In These Cheatgrass-Infested Hills

Matthew Miller, The Nature Conservancy writer/editor, has written a beautiful article about coming to grips with beautiful yet non-native landscapes.

In my opinion, there are too many conservationists lost in a dream of pure "native" nature, unable to see the flawed-but-still-beautiful world around them.  I empathize with his struggle to learn to love degraded places, even the hard-to-love places that are infested with cheatgrass.  

Trying to widen our circle of appreciation to include even nasty invasives helps us appreciate the natural in the unnatural: the native pollinators that use invasive wildflowers, the native birds that nest in invasive trees. 

To quote Princess Mononoke, our task now is "to see with eyes unclouded by hate."

Introduced versus Native Species

 Like almost all categories in nature, there are exceptions and ambiguities. 

How do we really know a species is non-native?  It might seem like an obvious category, but if you think about it, the "evidence" of absence before a certain date is just absence of evidence!  I know taxonomists who don't agree that certain species, widely regarded as non-native, are actually non-native.  They just think the species was under-collected before a certain date.  This is especially true when there is no strong ecological or geophysical reason for the species not to have spread naturally.  For example, species that are "native" to Eastern North America, but are considered "Introduced" in Western North America (e.g. American Bullfrog).

What about species that have both native and introduced genotypes?  Phragmites australis is a classic example from North America, where you have to ID to subspecies (often very difficult) to distinguish the native from invasive.  In iNat, if you only ID to species, it will say it is native.  Only the observations that have been ID'd to species have the Introduced tag. 

Other categories include:

Archaeophytes: plants which were probably introduced by humans to an area, but the introduction happened a very long time ago, and evidence is usually indirect. Most introductions before AD 1492 would fit in this category.  

Neo-natives: This is a rather new term denoting species that settle without human assistance in a new region (see Essl et al. 2019).  For example, range expansions due to global warming.  

More discussion:  https://forum.inaturalist.org/t/residency-status-for-archaeophyte-and-neo-native-plants/37252

Tamarisk Beetles Continue To Spread

Tamarisk beetles defoliate the invasive tree throughout its range:

Are Invasive Species Evil?

Mark Davis argues against seeing invasive species as evil aliens.

In his talk today, "Invasion Biology, the Science and the Ideology" Davis lambasted a prominent paper on Garlic Mustard invasion, Ready or Not, Garlic Mustard Is Moving In: Alliaria petiolata as a Member of Eastern North American Forests. 2008. Vikki L. Rodgers, Kristina A. Stinson, Adrien C. Finzi. Bioscience. He looked up a half dozen of their key citations and showed how the original papers did not support or even directly contradicted, the claims in this prominent paper. Davis argues, persuasively, that ecologists have been too quick to lay blame on invasive plants.

He wrote a paper in 2011, Don't judge species on their origins. 2011 Nature. Mark A. Davis, et al. arguing conservationists should assess organisms on environmental impact rather than on whether they are natives. Are invasive species drivers, or passengers of species loss. They may be beneficiaries rather than agents of change. Eventually, intraspecific competition triumphs over interspecific competition as invasive species run up against resource limitations. Over time, invasive species advantages may erode as other species learn to use them as resources, too. Negative soil feedbacks accumulate over time for non-native plant species. Ecology Letters. Jeffrey M. Diez, Ian Dickie, et al.

Rethinking Invasive Species

Some find all this thrilling: Florida has become an open-air zoo, richer in species than ever before. To others, it's the harbinger of a new and depressingly undifferentiated age, when the old biological borders begin to fade and everyplace starts to look like every other. Ecologists have even given it a name: the Homogecene.

"Florida was underwater not too long ago and it will be again soon. Global warming is gonna fix this problem."

http://www.newyorker.com/reporting/2009/04/20/090420fa_fact_bilger

Burkhard Bilger, The Natural World, “Swamp Things,” The New Yorker, April 20, 2009, p. 80

Read more: http://www.newyorker.com/reporting/2009/04/20/090420fa_fact_bilger#ixzz3y0rBiXE8

Comment on "Friendly Invaders", New York Times

Carl Zimmer writes in a recent New York Times piece "Friendly Invaders", that invasive species might not actually be that bad for ecosystems. He bases this interesting argument on new research from Dov Sax, at Brown. Dr. Sax has published a paper in TRENDS in Ecology and Evolution that argues, based on statistics, that invasive species, particularly plants, contribute to diversity rather than denigrate it. "Effects of exotic species on evolutionary diversification."

