Assessment of the Fragmentation of Forested Areas in West

Transkrypt

Pieńkowski, P., Kupiec, M. (2003) Assessment of the Fragmentation of Forested Areas in West Pomerania.
In: M. Gajos, U. Myga - Piątek (ed.). Geographical Information Systems. Interdisciplinary Aspects.
University of Silesia - GIS Forum – SILGIS Association, Sosnowiec – Zagreb, 453-462.
Geographical Information Systems - Interdisciplinary Aspects
University of Silesia - GIS Forum - SILGIS Association, Sosnowiec - Zagreb 2003
Paweł Pieńkowski, Michał Kupiec
Agricultural University of Szczecin, Department of Environmental Protection and
Development, Poland
Assessment of the Fragmentation
of Forested Areas in West Pomerania
Introduction
Along with development of agriculture and broadening settlement, there was
an increase in the acreage of farmlands and a shrinkage and fragmentation of
forested areas. Changes in usage intensity of this area depend mainly on soil type
and topographic features, which can clearly be seen on the example of forests, the
largest complexes of which were left on sandy terrace plains, sandrs and frontal
moraines. The introduction of agriculture in areas previously covered by forests has
caused forest fragmentation and spatial isolation. Dense forest complexes were left
on weaker soils, and on areas with high relief not allowing to take over of the area
to farmland (Pieńkowski, Podlasińki 2002). Fragmentation of forest areas for
several centuries (Bojarowski, Szacherska 1996, Pietrzak, Siwek 2000) has caused
numerous floral and faunal changes (Loster 1991). Assessment of the changes in
forestation is possible amongst other methods through analysis of archived
cartographic materials. Computer elaboration of these materials allows for its
geometrical fit and assessment of change dynamics (Jankowska 1990,
Wyczałek 1994). Also the data pertaining to settlement preferences of particular
plant and animal species allows for the assessment of bio and physiocenotic
changes which occur in the landscape (Blaschke 1997).
The purpose of this research was an assessment of the spatial and temporal
changes in forestation in Szczecin Coastland from the 15th century to the 1930’s
using indexes characterising surface fragmentation. Calculation of the indexes was
possible through digital maps created using of Geographic Information Systems
(GIS).
Materials and methods
The area of forests in history was assessed in the basis of utilisation charts
by Hartnack (1934), scale of 1:1,500,000. This author developed the forest charts
based upon charts: Lubinus 1618, Zierhold 1789, Engelhard 1811. Data from 1930
were taken from the Chart of the German Reich, scale of 1:100,000, and Survey
Map of Central Europe, scale of 1:300,000. Division of the area into meso-regions
was based upon physico-geographic rationalisation of Poland (Kondracki 2000).
All cartographic materials were registered in ArcInfo programme in WGS 84
system, and of forests outlines were digitalized. This program was used as well to
453
calculate parameters such as surface, number and perimeter of forest patches
needed for the assignment of indexes.
For the assessment of changes in forested areas in the region of Szczecin
Coastland indexes characterising dynamics of surface fragmentation processes
proposed by Jaeger (2000) were used.
Degree of coherence defined as the probability that two random points are
placed in different patches in the region of investigation.
A
C= ∑  i
i = n  At



n
2
where: Ai –sizes of the n patches At –total area of investigated region.
Degree of landscape division (D) defined as the probability that two
randomly chosen places in the landscape under investigation are not situated in the
same non dissected area.
A
D= 1 − ∑  i
i = n  At
n



2
Splitting index (S) defined as the number one gets when dividing the total
region into parts of equal size, in such way that configuration leads to the same
degree of landscape division (D).
S=
At2
n
∑A
2
i
n =1
Effective mesh size (M) denotes the size of areas when the region under
investigation is divided into S areas (each of the same size At/S) with the same
degree of landscape division (D).
