Popular ideas are not always factual ideas.
When the subject is a particular “invasive” plant species, common assumptions about its undesirable impacts are not always scientifically documented or even true. Add to this an inherent bias in the field of invasion biology for interpreting nearly all effects of non-native plants as detrimental without considering the possibility of positive outcomes and you’re sure to get villains nearly every time.
Let’s look at two well-known examples of so-called “invasive” plants that are under the gun: Tamarisk, aka Saltcedar (Tamarix spp.) and Russian Olive, aka Oleaster (Elaeagnus angustifolia). In the western United States, these two trees are now the third and fourth most frequently occurring woody riparian plants, and the second and fifth most abundant species along rivers. To eradicate them would entail destroying a significant amount of healthy vegetation (with no little amount of collateral damage to other flora) and would incur a hefty cost. Congress authorized $80 million for Saltcedar removal between 2005 and 2009, which included herbicide, but that is pennies compared to what would be needed for everything. So the case for removal needs to be strong.
But the case is not strong. The main claims made against both species are that they a) push out native flora, b) monopolize groundwater, and c) don’t provide for native fauna. Saltcedar is additionally accused of increasing the salinity of its immediate environment. Yet these claims have never been proven and plenty of evidence to the contrary has been produced.
Juliet Stromberg and Matthew Chew, who are faculty at the School of Life Sciences at Arizona State University, have been debunking these myths, and they say that scientists have been participating in “a rationalized scapegoating of Tamarix as an agent of change because of its ability to thrive in anthropogenic habitats.” Even less researched, Russian Olive has also been used as a scapegoat. For example, the USDA’s National Resource Conservation Service (NRCS) makes the contradictory claim that that Russian Olive “has been especially invasive in wet-saline riparian areas” even though the “wet-saline niche” it inhabits is inhospitable for many native woody species.
In the case of both these tree species, on-the-ground evidence shows they are not displacing native riparian trees, but are filling in after the native species decline due to changing environmental circumstances, namely, less water and saltier soils from irrigation and dams.
The Dominance Myth
First, on the assertion that Saltcedar and Russian Olive are pushing out native flora, namely Willow (Salix sp.) and Cottonwood (Populus sp.), numerous studies show that the newcomers have been filling in where the natives were already receding or gone and that “anthropogenic alteration of stream-flow regimes is a key driver of compositional shifts.” This includes the restriction of seasonal floods due to dams and associated water table changes.
The seeds of Saltcedar germinate far better in drier soils than those of Willow and Cottonwood, which require the wetter circumstances provided by seasonal flood events typical of free flowing rivers. Native tree seeds were found to germinate and grow right up through Saltcedar thickets after dam managers released more water into the Lower Colorado River, prompting ecologist Edward Glenn to investigate the claims against Saltcedar. When a manager at the Bosque del Apache National Wildlife Refuge opened a floodgate with the timing of Cottonwood seeding, he discovered that the native seedlings emerged first, showing that the dominance of Saltcedar seedlings is “only a symptom of river systems that had been robbed of their seasonal rhythms.” Cottonwood seedling establishment requires both the moisture and the bare soil provided by floods, with their sediment churning actions. Russian Olive has been found to germinate well amidst thick herbaceous vegetation of undisturbed riparian areas that lack the disruptive action of seasonal floods. These are the very areas where Cottonwood and Willow find establishment difficult.
The problem of less water has not been caused by Saltcedar or Russian Olive (or any other tree for that matter). It is human greed for water beyond what is needed for survival which has created environments that are better suited to these non-native trees than the natives.
It is worth noting that the origins of Saltcedar’s reputation as a water-monopolizer lay with extraction industries who sought to claim more water rights for “beneficial” use—that is, for their operations—and who devised a scheme to wrangle it from vegetation, who were “non-beneficial users” with no legal rights to the water.
In the 1930s, the Phelps Dodge Mining Corporation (PDC) in Eastern Arizona was desperate for water. They had been gearing up to pursue open-pit mining at Morenci copper mine but lacked adequate water to do so. Safford valley water rights were already fully allocated to other users. In 1939, the PDC was “in prime position to supply copper demands for the looming war” after Pearl Harbor. They just needed the water. So the U.S. federal War Department Engineer Office and Bureau of Indian Affairs financed a water resource inventory along the upper Gila River. This was conducted by the USGS staff. The PDC mining moguls had already been conducting the removal of trees along the Gila River in order to claim appropriable rights to the water thereby “saved.”
