Is Removing All Nonnative Plants Always the Answer?

As a cofounder of Native Species Network, I’m grateful for those who go beyond treasuring native plants and actually get out in the field to do the hard work of clearing away undesirable alien plants. But I have concerns about how some projects are affect the larger landscape, including the animals who live there. For instance, when I taught an animal-tracking class in Point Reyes National Seashore this past June, I was surprised to find that someone had uprooted all the cakile (sea rocket) in my favorite tracking spot on the open sand at Abbots Lagoon. And they had also removed the few harmless foxgloves that managed to grow along the trail, as well as some ice plant and a few other nonnatives. Tracking is an integrated practice in which we study all the visible lifeforms in certain areas and how they interact. In Sonoma County, where I’m based and have studied wildlife for virtually all of my 90 years, we like to see cakile because it has become a major food source for mice and voles, which themselves are a major food source for raptors, herons, foxes, bobcats, coyotes and weasels. Pipits, plovers, sand pipers and other insectivore birds like it because it harbors a rotating zoo of insects. Plus, it provides cover. At the end of the annual cycle, if there are any geese around, they graze the plant nearly to the ground, occasionally killing it. If ever there are any non-native plants welcomed into our biosphere, cakile should be among them. The California Invasive Plant Council acknowledges it is an invasive non-native, but is generally not a problem, and they do not recommend a removal plan. Plus, it is an attractive flowering plant for people, many of whom have tasted the peppery leaves. To my eye this plant is integrating productively into the landscape. There are a few places where it displaces natives, and in those locations, it could easily be controlled by selective hand pulling a few times a year. Ice plant is another plant that looks different through a tracker’s eye. We know that deer eat it a lot. Rabbits and voles eat it occasionally, as do some other critter we have not yet identified that takes the very tips of the leaves…maybe an insect. What seems to be the case around here is that in places where ice plant is getting enough moisture, like on the ocean facing side of Bodega Head, it becomes more invasive and displaces especially desirable, often uncommon, native plant life. But further inland, along the drier coastal terraces, it seems more like a hundred-year struggle is raging in slow motion between the ice plant and the natives. Ice plant thrives and spreads with damp weather, but in dry locations in the hind dunes, it dries out and dies back massively every summer. Now that the climate is warming, the natives are winning more battles. It makes me smile to find a waist-high yellow lupine blooming in a 20-foot circle of dead, black ice plant. I say, sure, pull out the ice plant, especially where it’s doing harm. But treat it as an actor in the larger landscape. On Bodega Head, for example, the summers are tough on deer. As the milk herd, with 20 or so does, forms up in the fall, forage becomes precious. Among invasive plants that helps sustain them, in addition to ice plant and nonnative forbs, are the nonnative wild radish/mustards. By fall their leaves are almost stripped bare, but in the moist air they grow small new leaves that are eaten by the deer. Recognize, too, that many native plants are unpalatable to native herbivores. I would like to see invasive plant priorities determined place by place, based on the role they now play in the local ecology. It seems pretty narrow for people to just pick projects based on the single principle that it’s good to eliminate any nonnative under all conditions, even where the species in integrating well. Removing a plant species is an intervention with impact on the local balance of nature that radiates out some distance. If we want to intervene, we should understand what we are doing not only to the species, but to the local environment. This is something you have to spend quite a bit of time in the landscape to learn to recognize. Trackers call this “dirt time.” In Sonoma County, we track a lot in the Salmon Creek estuary. This tidal creek snakes lazily down out of the coastal hills and makes a 90-degree bend on the south bank a hundred or so yards before the ocean, then runs north almost a quarter of a mile, before bending 90 degrees again into the sea. The peninsula dunes that formed between the creek and the ocean is composed of dune grass, ringed on three sides by patches of cakile and various native plants. Mice, voles, rabbits, and gophers colonized the area. Geese and occasionally ducks nested there. Otters cross it as a shortcut from the creek to the ocean. There were always large open sandy patches, with a few natives. It was a great