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

Chapter 3 Aboveground–Belowground Linkages, Ecosystem Development, and Ecosystem Restoration 57
conservation perspective, and this issue has generated significant recent debate
(Niklasson and Granström 2004). However, in Scandinavian forests, prescribed
burning has been increasingly introduced in forests that are managed for production,
mainly because of their perceived benefits for nutrient cycling and
long-term forest stand productivity (Niklasson and Granström 2004, Nilsson
and Wardle 2005). The studies described above for forested islands, as well
as other related studies (reviewed by Nilsson and Wardle 2005) provide evidence
that restoration of natural fire regimes (or implementation of prescribed
burning) should serve to reverse ecosystem retrogression, promote rates of soil
processes, and enhance forest productivity, at least in the order of decades. At a
more globally relevant level, these forests are also important global carbon sinks
or sources and restoration through introduction of a fire regime is likely to exert
major effects on the amounts of carbon these forests store or release as CO2.
Most of the forests in Scandinavia are under some form of management and
are utilized to varying degrees for timber and pulp production. Management for
conservation benefits and for production forestry are not necessarily incompatible,
and restoration of appropriate fire regimes may be useful for maximizing
goals associated with each of these activities.
3.5 Belowground Impacts of Invasive Nonnative Plants
Invasive nonnative plants are widely perceived to have major, negative impacts
in ecosystems (Pimentel et al. 2000, Mack et al. 2000, Myers and Bazley 2003),
and the nature of spread and increased abundance of invasive plants has been
documented for several species and systems. The relationships of these invaders
with aboveground properties such as NPP and native vegetation diversity have
been frequently studied (Daehler 2003, Ehrenfeld 2003, Levine et al. 2003),
and it is recognized that these relationships vary strongly among both systems
and species (see Hierro et al. 2005, Yurkonis et al. 2005; see Chapter 6). In
contrast, impacts on belowground properties, processes, and communities are
less well understood, although these may have profound implications for both
successional processes and restoration efforts (Suding et al. 2004, Wolfe and
Klironomos 2005, Young et al. 2005).
The best-documented belowground consequences of invasive plants are increases
in soil nutrient fluxes, particularly of N. This is because many of the
most widespread and successful invaders are plants associated with N-fixing
symbionts, for example, those in the genera Acacia, Cytisus, Lupinus, Melilotus,
Ulex, and Trifolium (Ehrenfeld 2003, Levine et al. 2003). These N-fixing plants
should have important belowground impacts in N-limited ecosystems, as was
first demonstrated by Vitousek et al. (1987) who found that the woody N-fixing
invader Myrica faya increased N availability in Hawaiian ecosystems above that
in native-dominated systems. Not surprisingly, many subsequent studies on the
impacts of N-fixing invaders have found elevated levels of N availability across
a range of species and systems (reviewed by Ehrenfeld 2003, Levine et al.
2003). A common assumption across these studies is that invading N-fixing
plants are better able to garner N than their native counterparts, presumably due
to their higher growth rates or greater per capita impacts on nutrient inputs into a
system (although these possibilities have been little explored to date). A recent
study by Weir et al. (2004) showed that different N-fixing bacterial mutualists