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Multivariate land class and land cover correlations in Northern Ireland
LANDSCAPE AND URBAN PLANNING
ELSEVIER
Landscape and Urban Planning 31 (1995) 11-19
Multivariate land class and land cover correlations in Northern Ireland Alan Cooper Department ofEnvironmental Studies, University of Ulster, Coleraine BT52 1SA, UK
Abstract Comparison of the scaled hierarchical structure of a multivariate land classification of Northern Ireland, with land class ordinations based on field-derived land coyer, has been made. Land class distribution on the land coyer ordination was reflected in the hierarchical structure of the land classification. This correlation contributes to a validation of the land classification as a sample stratification for landscape ecological survey. Land class ordination gave insight into the distribution of ecological resources in the landscape. Upland land classes showed the greatest degree of separation, indicating a greater heterogeneity of land coyer compared with the lowlands. The lowland land classes showed much less spatial separation on the ordination, a characteristic that probably relates to agricultural intensification. The distribution of the lowland land classes on the ordination was correlated with climatic, geological and landform gradients. This indicates regional differences in the farmed landscape and demonstrates the value of the land classification for stratifying landscape ecological survey and developing countryside management strategies. Keywords: Ecological survey; Landscape classification; Landscape
1. Introduction Landscape ecological research at the University of Ulster (Murray et al., 1992) has the main objectives of developing a structured method of describing, analysing and evaluating the distribution of land co ver, ecological resources and landscape attributes in Northem Ireland (NI). The NI land classification (Cooper, 1986) was constructed to provide a stratified random sampling programme on which to base the work. It is a multivariate classification ofkilometre squares, based on climatic, topographic, geological and soil map attributes representing a wide range of environmental factors. The assumption behind this approach, developed by Bunce et al. (1983),
is that ecological resources are associated with the map attributes used to produce the classification. The assumption has been tested by Bunce et al. (1983), who demonstrated that in Great Britain, there were strong correlations between the mean loadings ofland classes on ordinations of map attributes and ordinations of land coyer recorded in the field. The work highlighted correlations that largely reflected transitions from lowland to upland landscape types. The aim of the research in this paper was to compare a multivariate land classification of NI derived from map attributes, with a land co ver ordination derived from field survey, and to determine if the NI land classification provided an
0169-2046/95/$09.50 © 1995 Elsevier Science B.Y. Ali rigbts reserved
SSDI 0 169-2046 (94)01032-3
12
A. Cooper / Landscapeand Urban Planning 31 (1995) 11-19
appropriate regional biogeographic stratification for landscape ecological studies.
2. The Northern Ireland land classification The Ordnance Survey (OS) Irish grid was used as a standard reference system, with a grid size of 1 km 2 selected as an appropriate resolution for regional classification. The classification was based on 700 systematically placed grid squares representing approximately 5% of NI. Squares with less than 10% land area were not sampled. Map data were recorded from each sample grid square as either a quantitative variable or a presence/absence attribute. Information related to topography, hydrology and settlement patterns, was recorded for squares surrounding the sample squares, in order to differentiate areas that were heterogeneous from those that were more uniform. Map variables and attributes were selected by a process of successive refinement based on other land classification studies (Bunce and Smith, 1978; Chipperfield et al., 1978; Edwards et al., 1982) and experimental classifications to identify intercorrelated data. Variables and attributes were not weighted, except for the implicit assumption that a balanced set of data across the range of available maps was being used. 2.1. Climate
Initially, a range of available climatic variables (Meteorological Office, 1983) was reduced to three, following a trial classification that was dominated by climatic factors. The three variables used were mean maximum January temperature, mean maximum July temperature and the mean annual number of days with sleet orsnow.
low elevation farmland, marginal uplands, uplands and mountains. Land at less than 61 m elevation was selected to represent low elevation farmland; the 153 m contour was used to indicate the upper boundary of lowland agriculture and the high mountains were delimited arbitrarily as land over 305 m. The area of each elevation class in each grid square was recorded. The presence of contour tops was noted in order to differentiate drumlin landscapes. 2.3. Land use
Woodland, rough grazing, marsh and sand dune OS mapping symbols (1 :62 630) were recorded to incorporate a land use element into the classification. 2.4. Hydrology
Information describing the structure of streams, rivers and water bodies was recorded from 1:62 630 OS maps. 2.5. Seulement
Data re1ating to the urban and rural environment were the density of rural buildings, the types of community settlements and the length of roads present. They were recorded from 1: 62 630 OS maps. 2.6. Geology
Certain rock types such as granites, were grouped together for recording purposes, on the basis of their similar physiochemical characteristics. Geology was recorded from Geological Survey (NI) maps (1:625000). 2.7. Soifs
2.2. Elevation and topography
Data related to elevation, other topographic features, including slope, valley, hill and escarpment characteristics, and the coast were recorded from 1:62 630 OS (NI) maps. Four classes of elevation were recorded to represent
These were recorded from generalised soil survey maps (Gardiner and Radford, 1980) to indicate the distribution of glacial drift (1 :575 000). A total of 31 variables and 38 presence/absence attributes was recorded from OS maps. A
A. Cooper / Landscape and Urban Planning 31 (1995) 11-19
further 70 presence/absence attributes, for geological and soit types, were recorded. For the purpose of classification, aIl variables were converted to presence/absence attributes by equally subdividing the range recorded. The classification was carried out on a total of 198 attributes. These attributes are given in full by Cooper (1986). Data were classified by the computer program TWINSPAN (Hill, 1979a), a divisive clustering technique. The classification hierarchy was stopped if any division gave a land class with less than 20 squares. This gave 23 land classes (Fig. 1), the large st of which contained 55 squares. The classification hierarchy is given in full by Murray et al. (1992), along with statistical summaries ofthe physical attributes of each land class and distribution maps. The first division isolated the lowland land classes 1-16 from the upland classes 17-23. At the next division in the hierarchy, a group ofland classes (1-4) with a south-eastern distribution was defined within the lower elevation land classes. They were largely separated from the
13
other lowland land classes by mild climate, Silurian/Ordovician shale geology and drumlin terrain. Land class 1 was associated primarily with coastal areas in the south-east. Lowland land classes 5-12 represented flat to undulating terrain. Land class 5 was, in parti cular, associated with a lakeland environment. Land classes 6, 7 and 8 had a north-western distribution, with land classes 9-12 located in the north. Land classes 5-12 were separated from lowland land classes 13-16 largely by absence of the slope and topographical features associated with land classes 13-16. Land class 16 was confined mostly to northern areas and included parts of the coast. Within the upland land classes, a major division separated the highest hill tops and mountain plateau (land classes 22 and 23). Upland squares with settlement attributes (17-19), were subsequently separated from land classes 20 and 21. The main divisions within the upland group corresponded to the geomorphological structure and geological composition of the hills and
1.8
1.6
1.4
1.2
Cl
~ 1.0
ID >
~ 0.8
0.6
0.4
0.2
0.0 ~
____________________________
Lowland land classes
~IIL-
__________
~
Upland land classes
Fig. 1. TWINSPAN classification hierarchy of the 23 Northem Ireland land classes. The ordinate is the average Euclidean distance between clusters in a detrended correspondence analysis ordination. Standard deviation units (SD) approximate to half changes in the auribute composition of the samples (Gauch and Whittaker, 1981).
