The Offset Design Process
41
BBOP Pilot Project Case Study – Ambatovy Project
Table 3: Summary of attribute weighting (December 2008)
Attributes
Unit
Weighting (%)
Justification
Stems
(a)
number / ha
15
Reflects forest density, an important ecological attribute
for fauna, especially lemurs.
Number of tree
species (per ha)
number / ha
20
Provides overall floral diversity and habitat
heterogeneity. Higher numbers are better.
Canopy height
m
5
Indicator of forest maturity and canopy continuity. For
azonal habitat lower canopy height is better.
Basal area
(b)
m
2
/ ha
5
Indicator of habitat
CONDITION
. Higher value is better as
it is an indication of mature forest.
Dbh
m
5
Indicator of habitat condition. Higher value is better as it
is an indication of mature forest.
Propithecus
diadema
density
(c)
individual
number / ha
20
IUCN CR
(d)
status, species very sensitive to human
activities in their habitat.
Allocebus
density
Individual
number / ha
10
Nocturnal species sparsely distributed and appears to
be sensitive to forest structure.
Indri indri
density
Individual
number / ha
20
Madagascar’s largest lemur species sparsely confined
to eastern rain forest, IUCN EN status, and also has a
cultural value (the most taboo lemur species).
Total
100
(a)
Number of trees with diameter ≥10 cm, with measurements taken at 1.3 m above the ground.
(b)
Basal area is calculated as π x (diameter at breast height / 2)
2
.
(c)
Lemur species density is estimated based on line transect samples within a surface area, S = 2 x (Width x Length) in which density D
= individual number / S.
(d)
Was recently lowered to EN.
The selection and weighting of the attributes is examined below.
Selected attributes are divided in two groups:
– Forest structure, as a general surrogate for forest dependent biodiversity; and
– Lemur species, as an ‘umbrella species’ fauna group considered to be the most sensitive to human
disturbance in Ambatovy (bush meat, slash and burn, logging); the species selected include both
diurnal and nocturnal species.
Weighting: 60% and 40% importance were chosen for forest structure and faunal assemblage species,
respectively. Attributes that express biological diversity (e.g., tree
SPECIES DIVERSITY
and stem number) are
weighted with higher importance, as are species with CR rather than EN status. Since the mine is located
in a
BIODIVERSITY HOTSPOT
area, IUCN species of concern have been chosen as the main attributes to
reflect the principles of ‘
IRREPLACEABILITY
’ and no loss of
NON-OFFSETABLE
components.
TAXA
selection: lemurs were selected over other fauna groups, due to their wide presence in forest
habitats. Fish, amphibians and reptiles are restricted to specific habitats at Ambatovy, for example
microhabitats for herpetofauna. Therefore any impact occurring away from these specific microhabitats
(which are yet to be defined) might not reflect the Project’s impact on these taxa. The possibility of
considering some of the herpetofauna and pond invertebrate species will be explored after new data has
