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

A.L. Teixido et al. 2010. Impacts of changes in land use and fragmentation patterns on Atlantic coastal forests
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2. Methodology
2.1 Study area
Fragas do Eume NP covers 8 962 ha and it is located in the Galician dorsal range. The reserve
spans 43º20’-43º26’N, and 7º52’-8º08’W. There are three native forest types depending on
geomorphology: (1) oak forests, located on slopes; (2) alder forests, located on riversides with
flooding sediments; and (3) hazel forests, located on steep riversides with rocky river-beds.
Alder and hazel forests represent the riparian forests, and they contain threatened species such
as the vertebrates Chioglossa lusitanica and Galemys pyrenaicus, and the ferns Culcita
macrocarpa, Trichomanes speciosum and Woodwardia radicans.
2.2 Aerial image processing and land cover classes
We used American Army’s aerial photographs from flights for the years 1956-1957 (hereafter
1957) and digital orthoimages of the Geographic Information System of Agrarian Plots for the
years 2002-2003 (hereafter 2003). The 1957 aerial photographs consisted of 28 contact copies
(24×24 cm) with a scale of ca. 1:30 000. The photographs were scanned at ca. 2.55 m resolution,
and they were subsequently georeferenced with the software ERDAS IMAGINE 8.7 using 30-
40 ground control points for each frame. Orthoimages from 2003 had a spatial resolution of 0.25
m. The imagery set was implemented into a GIS based on ArcGIS 9.1.
Two maps were drawn showing the different land cover classes in the Fragas do Eume NP in
1957 and 2003. Land cover classification followed the system of the CORINE Land Cover 5th
level project (IGN 2002). Table 1 shows the classes we digitised. Riparian forests consisted of
extremely thin patches that it was practically impossible to digitise them as polygons. However,
given the importance of that habitat for the persistence of key red-listed and protected species,
we conducted a specific analysis for riparian forests by digitising the intersection between
forests and river courses as polylines to generate a map of riparian forest length.
2.3 Forest fragmentation analysis
Quantification and temporal comparison of the spatial configuration of forest patches were
conducted based on a set of standard landscape metrics reported in recent forest fragmentation
studies (e.g. Echeverria et al. 2006): (1) largest patch index (%), (2) mean patch size (ha), (3)
total edge length (km), (4) total core area (ha), (5) largest patch core area (ha), (6) mean distance
(m) and (7) adjacency index (total -km- and relative -%-). To calculate core area, the interior
forest was defined at a distance to edge of 50 m. In the case of riparian forest, quantification and
temporal comparison was based on lineal segments rather on areas. For each of the two dates,
we calculated the number of segments and the absolute and relative length of riparian forest
from the polyline maps. We quantified all absolute and relative changes in land cover areas and
lengths by calculating the difference between the values in 2003 and 1957.
3. Results
14 classes in 1957 and 12 in 2003 were identified (Table 1, Fig. 1). Forest suffered a 20%
decrease in area and more than a two-fold increase in the number of patches between over time.
In contrast, eucalypt plantations exhibited a 200% increase in area, accompanied by a moderate
increase in the number of patches. Table 1 shows the overall land cover patterns and changes.
In 1957, 86% of total forest area concentrated on a large patch of 2 848 ha located along the
Eume river gorge (Fig. 1); the remaining forest area occurred in patches that were smaller than
1000 ha, with only ca. 4% in patches under 100 ha. The 2 848 ha patch from 1957 suffered 28%
area loss as well as fragmentation into three patches of 273, 751 and 1 003 ha. The 1 003 ha
patch was the largest one in 2003 and was located along the low Eume River gorge (Fig. 1). The
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.