14
A. Cooper / Landscape and Urban Planning 31 (1995) 11-19
Table 1 Indicator attributes from the Northem Ireland land classification hierarchy
Climate
Seulement
Maximum January temperature, 0-6°C Maximum January temperature, 6.1-6.5°C Maximum January temperature, >6.5°C Maximum July temperature, 0-18°C Maximum July temperature, 18.1-18.5°C Maximum July temperature, > 18.5°C Mean annual number of days with sleet/snow, 0-20 Mean an nuai number ofdays with sleet/snow, 21-30 Mean annual number of days with sleet/snow, > 30
Buildings, 0-10 Buildings, 11-25 Buildings, > 25 Urban land in surrounding squares Primary road Surrounding squares with primary road, 1-4 Surrounding squares with secondary road, 1-4 Tertiary road Road forks, 1-2 Road forks, 3-6
Elevation Land 0-61 m, 76-100 ha Land 0-61 m in surrounding squares Land 61-153 m, 76-100 ha Land 61-153 m in surrounding squares Land 153-242 m in surrounding squares Land >242 m, 1-25 ha Land> 242 m, 76-100 ha Land> 242 m in surrounding squares Highest point, 0-153 m Highest point, 153-305 m Lowest point, 0-153 m Lowest point, 153-305 m
Topography Siope gradient, 1-6°C Siope gradient, 6.1-17.0°C Length ofslope, <0.5 km Aspect, northeast Height ofhill behind slope, 0-153 m Height ofhill behind slope, 153-305 m Height ofhill behind slope, > 305 m Distance to hill behind slope, 0.1-1 km Distance to valley bottom below slope, 0.1-1 km Flat valley bottom, > 250 m Contour tops, 1-2 Surrounding squares with contour tops, 3-5 Surrounding squares with contour tops, 6-8
Vegetation Rough grazing Woods, 1
Hydrology River Stream Water bodies, 1 Surrounding squares with water bodies, 1-2 Sea in surrounding squares Intertidal mud in surrounding squares
Geology Lower basalts Upper basalts Silurian shales Old red sandstone Calp limestone and shale-sandstone
Soifs Blanket peat Peaty gleys (mica schist, gneiss, quartzite and sandstone) Gleys (Ordovician, Silurian shale-sandstone glacial till) Gleys (basait glacial till) Gleys (Carboniferous limestone and shale-sandstone till ) Acid brown earths (granite or rhyolite glacial till) Acid brown earths (basait glacial till) Brown podzolics (sandstone)
A. Cooper / Landscapeand Urban Planning 31 (1995) 11-19
mountains, with land use, soils and climatic attributes playing a minor role in defining them. The indicator attributes in the classification hierarchy were subsequently used to classify every 1 km grid square in Northem Ireland (Table 1). The 700 km grid squares that produced the classification were also reclassified with the hierarchical key.
3. Land coyer field survey Land coyer in a sample set of25 ha grid squares from each land class was recorded in the field. Grid squares were sampled systematically within each land class at an intensity of 0.5% of the land area. The total sample size was 250 grid squares. Within each grid square, land co ver was mapped in the field, onto computer-coded data sheets. Five main types of land coyer were recorded, namely woodland and other semi-naturai vegetation types, field boundaries, agricultural grasslandjcrops and urban-rural structures. Ancillary data on land management, vegetation structure and species composition were also recorded. The structure of the field data sheets is given by Murray et al. (1992). The data sheets held a list of coded land coyer attributes, a map derived from OS 1: 10 560 or 1:10000 editions and a data recording matrix. The data recording procedure (Murray et al., 1992) consisted of inserting numeric codes onto the maps, then land coyer codes into the data matrix. Information was recorded with reference to a set of standard descriptors relating to land coyer. Land co ver areas and field boundary lengths were digitised directly from field data sheets, then converted to computer files for database analysis (Ashton-Tate, 1985). Database programming was subsequently carried out to estimate the percentage mean area or length of each land covertype in each sample square.