place to track because in that small, but productive area, we reliably found coyote, bobcat, fox, rabbit, skunk, raccoon, mice, and vole tracks, plus birds ranging from geese to sparrows and pipits. To us, this was a thriving ecozone. One day, going on three years ago, we were astonished to find a crew completely digging out all the dune grass from this entire peninsula. I talked to the supervisor, and he explained they had gotten a contract to remove the dune grass. There was quite a bit of community opposition. It was further explained that Cal Trans wanted to open a channel directly through the peninsula to protect the north cliff faces from potential erosion, which had never happened yet. I was never able to determine who let the contract. And as far as I know there was never any community outreach for such a large, high-impact project. I told the contractor that dune grass roots go down 10 feet and will probably resprout, which is now happening even though a few clusters of natives have taken hold. One or two maintenance visits were undertaken, but I suspect that is all that the contract covers. Personally, I think this was perfectly good grant money down the drain. Now all the predators, except for the otters and a couple of foxes, have disappeared — not only from that location, but in large measure from the adjacent mainland for a half mile or so south of the creek. What we see now are only occasional forays into the old hunting grounds. I tell this story for two reasons: One, to encourage native plant people to notice and account for the larger biological accommodations that the animals are making. Two, to show that removal projects at scale can affect not only the animals but the local human communities. A third consideration involves failure to plan for maintenance. I’m not sure there’s a gain in removing ice plant, say, only to let wild nonnative grasses and forbs take over. Anybody who’s been involved in broom removal, for instance, knows that success requires years and years of maintenance to deal with the long-lasting seed bank. One project near Ft. Bragg, some time ago, involved an expensive, massive, and welcomed removal of Scotch Broom, followed up with five years of contracted maintenance. In the sixth year it all came back, thicker than ever. And lastly, I want to mention priorities. In the Bodega Dunes and along the coast there have been several expensive campaigns to remove pampas grass, but now it’s returning. It would make sense to take it out now, while it’s relatively easy, rather than to wait until the infestation is unbearable. I think the parks understand this, but they’re starved for funding. This is much harder work than removing ice plant, but probably more important. Also, in addition to nonnative grasses, there are many other exotics that are at least as harmful as ice plant, ranging from poison hemlock to Monterey pines, and are seldom dealt with. I’m not against intervention. I’m suggesting we need to understand what our objectives are. Even native plants should sometimes be controlled. Meadows, which are rich in both plant and animal diversity, are also said to be better carbon sinks than conifer forests, which support very restricted levels of wildlife. Yet many meadows in my area are being overrun by Doug firs, eucalyptus, coyote brush, coffee berry, poison oak, and blackberries. The local Pomo and Miwok treasured the open grasslands and meadows and kept them vital by burning. We should control them, too. To this end, the natural succession in this coastal area has already been interrupted for ten thousand years by burning the coast facing hillsides. In years past, grazing performed some of that job. But now chaparral is forming, and Doug firs are working their way downhill, while invasive Monterey pines are working uphill. Without intervention, redwoods will probably ultimately crowd all the way to the beaches, destroying the beautiful, open and fruitful habitat that characterizes the south Sonoma County landscape. The most advanced regional resource I know of for science-based research into all of these problems is Pepperwood Preserve. I urge those who want to volunteer their efforts to acquaint themselves. All of that said, I don’t want to discourage the good work being done by native plant activists. But realistically, we will never be able to eliminate more than a fraction of the nonnative species that always accompany the expansion of human population. Moreover, the worst is still to come, as climate change increasingly alters the environments that native plants evolved to thrive in. I don’t have a solution to all of this, but I can attest that it’s rewarding to get out in the field and pay close attention to the struggles plants and animals are engaged in as they try to survive the epochal changes that characterize our era. I think we’ll make better choices if we respect some of the accommodations being made.