Geoscience Reference
In-Depth Information
Conservation rankings
All conservation rankings were calculated using the
publicly available spatial conservation prioritization
software Zonation (Moilanen
et al
., 2005, Moilanen
2007), using options specifically designed to
accommodate both the complementarity-based
analysis of environmental classification data
(described in detail in Leathwick
et al
., 2010) and
consideration of the effects of connectivity that
are appropriate to riverine ecosystems (Moilanen
et al
., 2008). Zonation uses a raster or grid-based
algorithm that starts by assuming that all input cells
are protected, and then uses a reverse stepwise
heuristic to progressively remove cells having
the lowest marginal contribution to conservation
outcomes (Moilanen
et al
., 2009). Grid cells can
be removed individually or in groups defined
by planning units. At the end of the removal
process all cells on a landscape are ranked, results
indicating those sites that best protect a full range
of ecosystem types
of protection, while taking account of both
current biodiversity condition and the desirability
of protecting connected sets of planning units.
A second set of gap-analysis rankings was
then calculated to identify high value sites that
currently lack legal protection. This used an
additional grid layer indicating those planning units
already having 80% or more of their geographic
extent under formal, legal protection (principally
Crown-owned conservation land focusing on the
protection of terrestrial values), but also including
regional reserves and covenanted private land.
These 'protected' planning units, accounting for
21.1% of the entire river network, were held back
until all other planning units had been removed,
so that rankings indicate both the relative priority
of sites within protected lands, and the ability
of non-protected sites to complement those river
environments already protected.
Finally, a third set of rankings was calculated to
identify sites with high regional values, recognizing
the important role played by historic disturbance
over geological timescales in determining some
distributional patterns. Priorities were calculated
separately within each of 29 biogeographic units
defined for New Zealand's freshwater ecosystems
(Leathwick
et al
., 2007), with these individual
regional rankings combined into a single layer for
the next phase of the analysis.
for any specified level of
geographic protection.
An initial Zonation analysis used a set of 200 grid
layers as its primary input, each describing the
distribution of one of the 200-level groups from
the river environments classification at a grid
resolution of 100m. While each of these grid layers
initially indicated just the presence (1) or absence
(0) of a single target classification group, they
were modified prior to the analysis by replacing
all zeroes with values describing the biological
similarity between the target group and those
groups occurring at other sites (Leathwick
et al
.,
2010). This enabled the prioritization process to
take account of similarities between environmental
groups (rather than treating them as unrelated
entities), allowing substitution between related
groups in proportion to their degree of biological
similarity. Two additional grid layers described the
estimated current biodiversity condition of river
segments and the membership of river segments
in the third-order planning units described above.
Results from the initial ranking using these
layers indicate those sites whose selection would
maximize the protection of a full range of
environment types nationally for any given extent
Identifying high value sites
for conservation
High value sites for conservation management
were identified using a manual selection process
built around the three sets of Zonation rankings
calculated nationally, with protected sites held
back, and regionally. National rankings were
considered first, with the most highly ranked
sites identified and assessed for their feasibility
of management. In some cases, lower-ranked
planning units were included within large
high value sites to improve the practicality of
management (e.g. where active management
of a degraded headwater planning unit would
also be required to ensure the maintenance of