4. Land coyer ordination Detrended correspondence analysis (Hill, 1979b) ordinations of field sample squares were
15
carried out based on their land co ver composition. The aim of the ordinations was to examine land class similarity in terms oftheir land coyer. Land coyer types occurring in less than 5% of sample squares were combined with related types (Table 2) so as not to distort the ordination. The percentage mean area or length of each land coyer type in each sample square was transformed by octaves (log2) in order to reduce the weighting of the most common land coyer types i.e. agricultural grassland in the lowland land classes and semi-natural vegetation in the upland land classes. In the sample square ordination diagrams (Figs. 2, 3 and 4), the me an axis loading of sample squares in each land class is plotted to illustrate land class similarity. Initially, an ordination was carried out using data from all 23 NI land classes. Axis 1 of the sample square ordination (Figs. 2 and 5) represents a general transition from lowland land classes (1-16) to upland land classes (17-23). Coastal and wetland land co ver types are involved in defining axes 2 and 3 (Figs. 3 and 6), with the coastal land classes 1 and 16 and the lakeland land class 5 separating out along the se axes. The upland land classes 17-23 separate most on the ordination, indicating a much greater heterogeneity ofland coyer variation compared with the lowlands (land classes 1-16). The relationship of upland land classes to each other on the ordination is similar to that in the land classification hierarchy. In contrast, the lowland land classes separate to a much less extent, reflecting a greater homogeneity of land coyer variation than in the uplands. The lakeland and coastal land classes 5, 1 and 16 are the more heterogeneous lowland classes. A second ordination was subsequentlY carried out using only the lowland land classes 2-4 and 6-15 to examine their similarity, without the weighting effect of the upland and coastal land classes (Figs. 4 and 7). These land classes contained the same range of land coyer types as the upland land classes. Separation of the land classes on axes 1 and 2 shows that in relative terms, each has a different land coyer composition. The greater cereals and vegetable crop coyer of land
A. Cooper 1 Landscapeand Urban Planning 31 (1995) 11-19
16
260
Table 2 Land cover categories used to ordinate the field survey sampie squares. Descriptors of each type are given by Murray et al. (1992)
-22
240
-20 -19
Ordination label
<:
Semi-natural broadleafwoodland Broadleaf and mixed woodland plantation Coniferous plantation Scrub
Semi-natural vegetation Sprdrgrs Sprwegrs Hillpast Gorsheth Ericheth Wetheath Bracken Wetdrbog Poorfen Reedbeds Fen Coastal Ruderal
Species-rich dry and calcareous grassland Species-rich wet grassland, rush pasture, fen meadow and sedge marsh Bent/fescue and mat-grass hill pasture Gorse heath and gorse heath/bracken mosaic Ericaceous heath, lichen/bryophyte heath and ericaceous heath mosaic Molinia grassland, wet heath, wet heath mosaic, mixed upland vegetation Bracken Wet and dry bog Poorfen Reedbeds, freshwater vegetation and swamp Fen, ditch and water margin vegetation Coastal vegetation Ruderal
Agriculture Cereals Vegcrop Ryegrass Mxothgrs Blfagri Rushagri
Cereals (wheat, barley, oats) Vegetables (potatoes, brassicas, legumes, root crops) Perennial and Italian ryegrass Mixed species and 'other' agricultural grassland Broadleafweed infested grassland Rush infested grassland
Field boundaries Hedges Stonewal Ruindwal Earthbnk Postwire Ditch
Hedge and hedge on wall Dry stone wall Ruined dry stone wall Earthbank Post and wire fence Ditch
Miscellaneous features Urban Amenigrs
6- -7 12- -a -15 10 9- 16:5 -4 {1 -14 13-3
C\I
'x '"
Woodland Brdlfnat Brdlfpla Conifers Scrub
220
Resource type
Urban Àmenity grassland
200
180
-21
-1a
-23
-2 -1
160 100
-17
200
300 Axis 1
400
500
Fig_ 2_ Axes 1 and 2 of a DECORANA ordination of field survey sample squares based on land cover. The position of each land class (1-23) is determined by the mean axis loading of the sample squares each contains.
200
-5
180
-21
140
120
100+----,---,----,----,---,----r---,-----i 500 400 300 200 100 Axis 1
Fig. 3. Axes 1 and 3 of a DECORANA ordination of field survey sam pie squares based on land cover. The position of each land class (1-23) is determined by the mean axis loading of the sample squares each con tains.
classes 2-4 and 13, contrasts with the fragmented wet heath, bog, poor fen and rush infested grassland parcels that characterise land classes 6-8, 14 and 15_ Field boundary types and urban-rural structures are also distributed differently across these land class groups_ The tirst two axes reflect climatic and landform gradients in NI, with the southeastern lowland land classes 2, 3, 4 and 13, the northern lowland land classes 9-12, and the north-western and marginal up-
A. Cooper / Landscapeand Urban Planning 31 (1995) 11-19 110
400,---------~-------------------------,
.Amenlgrs Reedbeds. -Srdlfpla Sprdrgrs
Urban.
'2
Srdllnal ' _Fen
300 100
Ruderal-
'3
200
'13
90 C\J
'4
17
C")
'11
«><
100
'x '"
«
80 '9
'Conifers
Ericheth-
RUindwal
St;~~~~~ken
Sprwegrs.
Scrub' 'Pos~lre
Hedges_ Mxothgrs Ryegrass. • Dltch' -Blfagn -Cereals
Gorsheth
.~ushagn
Earthbnk
-Hillpast • Poorfen
-Vegcrop
Wethealh
0
Wetdrbog-
'15
'7 '14
-100
'12
70
'10
·200 '6 '8
Coastal
60
·300+----,r----,--~,_--_.----,_----,_--~
40
100
80 Axis 1
60
120
Fig. 4. Axes 1 and 2 of a DECORANA ordination of field survey sam pie squares based on land coyer. The position of each land class (2-4 and 6-15) is determined by the mean axis loading of the sam pie squares each contains.
·100
-Veg crop
200
Wetdrbog.
Wétheath
200
'x
Earthbnk. Auderal.
. Oitch-
Hed9~~lfa9n
'x
•
• Mxothgrs
«
• Postwire
100
Wetditch·
0
·Cereals .Vegcrop -Urban
-Amenigrs
Sprdrgrs
.;:~~:~h Wetheath
·Poor fen
Postwire -Earthbnk
.Weedagri
~prwegrs
Scruti
•
Mxothgrs
Brdlpla- -
-Brdlfnat
~prdrgrs.
