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

Chapter 3 Aboveground–Belowground Linkages, Ecosystem Development, and Ecosystem Restoration 49
contribute to maintaining ecosystem-level properties through influencing key
ecosystem functions such as NPP, decomposition, and nutrient flux. As succession
proceeds, NPP increases sharply, but there is an increasing dominance
of those plant species that produce poorer litter quality (i.e., higher carbon to
nutrient ratios, greater levels of defense compounds), and thus retard decomposition
and mineralization processes. This is associated with an increasing
importance of those soil organisms that are associated with a tighter and more
conservative cycling of nutrients in the ecosystem, for example, domination
by fungi over bacteria, and ectomycorrhizal fungi over arbuscular mycorrhizal
fungi (Coleman et al. 1983). There is also a lower turnover of microbial tissues,
and a lower proportion of the microbial biomass is utilized by consumers (Wardle
2002). The net result is lower levels of available mineral nutrients in the soil,
greater accumulation of soil organic matter, lower NPP, and a slower turnover
of C and nutrients both aboveground and belowground through succession.
When ecosystems are left for significant periods without catastrophic disturbance
(i.e., thousands to tens of thousands of years), both primary and secondary
seres can proceed to a state of ecosystem retrogression (see Chapter 4). This
is often driven by a reduction of available phosphorus (P) over time (Walker
and Syers 1976, Vitousek 2004), and appears to occur in broadly similar ways
across vastly different ecosystems and successional types. In a study of six
long-term seres that ranged from the boreal zone to the tropics and for which
a retrogressive phase was present, substantial reductions in plant biomass over
time were matched with increasing limitation of P relative to N, and reduced
performance of the decomposer subsystem (Wardle et al. 2004b). Often this
was also matched by shifts in microbial community structure, and increasing
domination of bacteria relative to fungi in the oldest systems. Although aboveground
and belowground biota (and the processes that they drive) may show
similar patterns of decline during retrogression, much remains unknown about
the involvement of aboveground–belowground feedbacks in retrogressive processes.
Ecosystem restoration is focused on attempting to reverse human-induced
damage to changes in community- and ecosystem-level properties and processes,
and therefore represents an obvious application of the principles of succession
(including both primary and secondary succession). The aboveground–
belowground approach has proved its worth in several studies that have aimed
to understand how human activities affect communities and ecosystems, for
example, through land use change (Compton and Boone 2000), atmospheric
CO2 enrichment (Díaz et al. 1993), N deposition (Aerts and Berendse 1988),
global warming (Seastedt 2000), biological invasions (Ehrenfeld 2003), and
biodiversity loss (Wardle et al. 1999). Such studies enable us to predict the
state that aboveground and belowground properties of ecosystems should converge
to over time when the human-induced impact in question is minimized or
removed. This is, in turn, useful in allowing us to better understand the successional
trajectory that might be expected or encouraged, both at the community
and ecosystem level, when restoration efforts to allow recovery from humaninduced
impacts are implemented. Further, by comparing our understanding of
ecological interactions that occur along successional gradients (both primary
and secondary), we can better understand the starting and desired end points of
any restoration activity, and then try to mimic successional patterns from that
starting point.