Soil Seed Banks,
Heterogeneity, and Plant Community Assembly Following Disturbance by
Fire and Logging in Interior Douglas-Fir Forests
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.