Coastat -Gorsheth Reedbeds. -Fen •• Brdllnat - Ryegrass Sprwegrs- Scrub Hedges·
Ryegrass. Reedbeds 'Fen
0 ·100
-Cereals -Amenigrs
C\J
Rus.hagri
600
-Ruindwal Hillpast
300
100
500
Stonewal-
300 Urban_
Brdlfpla.
400
200 300 Axis 1
400.-----------------------------------~
·Conifers
«
100
Fig. 6. Axes 1 and 3 of a DECORANA ordination of land coyer types based on sample squares from land classes 1-23.
400,-------------------------------------,
C\J
·200
Wetdrbog-
'Poorfen
-100
-Rushagri
'Gorsheth
-Ruderat -Conifers
'Coastal
·200
Stonewâl ••Ruindwal
Braeken
-Hillpast
Erichet~
·200 ·200
-300 + - - - r - - - - , - - , - - - - , - - - . - - - r - - - - l ·100 -200 400 500 100 200 300 600 Axis 1
Fig. 5. Axes 1 and 2 of a DECORANA ordination of land coyer types based on sample squares from land classes 1-23.
land western land classes (6-8, 14 and 15), each located in different parts of the ordination. Distribution maps of the land classes are given by Cooper ( 1986) and Murray et al. (1992). These land class groupings reflect the distribution of land class clusters in the land classification hierarchy based on map attributes.
5. Discussion ln the classification hierarchy, the land classes separate within a narrow range of standard de-
·0
Axis 1
200
400
Fig. 7. Axes 1 and 2 of a DECORANA ordination of land coyer types based on squares from land classes 2-4 and 6-15.
viation units. This indicates that in terms of the map attributes used to produce the classification, differences in land class heterogeneity are minor. The greater land cover heterogeneity of the uplands compared with the lowlands is therefore surprising, particularly given the larger scale of variation of upland landscapes and the small scale patterned nature of the enclosed, farmed landscapes which characterise lreland. A wider range of variation in elevation, topography and land uses between land classes in the uplands compared with the lowlands may explain the difference. The large range of map attributes
18
A. Cooper / Landscapeand Urban Planning 31 (1995) 11-19
relating to urban-rural structures, soils, geology, hydrology, topography and climate, in the lowland land classes, is not reflected in land cover heterogeneity, except in the lakeland and coastal land classes. The uniformity of agriculturalland use in the lowland land classes may largely explain their relative land cover homogeneity. Land classes 2-4 and 6-15 represent the enclosed farmed landscapes of Northern Ireland. Land co ver differences compared with the uplands are mainly quantitative since the lowland land classes contain the same range ofland co ver types. This supports the hypothesis that loss of semi-natural vegetation land co ver has contributed to the relative land cover homogeneity of the lowland land classes. Ordination of the lowland land classes separately indicates that regional variation in land cover still exists and that the land classes reflect this variation. Furthermore, in separating the land classes, a wide range of land cover types are used. This suggests that the land classification and its associated database of physical attributes, land cover types, vegetation structure, management and species composition, could be used for quantifying regional biogeographic variation in the countryside and for developing countryside management strategies. Simple generalisations on countryside management derived from the land cover ordinations are as follows. ( 1 ) Each land class has both unique and typically representative land cover types that contribute to landscape diversity. (2) The most significant source of diversity lies in the uplands and marginal uplands. This diversity merits protection from single land uses which affect large areas uniformly. Agricultural intensification, afforestation and dereliction are examples. Conversely, a variety of land uses at different scales is more likely to maintain or promote land cover diversity. (3) The maintenance of semi-natural vegetation and field boundary land cover diversity in the lowland land classes is a priority. Landscape management practices that increase land cover diversity such as creating habitats also merit priority.
The land class ordination has applications for monitoring changes in landscape diversity. Following land cover resurvey, for example, an increase in land class clustering on the land cover ordination would indicate an increase in land cover homogeneity. Vectors linking the same land class between baseline and resurvey times could also be used to indicate change in relation to the ordination axes. The ordination has advantages over a comparative statistical analysis of individuallandscape elements in the database in that it presents an integrated, multivariate model. Cooper and Murray (1992) have shown how groups of similar land classes, repeating patterns of land class mosaics, geographical boundaries (for example between watersheds), geological formations or political entities can be used in combination, to delimit units oflandscape. Ifthe units delimited have a large enough number of field survey sample squares, their landscape ecological resources can be described. Cooper and Murray (1992) have stressed that the hierarchical nature of land classification provides a flexible, explicit method of subdividing a study area to any level of generalisation. This is particularly useful for landscape management when exploring local differences or highlighting regional similarities.
Acknowledgements Work was funded by the Environment Service of the Department of the Environment for Northern lreland. Ronald Murray (Research Officer) and Thomas McCann (Research Assistant) of the Department of Environmental Studies, University of Ulster are both thanked for their invaluable contributions.
References Ashton-Tate, 1985. dBase III PLUS. Ashton-Tate, Torrance. Bunce, R.G.H. and Smith, R.S., 1978. An ecological survey of Cumbria. Cumbria County Council and Lake District Special Planning Board, Kendal, UK. Bunce, R.G.H., Barr, C.l. and Whittaker, H., 1983. A stratification system for ecological sampling. In: R.M. Fuller
A. Cooper / Landscapeand Urban Planning 31 (1995) 11-19
(Editor), Ecological Mapping from Ground, Air and Space, Institute of Terrestrial Ecology, Symposium Number 10. Institute of Terrestrial Ecology, Cambridge, pp. 39-46. Chipperfield, E., Pilling, R., Gibson, R., Brown, A., Smith, R.S. and Bunce, R.G.H., 1978. An ecological survey of the Sedburgh region of the Yorkshire Dales National Park and of the ArnsidefSilverdale Area of Outstanding Natural Beauty. Report to the County Planning Officer, Cumbria County Council, Kendal. Cooper, A., 1986. The Northern Ireland Land Classification. Department of Environmental Studies, University of Ulster, Jordanstown. Cooper, A. and Murray, R., 1992. A structured method of landscape assessment and countryside management. Appl. Geogr., 12: 319-338. Edwards, S.J., Thomson, A.E., Hughes, M.G.B. and Porteous, A.E., 1982. An Ecological Classification of Strathclyde Region. Nature Conservancy Council, South West (Scotland) Region, Balloch.
