Document: JUL-3-64-24

The role of the soil seed bank in understory Ponderosa Pine restoration.

KORB, J.E.*, W.W.COVINGTON and P.Z.FULE

Northern Arizona University, Flagstaff, AZ 86011, U.S.A. ¹

Abstract:
The soil seed bank often plays an important role in the natural regeneration of herbaceous and woody vegetation following disturbance. Environments with numerous native seeds in the soil bank can often reestablish without manual seeding of native species. In addition, the soil seed bank can be used as a potential indicator of early successional community response following disturbance. The effects of restoration tree thinning on the soil seed bank in a northern Arizona ponderosa pine forest were investigated using the seedling emergence method. Three thinned units and three uncut controls of approximately 20-ha were each sampled. Seed bank samples were separated into different depth distributions: litter, 0-5 cm, and 5-10 cm. A total of 36 species were present to a depth of 10 cm. Five of these species were not present in the aboveground vegetation of the study area. Seed density and diversity were highest in the 0-5 cm depth for both thinned and uncut units. Seed diversity was unaffected by thinning treatments; however, seed density was greater in the uncut control units. The number of native viable seeds/m2 in the litter layer was a significantly higher (p<0.05) than the number of exotic viable seeds/m2 in the litter layer. There was no significant difference (p<0.05) between the number of native and exotic viable seeds/m2 in the 0-5 cm or 5-10 cm depth. As a result, prescribed fire may initially reduce the number of native viable seeds/m2 when the litter is consumed during burning. Verbascum thapsus, an exotic early successional species, dominated the number of viable seeds/m2 for the thinned (24%) and control (30%) units. These seeds were highly clustered and were more prevalent in areas subject to repeated historical disturbance (thinning and grazing). Similarily, native weedy annuals were more dominate in areas of repeated disturbance. These preliminary study results indicate that restoration thinning does not have a negative effect on soil seed bank species richness or the distribution of seeds within the soil profile. These results do indicate however, that land management history (amount of repeated disturbance over time) may play an important role in the recovery response of the herbaceous and woody understory in ponderosa pine restoration.

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This abstract is being presented at: 10:45 AM in session:
Oral Session #60: Forest Restoration.