M=
At 1 n 2
= ∑ Ai
S A i =1
Additionally the Landscape Dissection Index (LDI) (Bowen and Burges
1981), showing the relationship between area and perimeter of patches was
calculated. LDI is intensive (i.e. stays constant) when a region with a certain
landscape pattern is multiplied, however is not area proportionately additive
(where: Pi – perimeters of the n patches).
n
LDI =
∑
Pi
i=n
n
2 π ⋅ At ⋅ ∑ Ai
i =n
454
Assessment of the Fragmentation of Forested Areas in West Pomerania
Research area
Analysis of forestation changes was conducted for an area of 13 390 km2,
covering mainly Szczecin’s Coastland along with small parts of West Pomeranian
Lakeland (fig.1). The western and northern part of the researched area was the
current border of Poland, whereas the southern border was the former border of
Pomeranian Province from before WWII. The eastern limit was set at 16o30’ east
longitude.
The landscape of research area was formed during the last glaciation
(Vistulian). It is dominated by flat and wavy plains of ground moraine, cut with a
net of glacial channels and river valleys. Specific to this area are vast areas of
sandy Odra Flood Plain and Pyrzyce ice-dammed basins filled with sediments such
as loams and silts.
In order to point out the differences in forest fragmentation, the entire area
was divided into four regions, with different dynamics of forest disappearance
(fig.1): 1) area located on the western bank of Odra river, 2) area covering the
Wkrzańska Plain and Szczecin Hills (A), 3) Goleniów Plain (B), 4) Wełtyń Plain
along with part of Myślibórz Lakeland (C) and Ińskie Lakeland (D).
Results and discussion
Between the 15th century and the1930’s, there was a constant decrease of
forested area and increase of its fragmentation. This process took place particularly
between the 15th and 18th century, when the share of forests decreased from 52% to
24%, and the number of patches increased from 123 to 153 (table 1). The largest
changes occurred in the eastern part of the research area, particularly in the area of
mesoregions characterised with better soils – on Ińskie Lakeland and Nowogard
Plain. In the first mesoregions mentioned forest cover decreased from 68 to 19%;
in the second one from 64 to 25%. In the eastern part of research area only small
patches of forests were left, whereas in the western part forests were still growing
on large areas of podzols and podzolic soils generated from loose sands
(Pieńkowski, Podlasiński 2002).
Such significant decrease of forested areas, related with division of large
forest patches, is reflected in the indexes calculated for fragmentation of patches. In
the 15th century the average patch size was 56.6 km2, whilst in the 18th century it
was 21.1 km2. The degree of coherence C, determining the chance of finding two
randomly located points in the same patch decreased from 0.096 (15th century) to
0.003 (18th century). Thereby the splitting index, determining theoretical number of
patches for the degree of coherence C, increased from 10.4 to 348.3. Change of
LDI (from 0.151 to 0.165), was noted as well as evidence of increase of forest
lines.
455
Fig. 1. Study area (meso-regions - according to Kondracki 2000). A – Wkrzańska Plain
(313.33) and Szczecin Hills (313.26), B – Goleniów Plain (313.25), C – Wełtyń Plain
(313.28) and Mysliborskie Lakeland (314.41), D – Ińskie Lakeland (314.43). Remaining
meso-regions: 313.21 – Wolin and Uznam Islands, 313.22 – Trzebiatów Coast, 313.24 –
Lower Odra Valley, 313.27 – Bukowe Hills, 313.31 – Stargard – Pyrzyce Plain, 313.32 –
Nowogard Plain, 313.33 – Gryfice Plain, 313.41 – Słowińskie Coast, 313.42 – Białogard
Plain, 313.44 – Łobez Upland, 314.42 – Choszczno Lakeland, 314.45 – Drawsko Lakeland,
314.63 – Drawsko Plain, 314.64 – Wałcz Lakeland, 314.65 – Szczecinek Lakeland.
