those strangers that will continue to increase in population and negative impact on our woodlands.