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BREAKAGE VS. UPROOTING & HILLSLOPE GEOMORPHOLOGY

Just published in Geomorphology:

Samonil, P., Danek, P., Adam, D., Phillips, J.D. 2017. Breakage or uprooting: how tree death affects hillslope processes in old-growth temperate forestsGeomorphology 299: 276-284. 

The abstract is below:

Posted 14 November 2017

 

HOW COMPLEX CAN IT BE?

Back in 2006, novelist and country music singer-songwriter Kinky Friedman ran (unsuccessfully) for governor of Texas. His campaign slogan, a rather pointed reference to the fact that recent occupants of the office George W. Bush and Rick Perry were not the sharpest tools in the shed, was "how hard could it be?" I can't answer that, but I can answer, after a fashion, the question of how complex or simple an Earth surface system can be.

AXIOMS OF GEOMORPHOLOGY

Axiomatic approaches to science and mathematics depend on an underlying set of statements, principles, or propositions that apply to all situations within the domain of study. The axioms run the gamut from undisputed universal laws to widely or even universally accepted but unproved or unprovable generalizations, to propositional stipulations adopted for analytical convenience or because they raise interesting questions.

Examples abound in mathematics and formal logic, and in science, engineering and technological applications of math and logic. Although it is only occasionally referred to as such, the laws of stratigraphy (details in any geology textbook) form an axiomatic approach to sedimentology, sedimentary geology, and related palaeoenvironmental studies. The laws of original horizontality, lateral continuity, superposition, and cross-cutting relationships are assumed in this approach to apply to all sedimentary deposits, and therefore form an axiomatic system for interpretation.

Robustness of Chronosequences

The latest issue of Ecological Modelling (vol. 298) is out, a special issue on complexity of soils and hydrology in ecosystems. My article, The Robustness of Chronosequences, is available here. There's a lot of other interesting stuff in the special issue, too. Check it out!

Δ DELTAS

 

Several studies have noted the temporal coincidence between shoreline erosion around some major deltas (e.g., Nile, Mississippi, Ebro), and the reduction of stream sediment loads due to reforestation, soil conservation practices, and trapping of river sediment behind dams. There are, of course, excellent reasons to suspect a causal link, but the link itself has not, in my view, been fully established.

THE CYCLE OF EROSION

 

Out on the trails of Shaker Village at Pleasant Hill, Kentucky, this morning, I got to thinking about William Morris Davis’ “cycle of erosion” conceptual model (also called the geographical or geomorphological cycle). The drive-by, oversimplified version is that landscape evolution starts with uplift of a more-or-less planar, low relief surface. Weathering and erosion goes to work, and results in an initial stage of increasing relief as streams carve valleys, and slope processes operate on the slopes thereby created. Eventually, however, as the streams begin to approach base level, a new stage of decreasing relief begins as hilltops and drainage divides are lowered and valleys infilled. This continues until the entire landscape is about as close to baselevel as the geophysics of mass transport will allow, creating a low-relief, almost-planar surface called a peneplain. At some point a new episode of uplift occurs and the cycle begins anew.

I was thinking of this because many landscapes in the world, like the one I was viewing this morning, do give the impression of a dissected plateau or a low-relief surface into which denudational processes have cut.

BADASS GEOMORPHOLOGY II

The published version of Badass Geomorphology is hot off the press in Earth Surface Processes & Landforms. You can download it here.

HYDROPEDOLOGY: FLUX-STRUCTURE INTERACTIONS

Subfields such as biogeomorphology, ecohydrology, geoecology, soil geomorphology are areas of overlap between disciplines and subdisciplines. They are governed by the paradigms of the overlapping fields, and fit more or less comfortably within, and at the boundaries of, those fields. They do not have an independent paradigm or conceptual framework (which in no way reduces their importance or vitality).

Landscape ecology, by contrast, has developed its own paradigm—pattern, process, scale—that is independent from mainstream ecology, biogeography, and geospatial analysis.

Does, or can, hydropedology have such an independent paradigm? Is its development best served by, say, the ecohydrology or soil geomorphology model as an overlap field dominated by existing paradigms of pedology and hydrology? Or is a landscape ecology, separate paradigm direction more appropriate?

OPTIMALITY IN EARTH SURFACE SYSTEMS

 

A number of theories in geomorphology, ecology, hydrology, etc. are based on the idea that Earth surface systems (ESS) develop according to some optimal principle or goal function. That is, the ESS develops so as to maximize, minimize, equalize, or optimize some quantity—energy, exergy, entropy, work, mass flux, etc.  Some of these notions have some explanatory power and have resulted in some important insights. However, they have always bothered me--no one has ever been able to convince me that there is any inherent, a priori, rule, law, or reason that, e.g., a hillslope or a stream channel or a soil would operate so as to optimize anything. The conservation laws for mass, energy, and momentum are the only laws of nature that absolutely must hold everywhere and always.

So how does one explain the apparent success of some optimality principles in describing, and even predicting, real ESS behavior?

Suppose we use P to represent possible developmental pathways for an ESS. An optimality principle is essentially arguing that a particular P among all those possible is the most likely1. But the sufficient conditions for a particular path need not invoke any extremal or optimal goal functions.

DUST BOWL DYNAMICS

A conversation with other scientists about severe, dust-bowl type wind erosion and erosion risks got me to thinking about the key interrelationships involved. The severe erosion and land degradation in the U.S. Great Plains in the 1930s was a combination of a particular confluence of environmental factors that set up aeolian erosion risk (climate, periodic low soil moisture, topography), a prolonged drought, and human factors (replacing natural grassland vegetation with crops that left fields bare part of the year).  In other areas where the environmental risk factors are present, how stable or resilient is the landscape to severe wind erosion?

Archival photo from Kansas showing cropland degraded by wind erosion in the 1930s. 

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