Mw. Palmer et al., Changes in the understory during 14 years following catastrophic windthrowin two Minnesota forests, J VEG SCI, 11(6), 2000, pp. 841-854
We studied the effects of windthrow on the understory plant species composi
tion of a pine forest (dominated by Pinus strobus) and an oak forest (domin
ated by Quercus ellipsoidalis). We recorded the presence of vascular plant
species in randomly located quadrats in the two forests, and in three micro
site types associated with tipup mounds (pit, old soil and new soil) in the
pine forest at irregular intervals over the course of 14 years. The unders
tories of the two forests remained distinct throughout the study. The frequ
ency of occurrence of a number of forest floor species considerably increas
ed; few species decreased. The disturbance specialists Rubus idaeus and Pol
ygonum cilinode increased in frequency throughout the study in the pine for
est, but are beginning to decline in the less disturbed oak forest. Annuals
and biennials preferentially colonized the disturbed soil of microsites on
tipups, and declined in frequency after about 7 yr. Both forests have incr
eased in understory species richness, but have not changed substantially in
the distribution of growth forms. Despite early differences in species com
position, microsite types associated with tipup mounds became more similar
through time. Although small in magnitude, there was a directional change i
n understory composition at both forests, with no apparent sign of a return
to pre-disturbance conditions.