The stability of ecological corridors as illustrated by examples from Poland
Alina Gerlée
University of Warsaw, Faculty of Geography and Regional Studies, Department of Geoecology, ul. Krakowskie Przedmieście 30, 00-927 Warszawa
e-mail: a.gerlee@gmail.com
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Abstract: The paper presents a method that evaluate ecological corridors’ stability. It uses the CORINE Land Cover Change data. The method was applied to evaluate stability of ecological corridors linking the Natura 2000 network in Poland. Land cover change index and spatial uniformity index were constructed. The analysis was carried out as follows:
(1) Assessment of land cover suitability for the migration of large mammals; (2) Evaluation of land cover changes quality (3) Assessment of land cover changes balance within the ecological corridors and beyond them (4) Assessment of changes uniformity in the voivodeships (5) Analysis of positive, negative and neutral changes proportions. The results show that ecological corridors stability differs in analyzed periods (1990-2000 and 2000-2006) and regions (voivodeships). Two kinds of stability - static and dynamic were discussed. Strengths and weaknesses of the method were presented.
Key words: ecological corridor, landscape stability, land use, CORINE Land Cover Change
The aim and scope of the paper
The aim of the paper was to assess the stability of ecological corridors in Poland. The term ‘stability’ does not have one, generally accepted definition. Various interpretations of this term were discussed in an earlier paper (Gerlée 2008). For the purpose of this study stability is understood as persistence (constancy) of a given type of land use in time. It is analysed in the context of the function of ecological corridors. Changes in their use are examined in the light of how they might affect the corridors’ suitability for animal migration.
The analysis is based on a proposed network of ecological corridors connecting Natura 2000 areas (Jędrzejewski et al. 2005, fig. 1) and data from the CORINE Land Cover (CLC) Change 1990-2000 database and the CLC Change 2000-2006, containing information on changes in land cover in the specified periods.
Methods
The following procedure was applied: (1) Creating a scale of suitability of land cover for migration of large mammals and classification of CLC types; (2) Qualitative evaluation of land cover changes; (3) Evaluation of the balance of land cover changes within and outside of ecological corridors; (4) Evaluation of spatial uniformity of the changes across voivodeships; (5) Calculating area percentage of positive, negative and neutral changes.
(1) A five-class division of the types of CLC changes was developed by reducing the 6-level scale proposed by Stachura (2003, after Bielecka 2007) (tab. 1). I included data on habitat requirements and preferences of large mammals for which ecological corridors have been identified (cf Gerlée 2011, Jędrzejewski et al. 2004, Jedrzejewski et al. 2005, Fleury and Brown 1997, Hilty et al. 2006 pp. 181-189).
(1) A five-class division of the types of CLC changes was developed by reducing the 6-level scale proposed
by Stachura (2003, after Bielecka 2007) (Table 1). I included data on habitat requirements and preferences of large mammals for which ecological corridors have been identified (cf Gerlée 2011, Jędrzejewski et al. 2004, Jedrzejewski et al. 2005, Fleury and Brown 1997, Hilty et al. 2006 pp. 181-189).
(2) Qualitative evaluation of land cover changes (k) is based on the difference between land cover ratings on a given area before (Kbefore) and after a change in land use (Kafter), and is calculated with the formula:
k = Kafter – Kbefore
For example, if in 2000 an area was covered by forest (rating 4) and in 2006 it was utilised as an open-cast mine (rating 0), the qualitative rating of the change (difference between the two ratings) is -4 (tab. 1). The qualitative evaluation of a change in land cover use can take values from -4 to 4.
Table 1. Ratings of suitability of CLC types for functioning as an ecological corridor for large mammals. The table covers all land cover types used in Poland (source: own data)
Suitability rating Land cover types (CLC codes in brackets) 0 (unsuitable areas)
Continious Urban Fabric (111), Discontinious Urban Fabric (112), Industrial or commercial Units (121), Road & Rail Networks (122), Port Area (123), Airports (124), Mineral extraction Sites (131), Dump Sites (132), Construction sites (133), Green urban areas (141), Sports & leisure facilities (142), Fruit Tree & Berry Plantations (222), Complex cultivation patterns (242) 1 (poor suitability) Non-irrigated Arable Land (211), Permanently Irrigated Land (212), Pastures (231), Beaches,
dunes & sand plains (331), Bare rocks (332), Sparsely vegetated areas (333), Burnt areas (334)
2 (moderate suitability) Natural grasslands (321), Moors & heathland (322), Water courses (511), Water bodies (512), Seas & oceans (523) 3 (suitable areas) Areas used mainly for farming, with high abundance of natural vegetation (243), Forests and
shrub vegetation under changes (324) 4 (highly suitable areas
- optimal suitability) Broad-leaved forest (311), Coniferous forest (312), Mixed forest (313), Inland marches (411), Peat bogs (412)
(3) Evaluation of the balance of changes is based on the total land cover changes area with a given rating k(∑Pk), where k takes the values: -4,-3,-2,-1,1,2,3,4, and the sum of all areas on which changes took place (P).