Table 1. Measures of forest fragmentation in Western Pomerania region
Number
of
patches
15th century 123
18th century 153
20th century 198
Period
456
Mean
area
[km2]
56.64
21.09
10.79
Indices
Forestation
[%]
C
D
S
M
LDI
52.2
24.1
16.0
0.096
0.003
0.001
0.904
0.997
0.999
10.4
348.3
674.5
1293.4
38.4
19.9
0.151
0.165
0.170
In order to show differentiation in forest fragmentation, despite of
insignificant differences in forestation degree, four regions characterised with
different fragmentation of forested surfaces were chosen. The first area covers
Wkrzańska Plain and Szczecin Hills (fig. 2A). On this area due to poor soils,
forested areas underwent relatively small transformations. In the 15th century
forestation of this area amounted to 71% (table 2), 53%at the end of 18th century,
and in the 20th century it dropped to 37%. In the first period, the probability of
finding two randomly located points equalled 0.5, at the end of 18th century – 0.28,
and in the 20th century it dropped to 0.13.
Similar process of fragmentation was observed in the area of the Goleniów
Plain (fig. 2B), where relatively poor soils are covered with Goleniów Primeval
Forest. With an initial forestation of 80%, the coefficient C equalled 0.63 and in the
20th century its value decreased to 0.12 (similar to the in Wkrzański Primeval
Forest and Szczecin Hills). Therefore it can be noted, that regardless of relatively
different number of patches in both of those areas, the degree of coherence in the
20th century was approximate.
Calculation purposefulness of coefficient C could be investigated the best
way by comparison of two areas with identical forestation. For example forestation
of Wkrzańska Plain and Szczecin Hills in the 18th century was equal to forestation
of Goleniów Plain in the 20th century (53%). However, taking into consideration
coefficient C, the degree of fragmentation of those areas was different and for the
first one equalled 0.28 while for the second one – 0.12. Therefore the probability of
finding two randomly located points in the same patch was two times lower on
Goleniów Plain.
The next two areas had much better soils and higher hypsometric
diversification, which influenced different process of disappearance and
fragmentation of forests in comparison with the areas described previously. Due to
better soil conditions on Wełtyń Plain and Myślibórz Lakeland, forest cover
decreased from 65% (15th century) to 11% (20th century). A similar decrease
occurred in the area of Ińskie Lakeland (from 64 to 18%). The largest decrease
took place between the 16th and 18th centuries (fig. 2D).
Both of these areas were characterised (particularly in the 15th and 20th
centuries) with similar forestation, number of patches and their average size,
whereas the values of other indexes was diversified. The probability of finding two
randomly located points in the same patch in the 15th century equalled - 0.23 for
Wełtyń Plain and Myślibórz Lakeland and – 0.48 for Ińskie Lakeland.
The areas differ as well with LDI coefficient It is significantly higher in the
case of Wełtyń Plain and Myślibórz Lakeland. The highest value of this coefficient
amounting to 0.380, was observed in these mesoregions in the 20th century. It
should be associated with lobe forestation system as presented in fig. 2C and is
related to the poorest soils located in this area, their location depended on the
continental ice-sheet recession.
457
15th c.
18th c. (1790)
20th c. (1930)
A
B
C
D
Fig. 2. Forest fragmentation in four regions of Pomerania in 15th c. in 1790 and in
1930. A – Wkrzanska Plain and Szczecin Hills, B – Goleniów Plain, C – Wełtyń
Plain and fragment of Myślibórz Lakeland, D – Ińskie Lakeland.
