Here in the University of Kentucky physical geography program, we have a regular weekly meeting called BRAG (Biogeomorphology Research & Analysis Group) in which various faculty and graduate students from geography and other programs cuss, discuss, debate, and speculate about a wide range of topics centered on geomorphology-ecology interactions. A couple of years ago we focused quite a bit on the biogeomorphic ecosystem engineering effects of invasive species. That led to development of a review paper, which at long last was published, in the Annual Review of Ecology, Evolution, and Systematics—The biogeomorphic impacts of invasive species. The co-authors are myself, Songlin Fei, and Michael Shouse. Songlin, now at Purdue University, was then in the Forestry department at UK, and a regular participant in BRAG. Michael, now at Southern Illinois University-Edwardsville, was then a geography PhD student here.

The abstract is below, and a ScienceDaily news release is here: http://www.sciencedaily.com/releases/2014/12/141211115522.htm

ABSTRACT: Invasive species, often recognized as ecosystem engineers, can dramatically alter geomorphic processes and landforms. Our review shows that the bio- geomorphic impacts of invasive species are common, but variable in magnitude or severity, ranging from simple acceleration or deceleration of preexisting geomorphic processes to landscape metamorphosis. Primary effects of invasive flora are bioconstruction and bioprotection, whereas primary effects of invasive fauna are bioturbation, bioerosion, and bioconstruction. Land- water interfaces seem particularly vulnerable to biogeomorphic impacts of invasive species. Although not different from biogeomorphic impacts in general, invasive species are far more likely to lead to major geomorphic changes or landscape metamorphosis, which can have long-lasting impacts. In addition, invasive species can alter selection pressures in both macroevolution and microevolution by changing geomorphic processes. However, the differing timescales of biological invasions, landscape evolution, and biological evolution complicate assessment of the evolutionary impacts of invasive organisms.

Songlin and Michael have much more experience and expertise in invasive species than I, but one of my interests is the coevolution of biota, ecosystems, landforms, and soils. In particular, I’ve been thinking about how the appearance of new organisms via speciation and dispersal at evolutionary time scales can lead to landscape metamorphosis. The documentation of profound biogeomorphic changes due to newly-introduced species provides a nice proof-of-concept in this regard.

Reference:  Fei, S., Phillips, J.D., Shouse, M.A., 2014. Biogeomorphic impacts of invasive species. Annual Review of Ecology, Evolution, and Systematics 45: 69-87 doi: 10.1146/annurev-ecolsys-120213-091928.

Natural selection is most familiar with respect to Darwinian evolution. However, though some biologists will argue that selection acts only on genes, this is a very narrow and restricted view. Selection operates on a variety of environmental phenomena, and at a variety of scales. In hydrology and geomorphology, the principle of gradient selection dictates that the most efficient flow paths are preferred over less efficient ones, and that these paths tend to be reinforced. That’s why water flows organize themselves into channels (more efficient than diffuse flows), and channels into networks. The principle of resistance selection in geomorphology is simply that more resistant features will persist while less resistant ones will be removed more quickly. Thus geomorphic processes select for certain forms and features and against others. Among others, Gerald Nanson, Rowl Twidale, and Luna Leopold have written on selection in geomorphology, and Henry Lin, among others, in hydrology.

Principle of gradient selection at work--Board Camp Creek, Arkansas

Natural selection also operates at ecological scales. When seeds arrive on a patch of ground, for example, edaphic factors sort out which ones can or cannot germinate, and which of those that do falter or prosper. This sorting or sifting of arriving species is at the heart of Gleason’s individualistic concept of plant associations, but operates in ecological systems in general.

Andreas Lapenis has written on biogeochemical selection, whereby more efficient cyclers of energy, water, and nutrients are favored—obviously here selection is acting at the level of ecological function, not genes. In weathering and soil formation, resistant minerals are preferentially preserved and concentrated.

There are, no doubt, many examples of sorting, sifting, and preferential preservation in Earth and environmental sciences. Thus, while Darwin and Wallace first articulated this logic with respect to the origin of biological species, selective processes are ubiquitous in the natural world.

