International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
symbiosis. The indices are described below, followed by the nu
umerical criteria for evaluations in Table 1.
Index 1: Vegetation Naturalness Index (VN): All plant
communities within each unit were assigned a quantitative
natural value. The average naturalness was then calculated
by measuring the area within the unit occupied by each plant
communities.
N = Summation of [(Community Naturalness x Community
Area)/ Small Watershed Area]
The data is based on Natural Environment GIS (Ministry of
Environment, 1998). The average naturalness was then
calculated by measuring the area within the unit occupied by
each plant community, according to the following formula.
Index 2: Quantitative Index of Forest (QF): Quantitative index
of the forest is defined as the proportion of forest area to the
entire area of each small watershed.
BF = Forest Area/Small Watershed Area
Forest area is based on Natural Environment GIS (Ministry of
Environment, 1998).
Index 3: Index of Fragmentation of Natural Environment (FN)
according to Road Effect
Table 1. Evaluation of degree of natural symbiosis using four indices
Roads were analyzed as a major factor in fragmentation and
isolation of natural environments. The fragmentation index
of the natural environment“ was calculated based on the total
length of roads, defined as national motorways, national
roads, prefectural roads and municipal roads included in the
JMC Map (Japan Map Center, 1998).
FN = Total Road Length/ Small Watershed Area
Index 4: Land Development Rate (LD): To assess the
magnitude of human impact on the natural environment, an
index of land modification was calculated as the proportion
of the total watershed areas occupied by artificial structures.
LD = Land development Area/ Small Watershed Area
The data regarding distribution of artificial structures is based
on National Land Numerical Information (Natural Land
Agency, 1997).
The Total Score (Degree of Natural Symbiosis as calculated as
VN+QF+FN+L D
Evaluation
Level VN QF LD Degree of Natural Symbiosis
1 (7-10) (85-100) (0-0.05) (0-3) very high
IT (3-7) (55-85) (0.05-0.1) (3-10) high
I (1-3) (35-55) (0.1-0.15) (10-30) low
IV (0-1) (0-35) (0.15- ) (30- ) very low
3.3 Spatial Diversity Analysis
The spatial diversity index was used to measure horizontal
diversity between small watershed units. This technique, which
uses measurements of Is (Interspersion) and J, (Juxtaposition)
as components of spatial diversity, was described by Mead et al.
(1981), and is considered to be the most effective index for
quantitative and qualitative evaluation of habitats (Heinen &
Cross, 1983). In this technique, calculations were originally
implemented using raster (Clevenger et al, 1997, Clark et al.,
1993). In this research, however, measures of interspersion and
juxtaposition were also used in a mesh analysis applied to
polygon units within the small watershed units. In raster-based
analysis, a value of 1 or 2 is respectively assigned to diagonal
edges and to vertical or horizontal edges at juxtaposition by the
raster. This can result in an underestimation. In addition, when
the actual connectivity is considered, the length of a boundary
between small watersheds can have a powerful influence on
the suitability of the region as natural habitat, especially on
large mammals such as black bears. It should also be kept in
mind, however, that the connectivity calculated by either raster
or grid does not have an equal influence on all species. Areas
of utilization may vary among species. For these reasons, we
also assessed spatial diversity utilizing polygons, which
represent the actual situation as seen in the natural world.
Masuyama et al. (2003) have shown that when the results of
small watersheds evaluation are superimposed on a map
showing the distribution of critical species, the areas with high
degree of spatial diversity coincide with those in which these
species were identified, proving the effectiveness of this
evaluation method. Interspersion and Juxtaposition as spatial
analyses provide an understanding of the connectivity among
adjacent small watershed units. Following are descriptions of
the original calculation method using grid, and consequently,
small watersheds evaluation is suitable in conservation of
biodiverse habitat. These spatial analyses provided an
understanding of the connectivity among adjacent small
watershed units.
1) Original Calculation Method Using Grid
1-1 Interspersion (I)
L IL, HI and IV represent the small watershed evaluation
categories as described in Table | above. Interspersion is
calculated as the total number of changes recorded between
adjacent units divided by the
total possible number of 1 Il Il
changes. In this case, for TL
example, Is = 5/8 = 0.625 |
I I I
1-2 Juxtaposition (J,)
Diagonal edges are assigned a score of 1; and either vertical or
horizontal edges a score of 2. Various edge combinations can
then be assigned a relative weight factors ranging from 0 to l.
In the above case, for example, Jx = 6.6/12.0 = 0.55
Edge types Quantity*' Quality*? Total
/I 4 0.8 32
Un 3 0.6 1.8
IH 3 0.4 12
[/IV 2 c2 0.2 104
12 6.6
2) Calculation Method Using Polygons p^
2-1 Interspersion (Isp)
Isp is calculated as the number of different polygon evaluation
levels divided by the total number of polygons. In this case, for
example,
260
Internatior
Titel tette
Isp=3/4=0
2-2 Juxtapt
Quantitativ
greater t
perimeter/ [
Table 2. Ec
Evaluation
cells or poly
4-1 Ecosys
The resu
symbiosis
overall res
watershed
concentrate
units with
found alon
the northez
much lowe
4-2 Spatial
Analysis
shows that
high suitab
some units
are isolate
indicate thz
good conne
Fig