Date of Award:

5-1983

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Advisor/Chair:

Neil E. West

Abstract

The objectives of this research were to investigate the ecological importance of soil seed reserves and seed rain on regeneration of a good condition sagebrush- grass range vegetation after a wildfire and draw conclusions leading to better understanding and management of such ecosystems. Investigations were conducted for two successive years on a community where major plants were neither rhizomatous nor sprouting. In such cases soil seed reserves and seed rain have to be the main source of regeneration. In addition to monitoring soil seed reserves and seed rain, vegetation changes during the past two years and the historical conditions of the study area were examined.

Study of germinable soil seed reserve dynamics showed that fire can have a destructive effect on this portion of the community. Cheatgrass soil seed reserves were high even in good condition sagebrush-grass vegetation. Although fire reduced the Bromus tectorum seed bank by half, the cover of this grass increased to almost twice the level observed on the control (unburned) plots a year later. This shows the enormous reproductive capacity of this highly competitive weed species following a wildfire.

Even though the pre-burn vegetation contained a high proportion of native perennial plants, soil seed reserves and seed rain had very small proportions of their germinable seeds.

Timing of the fire is likely important in controlling undesirable range plants and their seeds. Had the fire occurred earlier when more seeds were attached to the culms, greater reduction in cheatgrass probably would have been obtained. Timing of the fire was just right to control sagebrush, because it occurred before their seed set and complete destruction of this species was achieved. Mormon tea was the only shrub to reestablish its cover relatively rapidly. This was related to its strong ability to sprout from root crowns.

Greater germinable soil seed reserves were found under shrub canopies than in the inter spaces. This is probably related to the semi-logarithmic dispersal of seed where seed fall is greatest closest to mother plants (Harper 1977). Since flammable fuel follows the same pattern, it was found that fire has a serious impact on soil seed reserves at "hot" points, but temperatures were apparently not hot enough to cause much damage on seed banks at "cold" points in the former interspaces.

Since soil seed reserves accumulate in significantly higher proportions in the surface 0-2 cm, fire has a more serious impact on the seeds in surface soil than those lower lower down.

Variance of the germinable seed rain was so high that none of the grand totals, life forms totals and species values were statistically significant at alpha

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