Soil seed banks and plant community assembly following disturbance by fire and logging in interior Douglas-fir forests of south-central British Columbia

Abstract

Relationships between soil seed banks and aboveground understory vegetation were examined in dry Douglas-fir (Pseudotsuga menziesii (Beissn.) Franco) forests near Kamloops, British Columbia, to compare the effects of different disturbance types (low and high severity fires and non-salvage logging), and to evaluate how seed banks contribute to post-disturbance vegetation establishment. Sites were selected to represent disturbances at 1, 5, and 10 years prior to sampling, and data were analyzed using nonparametric univariate and multivariate statistical techniques. Seed density and species composition of seed banks did not differ significantly among the 1 year disturbed sites; however, the rooted frequencies of seed-origin plants in the establishing vegetation decreased in the order: lightly burned > severely burned > logged. Seed dispersal within the first year following fire is believed to be an important recovery mechanism on burned sites. Low frequencies of seed-derived plants, particularly conifer seedlings, on logged sites pose concerns for the initial recovery of vegetation following logging; nonetheless, the lack of significant differences in understory species composition between sites burned 5 years prior to sampling and sites logged 10 years prior to sampling, and their corresponding undisturbed sites, suggests that vegetation recovery can occur relatively quickly. Rooted frequencies of plants establishing naturally in burned areas were similar to those in undisturbed areas, which suggests that post-fire erosion control seeding using agronomic species may not be necessary in these forests.

Variation in soil seed bank species composition of a dry coniferous forest: spatial scale and sampling considerations

“…In a companion paper (Stark et al 2006), we reported differences in the soil seed banks (seed density and species composition) of dry coniferous forests at 1, 5, and 10 years following different types and intensities of disturbance (undisturbed, low severity fire, high severity fire, and clear-cut logging). Here, we re-examine the seed bank data from mature forest and 1-yr post-logging and 1-yr post-fire disturbance types.…”

“…Seed limitation is most commonly observed in early stages of succession (Turnbull et al 2000), and can be manifested as an aggregated (under-dispersed) arrangement of seeds in the soil seed bank. As forests become more managed, there is increased need for baseline information not only on the role of the seed bank in post-disturbance plant community assembly (Stark et al 2006), but also on the extent to which seed bank species distribution patterns vary across the landscape. Pragmatically, this raises questions about the adequacy of current sampling approaches for capturing such variation and relating it to different scales of ecological inquiry (e.g., within-stand scales of \100 m versus between-stand scales of [10 km).…”

Impact of wildfire intensity and logging on fungal and nitrogen-cycling bacterial communities in British Columbia forest soils

“…We examined shifts in the community structure of soil fungi using LH-PCR, and of nitrogen-fixing and denitrifying microbes using T-RFLP analysis of nifH and nosZ genes, respectively. latifolia) (Stark et al, 2006). Sites classified as 'high severity burns' had been exposed to a stand-destroying wildfire, with all needles on the trees consumed during the fire.…”

Bark beetles and wildfires: How does forest recovery change with repeated disturbances in mixed conifer forests?

“…Neither distance to seed source nor any topographic variables could explain these differences as the influence of these bottom-up factors (i.e., slope, elevation, and distance to seed source) were consistent across disturbances. A decreased seed bank from repeated disturbances may be one explanation for the reduction in continued germination of Douglas-fir seedlings (Stark et al 2006. At the time of the wildfire these repeated disturbance stands were in the gray phase, thus we expect that these stands had similarly high seedling densities as we observed in gray phase stands.…”