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Re: what are your thoughts on this?

I did not hear this paper so these questions may have been answered:

1)  What were the textures of the soils at each "paired" observation sites?  To overly
simplify, fine textured (more rich in clay) will have greater infiltration than coarse
textured (more rich in sand).

2) What was the slope position of each member of the "paired" observations?
a)  Having visited Rolling Thunder several times, I have seen that this *remnant* prairie
is in an area of highly dissected topography -- this could mean that there are great
differences in soil type / soil map unit within very short distances.
b)  The Warren County Conservation Board restoration efforts are a wonder to see (and are
continuing).  I speculate that they quite correctly began their work where there were
visible prairie plants on the steep, clay-dominated paleosol slopes and not in the heavily
tree and brush invaded draws and stream valley.  This artifact of the restoration process
could bias the "prairie" part of each "pair" to be in an area of slower infiltration (see
1 above).
c)  From personal observation, in the narrow lower parts of Rolling Thunder, along draws
and the stream valley, there is considerable deposition of the topsoil eroded from
adjacent areas higher in the landscape (both on and off the preserve); this deposition has
happened since Euro-American settlement and can be found in every valley, draw, swale,
oxbow, pothole, and lake in Iowa.  These rich sediments have been stripped for over 150
years not only from row crop ground (extremely high erosion rates) but also from heavily
grazed pastures denuded by season-long grazing of both native prairie and domestic grass
pastures (lower, but still high erosion rates).  The boundry between this post settlement
alluvium / colluvium and the eroded soils of the adjacent slope often is very sharp and
could have been present between the members of "paired" observations which could cause
great differences in infiltration rates.

Perhaps all of the above has been taken into account in the paper in question (I now wish
that I had heard it!), but, no mention is made of them in the abstract.

Sandy Rhodes



Lee Stone wrote:

> Hello, Everyone,
>
> I just got back from a very pleasant and memorable 17th North American
> Prairie Conference in Iowa.  Iowa did a GREAT job hosting it.  It was
> the best of the four NAPCs I have attended.
>
> There was one paper which took me by surprise and I would like your
> comments on it.  The title and abstract are below.
>
> "The control of infiltration as a mechanism for the self-regulation of
> prairie ecosystems: Preliminary studies at Rolling Thunder Prairie State
> Preserve, Warren County, Iowa."  Steven H. Emerman, Dept. of Biology and
> Environmental Science, Simpson College, Indianola, Iowa 50125
>
> "All of Iowa's prairie preserves are subject to invasion by woody
> plants.  Most studies see the movement of the prairie / forest boundary
> as a passive response to the external forces of climate change,
> overgrazing and fire suppression.  An alternative hypothesis is that the
> prairie ecosystem actively repels woody invasion by growing in such a
> way as to keep the soil moisture too low for woody plants.  The soil
> moisture is kept low by inhibiting the infiltration of water which is
> controlled by the thickness of the plant roots and the activity of
> burrowing animals." (Note by me:  no evidence was provided for this
> statement.)  "The hypothesis was tested at Rolling Thunder Prairie State
> Preserve in southern Warren County in a portion of the prairie which had
> not been burned for two years.  At 8 widely-separated sites, the
> field-saturated hydraulic conductivity Kfs was measured 5 m upslope and
> 5 m downslope from the prairie / forest boundary.  In five cases, Kfs
> was greater within the woody invaders than within the prairie; in three
> cases, Kfs was the same within the woody invaders as within the
> prairie.  Mixed results were obtained from the burned portion of the
> prairie."
>
> I don't think highly of this study or the hypothesis.  Doesn't seem like
> rigorous science.
>
> Please note where the speaker states that the finer roots of the grasses
> make it harder for water to penetrate.  Yet prairie people here in Texas
> have been saying that grasslands are one of the finest plant communities
> for capturing and moving rainwater into the ground.  This is based on
> work done in the Seco Watershed in western Texas by the Agri Extension
> Service and Tx A&M where prolific junipers were removed from portions of
> a watershed, replaced by native grasses whose seeds were in the soil
> bank, and where springs began to flow again, etc. etc.
>
> Comments?
>
> lee stone
> Austin, TX
>
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