"Exotic species invasions create almost ideal conditions for promoting evolutionary diversification: establishment of allopatric populations in new environmental conditions; altered ecological opportunities for native species; and new opportunities for hybridization between previously allopatric taxa...Our review indicates that, although the well-documented reductions to biodiversity caused by exotic species might outweigh the increases resulting from diversification, a complete understanding of the net effects of exotic species on biodiversity in the long term will require consideration of both."

Aldo Leopold said, "To keep every cog and wheel is the first precaution of intelligent tinkering". But unfortunately for this machine metaphor, unexpected results can also arise from adding new, self-propagating parts. Dr. Sax urges science to remain unbiased in evaluating the cumulative impacts of invasive species, and statistically it may well be true that many invasives, particularly plants, do no harm and should be given their "green card" (e.g. Dandylions Taraxacum offiniale), if not honorary citizenship (e.g. Cleome serrulata). However, based on my personal experience, other introductions have perhaps the greatest potential to harm ecological systems. Some examples:

Buffel Grass in Tucson : this is a no-holds-barred fight for the very existence of the Sonoran Desert. This invasive threatens the extinction of hundreds of species and even our "way of life".

Tamarix in New Mexico: while not threatening extinction of the cottonwood bosques that line mid and low-elevation streams, is responsible (combined with anthropogenic disturbance) for degraded ecosystems throughout the American Southwest. The complex web of riparian corridors that sustains delicate desert and upland ecosystems cannot be repaired without bringing Tamarix under control.

Rio Grande Cutthroat Trout : threatened by interbreeding and habitat loss from non-native invasives. See, e.g. Comanche Creek Restoration Project.

Alien Invaders in Tucson, Arizona

Don't Panic, but the mayor and other elected officials are unanimous: this is an urgent threat to our home and way of life: if something isn't done soon, our fair city may be "unrecoverable".



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What are we doing out here?

"Forests are the lungs of our land, purifying the air and giving fresh strength to our people."
-Franklin D. Roosevelt


What are we doing out here? We come in with big yellow machinery, excavators and bulldozers and trucks, and lay waste to what we call unnatural and bad, to create a new ecosystem that we call good and natural. The alternative is accepting ecosystem "replacement" AKA ecological succession. Who can weigh all the ramifications of change to decide what is good and bad? How can we attempt to control what we don't understand? Is invasive species removal worth it?


For most of the riparian areas in the Southwest, the invasive species of focus is tamarisk:

"Tamarisk can usually out-compete native plants for water. A single, large tamarisk can transpire up to 300 gallons of water per day. In many areas where watercourses are small or intermittent and tamarisk has taken hold, it can severely limit the available water, or even dry up a water source.

Tamarisk can grow in salty soil because it can eliminate excess salt from the tips of its leaves. When the leaves are shed, this salt increases the salinity of the soil, further reducing the ability of native plants to compete. Because of its ability to spread, its hardiness, its high water consumption, and its tendency to increase the salinity of the soil around it, the tamarisk has often completely displaced native plants in wetland areas.

From a wildlife point of view, the tamarisk has little value and is usually considered detrimental to native animals. The leaves, twigs and seeds are extremely low in nutrients, and, as a result, very few insects or wildlife will use them. In one study along the lower Colorado River, tamarisk stands supported less than 1% of the winter bird life that would be found in a native plant stand. Because of the tamarisk's ability to eliminate competition and form single-species thickets, wildlife populations have dropped dramatically." Source: White Sands National Monument

So is invasive species removal worth it? It seems that, in the case of tamarisk, the best available science says yes. So we come in with the big yellow machinery.

We're not against natural change but we are against destructive change, change that impoverishes rather than re-invigorates. According to David Brower, restoration is the opposite of trying to stop the hands of time; it is an effort to keep the clock running: "The business of making something better, getting something back in shape--helping Nature heal--should make us feel good. And it will probably make our children feel better about us if we spent more time trying." David Brower Wild Earth Interview, Spring 1998.