“Phreatophytes” was the newly coined term assigned to Tamarisk and eighteen other valley dwelling trees who supposedly drew heavily on groundwater resources. This was deemed a non-beneficial use of water. But it was not until the wartime cultural climate that Tamarisk was singled out as a target.
In 1950, the inventory results were published in the USGS Water Supply Paper, Use of Water by Bottom-Land Vegetation in Lower Safford Valley Arizona. Tamarisk was declared to be a uniquely threatening alien, which “thrived and spread at the expense of nearly all the native plant life.” Accused of growing into “a dense jungle-like thicket that is difficult to penetrate,” the trees were assaulted by surveyors with a tool from the recent war: the flame-thrower, the iconic weapon of the ‘‘island-hopping’’ Pacific campaign. With no scientific backing, Saltcedar rose to the ranks of a national security threat by “standing in the way of mine expansion.”
The miners’ tall tale, despite its basis in “a reputation” not facts, grew legs and is still walking around today. “Conservationists” are among those who still endlessly repeat the spurious claim. And despite evidence to the contrary that has since emerged. For example: “After an extensive eradication of tamarisk along the Pecos River in Texas over five years from 1999, Charles Hart of Texas A&M University could find no evidence of any greater flow in the river.”
The results of a decade long investigation along three rivers in the Southwestern U.S. put the lie to the Saltcedar water myth again. The study found that there was no significant difference in the water usage between three vegetation communities regardless of the native/non-native make-up of the areas. The study chose three sites: the Lower Colorado River, consisting of 90% Saltcedar vegetation cover; the Middle Rio Grande in New Mexico, with an even vegetation cover of Saltcedar and native trees; and the San Pedro River, considered the last undammed river of the Southwest, with only a few scattered stands of Saltcedar. Measurements of transpiration (the gaseous moisture mix that trees exhale) were taken using sensitive flux towers designed for climate change studies. All three vegetation covers were found to transpire an average of one meter of moisture per year into the atmosphere. Thus, the amount of water that Saltcedar drinks has been shown to be on par with her native comrades, and—in places where sufficient moisture remains for the native species to survive—one can find cohabitation among natives and newcomers alike.
Nevertheless, history regresses and repeats. During a more recent period of drought, the discredited idea of salvaging water from wasteful vegetation was back on the table. On October 11th, 2006, President George W. Bush signed HR 2720, the ‘‘Salt Cedar and Russian Olive Control Demonstration Act,’’ which this time around also leaned on the crutch of “invasive species” to appeal to modern sentiments, environmental ethics be damned.
The lack of quantitative evidence has yet to make much of a dent in the plant’s undeserved reputation, so we see things like this: “In summer 2001, an article about tamarisk in a major Colorado newspaper declared, ‘It’s a water-gulping, fire-feeding, habitat- ruining, salt-spreading monster.’” Wow. As the old adage goes: “A lie can travel halfway around the world while the truth is putting on its shoes.” And even farther, maybe, when motivated by money, be it mining profits or grant funding?
Removing the vegetation willing to grow in these conditions will not change the conditions themselves. The NRCS, while still advocating eradication, recognizes that “decline of native cottonwood gallery forests and invasion by Russian Olive invasion are frequently associated with a change of the natural disturbance regime of riparian areas, frequently as a result of river regulation.” So even when it is known to not be the cause of disturbance, removal is the still the best thing to do? How perverse.
Salty Soils Myth
Soils throughout the western USA have been getting saltier due to irrigation and dams. The high permeability of the soils in many parts of those areas (i.e, their sandiness or gravely-ness) makes them highly susceptible to salinization through improper irrigation, which describes most irrigation practiced there. The process is nothing new to agriculture, and the effect was observed in the Middle East long ago; writes Chellis Glendenning: “By 2000 BC, there were reports of ‘earth turned white,’ a clear reference to salinization.”
Dams contribute to the salinity problem by concentrating salts. Evaporation from the large surface area concentrates salts and agricultural runoff flows bring more. Additionally, with lower stream flows and fewer flood events, salts also concentrate in riparian soils, negatively affecting vegetation. The water being released downstream is reduced in flow with an elevated salinity load. Further, the loss of seasonal floods removes the flushing effect that could reduce accumulated surface soil salinity caused by dry soils crusting over.
