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Intl. J. of Mol. Ecol. and Conserv. 2012, Vol. 2, No.3, 15-20
http://ijmec.sophiapublisher.com
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It is now generally being now accepted that
communities are dynamic assemblages of species, in
which all species should be regarded as potential
colonist, because fluctuations and disturbances allow
particular species to establish at certain times (Jordan
et al., 1987). Early colonist are typically short lived,
fast growing species and reproduce early while older
succession fields are dominated by longer lived
perennial species. Although the persistence and
abundance of species later in succession depends on
competitive ability, their ability to inhibit growth of
other species, or simply their longevity (Connell and
Slatyer, 1977), each species need to have the ability to
establish/colonize an area. In the past few years, the
concept of colonization credit (number of species yet
to colonize a patch) was proposed as a spatially
explicit framework to assess recovery in species
richness following restoration (Cristofoli and Mahy,
2010). Having such studies for target species might be
expensive yet very crucial in restorations especially if
this information is augmented with habitat quality
information. Conservation and restoration work must
urgently target strict specialists, showing colonization
problems in degraded patches.
3 Species disturbance theory and multiple
species assemblages
Natural disturbances shape community structures
(spatially and temporally) to create their range of
variability that will control ecological processes and
habitat variability (Jõgiste et al., 2007). These
disturbances regulate processes such as nutrient and
carbon cycles, temporal-spatial distribution of input
litter ultimately the net primary production of
ecosystems. Since it is known that disturbances
operate at multiple spatial scales; often fine/coarse-
scale disturbances interact in complex ways to produce
multi-scale habitat diversity from microhabitats to
landscape patterns (Sudding and Hobbs, 2009). The
scale is a therefore an important question when
applying natural disturbance concepts to restoration
exercises. The same level of disturbance can cause
catastrophic effects on a small area while having mild
effects on a relatively larger area. An example is a
localized mudflow that may destroy lots of species but
if it occurs in a forested mountain range, it creates
other habitats thereby increasing diversity of the forest. If
disturbance passes the intermediate stage then
degradation is triggered. Basing on intermediate
disturbance theory, a dominant species will "rule" in
areas with little disturbance while in areas with high
disturbance only species that are highly adapted to the
disturbance will survive (Hobbs and Norton, 1996). In
either way, there will be low biodiversity, but a perpetual
low level disturbance (e.g. floods and fire) allows more
diversity to flourish in the area. Restorationist can
intentionally bring in disturbance in the form of grazing,
bush control and forest product harvesting.
Equilibrium states concepts are no longer broadly
accepted by ecologists as adequately explaining
community structure. The amount of information
learnt from stead states is limited compared to
responses by ecosystem to external disturbances that
expose the dynamic connections of the systems. Often,
responses to disturbances are not necessarily linear,
meaning perturbations must be extreme (Jordan et al.,
1989). Many communities exist in perpetual states of
non-equilibrium or dynamic equilibria where natural
disturbance prevents most populations from reaching
maximum densities (Pickett et al., 1992). It should
therefore be noted during restorations that due to the
non-equilibrium state of ecosystems, application of
any method will not guarantee a single result; the
ecosystem trajectory might be slightly be different
from theory. Each attempted plan should therefore be
given enough time for managers to be sure of its
success/failure, and evaluation and monitoring should
be continual.
Since restoration efforts often involve a focus on
multi-species assemblages (Palmer, 1997); community
ecology theory becomes central and extremely
relevant to restorationists (Godefroid et al., 2010). The
composition and richness of plant assemblages are
both important to ecosystem functions such as
productivity, carbon and nitrogen dynamics and
canopy architecture. Restorationists should concentrate
on restoring functional groups if the initial goal is to
restore a functional community, but if goal is to
restore community structure then efforts should be to
understand spatial ecology, patch dynamics, and