Succession and management - Ecological Applications: Toward a Sustainable World - page 232

Fig. 8.14 (a) Mean
weed biomass, (b) mean
weed density and (c)
light penetration to
ground level 7 years
after the commence-
ment of seed-only and
full restoration of
tallgrass prairie, in
comparison to
unrestored grassland.
(After Blumenthal et al.
2003.)

(a) (b)

6

100

4

50

2

0 0

(c)

60

40

20

0

glauca ) (Figure 8.14). Full restoration reduced available light and it seems likely that
weed invasion was limited by decreasing availability of the crucial radiant energy
resource. Prairie seed addition alone had no signifi cant effect on weed biomass but
it did reduce weed density by 45%.
In a related study, Blumenthal et al. (2005) augmented soil concentrations of the
limiting plant nutrient nitrogen (by adding urea). This reduced the negative effect
of restoration on weed invasion, indicating that a lack of mineral resources during
late-successional stages also helps to account for poor weed performance in restored
grasslands.

8.4.2 Forest Invaders seem to do particularly well in disturbed situations, and one-to-one com-

petition studies often indicate that exotic species are more highly competitive than
their native counterparts. Given that early-successional communities have, by defi -
nition, been recently disturbed (Box 8.1), you might suppose that invaders will be
more prominent in early- than late-successional forests. If this is so, then restoration