Improper irrigation water management can elevate the water table, which aggravates the accumulation of excess salts in the soil. This condition is not favorable for woody species that do not grow well in saturated (wet), saline soils (which, besides Cottonwood and most Willows, also includes Redosier Dogwood). However, higher water tables are common where Russian Olive is found. She both tolerates this condition and remedies it. Saltcedar begins to appear along intermittent rivers with deep alluvial groundwater. Increasing arid conditions and heavy water use upstream exacerbate this condition. Deeper taproots and a high salt tolerance lend adaptive benefits to this species.
At one time, the presence of saline soils where Saltcedar thrives was mistaken as an effect of the tree’s presence, rather than one of the factors contributing to her ability to grow in such soils, where other plants could not. Russian Olive has also been found to tolerate elevated soil salinity levels. The NCRS points out the relative salt tolerances of these two species, stating that “Russian Olive gives way to saltcedar (Tamarix) on soils with elevated sodium levels.” These are soil salinity levels above the toleration of native riparian species such as Cottonwood and Willow. So, these “salt-of-the-earth” volunteers are “passengers, not drivers” of this condition. We are reminded of Lupine, a cosmopolitan genus of plants named Lupinus—“wolf”—by the Romans because they falsely believed the plant robbed the soil of fertility since it grows in waste places. In actuality, like many species in the Legume Family, Lupine improves its habitat by capturing (“fixing”) nitrogen from the air and adding it to the soil. Those who believe that contemporary people are so much smarter than ancient people might reflect on the lesson of Lupinus.
Intriguingly, data suggests that Saltcedar might be playing a similar role in overly salty places. Lower salinity levels have been measured where older stands of Saltcedar are established. If true, Saltcedar could ultimately be providing improved circumstances for native riparian species to re-vegetate. The NRCS described how Russian Olive loses its competitive edge on non-saline hydric soils, where Cottonwood and certain Willows shade the Russian Olive, pointing to a different niche adaptation, not competition. In fact, Russian Olive has been found to be eﬀective in re-vegetating saline landscapes, reducing elevated groundwater tables and thus mitigating dryland salinization. It seems these two species may actual be partnering in a desalinizating guild of succession: a symbiotic offering to their native friends to join them again later.
Dams and diversions created new water flow regimes and increased salinity loads. As Candace Hughes summed it up in Smithsonian magazine: “The real invasive species are the dams diverting water for agriculture and saline water being put back in the rivers.” The increased evaporation from the surfaces of reservoirs concentrates the amount of salts in the water. Summertime floods no longer rinse the riverbanks, so salts accumulate in a pale crust. In contrast, natural floods still exist on the San Pedro, where saline soils—and Saltcedar trees—are rare.
The “bad neighbor” myth
The aspect of ecological function is too often neglected when the “invasive species” flag is waved. That is, it is not asked whether the new species is interacting with neighboring flora and fauna in any positive ways. Or that these species are a part of natural succession given the environmental changes that have occurred. Russian Olive can also be recognized as a community type. In Montana, at least, according to the “Classification and Management of Montana’s Riparian and Wetland Sites,” Russian Olive is considered to represent a seral stage of various habitat types, including: green ash/common chokecherry (Fraxinus pennsylvanica/Prunus virginiana), box-elder common chokecherry (Acer negundo/Prunus virginiana), Ponderosa pine/redosier dogwood (Pinus ponderosa/Cornus sericea) or Douglas fir/redosier dogwood (Pseudotsuga menziesii/Cornus sericea). A seral succession is a stage on the path towards a longer lived, relatively stable but still dynamic community structure. There are processes to get to that stage, and it starts where it is and develops through many different interactions along the way. Denying the reality of this process in favor of particular players defies both science and common sense. By providing food or shelter, especially if another species previously playing those roles is now absent, Russian Olive and others keep the process of resilient renewal going. Put another way, the “invasive” label tends to elevate human perspectives of how things ought to be above non-human reliance on the present functions of how things are. How would we respond to the sudden eradication of agricultural crops, if we were to view them in the same light of stalled succession, deemed to represent a degraded habitat? Crisis! We might find a more gradual transition to be more considerate, since we presently depend on it. Perhaps our first thought would be that of planting wild foods in abundance.
A strongly held tenet of invasion biology is that non-native plants provide fewer benefits to wildlife compared to their native counterparts. In the case of both Saltcedar and Russian Olive, the data speaks otherwise. For birds in general, the composition of plant species in their habitat may be less important than the structural features those plants provide, whether native or not. Some ornithologists have even found that a wide range of birds may prefer Saltcedar over native trees.
