Succession and management - Ecological Applications: Toward a Sustainable World - page 233

Fig. 8.15 Changes in
(a) percentage exotic
plant cover and (b)
percentage of species
that are exotic in each
of 10 old-fi eld succes-
sions over a 40-year
period. The patterns for
native species are, of
course, the inverse of
these but note that
because cover is
summed across
overlapping species
canopies, total cover
can exceed 100%. The
patterns are similar
whether the starting
point of the succession
was a hay fi eld or a row
crop. (After Meiners
et al., 2002.)

(a) (b)

100

75 Row crops

Hay fields

75

50

50

25

25

0

0

0 10 20 30 40 0 10 20 30 40

Years since abandonment Years since abandonment

of late-successional communities may be an effective invader-control strategy (as for
the grassland example in Section 8.4.1). To address this question, Meiners et al.
(2002) analyzed a remarkable database of 40 years of accumulated results in ten
separate old-fi eld successions in New Jersey, USA.
Exotic species initially comprised more than 50% of plant cover, but during suc-
cession there were signifi cant declines in abundance and richness of exotic species
and increases in native species (Figure 8.15). And this occurred in the absence of
any management intervention. The loss of exotics seems to be related to forest
canopy closure. I have already noted how annual and biennial herbaceous species
usually decline as woody cover increases during old-fi eld succession. Many of the
pioneer species in the present study are in fact invaders, so it seems that in more
resource-limited, later-successional environments the native shrubs and trees out-
compete the exotic pioneers. But all in the forest garden is not rosy. Some shade-
tolerant invaders are showing signs of increasing after 40 years of succession. The
biennial Alliaria petiolata , for example, is becoming more obvious in situations
where understory diversity is low. And exotic shrub honeysuckles ( Lonicera maackii
and L. tartarica ) are increasing in abundance and may move further into gaps left
by the death of early-successional native trees. Simple successional changes may be
enough to see off exotic pioneers, but shade-tolerant invaders seem to require more
active management.

8.5 Managing
succession for
species
conservation

Successional theory is relevant to the fate of endangered species too. Some require
an early-successional stage, some a mosaic of patches at different stages, and others
rely on a late stage (Sections 8.5.1-8.5.3). Sometimes the success of a conservation
strategy depends on knowledge of the role of herbivores (enemy interaction theory
- Section 8.5.4) or of species that smooth the path of succession (facilitation theory
- Section 8.5.5; see Box 8.1).

8.5.1 When early
succession matters
most - a hare-
restoring formula for
lynx

For more than a century the common perception has been that Canada lynx ( Lyn x
canadensis ) inhabit remote North American primary forest unoccupied by people.
Indeed, a federal judge ruling in 1997 concerning the status of lynx inferred that
such forest is a prerequisite for them (Hoving et al., 2004). However, lynx are known
to be specialist predators of snowshoe hares ( Lepus americanus ) whose habitat is in
early-successional dense shrubland or immature forest.