Working on invasive plants is like managing the behavior of a defiant two year old. One must be consistent and firm in resolve, day after day, for at least sixteen years. Let up for even a little while and you lose a lot of ground. Of course, most two year olds grow up to be some sort of adult, but invasive plants never go away.
Why is it so hard? Beargrass Creek SNP is a particularly challenging property because of its land use history. After the Revolutionary war the property was named “Fox Hill” by the prominant Prather family, whose servants and slaves planted orchards, built stone walls, cut trees for lumber, and tended the crops, livestock and fine horses. Intensive land use continued till mid 20th century, just about the time plants like Bush Honeysuckle were unleashed into the landscape. The timing couldn’t have been worse; another damaged, vulnerable piece of land was quickly reclaimed by fast growing non-native plants just doing their job.
In this typical urban forest, invasive shrubs and vines now dominate much of the understory, and their seeds alone inhabit the “seed bank” (all seeds resting in the soil). Once invasive plant removal has begun the process needs to continue intensively, or it’s a waste of time.
As soon the forest floor is released from the deep shade of Bush Honeysuckle, a new growth cycle begins. Seeds that have been languishing are now able to germinate, and like the contents of Pandora’s fabled box, a whole cohort of “secondary” invasive plants spring up that were not a problem before. These include Garlic Mustard, Japanese Stiltgrass (makes a monoculture on the forest floor), Japanese Honeysuckle and Asiatic Bittersweet (the sapling tree stranglers), Porcelainberry (a grapevine relative that behaves like a mini-Kudzu) and others.
Three years ago all invasive plants on this site (pic above) were cut and stump treated with herbicide. The lush new growth suggests that recovery is going well; however it’s almost entirely composed of the original invasives and several new ones.
This is what we didn’t understand in the early years of invasive plant work – you can’t just go out every now and then, cut down an acre of Bush honeysuckle and go home thinking you’ve made things better. Though we painted herbicide on the Honeysuckle cut stumps, the seeds in the soil waiting to grow were the real problem. We cut and pulled and cut and pulled for years, before we realized there was no keeping up; invasive plants grew faster than we could work.
What to do? A more intensive technique was required – herbicide foliar spraying. This involves spraying a diluted mix of glyphosate (generic Roundup) on the gazillions of new invasives that pop up on any recently cleared site. I had never used herbicides prior to getting an applicator’s license – now I walk around with a backpack sprayer, killing young Bush Honeysuckle, Privet, and Wintercreeper plants. I would not describe this as fun. But to see Spicebush Swallowtail butterflies flitting through groves of young Spicebush, where only Bush Honeysuckle grew before, makes it worthwhile.
The pic above is an example of a site till recently overrun by thickets of Privet; it was foliar sprayed last fall (dead grey stems). Jewelweed and Virginia Wild Rye are rapidly covering the ground – it’s always fascinating to see what begins to “revive” on these sites. What makes it tricky, is that foliar spraying may still be needed even as native plants are recovering on a site. It’s possible to aim the sprayer wand with almost surgical precision, but maintaining such a high level of focus is tiring and time consuming.
Because I like my glass half full, focusing on the “revival” end of the process is really my cup of tea. (How’s that for mixing metaphors?) In the pic above, an intensively managed site near post #18 shows the beginnings of sustainability – many young Spicebush shrubs, Lindera benzoin, cover the ground. Though visitors to the preserve notice and comment on the decreasing amount of Bush Honeysuckle, it’s the revival of native shrubs that’s important.
This lovely “parklike” landscape is in recovery – five years ago it was dominated by Bush Honeysuckle, followed by Privet, Wintercreeper, etc. The shrub layer is full of deer-proof young Spicebush and Pawpaw, the default plants of mesic midwest forests. Though herbicides were used, care was taken to avoid most damage to native plants. Because there’s partial sun here, and more on the way due to dying Ash trees, the openness will not last. Spicebush, in particular, can create a tall, shrubby habitat that will help prevent reinvasion by Bush Honeysuckle. In fact, the two plants are remarkably similar in form, mature size, and method of dispersal (red berries). So it’s easy to see how Bush Honeysuckle took over this understory niche.
The best hope for the future is to keep whittling down the invasive plant population to a level of yearly routine maintenance, with the guidance of a long-term management plan. But on much of the preserve we’re still nowhere near this happy state of things. So I’ll keep my backpack sprayer on my back, because I do love to see Spicebush Swallowtails.