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UBC Theses and Dissertations

Soil seed banks, heterogeneity, and plant community assembly following disturbance by fire and logging in Interior Douglas-fir forests Stark, Kaeli Elizabeth

Abstract

Soil seed banks and establishing plant communities were examined in Interior Douglasfir forests within the first year following low severity fire, high severity fire, and logging, as well as on five-year-old burned sites and ten-year-old logged sites, and undisturbed sites in the vicinity. The effects of different types of disturbance on the regenerative potential and spatial structure of forest plant communities were compared using univariate and multivariate analytical methods. On the one-year-old severely burned sites, the species composition of the seed bank and establishing vegetation were similar because a high proportion of the establishing vegetation of was of seed origin; however, differences between seed bank and vegetation species composition were detected for the one-year-old lightly burned and logged sites, and the undisturbed reference sites. Whereas the frequency of seed-origin plants in the establishing vegetation decreased in the order lightly burned > severely burned > logged, the frequency of root-derived plants did not differ across disturbance types. The low frequency of seed-derived plants, particularly conifer seedlings, on logged sites poses concerns for the initial recovery of vegetation following logging; nonetheless, the lack of significant differences in species composition between five-year-old burned sites, ten-year-old logged sites and their corresponding undisturbed sites suggests that vegetation recovery occurs with time. Considerable spatial variation in seed bank and vegetation species composition occurred both among and within the one-year-old sites. In general, disturbed sites exhibited less among-site heterogeneity than undisturbed sites, likely because of homogenizing, post-disturbance seed rain events; however, within-site variability in seed bank species assemblages was greatest on severely burned and logged sites. Species-area curves and jackknife estimates indicated that 63- 83% of species actually present were detected in seed bank sampling. The results presented in this thesis provide forest managers with deeper insights into the interaction between disturbance and re-vegetation processes in Interior Douglas-fir forests.

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