I formulated an index of changes (Wz), expressed by the following formula:
Fig. 1 Regions (voivodeships) in Poland and the ecological corridor network linking Natura 2000 areas (after Jędrzejewski et al. 2005, modified)
∑
=−= 4
4
k k
z W
W , where = ∑
P k P
Wk k
Evaluation of the balance of changes excludes changes in land cover that have the same suitability rating (are in the same rating class). In this case the final rating (the sum of all changes’ ratings) is 0. The index value of –4 means that on a given area 100% changes have rating – 4, while the index value of 4 means that all changes on the area have rating 4. The 0 value indicates that positive (with positive sign) and negative (with negative sign) changes cancel out.
I also examined the difference in the index value (Rwz) between the earlier (Wz1990-2000) and the later period (Wz2000-2006), where:
Rwz = Wz2000-2006 – Wz1990-2000
This index shows a trend of changes and allows to assess whether the situation is improving (positive difference) or getting worse (negative difference) in time.
(4) The index of changes uniformity (Wr) is the difference between the area percentage of changes in the corridors of a given voivodeship (Zk) and the area percentage of corridors in this voivodeship (Wk), and it can take positive or negative values. It is expressed by the formula:
Wr = Zk – Wk
The index of uniformity allows to examine whether a network of ecological corridors has undergone greater changes than the area outside of the network. The 0% value means that the sum of percent areas on which changes took place in corridors is exactly the same as the percent area of corridors. Positive values mean that changes in the area of corridors prevail. Negative values mean that there are more changes outside of the corridors.
Furthermore, I analysed the difference in the changes uniformity index (Rwr) between the earlier (Wr1990-2000) and the later period (Wr2000-2006), where:
Rwr = Wr2000-2006 – Wr1990-2000
This difference shows whether in the later period the prevalence of changes within the corridors network increased (positive value) or decreased (negative values) compared to the earlier period.
(5) I calculated the percentage of areas with negative (values between -4 to -1), positive (1 to 4) and neutral (0) values in each voivodeship, separately for the areas in and outside of ecological corridors.
Results
In the area of ecological corridors the highest balance of changes index (Wz) was observed in the Pomorskie and Zachodniopomorskie voivodeships between 1990-2000. In this period the lowest index values were obtained for the Opolskie and Śląskie voivodeships. In areas outside of the ecological corridors network the highest values were recorded in the Podlaskie voivodeship between 1990-2000 and in the Małopolskie voivodeship between 2000-2006. The lowest values were recorded in the Łódzkie voivodeship in both periods and in the Opolskie voivodeship between 1990-2000 (tab. 2).
Differences between change indices (Rwz) for each voivodeship (within the ecological corridor network and outside of them) are shown in figure 2.
The uniformity index (Wp) in corridors was calculated for two cases: 1) for all changes (including those considered neutral) and 2) for considerable changes (i.e. for positive and negative changes, excluding neutral changes), in both periods under study. The obtained results clearly indicate predominance of changes within ecological
corridors (positive values). Only in one case (Pomorskie voivodeship) was the index negative, which indicates a tendency to changes outside of the corridors network (tab. 3).