My own earlier thoughts on these issues can be found in the citations below.

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Phillips, J.D.  2011.  Emergence and pseudo-equilibrium in geomorphology. Geomorphology 132: 319-326.

Phillips, J.D. 2010. The job of the river. Earth Surface Processes and Landforms 35: 305-313.

Phillips, J.D. 2008. Goal functions in ecosystem and biosphere evolution.  Progress in Physical Geography 32: 51-64. 

Recently published in Earth Surface Processes & Landforms: Anastamosing Channels in the Lower Neches River Valley, Texas. The abstract is below: 

Active and semi-active anastomosing Holocene channels upstream of the delta in the lower valley of the meandering Neches River in southeast Texas represent several morphologically distinct and hydrologically independent channel systems. These appear to have a common origin as multi-thread crevasse channels strongly influenced by antecedent morphology. Levee breaching leads to steeper cross-valley flows toward floodplain basins associated with Pleistocene meander scars, creating multi-thread channels that persist due to additional tributary contributions and ground water inputs. Results are consistent with the notion of plural systems where main channels, tributaries, and sub-channels may have different morphologies and hydrogeomorphic functions. The adjacent Trinity and Sabine Rivers have similar environmental controls, yet the Trinity lacks evidence of extensive anastomosing channels on its floodplain, and those of the Sabine appear to be of different origin. The paper highlights the effects of geographical and historical contingency and hydrological idiosyncrasy.

Grayscale slope map of study area showing the large depressions in the lower Neches River floodplain (black=zero slope to white = maximum slope = 0.06).

Reference: Phillips, J.D., 2014. Anastamosing channels in the lower Neches River valley, Texas. Earth Surface Processes and Landforms 39, 1888-1899.

I recently watched an episode of the Syfy Channel’s post-apocalyptic zombie show Z-Nation. The human survivors were making their way across the U.S. Midwest when a massive tornado spun up, picking up zombies and flinging them all over the place.

“Is that what I think it is?” asks one character, observing the oncoming cyclone of the undead. “It ain’t sharks,” says his companion. This is, of course, a reference to the infamous “Sharknado” movie in which a tornado at sea (technically a waterspout, I reckon) sucks up a bunch of sharks and blows them into Los Angeles. Sharknado is, by all accounts, a thoroughly ridiculous movie with no scientific validity.

The tornado in the background is just about to suck up these flesh-eating freaks from beyond the grave to form an un-deadly Z-nado!

This movie poster tells you all you need to know. 

But . . . biogeographers have shown that long-distance dispersal of species does occur due to storms!  Rapid, long-distance movement (geographic range expansion) is called jump dispersal. A classic example involving storms is the cattle egret. Native to Africa, the birds were essentially blown across the Atlantic to the Americas by a tropical cyclone (this example is covered in many biogeography textbooks). Other studies show jump dispersal of lizards by hurricanes. A recent article by Monzón-Argüello and company (2012) demonstrates storm-driven jump dispersal for sea turtles.  From their abstract: “As such, storms may be a route by which unexpected areas are encountered by juveniles which may in turn shape adult migrations. Increased stormy weather predicted under climate change scenarios suggests an increasing role of storms in dispersal of sea turtles and other marine groups with life-stages near the ocean surface.”

So, get ready for the possibility of more jump dispersals! There is no reason the phenomenon should be limited to marine life, however—wind-dispersed seeds, for instance, could be subject to storm-driven range expansion.

Which brings me to my idea for a script, in the spirit of Sharknado. I call it “Hurri-cane Toads.” A tropical cyclone whips across northern Australia, sucking up millions of invasive cane toads—huge, ravenous, poisonous amphibians—and dumps them on the unsuspecting citizens of, say, Brisbane or Sydney.

Cane toads (above) + hurricane = Hurri-cane Toads = hit movie?