19
Gardiner, M.J. and Radford, T., 1980. Soil Associations of Ireland and their Land Use Potential. National Soil Survey ofIreland, Dublin. Gauch, H. and Whittaker, R.H., 1981. Hierarchical classification of community data. J. Ecol., 69: 537-557. Hill, M.O., 1979a. TWINSPAN: a FORTRAN program for arranging multivariate data in an ordered two-way table by classification of the individuals and attributes. Cornell University, New York. Hill, M.O., 1979b. DECORANA: a FORTRAN program for detrended correspondence analysis and reciprocal averaging. Cornell University, New York. Meteorological Office, 1983. The climate of Northern Ireland. Meteorological Office, Belfast. Murray, R., McCann, T. and Cooper, A., 1992. A land classification and landscape ecological study ofNorthern Ireland. Report to the Environment Service, Department of the Environment for Northern Ireland, University ofUlster, Coleraine.
ELSEVIER
Landscape and Urban Planning 31 (1995) 11-19
Multivariate land class and land cover correlations in Northern Ireland Alan Cooper Department ofEnvironmental Studies, University of Ulster, Coleraine BT52 1SA, UK
Abstract Comparison of the scaled hierarchical structure of a multivariate land classification of Northern Ireland, with land class ordinations based on field-derived land coyer, has been made. Land class distribution on the land coyer ordination was reflected in the hierarchical structure of the land classification. This correlation contributes to a validation of the land classification as a sample stratification for landscape ecological survey. Land class ordination gave insight into the distribution of ecological resources in the landscape. Upland land classes showed the greatest degree of separation, indicating a greater heterogeneity of land coyer compared with the lowlands. The lowland land classes showed much less spatial separation on the ordination, a characteristic that probably relates to agricultural intensification. The distribution of the lowland land classes on the ordination was correlated with climatic, geological and landform gradients. This indicates regional differences in the farmed landscape and demonstrates the value of the land classification for stratifying landscape ecological survey and developing countryside management strategies. Keywords: Ecological survey; Landscape classification; Landscape
1. Introduction Landscape ecological research at the University of Ulster (Murray et al., 1992) has the main objectives of developing a structured method of describing, analysing and evaluating the distribution of land co ver, ecological resources and landscape attributes in Northem Ireland (NI). The NI land classification (Cooper, 1986) was constructed to provide a stratified random sampling programme on which to base the work. It is a multivariate classification ofkilometre squares, based on climatic, topographic, geological and soil map attributes representing a wide range of environmental factors. The assumption behind this approach, developed by Bunce et al. (1983),
is that ecological resources are associated with the map attributes used to produce the classification. The assumption has been tested by Bunce et al. (1983), who demonstrated that in Great Britain, there were strong correlations between the mean loadings ofland classes on ordinations of map attributes and ordinations of land coyer recorded in the field. The work highlighted correlations that largely reflected transitions from lowland to upland landscape types. The aim of the research in this paper was to compare a multivariate land classification of NI derived from map attributes, with a land co ver ordination derived from field survey, and to determine if the NI land classification provided an
0169-2046/95/$09.50 © 1995 Elsevier Science B.Y. Ali rigbts reserved
SSDI 0 169-2046 (94)01032-3
12
A. Cooper / Landscapeand Urban Planning 31 (1995) 11-19
appropriate regional biogeographic stratification for landscape ecological studies.
2. The Northern Ireland land classification The Ordnance Survey (OS) Irish grid was used as a standard reference system, with a grid size of 1 km 2 selected as an appropriate resolution for regional classification. The classification was based on 700 systematically placed grid squares representing approximately 5% of NI. Squares with less than 10% land area were not sampled. Map data were recorded from each sample grid square as either a quantitative variable or a presence/absence attribute. Information related to topography, hydrology and settlement patterns, was recorded for squares surrounding the sample squares, in order to differentiate areas that were heterogeneous from those that were more uniform. Map variables and attributes were selected by a process of successive refinement based on other land classification studies (Bunce and Smith, 1978; Chipperfield et al., 1978; Edwards et al., 1982) and experimental classifications to identify intercorrelated data. Variables and attributes were not weighted, except for the implicit assumption that a balanced set of data across the range of available maps was being used. 2.1. Climate
Initially, a range of available climatic variables (Meteorological Office, 1983) was reduced to three, following a trial classification that was dominated by climatic factors. The three variables used were mean maximum January temperature, mean maximum July temperature and the mean annual number of days with sleet orsnow.
