February 23, 2011

Papers I'm reading: Declining sand dune activity in the southern Canadian prairies

"Visually, the dunes were incredible. They were at least four to five meters in height standing from the top, and there were about four-five rows of dunes. Most of them ran north-south in length. The wind picked up while we were there and I can understand how the dunes are moving so many mm's/cm's each year. The area surrounding the dunes was very desert-like (we spent one night nearby and I managed to get a cactus stuck in my foot, hurt very much). We could also hear the coyotes howl all night and in the morning witnessed several hawks flying by. The area was extremely dry, so much so that I even came across a sort of animal grave yard at the far north part of the main dunes. There was several skeletal remains of what I assumed to be cattle, though the bones were quite small and could have been deer. There were also plenty of little bugs wandering around the dunes, leaving their tracks in the sand, though I couldn't say what kind of bugs they were (although there were many "tiger bugs" I think that's what they are called)."
The above excerpt is courtesy of an aspiring journalist friend who has a keen instinct for the geographic/geologic, detailing an experience among some spectacular sand dunes: Writer's Fidelity

Her description of majestic dunes in southern Saskatchewan segues into the latest dozen-page intellectual nugget, coming courtesy of the Journal of Aeolian Research. The article is titled Declining sand dune activity in the southern Canadian prairies: Historical context, controls and ecosystem implications, authored by Chris Hugenholtz, Darren Bender, and Stephen Wolfe. The paper goes into detail about how the patchy sand dunes located in Southeast Alberta-Southwest Saskatchewan have been seeing a slow but steady decline for the past hundred years or so, and how this decline affects the ecosystem balance and the organisms that reside in the relict landforms:
Sandhills are islands of biodiversity in the southern Canadian prairies that sustain habitat for many rare and endangered species. These unique areas consist of large expanses of dune fields now mostly stabilized by grassland vegetation. Historically, the number of active dunes has decreased significantly due to vegetation stabilization, resulting in a dramatic decline of open-sand habitat for a variety of dune-dependent species. Without a certain level of wind erosion, opportunities for establishment of early-stage, species-rich vegetation types are diminished and open-sand habitat decreases by encroachment of the surrounding grassland vegetation. The current trend of dune stabilization, however, implies that wind erosion is decreasing, thereby threatening the continued existence of a variety of dune-dependent plants, arthropods and vertebrates, as well as other less-specialized species that benefit indirectly from these habitats. By reviewing factors contributing to the historical decline of active dunes, as well as the ecological implications of dune stabilization, the aim of this paper is to establish the biophysical context for new land management strategies that conserve valued landscape components, such as active dunes, and the processes therein. As dune stabilization continues management interventions will be required to sustain or re-establish open sand and the species that rely on these habitats.
Blowout dunes of Great Sand Hills, SW Saskatchewan
You can take a look in Google Earth @  50° 41.326'N 109° 17.069'W; most of the dunes are of the parabolic variety. The dunes are essentially relics from end of Pleistocene ice ages, notably the Wisconsonian, that have persisted due to a semi-arid precipitation regime and infrequent prolonged droughts typical of the prairies in SE Alberta/SW Saskatchewan. The southern prairies exhibit heavily glaciated terrain, wherein these glaciomarine-glaciodeltaic-glaciofluvial sands were derived from meltwaters at glacial fronts, and the region was subjected to katabatic winds flowing down off the front. The cold, sweeping winds were an excellent local atmospheric mechanism for sorting the sand into dunes.

The paper shows dune activity in 1900's declining due to dune stabilization via vegetation. Provincial action plans to reduce soil erosion has had a lateral effect upon the fragile ecosystem of the dunes and their plant & animal inhabitants. Thus in many ways, it is a "Damned if you do, Damned if you don't" issue, with anthropogenic activities being vastly responsible for currently affecting dune stabilization or proliferation. If left alone, the current climate change trend towards warming & disruption of precipitation regimes would likely lead to an increase in dune areal coverage, but only if decade-long droughts consistently occur. How does that work, though? If humans don't interfere with the dunes, our interference in the atmosphere will allow them to flourish?? In any case, the latter is already assured due to the lag of GHG's.

Ord's Kangaroo rat on sand hills
The real crux of the paper outlines what the implications are for the endemic flora & fauna. Since sand transport is effectively eliminated when vegetation cover exceeds 15%, the fragility of the dunes is acute due to the presence of rare, endangered species that habituate on blowout dunes. Within the paper there is listed over a dozen species of plants and animals in danger of extirpation. Examples include liverworts, arthropods, and the unique Ord's kangaroo rat. The latter is under threat due to dune stabilization allowing predators to corner the rats into an increasingly smaller territory with less space for effective burrowing. The dunes are stabilized by vegetation in a positive feedback mechanism that allows ruderal plants to proliferate on the dune perimeter by increasing surface roughness and changing soil properties to suite further veg expansion → if this goes too far, it will push out endangered dune-loving species like Ord's rat. The endemic animal plays a key role in the food web ecology of the southern prairies, extending an indirect influence outside the dune hills.

Co-operative efforts are underway in the prairies to allow some wind-driven erosion to facilitate natural dune migration & extent, though there is some back-forth wrangling with farm associations that prefer stabilization that protects soil resources. When looking at, for instance, the Great Sand Hills near Leader using Google Earth, you can see how farm lots completely surround the dunes. To conclude my observations, I generally get 3 things out of a peer-reviewed paper: 
  1. A new term learned; in this case it was ruderal
  2. A new question raised; in this case how does food security fit into the mix? If prairie farmers are wishing to avoid migrating dunes overtaking their lots, how do we address their concerns while allowing the dunes to flourish?
  3. A new realization; in this case connecting elements to learn how glaciers can form picture-perfect dunes. I knew of katabatic winds, I knew that wind is the greatest terrestrial sorter, and that glaciofluvial is second greatest & capable of transporting & sorting fine sand. Integrate the mechanisms together to make the dunes?....I did not realize that til now.
Additional Info:

    2 comments:

    Jesse said...

    very nice, Malcolm! Would also like to check out the Athabaska sand dunes, if poisons from the neighbouring tar sands don't destroy them first.

    Sean said...

    wouldn't want to destroy lifeless sand for the sake of people having jobs. Jobs that feed their family and pay for the nations healthcare