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Monzón-Argüello, C. & 8 others, 2012. Lost at sea: genetic, oceanographic and meteorological evidence for storm-forced dispersal. Journal of the Royal Society Interface, doi: 10.1098/ rsif.2011.0788. 

Hot off the press, our (myself, Dan Marion, Chad Yocum, Stephanie Mehlhope, and Jeff Olson) study of geomorphic impacts of a tornado blowdown event. You can get a copy here: https://www.researchgate.net/profile/Jonathan_Phillips4/publications

The abstract is below:

Geomorphological Impacts of a tornado disturbance in a subtropical forest.

We studied tree uprooting associated with an EF2 tornado that touched down in portions of the Ouachita Moun- tains in western Arkansas in 2009. In the severe blowdown areas all trees in the mixed shortleaf pine–hardwood forest were uprooted or broken, with no relationship between tree species or size and whether uprooting or breakage occurred. There was also no significant relationship between tree species and amount of soil displaced, and only a weak relationship between tree size and rootwad size. Uprooting resulted in a mean bioturbation rate of 205 m³ ha⁻¹ (about 240 t ha⁻¹). Direct transfer of wind energy via tree uprooting to geomorphic work of soil displacement was about 75 to 190 J m⁻². Given the infrequency of tornadoes, this energy subsidy is minor with respect to the long-term energetics of pedogenesis and landscape evolution. However, it does represent a highly significant pulse of geomorphically-significant energy relative to other mechanical processes. Tornadoes such as that of April, 2009—not atypical for the region—are disturbances causing severe, non-selective impacts within the affected area. At a broader, landscape scale, tornadoes are highly localized disturbances, and occur infrequently within any given landform element or forest stand. Only about a third of the uproots revealed root penetration of bedrock, compared to about 90% in other areas of the Ouachita Mountains. This is attributable to the thicker colluvial soils at the study site, and is consistent with the idea that root–bedrock interaction is more likely in thinner regolith covers.

Last month the climatologist Justin Maxwell from Indiana University gave an interesting talk at our department about drought-busting tropical cyclones. In his talk, and in conversations before and after with our physical geography crew, he had some interesting things to say about climate teleconnections involving mainly sea surface temperature and pressure patterns such as ENSO, NAO, etc. If teleconnections and the various acronyms are unfamiliar, check out the National Climatic Data Center’s teleconnections page: http://www.ncdc.noaa.gov/teleconnections/

In the northern hemisphere there are at least 10 of these that influence our weather and climate. So after talking and listening to Justin I got the idea to apply some algebraic graph theory methods I’ve been using to assess complexity and to identify patterns in geomorphology and pedology to these teleconnections. The idea was to set up a network (graph) where each of these teleconnection patterns is a node. These nodes would be considered positively connected if their phases are synchronized—that is, they both tend to be in positive or negative phases at the same time. A negative connection would exist if they tend to be in opposite phases, and no link if their phases are apparently unrelated.  

I got the time series of monthly teleconnection pattern indices here: http://www.cpc.ncep.noaa.gov/data/teledoc/telecontents.shtml. I then used these time series (1950 to present) to try to identify the connections. Unfortunately, the plots all look more or less like this:

Plot of values of the North Atlantic Oscillation (NAO) index (vertical axis) vs. the East Atlantic (EA) index (horizontal axis).

Once could interpret this either of two ways. One is that the indices are all unrelated to each other, producing a meaningless graph/network of completely unconnected nodes. Another interpretation is that ALL connections are possible—that is, a positive or negative phase of any teleconnection pattern may be associated (synchronous) with a positive or negative phase of any other. This would result in mathematical graph of the maximum possible complexity for the number of nodes.

Climatologists are increasingly able to explain more and more phenomena based on these teleconnection patterns, and that trend will continue. But my little foray into that work shows that as all of these global teleconnections operate contemporaneously, with their weather and climate impacts superimposed on each other, the system is extremely and inherently complex—consistent with earlier determinations of chaotic dynamics of the atmosphere.

As Yogi Berra is supposed to have said: “Prediction is difficult; especially the future.”