Table 2. The balance of changes indices (Wz) and differences between the balance of changes index (RWz) for each voivodeship. The highest and the lowest values in a given region within and outside of the ecological corridors network are in bold (source: own analysis)
Area of analysis Index Dolnośląskie Kujawsko-pomorskie Lubelskie Lubuskie Łódzkie Małopolskie Mazowieckie Opolskie Podkarpackie Podlaskie Pomorskie Śląskie Świętokrzyskie Warmińsko-mazurskie Wielkopolskie Zachodniopomorskie
within network
Wz 1990-2000 0.14 -0.54 -0.25 0.16 -0.34 0.57 0.07 -0.910.27 -0.061.09 -0.85-0.19 0.76 -0.061,08 2000-2006 0.03 -0.36 0.03 0.13 0.52 -0.1 -0.43 0.72 0.67 -0.02 -0.32 0.76 0.26 -0.73 -0.17 0,09 RWz -0,11 0.18 0.28 -0.03 0.86 -0.67 -0.50 1.63 0.40 0.04 -1.41 1.61 0.45 -1.49 -0.11 -0.99
outside network
Wz 1990-2000 0.36 -0.03 0.12 0.94 -1.160.28 -0.58 -0.81 -0.331.29 0.18 -0.59 -0.07 0.65 -0.22 1,01 2000-2006 0.19 -0.46 -0.37 -0.12-0.81 1.26 -0.39 0.45 0.75 0.76 -0.17 0.68 0.27 0.11 -0.12 0,57 RWz -0,17 -0.43 -0.49 -1.06 0.35 0.98 0.19 1.26 1.08 -0.53 -0.35 1.27 0.34 -0.54 0.10 -0.44
Fig. 2. Difference in the balance of changes index between 1990-2000 and 2000-2006 within and outside of the network of corridors, by voivodeships
Figure 3 presents differences between changes uniformity indices in the two periods: 1990-2000 and 2000- 2006, for each voivodeship . This analysis shows that if all changes are taken into account, in half of the voivodeships a positive and in the other half a negative trend of changes within ecological corridors is observed.
If only considerable changes are included, the prevalence of changes is lower.
It can be noted that between 1990-2000 there is a higher percentage of neutral changes than between 2000- 2006, both within and outside of the ecological corridors network. In both periods within ecological corridors a higher percentage of considerable changes (positive and negative) is observed, compared to the area outside of corridors, where a relatively higher percentage of neutral changes is observed (fig. 4).
Table 3. The trend index (expressed as percent) for all changes and for considerable changes in the analysed periods.
Minimum and maximum values are in bold (source: own analysis)
Periods Change type
Dolnośląskie Kujawsko-pomorskie Lubelskie Lubuskie Łódzkie Małopolskie Mazowieckie Opolskie Podkarpackie Podlaskie Pomorskie Śląskie Świętokrzyskie Warmińsko-mazurskie Wielkopolskie Zachodniopomorskie POLAND
1990-2000 Considerable
changes 35 45 22 28 32 13 20 34 34 24 21 39 22 18 30 37 28
All changes 6 53 8 26 29 8 11 24 41 14 - 4 37 20 4 20 34 20
2000-2006 Considerable
changes 20 34 23 24 21 17 19 39 27 24 15 29 17 38 16 33 25
All changes 17 32 20 23 20 10 17 32 19 21 6 24 16 33 15 29 22
Fig. 3. Changes in the trend index in the later period (2000-2006) compared to the earlier period
Fig. 4. Area percentage of negative, neutral and positive changes in each voivodeship and for the whole Poland (by
Conclusions
The stability of ecological corridors, understood as constancy of suitability of an area to function as a migration corridor does not have to mean lack of changes. Two types of stability can be identified here – in the first one changes do not affect the suitability of an area (they are given the rating of 0) and in the second one the size and quality of positive and negative changes on a given area cancel out (the balance of the changes index is 0).
The results obtained in this study fall between these two extreme cases.
Examination of the difference between balance of changes indices allows to calculate a trend between the two periods. However, they should be analysed together with the balance of changes indices, as even though the trend might be positive on some areas, the indices may be different in terms of changes evaluation. This can be illustrated by a network of ecological corridors of the Lubuskie and Wielkopolskie voivodeships.
The stability of the ecological corridors network analysed here is more dynamic than of the areas outside the network. This stems more from the fact that negative changes are balanced by positive changes than from neutral changes, which is indicated by the higher (except for two cases) values of the trend index for considerable changes than for all changes.
The method presented in this paper does not allow to evaluate the real suitability of corridors for migration as it does not cover barriers such as the transport network, which are crucially important. Furthermore, because of the low accuracy of the input data one can only talk about large scale changes, which point to the nature of changes on smaller areas, not covered by the applied database (CLC). The numeric values of stability (such as those used in this study) should be regarded as relative.
In terms of the role in migration the stability of ecological corridors is not optimal for them. Directional positive changes would be more desired. The reasons for the variation in the analysed stability indices should be the subject of further detailed analyses that would include social and economic factors.
References
Bielecka E. (2007) Potential applications of the Corine Land Cover database in landscape mapping and analysis (in Polish) [in:] Importance of landscape research for sustainable development. Geography and Regional Studies Department, Warsaw University, Warsaw
CORINE Land Cover (CLC). Web portal [online]. Environmental Protection Inspectorate. Site available in the Internet: http://clc.gios.gov.pl/ (accessed 15.05.2010)
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