low elevation farmland, marginal uplands, uplands and mountains. Land at less than 61 m elevation was selected to represent low elevation farmland; the 153 m contour was used to indicate the upper boundary of lowland agriculture and the high mountains were delimited arbitrarily as land over 305 m. The area of each elevation class in each grid square was recorded. The presence of contour tops was noted in order to differentiate drumlin landscapes. 2.3. Land use
Woodland, rough grazing, marsh and sand dune OS mapping symbols (1 :62 630) were recorded to incorporate a land use element into the classification. 2.4. Hydrology
Information describing the structure of streams, rivers and water bodies was recorded from 1:62 630 OS maps. 2.5. Seulement
Data re1ating to the urban and rural environment were the density of rural buildings, the types of community settlements and the length of roads present. They were recorded from 1: 62 630 OS maps. 2.6. Geology
Certain rock types such as granites, were grouped together for recording purposes, on the basis of their similar physiochemical characteristics. Geology was recorded from Geological Survey (NI) maps (1:625000). 2.7. Soifs
2.2. Elevation and topography
Data related to elevation, other topographic features, including slope, valley, hill and escarpment characteristics, and the coast were recorded from 1:62 630 OS (NI) maps. Four classes of elevation were recorded to represent
These were recorded from generalised soil survey maps (Gardiner and Radford, 1980) to indicate the distribution of glacial drift (1 :575 000). A total of 31 variables and 38 presence/absence attributes was recorded from OS maps. A
A. Cooper / Landscape and Urban Planning 31 (1995) 11-19
further 70 presence/absence attributes, for geological and soit types, were recorded. For the purpose of classification, aIl variables were converted to presence/absence attributes by equally subdividing the range recorded. The classification was carried out on a total of 198 attributes. These attributes are given in full by Cooper (1986). Data were classified by the computer program TWINSPAN (Hill, 1979a), a divisive clustering technique. The classification hierarchy was stopped if any division gave a land class with less than 20 squares. This gave 23 land classes (Fig. 1), the large st of which contained 55 squares. The classification hierarchy is given in full by Murray et al. (1992), along with statistical summaries ofthe physical attributes of each land class and distribution maps. The first division isolated the lowland land classes 1-16 from the upland classes 17-23. At the next division in the hierarchy, a group ofland classes (1-4) with a south-eastern distribution was defined within the lower elevation land classes. They were largely separated from the
13
other lowland land classes by mild climate, Silurian/Ordovician shale geology and drumlin terrain. Land class 1 was associated primarily with coastal areas in the south-east. Lowland land classes 5-12 represented flat to undulating terrain. Land class 5 was, in parti cular, associated with a lakeland environment. Land classes 6, 7 and 8 had a north-western distribution, with land classes 9-12 located in the north. Land classes 5-12 were separated from lowland land classes 13-16 largely by absence of the slope and topographical features associated with land classes 13-16. Land class 16 was confined mostly to northern areas and included parts of the coast. Within the upland land classes, a major division separated the highest hill tops and mountain plateau (land classes 22 and 23). Upland squares with settlement attributes (17-19), were subsequently separated from land classes 20 and 21. The main divisions within the upland group corresponded to the geomorphological structure and geological composition of the hills and
1.8
1.6
1.4
1.2
Cl
~ 1.0
ID >
~ 0.8
0.6
0.4
0.2
0.0 ~
____________________________
Lowland land classes
~IIL-
__________
~
Upland land classes
Fig. 1. TWINSPAN classification hierarchy of the 23 Northem Ireland land classes. The ordinate is the average Euclidean distance between clusters in a detrended correspondence analysis ordination. Standard deviation units (SD) approximate to half changes in the auribute composition of the samples (Gauch and Whittaker, 1981).
14
A. Cooper / Landscape and Urban Planning 31 (1995) 11-19
Table 1 Indicator attributes from the Northem Ireland land classification hierarchy
Climate
Seulement
Maximum January temperature, 0-6°C Maximum January temperature, 6.1-6.5°C Maximum January temperature, >6.5°C Maximum July temperature, 0-18°C Maximum July temperature, 18.1-18.5°C Maximum July temperature, > 18.5°C Mean annual number of days with sleet/snow, 0-20 Mean an nuai number ofdays with sleet/snow, 21-30 Mean annual number of days with sleet/snow, > 30
Buildings, 0-10 Buildings, 11-25 Buildings, > 25 Urban land in surrounding squares Primary road Surrounding squares with primary road, 1-4 Surrounding squares with secondary road, 1-4 Tertiary road Road forks, 1-2 Road forks, 3-6
Elevation Land 0-61 m, 76-100 ha Land 0-61 m in surrounding squares Land 61-153 m, 76-100 ha Land 61-153 m in surrounding squares Land 153-242 m in surrounding squares Land >242 m, 1-25 ha Land> 242 m, 76-100 ha Land> 242 m in surrounding squares Highest point, 0-153 m Highest point, 153-305 m Lowest point, 0-153 m Lowest point, 153-305 m
Topography Siope gradient, 1-6°C Siope gradient, 6.1-17.0°C Length ofslope, <0.5 km Aspect, northeast Height ofhill behind slope, 0-153 m Height ofhill behind slope, 153-305 m Height ofhill behind slope, > 305 m Distance to hill behind slope, 0.1-1 km Distance to valley bottom below slope, 0.1-1 km Flat valley bottom, > 250 m Contour tops, 1-2 Surrounding squares with contour tops, 3-5 Surrounding squares with contour tops, 6-8
Vegetation Rough grazing Woods, 1
Hydrology River Stream Water bodies, 1 Surrounding squares with water bodies, 1-2 Sea in surrounding squares Intertidal mud in surrounding squares
Geology Lower basalts Upper basalts Silurian shales Old red sandstone Calp limestone and shale-sandstone
Soifs Blanket peat Peaty gleys (mica schist, gneiss, quartzite and sandstone) Gleys (Ordovician, Silurian shale-sandstone glacial till) Gleys (basait glacial till) Gleys (Carboniferous limestone and shale-sandstone till ) Acid brown earths (granite or rhyolite glacial till) Acid brown earths (basait glacial till) Brown podzolics (sandstone)
A. Cooper / Landscapeand Urban Planning 31 (1995) 11-19
mountains, with land use, soils and climatic attributes playing a minor role in defining them. The indicator attributes in the classification hierarchy were subsequently used to classify every 1 km grid square in Northem Ireland (Table 1). The 700 km grid squares that produced the classification were also reclassified with the hierarchical key.
