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

62 David A. Wardle and Duane A. Peltzer
indigenous systems and un-manipulated systems. Similarly, do manipulations
of animal herbivore densities, either through restoration of native species or
the reduction of pest species, also restore soil communities? Models, long-term
experiments, and observational studies (such as across well defined chronosequences)
can be also used to determine what the long-term consequences of
restoration treatments are for successional processes or ecosystem properties,
although these approaches are probably most useful for systems that are highly
predictable.
Altering the aboveground or belowground community by removing herbivores
or invasive plants may not always produce the desired result for succession
or ecosystem properties (i.e., their impacts are not immediately reversed
by removals) because of belowground legacies that may persist for a long time.
For example, plant invaders interact strongly with belowground communities
both directly through promoting NPP (higher C inputs), and influencing litter
quality and nutrient inputs to the soil; and indirectly through interactions
with native plants or species that show different plant–soil feedbacks. Many
of these effects will have long-term implications for successional trajectories
and ecosystem properties that cannot be mitigated by the removal of weeds,
the most commonly used tool in restoration efforts. In addition to persistent
effects or legacies of treatments, there will also be important lags in response
to different components of the soil subsystem to aboveground manipulations.
For example, if nutrient inputs into a system (e.g., from a N-fixing weed or
atmospheric deposition) are offset by reducing these inputs or through soil impoverishment
treatments, does the belowground system return to its previous
state quickly or does it retain accumulated nutrients and switch to an alternative
steady state dominated by early successional, nutrient-demanding species?
Some components of the soil subsystem, such as the microbial biomass, will
respond rapidly to aboveground treatments (i.e., weeks to months) and will be
more sensitive indicators of changes in belowground processes to restoration
treatments than will more slowly responding soil meso- and macrofauna (i.e.,
months to years) or pools of soil organic matter and nutrients (i.e., months to
decades). The key unresolved issue is which long-term ecosystem properties or
community trajectories in restoration are predictable from short-term shifts in
aboveground–belowground interactions.
In summary, there are several critical areas for future research linking aboveground
and belowground processes in succession to understanding restoration.
First, are the shifts or trajectories in aboveground communities manipulated in
restoration also mirrored belowground? Current studies document shifts in both
aboveground and belowground communities, and clearly point to links between
these components, but recognizing the importance of these links to succession,
ecosystem development or restoration requires the inclusion of soil biologists
alongside aboveground expertise. Examples of research that should provide
insights into restoration include: (i) determining whether successful restoration
aboveground also restores belowground communities, (ii) understanding
whether soil mutualists or pathogens can be used to either promote native species
or suppress nonnative species respectively, (iii) understanding in what situations
soil manipulations (e.g., C additions) help or hinder ecosystem restoration, and
(iv) identifying to what extent shifts in belowground processes during primary
and secondary succession from field studies can be used to determine restoration
success. The implications of these topics for restoration are obvious: soils and