Biology Reference
In-Depth Information
ecosystem properties; therefore, invasive species control has to be carefully consid-
ered in a whole-ecosystem context (Zavaleta et al. 2001).
5.4.5 Research Focus
Research is foremost needed that addresses the functioning of natural ecosystems
and the ecology and functional roles of common and rare native species in the light
of a multitude of global change agents and their synergetic interactions (Didham
et al. 2007). Studies are needed to carefully assess the relative importance of inva-
sive species vs. other environmental stressors on management objectives in refer-
ence habitat so as to identify the most efficient use of management resources
(Hulme 2006). Indirect human impacts on reference habitat, such as climate change
or increase in CO
2
partial pressure in the air, may increase the vulnerability of refer-
ence habitat to biotic invasions, and these effects need to be better understood. For
instance, increased atmospheric CO
2
may accelerate the spread of native and alien
invasive vines in deep shade (Granados and Koerner 2002), or mountains ecosys-
tems that are currently relatively resistant to biotic invasions may become vulnera-
ble to invasions with global change (Dietz et al. 2006; Pauchard et al., in press and
see http://www.miren.ethz.ch). Further, a better understanding of evolutionary
responses of invasive and native species is needed to determine whether such responses
are more likely to increase or decrease impacts of invasive species in undisturbed
habitat (cf. Dietz and Edwards 2006).
5.5 Abandoned Habitat
5.5.1 Habitat Characteristics
Abandoned habitats are areas that have been heavily disturbed or intensively man-
aged in the past, e.g. old fields (Cramer et al. 2008) or abandoned plantation forests
(Lugo 2004), or they are former reference habitats that have been highly degraded
due to anthropogenic influence or invasion. Abandoned habitat often contains new
combinations of native and alien species, and such ecosystems have been termed
novel ecosystems
or
emerging ecosystems
(Hobbs et al. 2006). The terms
aban-
doned habitat
and
novel ecosystem
are similar, but
abandoned habitat
does not
imply that ecosystem properties have to be novel. The species of novel ecosystem
have often not coevolved (Wilkinson 2004; Hobbs et al. 2006), and abiotic condi-
tions may also be considerably different than in the typical native vegetation at a
site (Lugo 2004). Ecosystem functioning and species assembly and interactions are
difficult to predict because they depend on the disturbance history of the site,
assembly history, and the local pool of alien and native species (Chazdon 2003;
