Succession and management - Ecological Applications: Toward a Sustainable World - page 219

The nature of many plant communities is strongly infl uenced by the local fi re
regime. A natural pattern of fi re intensity and frequency will have selected for plants
able to survive the fi res or with seeds keyed to germinate after the fi re goes out. The
great plains of North America evolved under the infl uence of relatively small-scale
fi res. The probability of fi re is greatest where a large biomass has accumulated
during a period without fi re. Recently burnt patches, with their dominant tallgrass
vegetation, tend to attract grazing animals (most notably the bison - Bos bison ) that
reduce grass biomass, increase the amount of bare ground and shift the plant com-
munity towards nongrass herbaceous species. These changes reduce the likelihood
of fi re and of further grazing, because the animals now move to more recently burnt
areas. The patch then shifts back to a tallgrass successional stage, again increasing
the likelihood of fi re and of further grazing in future (Figure 8.3). Thus, small-scale
fi res and grazing together produce a shifting mosaic across the landscape, enhancing
heterogeneity and promoting biodiversity.
The traditional management practice when restoring these grasslands has been
to minimize patchy disturbance, leading to a reduction in patchiness of the succes-
sional mosaic. By contrast, Fuhlendorf and Engle (2004) recommend that manage-
ment should involve application of spatially discrete fi res together with free access
of grazing animals to a diversity of patches in a large landscape mosaic.
In contrast to the previous example (a shifting prairie mosaic), the goal of restora-
tion ecology is sometimes a relatively stable and homogeneous successional stage.
When the aim is to restore land previously under agriculture, managers need not
intervene if they are prepared to wait for natural succession to run its course. Thus,
abandoned rice fi elds in mountainous central Korea proceed from an annual grass
stage ( Alopecurus aequalis ), through forbs ( Aneilema keisak ), r ushes ( Juncus effusus )
and willows ( Salix koriyanagi ), to reach w ithin 10 -50 years a species-rich and
stable alder woodland community ( Alnus japonica ). In this case the only active
intervention worth considering is the dismantling of artifi cial rice paddy levees
to allow the land to drain, and to accelerate, by a few years, the early stages of
succession (Lee et al., 2002).

Fig. 8.3 Diagram of the
dynamics of a patch of
prairie in a shifting
mosaic landscape where
each patch experiences
similar but out-of-phase
dynamics. Ovals
represent the key
factors of fi re and
grazing while squares
represent the communi-
ties within a single
patch in relation to
time since fi re
disturbance. Solid
arrows indicate positive
(+) and negative (−)
feedbacks in which
plant community
structure is infl uencing
the probability of fi re
and grazing. Forbs are
nongrass herbaceous
species. (From
Fuhlendorf & Engle,
2004.)

Probability of
selection by
grazing animals

(+) (-)

Recently burned,
currently grazed

Transitional
state

No fire for 3 years,
minimal grazing

<1
year

2-3
years

High production,
quality and
availability
of forage

High bare ground
and forbs and low
litter and standing
biomass

Accumulated litter
and standing
biomass of mostly
grasses

(-) (+)

Probability
of fire