458
Table 2. Measures of forest fragmentation in selected areas
Period
Number
of
patches
15th century
18th century
20th century
2
2
3
15th century
18th century
20th century
5
12
10
15th century
18th century
20th century
4
9
20
15th century
18th century
20th century
4
18
24
Forest
Mean
area
area
C
D
S
[%]
[km2]
Wkrzańska Plain and Szczecin Hills
201.47
71.0
0.50
0.50
1.8
151.46
53.4
0.28
0.72
3.5
69.2
36.6
0.13
0.87
7.6
Goleniów Plain
158.62
80.5
0.63
0.37
1.6
34.93
60.4
0.15
0.85
6.6
50.57
53.2
0.12
0.88
8.5
Wełtyń Plain and Myśliborskie Lakeland
112.98
65.8
0.230
0.770
8.9
25.07
32.8
0.030
0.970
68.6
8.98
11.6
0.002
0.998 1097.8
Ińskie Lakeland
179.1
68.0
0.458
0.542
2.2
15.29
18.9
0.069
0.931
143.1
3.87
8.4
0.001
0.999 1439.3
M
LDI
311.4
162.8
74.3
0.119
0.156
0.139
621.0
148.3
115.4
0.126
0.154
0.200
110.2
14.4
0.9
0.214
0.269
0.380
481.9
7.4
0.7
0.114
0.170
0.086
Conclusions
Digital maps prepared based on archive materials made possible the assess
changes in surface and forest fragmentation in the Szczecin Coastland. Data
obtained by using GIS programmes allowed for the calculator of coefficients used,
confirming their usefulness in assessment of forest patches fragmentation. These
measurements supplement information obtained by determining: forestation,
average patch size and number of patches and can be useful in particular for the
analysis of landscape changes and its influence on biocenosis formation.
Comparison of digital maps indicated that for the study period (15th-20th
century), the largest fragmentation took place between the 15th and 18th centuries,
when the forest cover decreased from 52% to 24%. Average patch size decreased at
that time from 56.6 km2 to 21.1 km2, whereas the degree of coherence, determining
the chance of finding two randomly located points in the same patch decreased
from 0.096 (15th century) to 0.003 (18th century).
459
Bibliography
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Modellierung von Lebensräumen mit GIS als Grundlage der Bewertung und
Planung. In: GIS im Naturschutz. Forschung, Planung, Praxis, red. R. Kratz,
F. Suhling. Frank.-Magdeburg: 31–49.
2. Bojarowski K., Szacherska M. K., 1996: Ocena zmian kompleksów leśnych z
wykorzystaniem komputerowego systemu przetwarzania informacji
pozyskanych z map XVIII-XX wieku. Konf. Nauk. pt: Kartograficzne Metody
Badania Zmian Środowiska, Poznań 25 X 1996: 115-136.
3. Bowen G. W., Burgess R.L. 1981: A quantitative analysis of forest island
pattern in selected Ohio landscapes. ORNL Environmental Sciences Division,
Publication No 1719, ORNL/TM-77598. Oak Ridge.
4. Hartnack W. 1934: Wirtschafts- und verkehrsgeographischer Atlas von
Pommern. red. W. Witt Ostsee-Druck und – Verlag A. –G. Stettin.1934.
5. Jaeger J. A.G 2000: Landscape division, splitting index, and affective mesh
size: new measures of landscape fragmentation. Landscape Ecology 15: 115130.
6. Jankowska M., 1990: Problemy badania zmian elementów rolniczej
przestrzeni produkcyjnej IUiPTW AR Wroc.: 85-97.
7. Kondracki J., 2000: Geografia regionalna Polski. Wydawnictwo Naukowe
PWN. Warszawa 2000.
8. Loster S., 1991: Różnorodność florystyczna w krajobrazie rolniczym i
znaczenie dla niej naturalnych i pół naturalnych zbiorowisk wyspowych.
Fragm. Flor. Geobot. 36(2): 427–457.
9. Pieńkowski P., Podlasiński M., 2002: Changes in forest cover of Szczecin
lowland from the 16th to the end of the 20th century, in relation to soil cover.
Electron. J. Pol. Agric. Univ., For. - 2002, Vol. 5.
10. Pietrzak M., Siwek J., 2000: Wykorzystanie map historycznych,
przetworzonych przy użyciu GIS do oceny zmian użytkowania ziemi na
Podgórzu Wiśnickim. [In] Przemiany środowiska na Podgórzu Karpackim.
red. W. Chełmicki. Instytut Geografii UJ, Kraków 2000.
