Environmental Engineering Reference
In-Depth Information
and natural ecological processes to carry out the management (Schmitz
2005).
Traditional forest management implicitly eschews biodiversity (specifi-
cally plant species diversity broadly and trophic linkages) by intensively
managing for a few economically valuable timber species, and discouraging
through hunting the presence of large herbivores such as white-tailed deer
and moose that are viewed as damaging to regeneration (Schmitz 2005).An
alternative view, which may be more compatible with the whole-ecosystem
perspective outlined in chapter 1, recognizes that plant species such as aspen
and spruce represent dominant and subordinate competitors whose dynam-
ics might be mediated by herbivores (e.g., figure 8.1, cf. figure 2.2c). Deer
and moose preferentially feed on aspen because it contains more nutrition
than spruce.This leads to the hypothesis that these herbivores might tip the
competitive dynamics in favor of mixed wood regeneration.This hypothe-
sis was tested experimentally in a boreal forest site in northwestern Sas-
katchewan, Canada (Schmitz 2005).
The experiment comprised a systematic comparison of two management
treatments: traditional, labor intensive site preparation followed by replant-
ing spruce seedlings, against treatments in which harvested sites were left
untouched, including letting natural spruce seedlings grow. Herbivory by
deer and moose was further manipulated by allowing herbivores free ac-
cess to half of both treatment sites and excluding them from the other half.
The experiment revealed that deer and moose suppressed aspen regenera-
tion thereby releasing spruce regeneration.The regeneration rate of both
tree species exceeded that resulting from traditional management. More-
over, herbivore mediation of aspen-spruce competition resulted in increased
diversity of herb and woody plant species that are part of the forest under-
story (Schmitz 2005).
In the experiment, balanced regeneration of aspen and spruce was best
achieved by encouraging greater biodiversity (attracting large herbivores)
and enlisting ecological processes (consumer-mediated competition).This
case study illustrates that the species within this ecosystem offer an impor-
tant service: a cost-effective, ecologically compatible way to sustain boreal
forest productivity by preserving the trophic structure of the ecosystem.
The recognition that biodiversity offers humankind important services
has led to a sea change in thinking about the linkages among biodiversity,
ecosystem function, and the economic value of services arising from
those functions (Daily 1997). The annual net value of these services is
