Invasive honeysuckles and birds

 

A western Ohio woodland, its understory utterly dominated by Amur Honeysuckle (Lonicera maackii). While there are other species of Asiatic honeysuckles running amok in the Midwest, this one is by far the worst culprit in most areas I visit. It is firmly entrenched in our flora, much to the detriment of the indigenous plants.

As always, click the image to enlarge

It wasn't always so. The nonnative bush honeysuckles like Amur Honeysuckle weren't a major problem until fairly recently. In Lucy Braun's The Woody Plants of Ohio (1961), she devotes a scant two sentences to it. Braun knew it only in the wild from the far southwestern corner of Ohio (Hamilton County) but did note that it was "becoming abundant".

This map is from Tom Cooperrider's decidedly unsexily titled The Dicotyledoneae of Ohio: Part 2: Linaceae through Campanulaceae. The book was published in 1995 and gives a snapshot of the progress of Amur Honeysuckle in Ohio. Twenty counties have been added since Braun's publication 34 years prior. It should be noted that botanical works such as these rely on vouchered specimens as evidence, and there are relatively few botanists that collect and archive material in herbaria. By 1995, Amur Honeysuckle was undoubtedly in counties beyond those depicted on this map but was definitely not the scourge it is now.

Cut to today, and documentation of the horror show that Amur Honeysuckle has become. The orange squares representing reports congeal into blobs, so frequent are the observations. This is part of the iNaturalist map, which relies on peer-reviewed photos submitted by observers. Ohio is smack in the middle of this snippet of the map, and honeysuckle pretty well blankets the state. Good old Lonicera maackii is certainly in all 88 counties, and at least locally abundant in many or most of them.

How did it get here? Apparently, the original escapes came from the New York Botanical Garden, which began promoting Amur Honeysuckle as an ornamental in 1898. By the 1930's and '40's, wildlife agencies greatly exacerbated the problem-to-be by widely promoting honeysuckle as a ground cover, soil stabilizer, and wildlife food plant. As often seems to happen with invasives, there was a few decades long gestation period where the plant did not run amok, but probably largely stayed where it was put. In Ohio and this region of the Midwest, the spread probably began in earnest in the 1980's and the trajectory was obvious by the time of Cooperider's 1995 book. One need only glance at the iNaturalist map to see what has happened since.

Small wonder people were smitten with Amur Honeysuckle. It is pleasing in form, and sports abundant showy white flowers.

Alas, those flowers later become equally showy fruit, also abundant. Brightly colored berries probably evolved to lure agents of dispersal, especially birds. Birds are drawn to bright fruit, and it is to the honeysuckle's advantage to have its berries eaten by highly mobile winged creatures. A frugivorous (fruit-eating) bird might expel the seeds a long distance away, effectively playing the unwitting role of avian Johnny Appleseeds. Birds are surely the primary reason for the remarkably rapid invasion across a broad swath of eastern North America.

An American Robin (Turdus migratorius) sits among a sea of Amur Honeysuckle fruit. It is akin to a kid in a bowl of M & M's. The 50-acre preserve where I made this shot is in Columbus, and I visited last Sunday. The site was thoroughly infested with honeysuckle, and dozens if not hundreds of robins gorged themselves on the fruit.

A first-year White-throated Sparrow (Zonotrichia albicollis) caught in the act, berry in beak. This species is probably our most abundant migratory sparrow, and many were present here - same site as the robin above.

With abundant frugivores such as the American Robin and White-throated Sparrow (not a major frugivore but nonetheless they have a taste for honeysuckle berries) eating this stuff, it's small wonder that honeysuckle has spread so rapidly and continues to do so. Many other bird species eat it as well including a hyper-abundant nonnative, the European Starling (Sturnis vulgaris). What is curious to me is the apparent lag time from when Amur Honeysuckle began to be planted commonly (1930's-40's), to when it became an obvious and worsening invasive plant (1980's). I wonder if birds, confronted rather abruptly with a completely foreign plant, basically ignore it for a while, not recognizing a potential food source. Maybe it takes a few decades for the feathered crowd to develop a taste for the stuff and begin ravishing it in earnest. But once they do, the game is over.

Amur Honeysuckle is so thoroughly entrenched now that there is no way to eliminate the overwhelming majority of it. Localized control in targeted parks and natural areas can be successful but constant vigilance is necessary as new seed sources will be introduced annually.

We can hope that Amur Honeysuckle eventually runs its course, and fades out, as some invasive species seem to do. But there's no sign of that happening yet.