11. Wyczałek E., 1994: Badanie środowiska rolniczego na podstawie analizy
komputerowej archiwalnych map topograficznych. Rocz. AR Pozn. 267,
Melior. Inż. Środ. 15, cz.2:79–87.
460
Agricultural University of Szczecin, Department of Environmental Protection and
Development, Poland
Summary
Analysis of fores changes was conducted for a 13390 km2 and covering
mainly Szczecin’s Coastland along with small parts of the West Pomeranian
Lakeland.
Historical forest cover was assessed from charts by Hartnack (1934), scale of
1:1,500,000 who developed the forest charts based on charts: Lubinus 1618,
Zierhold 1789, Engelhard 1811. Data from 1930 were taken from the Chart of the
German Reich, scale of 1:100,000, and the Survey Map of Central Europe, scale of
1:300,000. Indexes, proposed by Jaeger (2000), characterise the dynamics of
surface fragmentation processes were used to assess changes in forested area.
Digital maps prepared based on archive materials made in possible to assess
changes in surface and forest fragmentation in the area of Szczecin Coastland. Data
obtained by using GIS programmes allowed for the calculation of coefficients used
confirming their usefulness for assessing of forest patch fragmentation. These
indices supplement information obtained by determining: forest cover, average
patch size, and the number of patches and can be useful in particular for the
analysis of landscape changes and its influence on biocenosis formation.
Digital map comparisons of the division of forested surfaces indicated that in
the period compared (15th-20th century), the largest fragmentation took place
between the 15th and 18th century, when the share of forests decreased from 52% to
24%.
Keywords: GIS, changes in forest area, fragmentation of landscapes
Akademia Rolnicza w Szczecinie , Katedra Kształtowania i Ochrony Środowiska,
Polska
Ocena Fragmentacji Obszarów Leśnych Pobrzeża Szczecińskiego
Streszczenie
Analizę zmian zalesienia wykonano dla obszaru o powierzchni 13390 km2,
położonego na Pobrzeżu Szczecińskim oraz niewielkiej części Pojezierza
Pomorskiego. Powierzchnie lasów w poszczególnych okresach historycznych
oszacowano na podstawie map użytkowania Hartnacka (1934) wykonanych w skali
461
1:1500 000. Autor ten mapy stanu lasów opracował m.in. na podstawie map:
Lubinusa z 1618, Zierholda z 1789 i Engelharda z 1811 roku, natomiast
użytkowanie w roku 1930 w oparciu o Mapę Rzeszy Niemieckiej w skali
1:100 000 oraz Przeglądową Mapę Europy Środkowej w skali 1: 300 000. Do
oszacowania zmian powierzchni leśnej na obszarze Pobrzeża Szczecińskiego
zastosowano wskaźniki, charakteryzujące dynamikę procesów fragmentacji
powierzchni zaproponowane przez Jaegera (2000).
Wykonane na podstawie materiałów archiwalnych mapy numeryczne
umożliwiły ocenę zamian powierzchni oraz fragmentacji lasów na obszarze
Pobrzeża Szczecińskiego. Dane uzyskane dzięki zastosowaniu programów GIS
pozwoliły m.in. na wyliczenie zastosowanych wskaźników, potwierdzając ich
przydatność do oceny fragmentacji płatów leśnych. Mierniki te uzupełniają
informacje uzyskiwane przy określeniu: lesistości, średniej wielkości płata i ilości
płatów, i mogą być przydatne zwłaszcza do analizy zmian krajobrazu i ich wpływu
na funkcjonowanie biocenoz.
Porównanie map numerycznych pod kątem podziału powierzchni leśnej
wykazało m.in., że w porównywanym okresie (XV-XX w.) największa
fragmentacja powierzchni leśnych miała miejsce pomiędzy XV a XVIII w., kiedy
to udział lasów obniżył się z 52% do 24%.
Słowa kluczowe: GIS, zmiany zalesienia, fragmentacja krajobrazu
462

Assessment of the Fragmentation of Forested Areas in West

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