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M. Ortega et al. 2010. Monitoring vulnerability of the Spanish forest landscapes: the SISPARES approach
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2.1 Data analysis
In each square FLV has been calculated as:
FLV=FLF*RD/100 (1)
Where RD is road density in the square and FLF is an index of forest landscape fragility, which
has been calculated as:
FLF=IJI*WFN (2)
Where IJI is an index of interspersion and juxtaposition that considers the neighbourhood
relations between patches. Each patch is analysed for adjacency with all other patch types and
measures the extent to which patch types are interspersed i.e. equally bordering other patch
types. The IJI is a relative index that represents the observed level of interspersion as a
percentage of the maximum possible given the total number of patch types (McGarigal et al.
1995).
m = number of patch types,
(3)
E ik = length of edge between patch type i and patch type k.
IJI approaches 0 when the distribution of adjacencies among unique patch types becomes
increasingly uneven. IJI = 100 when all patch types are equally adjacent to all other patch types
(i.e., maximum interspersion and juxtaposition.
WFN in equation 2 is the contrast between forest and non forest areas in the square and is
measured as:
(1-| Forest area – Non Forest area|)/100 (4)
A landscape square will be more fragile when a higher WFN and a higher IJI have.
Besides if the square has a higher road density it will be a high value of vulnerability.
Fragstat software was used to calculate the IJI index. Repeated measures ANOVA was used to
analyse FLV, FLF, IJI, WFN and RD of 206 squares of SISPARES in three dates: 1956, 1984
and 1998 by means of Statistica softhware.
3. Results and discussion
FLV index showed a significant increase in Spain along the study period (F=3.36; p=0.04) as it
is observed in the figure 1. The increase between 1956 and 1984 was 2% and during the last 24
years of this study period the mean number of forest fires was 3,940 per year (Table 2).
Between 1984 and 1998 data, the increase of FLV was 12% more and only during these 14
years the mean number of forest fires was 15,844 per year. In the same way the burnt areas were
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.