Physiognomic stratification of the vegetation provided the basis for its inventory. Four formations were identified corresponding to the landscape elements: forests (including woodlands), shrublands, grasslands and rocky sites. The plot sizes were chosen according to the minimum area concept (GLAVAC 1996).The plot size was set to 100
m2 for the forests and shrublands, 20 m2 for the grasslands and 10 m2 for the rocky sites (Table 3.1).
Table 3.1 Plot characteristics Vegetation formation Plot size (m2) Plot dimensions Number of plots Forest/woodland 100 8m x 12,5m* 179 Shrubland 100 8m x 12,5m 31 Grassland 20 4m x 5m 157 Rocky sites 10 2m x 5m 43 Total 410
To facilitate the comparison of vegetation data with different plot sizes, a nested plot design (KENT & COKER 1992,STOHLGREN et al. 1997) was adopted for the inventory
(Fig.3.1). Specifically, inside each plot of 100 m2 or 20 m2, a subplot of 10 m2 was set for inventory. Furthermore, for fifty (50) plots of the grassland vegetation the 20 m2 plot was expanded to 100 m2. In each case the 100 m2 plot contained the 20 m2 and the 10 m2 plot. Also forty (40) plots of the forest type were expanded to the 200 m2. This was decided for the forests of the gorge, where the extended forest cover and the
* The tree hedges, which were also included to the forest/woodland formation, were inventoried with a plot size of 100 m2, but with no standard dimensions due to their linear structure.
homogeneous site conditions permitted the inventory of a larger plot size than that of 100 m2.
The inventory of the vegetation was conducted from May till July of the years 1999, 2000 and 2001. Each year the grasslands, rocky sites and shrublands (open vegetation) were inventoried between May and June. The forests and woodlands (woody vegetation) were sampled from the end of May till July. At the same time the
open vegetation was also inspected for late growing species.
Two extra visits at the study area, once early in spring and a second late in autumn of the year 2001, contributed to the identification of early and late growing species respectively, which have been registered at the plots, but remained unidentified due to missing floral parts. During these visits all new plant species encountered in the area were also registered.
10m2 5m 2m 12.5m 8 m 4m
Fig.3.1 The nested plot design used for the vegetation inventory.
A systematic inventory was applied initially by the use of a grid. The distance between the plots was set to 100 m, due to the alteration of the vegetation in relatively short distance (Fig.3.2). The 100 m distance between the plots allowed all vegetation formations to be inventoried, although with different plot numbers (KENT &COKER
1992). At the grid nodes falling at two vegetation formations the sampling plot was moved accordingly, so that only one formation was inventoried. A supplementary random sampling provided additional plots for vegetation types under-represented in the systematic sampling. The numbers of plots in the two designs are given in Table 3.2.
Table 3.2 Plots of the systematic and random inventory
Number of plots Vegetation type Systematic
inventory Random inventory Total Open vegetation 63 168 231 Woody vegetation 130 49 179 Total 193 217 410
The vegetation was inventoried at three layers (herbs, shrubs and trees) of fixed height. The herb layer included all herbaceous species and also all woody species found in a zone up to 1 m above ground. The shrub layer contained all woody species found between 1 and 5 m above ground. Woody species with a height of 5 m or more formed the tree layer. The plant species of the shrub and tree layer are marked with the letter “S” or “T” respectively at the vegetation table. At each plot and for each vegetation layer the presence of all vascular plant species was recorded and their abundance was visually estimated according to an adjusted BRAUN–BLANQUET scale
(GLAVAC 1996) (Table 3.3).
Also, the total cover value of each vegetation layer and that of the soil, rocks and mosses were estimated. Site parameters, such as altitude, exposition, inclination, relief type and land use type (Table 3.4) were also registered at each sampling plot. Data of the geology were provided from the geological map of the study area (PERRIER et al.
1970). Soil samples were also collected from plots considered representative for each vegetation type and geological substrate.
Non-vascular plant species such as mosses and lichens were not inventoried. These species vary strongly in short distance depending on the micro-climatic and micro-site (humus quality, quantity of dead wood) conditions. Their inventory is also time
consuming and requires expertness in the knowledge of the cryptogamous flora
(WILMANNS 1998).
Table 3.3 BRAUN-BLANQUET cover-abundance scale and respective transformed mean cover values
BRAUN - BLANQUET
scale
Abundance / cover range*
mean cover value
(%) r 1-3 individuals & cover <1% 0.01 + 4-10 individuals & cover <1% 0.1 1 11-50 individuals & cover 1-3% 2 2m >50 individuals & cover 3-5% 4 2a any number of individuals, cover 5-15% 10 2b any number of individuals, cover 15-25% 20 3 any number of individuals, cover 25-50% 37.5 4 any number of individuals, cover 50-75% 62.5 5 any number of individuals, cover 75-100% 87.5 * adjusted from GLAVAC (1996)
PLANT SPECIES IDENTIFICATION
Specimens of the plant species were collected and identified based on Flora Europaea (TUTIN et al. 1964-1980), Mountainous Flora of Greece Vol.1 (STRID 1986) & Vol.2
(STRID &TAN 1991) and Flora Hellenica Vol.1 (STRID &TAN 1997).
The plant life form spectrum was assigned according to the major divisions of the
RAUNKIAER’S system in phanerophytes, chamaephytes, hemi-cryptophytes,
geophytes, and therophytes (MUELLER-DOMBOIS &ELLENBERG 1974,ATHANASIADIS
1984). The necessary information on the life forms was based on DROSSOS &
ATHANASIADIS (1989), ATHANASIADIS & DROSSOS 1990, BÖHLING (1995) and
Table 3.4 Land-use types
Land-use type Main characteristics
Meadow Grassland mown once per year and grazed afterwards Forested field Terraced land with successional woody vegetation Old garden Fallow land recently abandoned (< 10 years) Pasture Grassland grazed by sheep
Wood pasture Shrubland and open forest grazed by goats Shredding
/Pollarding Cutting the young tree branches for fodder
Coppice forest Vegetatively regenerated woodland, cut in short rotation (15-20y) for firewood, occasionally grazed Middle forest Forest with coppiced undergrowth and standards