Landscape change, ecological and visual impact in relation to the marble quarries

3.4.2 Quantification of landscape metrics of quarry patches in 1984 and 2000

A discussion of the change in landscape metrics of quarry patches between 1984 and 2000, summarised in Table 7 is necessary to describe the characteristics of the landscape change as a result of quarrying activity.

Table 7: Landscape metrics of marble quarries in the island of Thasos in years 1984 and 2000

% difference

Attribute of quarries

Difference on 1984

levels

Number of patches

+149.49 +487 % Quarries

Total (class) area (ha)

Percent of landscape (%)

Mean elevation (m)

Mean patch size (ha)

Median patch size (ha)

+53.97 +47 % Patch

Patch size coefficient of

variation (%PSSD/MPS) Largest patch index (% total

area of quarries) Patch Density (#/100 ha)

Total edge (m)

Mean patch edge (m)

Edge density (m/ha island)

Area weighted Mean Shape

Area weighted Mean Patch

Fractal Dimension Mean Nearest Neighbour

distance: patch centroids (m)

(p<0.01) +28 %

Mean Nearest Neighbour

Distance: patch edges (m)

Proximity - Aggregation Nearest Neighbour

coefficient of variation (%NNSD/MNN) Mean Proximity Index

(area/distance 2 of quarry patches)

The comparison of landscape metrics for marble quarries between 1984 and 2000 reveals that there has been an expansion of quarrying activity in the intervening 16 years. This expansion is characterised by an almost fivefold increase of the area of quarries which grew from 0.08% of the island of Thasos in 1984 to cover 180 ha or 0.47% of the island in 2000. This increase happened by both the enlargement of existing quarries and the

Report of Case Study: Thasos island, NE Greece Report of Case Study: Thasos island, NE Greece

The spatial distribution of the marble quarries in Thasos is neither uniform nor random. Spatial pattern analysis (Average Nearest Neighbour Distance) in ArcGIS 9.0 (available only for polygon centroids) revealed that they are clustered in the north-east part of the island at a mean elevation of about 270 m (S.D. 131m in 1984 and 153m in 2000). The creation of the new quarries increased the mean nearest neighbour distance of their centroids from 232m to 296m in 2000. The expected mean distance for randomly or uniformly dispersed patches in 1984 was 1756m and 1509m in 2000 and the ratios of observed to expected distances was 0.13 in 1984 and 0.20 in 2000. These ratios reveal clustering i.e. that the nearest neighbour distance between quarries is highly significantly smaller than a random or uniform distribution. This may reflect that the marble substrate is most pure, abundant and/or accessible in this part of the island but also the proximity to the main port of the island. At the same time the enlargement of existing quarries reduced the mean nearest neighbour distance measured from their edges from 158m to 116m. This does not contradict the mean nearest neighbour distance calculated from patch centroids because centroid distance is less realistic as a measure of proximity than proximity calculated from patch edges. It indicates that new quarries and enlarged existing quarries tend to coalesce, making their presence more noticeable in NE Thasos.

An even more effective measure of patch proximity and area which combines the influence of all neighbour distances with the area of the patches is the mean proximity index which is defined as the area of a given habitat patch divided by the square of the distance from each patch of the same type. This index increased to 41.89 from 3.44 in 1984, a 1118% increase which reflects that the landscape in 2000 has larger quarries and closer to each other which corroborates the conclusion above.

The increase of the mean patch size was accompanied by an increase of the mean perimeter of the quarries. Likewise, the total edge and the edge density of quarries in the island increased by a factor of 2.3 reaching 44340m in 2000 or 1.16m per ha of the island. Quarry shapes did not enlarge uniformly their edges but the enlargement diverged from the shape of a square to more complex shapes - mainly a lateral enlargement of the quarry face parallel to the contours which was captured by increased shape indices.

The impact of the expansion of marble quarries on the landscape of Thasos from 0.08% to 0.47% of the island, does not seem alarming. However, these ratios that give equal

Report of Case Study: Thasos island, NE Greece Report of Case Study: Thasos island, NE Greece

3.4.3 Visual impact assessment and change

The cumulative quarry viewshed in 1984 (Figure 40) and 2000 ( Figure

41) affect the north east part of the island. The viewsheds are contingent on the landform of the island (Figure 3, p.11) and they are bounded by mountain ridges that block visual contact to quarries to areas where the line of sight is not interrupted by the intervening landform.