The endangered Southwestern Willow Flycatcher (Empidonax traillii extimus) numbers under 500 breeding pairs. Their main threat is habitat loss, which currently includes Saltcedar. In some areas, 75% of these birds found are nesting in Saltcedar. There is also no evidence that the Flycatcher is any less provided for using Saltcedar. In Arizona, 49 different other bird species also nest in the salty boughs.
Bees are fond of Russian Olive flowers, and the trees were often planted for honey production. The blossoms are rich in B vitamins too. Over one third of the bird species in the Gila River valley in New Mexico were observed to use the thorny cover of Russian Olive as nesting sites. Since the 1950’s, it has been known that at least 44 different birds (as well as fox, rabbit, squirrel, skunk, raccoon, deer and elk) eat Russian Olive berries as a hardy winter food. Deer and livestock feast on the leaves. Beavers gnaw the branches. Shelter and warmth is provided by Russian Olive. Doves, mocking birds, roadrunners and other birds use the thick growth of branches as nesting sites.
Russian Olive as Soil Remediator and Superfood
Defying all claims of inferior forage value, the berries contain 19 detectable minerals and are rich in water and fat soluble vitamins (especially A, C and E), flavonoids, carbohydrates, alkaloids and biological active lipids. (see here, here, here and here). Theses lipids are high in essential fatty acids, which is unusual for a fruit. One study foundoleic acid and linoleic acid made up 92.8% of the fruit lipids. The nutritional and medicinal properties of Russian Olive are actually well studied, with indications for everything from muscle tension to malignant tumor reduction, “validated based on a scientific point of view.” This looks more like a wildlife super-food than an dangerous invader.
All of these services and benefits offered, and more, even after being acknowledged, are cast aside for an ideal that would take all the trees away. The USDA NRCS stated that, “although Russian Olive provides food and cover for many species, it negatively impacts cavity-nesting birds.” This is claimed even when the paper could offer no data that there is any competition with native species. In fact, all the papers we found could only point to Russian Olive replacing declining native trees due to various human-induced hydrological changes, and no conflict when conditions could still support natives. So the fact that these ecosystems cannot grow cavity-providing tree species is caused by environmental factors, not the new volunteers.
With remediation goals in mind, Russian Olive has repeatedly appeared in scientific literature with respect to bioabsorption, phytoremediation and degraded soil regeneration qualities. Indeed, the original motivation for planting was to re-vegetate land contaminated by paper mill wastewater, mine spoilings and as a bioindicator of heavy metal pollution (see here and here). The fruits have been found to remove chromium, cadmium and nickel from aqueous solution. Curiously, Russian Olive is deemed a promising species for engineered phytoremediation for herbicide manufacturing operations, and seedlings have displayed herbicide-resistance. So hopefully they will be there to remediate riparian soils after aerial spraying. Ironic.
The ability of Russian Olive to rehabilitate the effects of agriculture are stunning. Nutrient loss is a big factor in degraded soils, both in the field and downstream. In the field nutrients that in a natural process would be recycled back into the local soil are instead removed with the crop. Downstream from dams and the fields they irrigate, the nutrition offered by flood deposition decreases, while agricultural runoff increases salinity, affecting nutrient cycling. Endosymbiosis with soil bacteria help Russian Olive act as a nutrient pump, enabling the improvement of saline conditions by increasing “content of organic matter, nitrogen and phosphorus, as well as the number of fungus, bacteria, salt-tolerant bacteria, actinomycetes and salt-tolerant actinomycetes.” Since there is no competition actually documented, and her presence remediates saline soils, it seems likely Russian Olive can pave the way for other vegetation to be able to thrive again. Russian Olive will grow in some of the most dismal conditions and has the ability to somewhat restore the historic quality of toxic sites. It seems she is here to help!
But too often, these many benefits are mentioned only as an aside in the scientific literature and the focus immediately returns to methods of control, with no pause to ponder the ramifications. This behavior displays a pathological mind, unwilling to recognize facts and change course.
The tenacity of ignorance
These two maligned species, entering the scene as others are exiting, are offering significant benefits to their new neighbors: food and shelter. As it currently stands, then, removal of Saltcedar and Russian Olive—as a stand-alone action—will make some wildlife homeless and take away their food. That’s a fact.
