Landscapes Forest and Global Change - ESA - Escola Superior ...

R.A. Diaz-Varela et al. 2010. Extent and characteristics of mire habitats in Galicia (NW Iberian Peninsula)
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Franses 2006). CHAID technique was applied using mire classes as response variables against
the abovementioned collection of potential predictors. For the validation of the model, we
randomly split the original data in a training and validation with 50 % of the cases assigned to
each subset. We finally generated a contingency matrix for the contrast of the observed and
predicted classes for the validation set, and subsequently we computed the KAPPA statistic
(Bishop et al. 1975) as a measure of model accuracy.
3. Results and Discussion
Results of the CHAID classification are presented in figure 2. According the diagram, the most
powerful discriminant variable was distance to sea. In the second level nodes other variables
related to geology, topography and climate were taking into account for the discrimination of
mire types. Finally, water balance was considered for the discrimination in the third level
between some blanket bogs and Cladium fens with similar values regarding their distance to sea
and slope. Overall accuracy reached more than 96 % (table 3) while the estimation of KAPPA
index, regarded as a more reliable indication of the overall accuracy due to its compensation of
chance agreement (Congalton 1991), achieved a value of 0.93, indicating an almost perfect
agreement between the classification and reference values (Landis and Koch 1977). Per class
accuracies reached particularly high values for blanket bogs and tufa, while fen and Cladium
mires accuracies were lowered because the confusions with each other and also with tufa mires.
According these results, blanket bogs occur on sub-coastal areas at different exposures, more
frequently facing north and under high annual rainfall or water balance, as previously stated by
biogeographic studies of this habitat in NW Iberian Peninsula (Rodríguez Guitián et al. 2007).
Cladium fens are located close to the coastline, on sedimentary deposits (corresponding in most
cases with the inland border of coastal salt marshes). They also occur in the inland, on flat
surfaces under not particularly high water balances, where some confusion with tufa or fens
could happen. Even when some fen localities may occur in the inland, they tend to appear close
to the coast, on ultra basic material sharing these environmental conditions with localities of
Cladium fens and tufa formations. Finally, tufa occurs on the coast, in springs or water table
ruptures leaching fossil/raised coastal dunes systems still rich in carbonates on coastal cliffs, or
alternatively in the inland, linked to the few ditches of limestone rocks in the region (Ramil
Rego et al. 2008).
4. Conclusions
In the present work we explored the role of different environmental controls on the occurrence
of four types of mire habitats. We found out that the degree of continentality (using the reliefcorrected
distance to sea as an indicator) play a potential key role in the differences in spatial
distribution of types in the region of Galicia. However mire types occurrence can not be
differentiated or explained on the basis of just one kind of environmental control, but rather a
combination of different controls (as geology, distance to sea, climate or lithology), being the
importance of each one related to the ecology, tolerance and requirements of each particular
habitat.
The results corroborate in a quantitative and spatially explicit way the previous knowledge on
the ecological differences between the different mire habitats in the region. This information has
a potential application in habitat management plans for protected areas in combination to other
datasets (e.g. spatial pattern and distribution, vulnerability and resilience, future climatic and
land use scenarios) and also constitutes a first step towards a predictive biogeographic
modelling of habitat distribution.
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.