I got a few e-mails last week about fluvial geomorphology—not because of anything I have done, or any current issues or unresolved questions in that field. No, it was because a character in the irreverent Comedy Central show South Park was identified on the show as a fluvial geomorphologist. Apparently that gives us a measure of popular culture street cred.

South Park character Randy Marsh, in his pop singer Lorde disguise.

An actual geomorphologist named Randy (R. Schaetzl, Department of Geography, Michigan State University).

Early in October, an episode of the show was based on the premise that the New Zealand pop singer Lorde is actually a 45 year old man, Randy Marsh, a regular character on the show. As explained during the episode, “Lorde isn’t just a singer, she’s also a very talented scientist who specialises in fluvial geomorphology.” If this is all a bit confusing, see http://musicfeeds.com.au/news/lordes-true-identity-revealed-on-south-park/

Randy Marsh has long been identified as a geologist on the show; I seems to have some memory that in the past he was identified as a volcanologist. True or not, we welcome all to the ranks of geomorphologists, fictional characters or not. 

I've thought, written, and talked a lot about the need to incorporate geographical and historical contingency--that is, idiosyncratic characteristics of place and history--in geosciences, in addition to (not instead of!) general or universal laws. I've also emphasized the fact that places and environmental systems have elements of uniqueness. This leads to the issue of how to measure or assess place similarity (or the similarity of different, e.g., landscapes, ecosystems, plant communities, soils, etc.). This is a way of thinking about this problem, dressed up with some formal mathematical symbolism. Though I'm personally pretty informal, I'm a big believer in formal statements in science, as it makes arguments at least partly independent of linguistic skills (or lack thereof). 

In fluid dynamics the Reynolds Number is the ratio of inertial to viscous forces, and is used to distinguish laminar from turbulent flow. Peter Haff (2007) applied this logic to develop a landscape Reynolds number, and also suggested how other generalized “Reynolds numbers” can be constructed as ratios of large-scale to small-scale diffusivities to measure the efficiencies of complex processes that affect the surface. As far as I know, there has been little follow-up of this suggestion, but the premise seems to me quite promising at an even more general level, to produce dimensionless indices reflecting the ratio of larger to smaller scale sets of processes or relationships. The attached file gives a couple of examples. 

Climate change is here, it’s real, and it won’t be easy for humans to deal with. But few things are all good or all bad, and so it may be for climate change, at least with respect to environmental science and management.

A vast literature has accumulated in the past two or three decades in geosciences, environmental sciences, and ecology acknowledging the pervasive—and to some extent irreducible—roles of uncertainty and contingency. This does not make prediction impossible or unfeasible, but does change the context of prediction. We are obliged to not only acknowledge uncertainty, but also to frame prediction in terms of ranges or envelopes of probabilities and possibilities rather than single predicted outcomes. Think of hurricane track forecasts, which acknowledge a range of possible pathways, and that the uncertainty increases into the future.

Forecast track for Hurricane Lili, September 30, 2002. The range of possible tracks and the increasing uncertainty over time are clear. Source: National Hurricane Center.

Applied environmental science and environmental management has traditionally been based on what I think of as a medical-style model—if a patient is presenting certain symptoms, then this is the treatment. The environmental analogy, be it forest or range management, agricultural policy, stream restoration, etc., has been similar—if this is the problem or the situation, then that is what you do. Sometimes this works; sometimes it doesn’t.

An approach more consistent with the way environmental systems actually work is based on flexibility, adaptability, and identifying ranges of options. This is the case with or without climate change, but perhaps dealing with the uncertainties, path dependence, complex interconnections, and inevitable surprises we know are associated with ongoing and near-future climate change, we can change the culture of environmental and natural resource policy and management. Rather than (at least implicitly) pretending certainty in forecasts, we acknowledge uncertainty, contingency, and possible surprises. Rather than single prescribed management options, we develop and present ranges of options, with multiple objectives and multiple potential pathways. And rather than implementing a policy, restoration scheme, etc., and “riding it until it crashes,” we build in flexibility and adaptive capacity.