Gradual
replacement of meadow by forest species. Among
meadow species cover declined steeply with establishment of grand
fir and associated reductions in light (figure, below: upper left
panel), but richness (upper right panel) declined more slowly.
Forest
herbs colonized rapidly (within decades), and within 60-80 yr dominated
the understory (lower panels).
Richness
and cover of forest understory species showed weaker relationships
with overstory structure than did richness and cover of meadow species
(regression model R2 for forest species: 0.34-0.42;
model R2 for meadow species: 0.48-0.54).
Conclusions
| Rapid
replacement of meadow species |
_15%20Jul%202007_lg.jpg) |
| Forest
understory plants rapidly colonize beneath young stands
of grand fir. |
|
With conifer
establishment, replacement of meadow by forest species is rapid.
The pace of conversion, reinforced by positive feedbacks between
trees and soils, may be indicative of a shift to an alternative
stable state.
Loss
of cover and richness of meadow species (and limited presence of
these species in the seed
bank) may pose barriers to restoration of native meadows.
Removing
trees during the earliest stages of encroachment may be the most
effective strategy for maintaining these ecosystems. |
Introduction
& methods
