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Infiltration of Prairie Soil

I'm inclined to agree with you.  Many fine roots in the soil usually
increases infiltration due to improved soil structure.  If prairies
prevented infiltration of rainfall, we'd see a fair amount of runoff from 
prairies, which we don't.

I believe that the researcher was correct in finding that the prairie soil
is generally dryer than forest soil, and this probably negatively
affects the germination of woody plants, but that doesn't mean
that rainfall infiltrates prairie soil more slowly than forest soil.  In
fact, the opposite may be the reason:  Is it possible that prairie soil
is dryer than forest soil partly because the water moves quickly down into
the subsoil/groundwater, out of the reach of the young woody plants?  Of
course the soil is dryer for other reasons too, like more exposure to
wind, sunlight, etc.

Chris.

On Mon, 24 Jul 2000, 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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