Environmental Engineering Reference
In-Depth Information
The Department of Conservation purchased this important patch of gorse from
the landowner who insisted his cattle should still be allowed to overwinter in the
reserve. Conservationists were unhappy about this but the cattle proved to be part
of the weta's salvation. By opening up paths through the gorse, cattle provide entry
for feral goats ( Capra hircus ) that browse the gorse, producing a dense hedge-like
sward and preventing the gorse habitat from succeeding to a stage inappropriate to
the wetas. This story involves a single endangered native insect together with a
whole suite of invaders (gorse, rats, goats, etc.) and introduced domestic animals
(c att le). Before the arrival of people in New Zealand, the island's only land mammals
were bats, and New Zealand's endemic fauna has proved to be extraordinarily vul-
nerable to the mammals that arrived with people. However, by maintaining gorse
succession at an early stage, the grazing goats provide a habitat in which the weta
can escape the attentions of mammalian predators.
8.5.5 Nursing a
valued plant back to
cultural health
The very identity of cultures often depends to some extent on native fl ora and fauna.
Take the Mohawk Nation, for example, where great value is placed on the sweetgrass
Anthoxanthum nitens for its use in basketry, a cultural practice that evolved from
early utilitarian forms to intricate and ornate basket work. Sweetgrass is a mid-
successional species, typically occurring with other grasses, herbs and shrubs. The
species once grew along the Mohawk River valley in eastern New York State, near
to the farming community known as Kanatsiohareke, but the nearest gathering site
now is 325 km away. The local vegetation is now a late-successional grassland com-
munity dominated by exotic species.
Shebitz and Kimmerer (2005) evaluated the restoration potential of sweetgrass
using four experimental treatments: (i) sweetgrass alone (weeded to remove com-
petition from other grassland plants); (ii) together with existing old-fi eld vegetation;
(iii) weeded and planted with hairy vetch ( Vicia villosa ) as a nurse plant (Section
8.3.5); and (iv) weeded and planted with ryegrass ( Lolium multifl orum ) as a nurse
plant. Hairy vetch is an annual legume with the desirable properties that it does not
persist through succession and has a nitrogen-fi xing ability that may enhance grass
growth. Ryegrass, another annual, also readily establishes, has weed-suppressing
properties and might therefore serve as a nurse crop, but its tendency to persist may
threaten local biodiversity.
Sweetgrass biomass, height, reproduction rate and survivorship were greatest in
plots that were weeded to eliminate competition and where hairy vetch was present.
Planting sweetgrass with hairy vetch also generated characteristics desired by bas-
ketmakers, such as high abundance and tall blades. The annual ryegrass, on the
other hand, reduced sweetgrass growth and reproduction - the term 'nurse crop'
clearly does not apply in this case. Hairy vetch can thus be used to restore the native
sweetgrass into its place in old-fi eld succession at Kanatsiohareke and to bring back
a signifi cant cultural tradition.
Summary
Allogenic and autogenic succession
Most natural communities are in a constant state of fl ux. In the case of allogenic
successions, the shifting pattern of species composition depends on a slowly chang-
ing physical environment, while interactions among the species themselves are of
secondary importance. Autogenic successions, on the other hand, begin as a result
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