Yet somehow we still refuse to participate with the process and need to dominate. The Pecos River Native Riparian Restoration Organization, along with “weed specialist” Keith Duncan, raised $1 million to manually and aerially spray a mixture of herbicides including Arsenal, Rodeo and Roundup on Saltcedar groves on 5,000 acres along this New Mexico River. The project applied such poisons for three years, from above and below. Duncan seems to think that the dead skeletons of the trees provide a better nursery setting than a live shaded cover would, and that decimation is essential. However, Saltcedar provides a perfect nursery habitat for native vegetation to thrive when it is living. Studies have shown that planting native vegetation under Tamarisk is a viable way to increase avian abundance.
But agricultural weed scientist Duncan assumes that destruction is the best first stage of succession. As he claimsof the wasteland he created: “It won’t be like a parking lot tomorrow.” He goes on to intensify the crime, insisting that efforts “must include the entire courses of the Pecos and Rio Grande rivers as well as tributaries,” and has garnered funds to the tune of $5 million dollars. No environmental objections have been raised to the continued aerial herbicide application. The response has been support from Aububon, the Sierra Club and others, and the herbicide Arsenal is a big reason for the support. Wait, what? Oh, because the label states it is “habitat safe.”
Duncan and his corporate environmental sponsors are still acting on the scientifically false notion that Saltcedar is drying up the rivers. Meanwhile Duncan states that “if the region gets back to more normal rainfall and snow-pack patterns, eradication efforts will become evident.” Thats convenient. Only if these things improve will we be able to measure success. This statement also exposes Duncan as a climate change denier. The reliable rainfall and snow-pack patterns of yesteryear are gone and they ain’t coming back.
When the starting point is demonization, there’s no room for appreciation. A blind insistence on ripping out species just for being newer, especially when they are well-established and integrated, runs the very real risk of making landscapes lifeless and barren. This is certainly the case for Saltcedar and Russian Olive, which have become so common, and especially with climate change threatening the ability of the original natives to survive, period. Different groups have been trying to eradicate Saltcedar for over 70 years, and control programs for Russian Olive were demonstrated in the 1960s. Even when the true factors behind changing landscapes have been established, biocontrol agents remain the first choice.
An ugly truth is glaringly exposed by the “debate” over Saltcedar and Russian Olive. Despite the fact that the overwhelming preponderance of evidence shows that neither species is guilty of the many sins they are accused of, neither one can become exonerated in people’s eyes. Saltcedar will still be seen as a sign of desolation, and remembered for that, not for the way she stepped in to provide and mitigate human error. Russian Olive will still be considered less than other trees, even when she gave in ways that no native could. People talking about “restoration” become hooked on a picture of the past as the only healthy community possible, and all efforts are aimed at returning there, no matter the cost. There is no respect given to the resilience of ecosystems under attack by us.
Humans will never be able to celebrate healing with the rest of the world while their ideals, all of them the products of unexamined ego, continue to reign on high from above, thinking they know better than what is being offered, always.
At this juncture, the problem is not a matter of a lack of information to guide beneficial engagement. The problem is the extreme resistance to giving up our perceived place of hierarchal dominion. As ecologist Robin Wall Kimmerer recognizes: “the land shows the bruises of an abusive relationship. It’s not just land that is broken, but more importantly, our relationship to land.” This cycle of abuse is doomed to continue endlessly if we do not address our own embattled psyches.
This is part two of a three part series. Part one can be found here.
In Part 3, we will discuss the ramifications of climate change for invasion biology and the cultural issues highlighted by the field’s popularity.
 Pearce, Fred. The New Wild: Why Invasive Species will be Nature’s Salvation (Beacon Press: Boston, MA, 2015), E-pub pp.152.
 Pearce, pp. 54-58.
 Glendenning, Chellis. My Name is Chellis and I’m in Recovery from Western Civilization (Boston: Shambhala Press, 1994), p. 78.
 Sonnenblume, Kollibri terre. “Grape Soda Lupine (Lupinus excubitus var. excubitus)” entry in Wildflowers of Joshua Tree Country ebook (Macska Moksha Press, 2015).
 Pearce, pp. 54-58.
 Pearce, pp. 54-58.
 Kimmerer, Robin Wall. Braiding Sweetgrass (Milkweed Editions: Canada, 2013), p. 38.
Nicole Patrice Hill holds a bachelors degree in Environmental Science with a minor in Botany. She is a former farmer who has been exploring the wildtending life in the US American west. Ms. Hill can be reached at wildwiskedjak (AT) riseup (DOT) net
Kollibri terre Sonnenblume is a writer, photographer, tree hugger, animal lover and dissident, whose work can be found at Macska Moksha Press. Kollibri can be reached at kollibri (AT) macskamoksha (DOT) com