An initial assessment of the visual impact of quarry expansion in Thasos is the difference in the total area of the viewshed of the quarries that is the area of the island affected by having visual contact with at least one portion of marble quarry (segment of 30m that is the pixel size of quarry boundaries). This is shown in Table 8 and Figure 42 where it is evident that the 31 ha of quarries distributed in 28 patches in 1984 had a visual impact over an area of 4700 ha or 12.29% of the island. In 2000 the area of quarries increased to 180 ha distributed in 36 patches affecting an area of 5180 ha or 13.54% of the island.

These percentages of the visually affected landscape of Thasos provide a more realistic quantification than the absolute area of the quarries. The increase of the total area affected is not dramatic reflecting that the new quarries were created in the vicinity of existing quarries.

Table 8: Expansion of viewshed of marble quarries between years 1984 and 2000 in Thasos island.

1984 2000 Viewshed area of

marble quarries (ha)

Viewshed area as % of island surface

The next level of detail of visual impact assessment is to quantify the intensity of this impact, its change and finally the cumulative visibility load.

Report of Case Study: Thasos island, NE Greece

Environmental Impact Assessment

Figure 40: Quarry locations, viewshed extent and spatial variation in intensity of visual impact in 1984 Figure 41: Quarry locations, viewshed extent and spatial variation in intensity of visual impact in 2000

Figure 42 (left): Quarry Viewshed expansion

Figure 43 (right): Level of visual impact change between 1984 and 2000

Figure 44 (below): Quantification of level of visual impact change with moving average trendline.

The product of viewshed area difference by no of visible quarry

edge pixels

Area difference*visible quarry edge pixels

10 per. Mov. Avg. (Area

difference*visible quarry edge

ce edge

pixels)

n y 1000

ibl -500

ls -1500 e

of

iew x -2000

V pi

Number of visible quarry perimetre pixels

Report of Case Study: Thasos island, NE Greece

The intensity of visual intrusion of marble quarries increased dramatically considering the amount of quarry edge visible in the viewshed of 1984 and 2000 as shown in Figure 44 of the previous page, which is a map of the difference in the number of quarry edge pixels visible.

The maximum value of quarry (perimeter) pixels visible in 1984 was 201 pixels which corresponds to 6030 m of quarry edge (45.5% of the total edge of quarries) while in 2000 the maximum value was 542 pixels which corresponds to 16260 m of quarry edge (36.7% of the total edge of quarries in 2000).

Obviously an increase in viewshed area of pixels with low visibility of quarry edges does not add as much visibility load as the same increase of the viewshed pixels with high visibility of quarry edges.

To quantify visibility load each viewshed pixel (0.09 ha) was multiplied by its visibility score (number of quarry edge pixels visible) to assess the cumulative increase of the visual impact.

The change in the cumulative amount of visual impact between 1984 and 2000 is shown as a graph in Figure 44, p.40 which summarizes the map of Figure 44 in quantitative terms.

The change of visibility load between 1984 and 2000 indicated that the visual impact

( N i ∗ A i ) 2000 = 2 . 52 ∗ ( N j A j ∑ . ∑ ∗ ) 1984

increased by a factor of 2.52, i.e.

The spatial distribution of areas of the viewshed with high visibility load increase (Figure 44), includes the location of the capital town of the island, main touristic destination and port of the island which can be considered the ‘front yard’ of Thasos island.

This indicates that quarry expansion planning did not take into account the visual effects on the potential of the island to maintain a forested landscape view, uphill from the island capital.

4. Conclusions

Remote sensing, GIS and landscape analysis proved to be efficient in identifying, quantitatively assessing and monitoring environmental impacts caused by forest fires and mining activities in Thasos. Accurate assessments aid in evaluating the effectiveness of measures taken to rehabilitate the damaged areas, and allow land managers to identify and target areas for intensive or special restoration, thus avoiding long-term site degradation.

