Linking Restoration and Ecological Succession (Springer ... - Inecol

Chapter 3 Aboveground–Belowground Linkages, Ecosystem Development, and Ecosystem Restoration 53
As discussed, restoration of New Zealand forests, and promotion of successional
changes in these forests to a less human-modified condition, would in the
first instance require the removal of browsing mammals. Studies such as those
described above enable us to predict, at both the community- and ecosystemlevels,
the likely consequences of removing these mammals over the order of
a few decades, and therefore the extent to which these forests can be restored.
However, if restoration goals are to be focused on restoring these forests to
their “natural” prehuman state, then the situation becomes more complex. This
is because, prior to human settlement ca. 1000 years ago, New Zealand was
dominated by moas—a guild of large browsing native birds that were hunted to
extinction a few hundred years ago and for which no contemporary substitutes
exist. This effectively makes the goals of ecosystem restoration (i.e., reversion
of these forests to a prehuman state) unattainable. Our knowledge of what
effects moas had in these forests relative to those currently exerted by browsing
mammals is far from clear (Atkinson and Greenwood 1989, McGlone and
Clarkson 1993), although the effects of moas were probably less than the current
impacts of introduced mammals (McGlone and Clarkson 1993). Further, deer
probably exert greater soil disturbance per unit body mass (and therefore have
more adverse effects on litter dwelling invertebrates) than did moas, because
of the relative shapes of their feet (Duncan and Holdaway 1989). In any case,
it is apparent that deer and goats can exert important effects in natural forests
at both the community- and ecosystem-levels, and both aboveground and belowground,
through altering successional pathways in the ecosystem. Although
goals to strictly restore these forests to prehuman conditions are unattainable
because moas are extinct, it is apparent from the above example that significant
restorative benefits to these forests are likely to result from targeted reductions
in the densities of introduced mammals.
3.4 Fire Regime and Swedish Boreal Forests
Wildfire is the primary natural disturbance regime in boreal forests worldwide
(Bonan and Shugart 1989), including those in Scandinavia (Niklasson and
Granström 2000). Fire arrests forest successional development and prevents the
system from entering long-term retrogressive phases by enabling greater availability
of nutrients to rejuvenate the system (Zackrisson et al. 1996, De Luca
et al. 2002a). Understanding the ecological influence of fire is therefore critical
for understanding secondary succession in a wide range of ecosystems globally.
Over the past 200 years, human activities have increased in the boreal forest
zone of Scandinavia, and interrupted the natural fire cycle through fire suppression.
Prolonged suppression of wildfire may have important effects on global
carbon storage patterns, through promoting greater sequestration of carbon in
the ecosystem. This may help to partly explain the so-called “missing carbon”
sink, or that carbon that is evolved as CO2 by fossil fuel burning but remains
unaccounted for in global carbon budgets (Schimel 1995, Hurtt et al. 2002).
Understanding these kinds of effects are highly relevant to restoration, because
restoration of natural fire regimes in these forests, and the consequences of
this for ecosystem succession, are likely to be very important as determinants
of whether they act as net sources or sinks of carbon not just locally but also
globally.