Masters Theses

Date of Award

12-1981

Degree Type

Thesis

Degree Name

Master of Science

Major

Botany

Major Professor

Edward E. C. Clebsch

Committee Members

H. R. DeSelm, J. S. Olson

Abstract

Information concerning the regeneration capabilities of plant species contributes substantially to the understanding of their ecology. Three factors of the regenerative phase of the life cycle are considered: (1) the quantity of resources allocated to reproduction, (2) the general mode(s) of reproduction, and (3) the timing of regeneration. The relationships among these three factors are examined for 11 herbaceous species colonizing annually disturbed soil. In addition, the current literature on regeneration in herbaceous plants and the internal budget-ing of resources is reviewed.

The responses of invading plant communities to season of soil disturbance were also considered. First year plant communities were plowed at different times of the year with three replications per plow-ing treatment. The resultant communities were distinct with respect to species composition, species diversity, and vegetative cover. A number of species, the majority of them perennials, failed to regenerate in the late spring and summer plowed fields. Consequently, total species richness was low in the late spring and summer treatments.

Seasonal variation in the regeneration capabilities of each life cycle grouping (annual, biennial, or perennial) was assessed by the examination of plant density, frequency, percent cover, and species richness in each treatment. The regeneration of annuals was greatest in the April and June plowed fields, while the regeneration of perennials was greatest in the December plowed fields. Few perennials appeared in the April treatment, suggesting a lack of summer regeneration within this group.

A biomass allocation study provided information on the reproductive capacity of 11 herbs. Reproductive allocation was found to be inversely related to stem allocation. As stem allocation increased in light-limited conditions, reproductive allocation decreased. It was concluded that biomass allocation may have been an unreliable measure of resource budgets because of phenotypic responses to light availability.

Estimates of high total reproductive allocation for two perennial species challenge theoretical predictions that perennial plants should have lower reproductive budgets than related annual plants. A model that considers the cost of dispersal is proposed to explain the differences in sexual reproductive allocation between annual and perennial species.

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