A quantitative study of the vegetation of dry and dry-mesic sand prairies in Central and Northwestern Illinois

Moore, Michael James

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https://hdl.handle.net/2142/123948 Copy

Description

Title

A quantitative study of the vegetation of dry and dry-mesic sand prairies in Central and Northwestern Illinois

Author(s)

Moore, Michael James

Issue Date

1999

Director of Research (if dissertation) or Advisor (if thesis)

Robertson, Kenneth R.

Committee Member(s)

• Seigler, David
• Sargent, Malcolm S.

Department of Study

Plant Biology

Discipline

Plant Biology

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

M.S. (master's)

Degree Level

Thesis

Keyword(s)

• Quantitative Study
• Vegetation
• Dry Sand Prairies
• Central Illinois
• Northwestern Illinois
• Prairie Ecosystems
• Plant Communities
• Ecological Survey
• Habitat Analysis

Language

eng

Abstract

Dry and dry-mesic sand prairies in Illinois are mainly restricted to the glacial outwash and valley train deposits bordering major rivers in the northern half of the state, particularly the Illinois, Mississippi, and Rock Rivers. When compared to typical Illinois blacksoil prairies, these sand prairies are characterized by short vegetation and many species which are more common on prairies further west. Although the greatest amount of remaining high quality prairie in Illinois is in the form of dry and dry-mesic sand prairie, little research has been conducted on these sandy grasslands. This thesis focuses on studying the floristic and structural diversity, as well as the possible causes of such diversity, on ten of the remaining high quality dry and dry-mesic sand prairies in Illinois. Values for percent cover of every species in 1-m2 quadrats were obtained for transects at each site and used to determine values for total cover, Importance Value, and for species richness (S), diversity (H'), evenness (E), and dominance (C). The species composition at each site was used to compute Mean Coefficient of Conservatism, Floristic Quality Index, and Sorensen's Index of Similarity (to detect similarity in flora). Average percent cover values of species in transects were used for Principal Components Analyses (PCA). Schizachyrium scoparium was found to be the most important species across all sampling sites, although some sites were dominated by other species. Analysis of floristic similarity and ordinations indicated that all sites could be divided in one of two ways: (1) Mason County sand prairies and nonMason County (northwest Illinois) sand prairies, and (2) prairies dominated by Schizachyrium scoparium and prairies dominated by other species. Floristic similarities and differences were most important in supporting the first division, while values for structural diversity associated with presence or absence of S. scoparium were most important in the second division. Differences in floristic and structural diversity found among these two divisions are likely to be in response to two major ecological factors: moisture and disturbance history. Sites with higher soil moisture typically contained mesic species not found in drier prairies. Since these mesic prairies all lie outside Mason County, soil moisture appears partly to influence the separation of northwest Illinois sites from Mason County sites. This separation is loosely supported by the all sites ordination, in which the first axis appears to reflect a moisture gradient. Disturbance history is likely more important than moisture in explaining the overall differences in flora and structural diversity. Soil disturbance and grazing are likely to have caused the relatively low importance of S. scoparium and the high overall structural diversity that characterize a number of sites. Fire ( or lack thereof) does not seem to have affected the abundance of this grass, and thus is probably less important in explaining site differences. Of these three disturbances, soil disturbance appears to be the most important variable affecting the first PCA axis. Sites with the lowest abundance of S. scoparium all have a history of moderate to heavy soil disturbance, and these prairies ordinate along the first axis strongly opposite those sites with little history of soil disturbance (and thus high proportions of S. scoparium).

Type of Resource

text

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