I was an enabler, a role I regret.

I am a riparian plant ecologist, now retired, who worked in the semiarid American Southwest. Like many in my field, I was firmly entrenched in the belief that we should allow no plants or animals in “our” region other than those who could verify that their ancestors evolved here.

Yes, I was deep in the nativist movement. I propagated this biased view, until doubts, like some of the green plants themselves, began to creep in. I began questioning the value, and origin, of tribal and divisive terms such as “exotic” and “alien” that separate “us” from “them.” Having focused my studies on rare and endangered wetland plants and ecosystems, I’ve now found myself becoming an advocate for another type of underdog: the misunderstood overabundant.

On a summer day in the mid-1990s, I was tromping around a tamarisk thicket on the San Pedro River, one of the few rivers in Arizona whose flow is not impeded by large dams. The US Geological Survey calls tamarisk an “invasive” species. The shrubs were imported into the American West a century ago to help reduce soil erosion and reservoir silting, which they did. But the plants proliferated and hybridized. Somewhat akin to US Postal Service workers, neither salt nor drought nor heat nor floods would stay these shrubby creatures from the swift completion of their fixation of carbon. (What more could you ask of an immigrant?)

Among plant ecologists, tamarisk has engendered strong emotions. Before my research trip to the San Pedro, I had been reading about the litany of environmental changes attributed to tamarisk, including the creation of “biological deserts.” The shrub was being blamed for out-competing native understory plants and leaving nothing but barren ground. The first time I heard someone refer to tamarisk as “evil,” I admit that I flinched.

So, as I peered down at my study plot, I was expecting to see bare soil beneath the tamarisk. Instead, I found vines, forbs, and grasses! The understory was as dense and diverse as in the nearby Fremont Cottonwood patch. Hmm, I thought. Maybe it is not tamarisk that’s causing the changes that others have seen? Maybe those changes were a result, instead, of damming of rivers and suppression of floods, or grazing by livestock.

Context is important. So are root causes. The San Pedro’s banks still overflow after winter rains. The river’s floods remain powerful enough to flush salts from soils and thin stands of trees, enabling dense growth of the herbaceous. The water table remains high, allowing the shallow-rooted to survive. Correlation is not causation.

Increase of tamarisk, decline of cottonwoods, reduction in plant species diversity, and salinization of the soil, I eventually concluded, were being driven by the same underlying factor: changes in river and floodplain management, including damming of surface water, pumping of ground water, and grazing by cattle. I had met the invader, and, as Walt Kelly’s comic strip character Pogo might say, the invader is us. Tamarisk was being vilified and used as a scapegoat.

Fast forward 25 years. I was visiting a restored urban stretch of the Salt River near my house in Phoenix. On this trip, I was not collecting data, but simply intending to relax and enjoy soothing birdsong and fragrant flowers. Instead, I heard chain saws and smelled poison. “They really used Garlon?” I grumbled to myself. The sign warning of the toxic herbicide was clearly posted, to protect me and other literate creatures from becoming non-target victims. The intended? Tamarisk, chaste tree, and others who “didn’t belong.”

I believe the intentions of those in charge were good. They were trying to recreate the flora that was present before the dams were erected and before the river’s water was diverted to feed farms and lawns as well as playgrounds of the rich (by which, of course, I mean golf courses).

But a fallacy gnawed at my mind. When you insist that the biological elements of your restoration site not differ from those of the past, without insisting that the physical processes which influence the biota adhere to this same standard, you will succeed only in failing. If you are not willing to restore the powerful floods that once laid bare the seed beds for the mighty cottonwoods and willows, and not able to adequately replenish the aquifer for those whom you are trying desperately to restore (and at a loss as to how to reset the nitrogen cycle, uncompact the soils, and defragment the landscape), you had better be willing to accept the life that will grow.

While I was thinking these thoughts, at the Salt River, I encountered a ranger. We stopped to chat in the shade of a mesquite. He explained that the Arizona Game and Fish Department had completed their surveys for the protected willow flycatchers that often nest in tamarisk. They found no evidence of the birds and thus had given the OK to proceed with the clearing of tamarisk.

“It’s a good thing they didn’t find any nests,” the ranger said proudly, “so we could go ahead with the killing.”

“Wait, what?” I responded. “Don’t we want the flycatchers to be there, making more of themselves?” Wasn’t that a goal of the restoration, to encourage new life and protect the endangered? So much has become twisted! Trying to uncoil these Gordian knots is as tricky as uncoiling the pods of the screwbeans that dangled from the mesquite above.

This much is clear: Seven decades is long enough. That is how long conservationists and land managers have been waging war on tamarisk. (Others similarly christened as “alien invaders” have their own timelines of hate.) The war continues. Strike forces continue to rain poison from airplanes and yank out the unwanted with bulldozers, shovels, and fists, despite new studies espousing a more moderate mix of new plants and old, co-existing on shared space, to provide the habitat desired. (Read for yourself, if you wish.)

The time has come, I believe, for a less adversarial approach. The time has come to open our minds a bit wider, and to strive to steer clear of the evolutionary tendency to be wary of the “other.” Let’s go back to basics and remember that ecosystems, as described by the botanist Sir Arthur Tansley, are but mental isolates with no definite boundaries. It is we, our territorial animal selves, who erect the walls to keep out the ones we fear.

Yet, there is much work to be done to avoid training another generation of conservation soldiers.

Not long ago, I was exploring the Salt River again with a botanist friend and a student. When my friend pointed out a plant of interest, the student asked, “Is it native?” His question was typical of the times. It is code for “Does it belong?” and provides scaffolding for ordering one’s universe. But it is a simplistic and outmoded code, I have come to believe. (And a bit rude.)

Many pertinent questions bubble up when encountering a green plant has not previously met. If we follow the basics of information gathering, we would start with who are you? (What is your evolutionary lineage? Are other members of your family or genus nearby?) and proceed to what. (What do you do? What are your habitat preferences and tolerances, and what can your presence tell us about the environment we are in?) And, sure, we could then cover the when and the where questions (When did you arrive? From where?) before moving on to the why and the how. Contextualizing the new arrivals with nuance and depth takes effort but opens the door to greater ecological understanding and respect.

When we delve into the science, we learn that place-of-origin does not map neatly onto functional capacity in our ever-changing world. We also realize what a fraught proposition it is to accurately determine who came from where, and when, and how they have diverged and intermingled since. Times change and so do priorities. Preoccupation with provenance, I believe, diverts conservationists from the pressing issues of the day, such as the changing climate and the high rate of extinction. (And no, introduced plants are not the main cause of the latter; read peer-reviewed papers by Chew, Davis, and others, if you wish to read for yourself.)

Before assuming the worst, let’s ask how the newcomers may be helping. We may find out they are “carbon warriors.” Who else can thrive and photosynthesize in this hodge-podge of environmental mayhem we have created, and in so doing help stabilize the climate? Let’s retire old buzzwords such as “invasive” before they dazzle more grant-seekers and lead more researchers astray. We don’t need yet one more study on the best way to kill.

Yes, I was an enabler. I regret my role in helping to propagate the fear and dislike of those who came from somewhere else. But I have hope in the power of knowledge to change minds. Just as the powerful flood waters of desert rivers scour new channels, leaving the abandoned ones high and dry, the stream of thought within conservation biology can change too. Then, hopefully, my vision will align with that of my fellow plant lovers, many of whom, like me, were once hijacked by rhetoric and myth.