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Forest floor seed banks and their response to slashburning in some forest ecosystems in south central British Columbia

University of British Columbia

Soil seed banks are part of the flora of many ecosystems, but little is known about those of temperate coniferous forests in B.C., or their response to different disturbances. As a result, a study of forest floor seed banks and their response to the common disturbances of clearcutting and slashburning, was conducted in the Engelmann Spruce - Subalpine Fir (ESSF) and Interior Cedar - Hemlock (ICH) biogeoclimatic zones of south central B.C. Studies were carried out on the Devil's Club - Ladyfern sites series in the ESSFwc2 variant and on the Oak fern site series in the ICHwkl variant in the Clearwater Forest District. The species composition, numbers and distribution of seeds were determined through greenhouse germination of forest floor samples split into 1 cm layers. Germinant density was 2591/m² and689/m² in the ESSF and ICH samples, respectively. Most germinants (82 and 92% in the ESSF and ICH, respectively) belonged to the five most abundant taxa from each site and most (78 and 97% in the ESSF and ICH, respectively) were present in the top 3 cm of the forest floor. Seeds were poorly dispersed among the samples and highly clustered in the samples in which they occurred. Germinants of most taxa decreased with depth, but other distributions were found. Vertical distribution patterns varied widely among samples. Germination from the seed bank in both unburned and burned areas on the study sites showed that 1) germinant density was much lower in the field than in the greenhouse samples, and 2) burned areas had many fewer germinants than did unburned areas on the ESSF site, but the reverse was found on the ICH site. Soil temperatures were measured during and after slashburning on the study sites. Forest floor depth of burn was also measured, and no relationship could be demonstrated between depth of burn and soil temperatures during burning. Therefore, the effect of elevated temperatures on buried seeds could not be determined. Shading reduced post-burn soil temperatures on both sites, but the influence of these temperatures on germination was not clear due to inconsistent results and lack of replication. Burning significantly reduced germination, whereas shading resulted in significantly more germinants in burned, but not unburned, areas of the ESSF site. The effect of shading and burning on germination on the ICH site could not be determined due to a lack of germinants.

Thesis/Dissertation

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2008-09-22

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http://hdl.handle.net/2429/2340

Forestry

University of British Columbia

UBCV

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