3. Land coyer field survey Land coyer in a sample set of25 ha grid squares from each land class was recorded in the field. Grid squares were sampled systematically within each land class at an intensity of 0.5% of the land area. The total sample size was 250 grid squares. Within each grid square, land co ver was mapped in the field, onto computer-coded data sheets. Five main types of land coyer were recorded, namely woodland and other semi-naturai vegetation types, field boundaries, agricultural grasslandjcrops and urban-rural structures. Ancillary data on land management, vegetation structure and species composition were also recorded. The structure of the field data sheets is given by Murray et al. (1992). The data sheets held a list of coded land coyer attributes, a map derived from OS 1: 10 560 or 1:10000 editions and a data recording matrix. The data recording procedure (Murray et al., 1992) consisted of inserting numeric codes onto the maps, then land coyer codes into the data matrix. Information was recorded with reference to a set of standard descriptors relating to land coyer. Land co ver areas and field boundary lengths were digitised directly from field data sheets, then converted to computer files for database analysis (Ashton-Tate, 1985). Database programming was subsequently carried out to estimate the percentage mean area or length of each land covertype in each sample square.
4. Land coyer ordination Detrended correspondence analysis (Hill, 1979b) ordinations of field sample squares were
15
carried out based on their land co ver composition. The aim of the ordinations was to examine land class similarity in terms oftheir land coyer. Land coyer types occurring in less than 5% of sample squares were combined with related types (Table 2) so as not to distort the ordination. The percentage mean area or length of each land coyer type in each sample square was transformed by octaves (log2) in order to reduce the weighting of the most common land coyer types i.e. agricultural grassland in the lowland land classes and semi-natural vegetation in the upland land classes. In the sample square ordination diagrams (Figs. 2, 3 and 4), the me an axis loading of sample squares in each land class is plotted to illustrate land class similarity. Initially, an ordination was carried out using data from all 23 NI land classes. Axis 1 of the sample square ordination (Figs. 2 and 5) represents a general transition from lowland land classes (1-16) to upland land classes (17-23). Coastal and wetland land co ver types are involved in defining axes 2 and 3 (Figs. 3 and 6), with the coastal land classes 1 and 16 and the lakeland land class 5 separating out along the se axes. The upland land classes 17-23 separate most on the ordination, indicating a much greater heterogeneity ofland coyer variation compared with the lowlands (land classes 1-16). The relationship of upland land classes to each other on the ordination is similar to that in the land classification hierarchy. In contrast, the lowland land classes separate to a much less extent, reflecting a greater homogeneity of land coyer variation than in the uplands. The lakeland and coastal land classes 5, 1 and 16 are the more heterogeneous lowland classes. A second ordination was subsequentlY carried out using only the lowland land classes 2-4 and 6-15 to examine their similarity, without the weighting effect of the upland and coastal land classes (Figs. 4 and 7). These land classes contained the same range of land coyer types as the upland land classes. Separation of the land classes on axes 1 and 2 shows that in relative terms, each has a different land coyer composition. The greater cereals and vegetable crop coyer of land
A. Cooper 1 Landscapeand Urban Planning 31 (1995) 11-19
16
260
Table 2 Land cover categories used to ordinate the field survey sampie squares. Descriptors of each type are given by Murray et al. (1992)
-22
240
-20 -19
Ordination label
<:
Semi-natural broadleafwoodland Broadleaf and mixed woodland plantation Coniferous plantation Scrub
Semi-natural vegetation Sprdrgrs Sprwegrs Hillpast Gorsheth Ericheth Wetheath Bracken Wetdrbog Poorfen Reedbeds Fen Coastal Ruderal
Species-rich dry and calcareous grassland Species-rich wet grassland, rush pasture, fen meadow and sedge marsh Bent/fescue and mat-grass hill pasture Gorse heath and gorse heath/bracken mosaic Ericaceous heath, lichen/bryophyte heath and ericaceous heath mosaic Molinia grassland, wet heath, wet heath mosaic, mixed upland vegetation Bracken Wet and dry bog Poorfen Reedbeds, freshwater vegetation and swamp Fen, ditch and water margin vegetation Coastal vegetation Ruderal
Agriculture Cereals Vegcrop Ryegrass Mxothgrs Blfagri Rushagri
Cereals (wheat, barley, oats) Vegetables (potatoes, brassicas, legumes, root crops) Perennial and Italian ryegrass Mixed species and 'other' agricultural grassland Broadleafweed infested grassland Rush infested grassland
Field boundaries Hedges Stonewal Ruindwal Earthbnk Postwire Ditch
Hedge and hedge on wall Dry stone wall Ruined dry stone wall Earthbank Post and wire fence Ditch
Miscellaneous features Urban Amenigrs
6- -7 12- -a -15 10 9- 16:5 -4 {1 -14 13-3
C\I
'x '"
Woodland Brdlfnat Brdlfpla Conifers Scrub
220
Resource type
Urban Àmenity grassland
200
180
-21
-1a
-23
-2 -1
160 100
-17
200
300 Axis 1
400
500
Fig_ 2_ Axes 1 and 2 of a DECORANA ordination of field survey sample squares based on land cover. The position of each land class (1-23) is determined by the mean axis loading of the sample squares each contains.
200
-5
180
-21
140
120
100+----,---,----,----,---,----r---,-----i 500 400 300 200 100 Axis 1
Fig. 3. Axes 1 and 3 of a DECORANA ordination of field survey sam pie squares based on land cover. The position of each land class (1-23) is determined by the mean axis loading of the sample squares each con tains.
classes 2-4 and 13, contrasts with the fragmented wet heath, bog, poor fen and rush infested grassland parcels that characterise land classes 6-8, 14 and 15_ Field boundary types and urban-rural structures are also distributed differently across these land class groups_ The tirst two axes reflect climatic and landform gradients in NI, with the southeastern lowland land classes 2, 3, 4 and 13, the northern lowland land classes 9-12, and the north-western and marginal up-
A. Cooper / Landscapeand Urban Planning 31 (1995) 11-19 110
400,---------~-------------------------,
.Amenlgrs Reedbeds. -Srdlfpla Sprdrgrs
Urban.