Report of Case Study: Thasos island, NE Greece

In relation to the specific objectives the following can be concluded:

1. Nearly half the island of Thasos was burned within a period of 16 years (1984- 2000). The mostly affected landcover type was high coniferous forest (77%). Specifically 62% of the burned area was P. brutia forest (60% of its original area), 12% was shrubland (45% of its original area), 11% was arable land, 9% was P. nigra forest (46% of its original area), 4% was mixed P. brutia and P. nigra forest (74% of its original area), while the remainder 2% of the burned area belonged to the rest landcover types.

2. Αn adequate vegetation cover re-established on 2/3 of the burned area. Vegetation recovery success differed greatly between different landcover types with bare land having the worst vegetation recovery (29%) and broadleaved deciduous forest having the best recovery (95%). Grassland and shrubland had relatively low recovery (55%) while for coniferous forest, revegetation was adequate at 68.4% of its area. Vegetation recovery was slightly higher in areas originally covered by Pinus brutia (66%) than Pinus nigra (69%) forest and worst for their ecotones (59%). Regarding the comparison of the 7 Vegetation Indices evaluated for their efficiency to indicate percentage vegetation cover, MSAVI proved to be the best and NDVI was second-best.

3. Between 1984 and 2000 new quarries were created and existing quarries were enlarged from an average size of 1.1 ha to 5 ha. The total area of the quarries increased c. 500% to occupy 0.5% of the island. Marble quarries are clustered in the north-east part of the island at a mean nearest neighbour distance of 116m. The quarries were created mainly (>90%) in areas covered by coniferous forest that had not been affected by forest fires during the study period. Regarding the comparison between the two methods for quarry expansion monitoring, post- classification comparison gave practically the same results as image differencing.

4. In terms of visual and landscape impact, marble quarries tend to assume a dominant role in the landscape character of the northern part of Thasos. Viewshed analysis revealed that the visibility load between 1984 and 2000 increased 252% affecting 14% of the island, including areas such as the island’s capital and nearby coasts.

It should be noted that the work described in this manuscript is fully compatible with the DPSIR framewotk. The DPSIR parameters of Terrestrial Environmental Impact for Thasos were identified and are reported in Table 13, p.52 of the Annex.

Report of Case Study: Thasos island, NE Greece

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Report of Case Study: Thasos island, NE Greece

ANNEX

Table 9: Landcover classes burned by all fires as percentages of total area burned and original area of classes

Area burned

Original

% of total

% of original

Landcover

class area

in ha

area burned

class burned

in ha

59.38% SHRUBLAND

PINUS BRUTIA

44.96% ARABLE LAND

45.79% PINUS BRUTIA - PINUS NIGRA

PINUS NIGRA

BARE LAND

ABANDONED FARMLAND

PINUS BRUTIA - PLATANUS

PINUS NIGRA - ABIES

Table 10: Application of MSAVI thresholding to each burned area.

MSAVI VALUE

AREA (ha) AREA %

FIRE 1985-89

Report of Case Study: Thasos island, NE Greece

Table 11: Percentages of areas below and above the selected MSAVI threshold

MSAVI

Zone of vegetation type

AREA (ha) AREA %

BARE LAND &

TOTAL AREA

SUM 18999.08 100

Table 12: Selected vegetation indices

INDEX

FORMULA

1 II (Infrared Index) II = (TM4-TM5)/(TM4+TM5) 2 NDVI (Normalized NDVI=(pNIR-pRED)/(pNIR+pRED)

Difference Vegetation Index) 3 MSR (Modified MSR=((pNIR/pRED)-1))/((pNIR/pRED)1/2+1) Simple Ratio)

4 MSAVI (Modified MSAVI=((2NIR+1-( √(2NIR+1)2-8(NIR-R))) / 2 Soil Adjusted Vegetation Index) 5 GVI (Greenness GVI= -0.2728(TM1)-0.2174(TM2)-0.5508(TM3)+ Vegetation Index) 0.7221(TM4)+0.0733(TM5)-0.1648(TM7).

6 SR (Simple Ratio) SR=pNIR/pRED 7 MNLI (Modified MNLI=((p2NIR-pRED)(1+L))/ ((p2NIR+pRED)+L)

non-Linear Vegetation Index

Report of Case Study: Thasos island, NE Greece

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