Biology Reference
In-Depth Information
5.4 Reference Habitats
5.4.1 Habitat Characteristics
Reference habitats have a special value for nature conservation because of some
habitat quality that is considered a reference state for “high quality nature” (Fig. 5.3).
They typically are relatively undisturbed habitats dominated by native species.
Reference habitats are often characterized by high functional and species diversity
and low levels of unused resources. Empty niche opportunities are relatively low
and pest loads and diversity are high. Nowadays, many reference habitats are on
marginal land that is characterized by harsh environmental conditions (e.g. high
altitude or dry habitats). All these factors in combination may make reference habi-
tats more resistant to invasions than disturbed habitats (Elton 1958; Richardson and
Pysek 2006). However, today alien species can be found in even the most remote
and pristine habitats such as boreal forests (Rose and Hermanutz 2004) or
Antarctica (Frenot et al. 2005). Furthermore, the fragmentary nature of many undis-
turbed habitats increases their vulnerability to invasion (Pysek et al. 2002). Over
time, reference habitat can become degraded due to invasion or anthropogenic
influences, leading to a shifting baseline in our notions of “high quality nature”
(Knowlton and Jackson 2008). If degradation is perceived to be extreme, reference
habitat may be abandoned as a reference, and it will have the same features as
abandoned habitat (see later).
Fig. 5.3 Invasions in reference habitat. Relatively undisturbed habitat such as native palm forests
on an oceanic island of the Seychelles group ( picture ) are often relatively resistant to invasions.
Palm forests in Seychelles have recently also been invaded by alien vines, such as Merremia pel-
tata , and it is not known if an increase in air CO 2 levels may have contributed to this. Invaders
with novel traits, such as rats, may have strong impacts on palm forest, for instance by predating
on seeds (Photo Eva Schumacher)
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