'2
Srdllnal ' _Fen
300 100
Ruderal-
'3
200
'13
90 C\J
'4
17
C")
'11
«><
100
'x '"
«
80 '9
'Conifers
Ericheth-
RUindwal
St;~~~~~ken
Sprwegrs.
Scrub' 'Pos~lre
Hedges_ Mxothgrs Ryegrass. • Dltch' -Blfagn -Cereals
Gorsheth
.~ushagn
Earthbnk
-Hillpast • Poorfen
-Vegcrop
Wethealh
0
Wetdrbog-
'15
'7 '14
-100
'12
70
'10
·200 '6 '8
Coastal
60
·300+----,r----,--~,_--_.----,_----,_--~
40
100
80 Axis 1
60
120
Fig. 4. Axes 1 and 2 of a DECORANA ordination of field survey sam pie squares based on land coyer. The position of each land class (2-4 and 6-15) is determined by the mean axis loading of the sam pie squares each contains.
·100
-Veg crop
200
Wetdrbog.
Wétheath
200
'x
Earthbnk. Auderal.
. Oitch-
Hed9~~lfa9n
'x
•
• Mxothgrs
«
• Postwire
100
Wetditch·
0
·Cereals .Vegcrop -Urban
-Amenigrs
Sprdrgrs
.;:~~:~h Wetheath
·Poor fen
Postwire -Earthbnk
.Weedagri
~prwegrs
Scruti
•
Mxothgrs
Brdlpla- -
-Brdlfnat
~prdrgrs.
Coastat -Gorsheth Reedbeds. -Fen •• Brdllnat - Ryegrass Sprwegrs- Scrub Hedges·
Ryegrass. Reedbeds 'Fen
0 ·100
-Cereals -Amenigrs
C\J
Rus.hagri
600
-Ruindwal Hillpast
300
100
500
Stonewal-
300 Urban_
Brdlfpla.
400
200 300 Axis 1
400.-----------------------------------~
·Conifers
«
100
Fig. 6. Axes 1 and 3 of a DECORANA ordination of land coyer types based on sample squares from land classes 1-23.
400,-------------------------------------,
C\J
·200
Wetdrbog-
'Poorfen
-100
-Rushagri
'Gorsheth
-Ruderat -Conifers
'Coastal
·200
Stonewâl ••Ruindwal
Braeken
-Hillpast
Erichet~
·200 ·200
-300 + - - - r - - - - , - - , - - - - , - - - . - - - r - - - - l ·100 -200 400 500 100 200 300 600 Axis 1
Fig. 5. Axes 1 and 2 of a DECORANA ordination of land coyer types based on sample squares from land classes 1-23.
land western land classes (6-8, 14 and 15), each located in different parts of the ordination. Distribution maps of the land classes are given by Cooper ( 1986) and Murray et al. (1992). These land class groupings reflect the distribution of land class clusters in the land classification hierarchy based on map attributes.
5. Discussion ln the classification hierarchy, the land classes separate within a narrow range of standard de-
·0
Axis 1
200
400
Fig. 7. Axes 1 and 2 of a DECORANA ordination of land coyer types based on squares from land classes 2-4 and 6-15.
viation units. This indicates that in terms of the map attributes used to produce the classification, differences in land class heterogeneity are minor. The greater land cover heterogeneity of the uplands compared with the lowlands is therefore surprising, particularly given the larger scale of variation of upland landscapes and the small scale patterned nature of the enclosed, farmed landscapes which characterise lreland. A wider range of variation in elevation, topography and land uses between land classes in the uplands compared with the lowlands may explain the difference. The large range of map attributes
18
A. Cooper / Landscapeand Urban Planning 31 (1995) 11-19
relating to urban-rural structures, soils, geology, hydrology, topography and climate, in the lowland land classes, is not reflected in land cover heterogeneity, except in the lakeland and coastal land classes. The uniformity of agriculturalland use in the lowland land classes may largely explain their relative land cover homogeneity. Land classes 2-4 and 6-15 represent the enclosed farmed landscapes of Northern Ireland. Land co ver differences compared with the uplands are mainly quantitative since the lowland land classes contain the same range ofland co ver types. This supports the hypothesis that loss of semi-natural vegetation land co ver has contributed to the relative land cover homogeneity of the lowland land classes. Ordination of the lowland land classes separately indicates that regional variation in land cover still exists and that the land classes reflect this variation. Furthermore, in separating the land classes, a wide range of land cover types are used. This suggests that the land classification and its associated database of physical attributes, land cover types, vegetation structure, management and species composition, could be used for quantifying regional biogeographic variation in the countryside and for developing countryside management strategies. Simple generalisations on countryside management derived from the land cover ordinations are as follows. ( 1 ) Each land class has both unique and typically representative land cover types that contribute to landscape diversity. (2) The most significant source of diversity lies in the uplands and marginal uplands. This diversity merits protection from single land uses which affect large areas uniformly. Agricultural intensification, afforestation and dereliction are examples. Conversely, a variety of land uses at different scales is more likely to maintain or promote land cover diversity. (3) The maintenance of semi-natural vegetation and field boundary land cover diversity in the lowland land classes is a priority. Landscape management practices that increase land cover diversity such as creating habitats also merit priority.
The land class ordination has applications for monitoring changes in landscape diversity. Following land cover resurvey, for example, an increase in land class clustering on the land cover ordination would indicate an increase in land cover homogeneity. Vectors linking the same land class between baseline and resurvey times could also be used to indicate change in relation to the ordination axes. The ordination has advantages over a comparative statistical analysis of individuallandscape elements in the database in that it presents an integrated, multivariate model. Cooper and Murray (1992) have shown how groups of similar land classes, repeating patterns of land class mosaics, geographical boundaries (for example between watersheds), geological formations or political entities can be used in combination, to delimit units oflandscape. Ifthe units delimited have a large enough number of field survey sample squares, their landscape ecological resources can be described. Cooper and Murray (1992) have stressed that the hierarchical nature of land classification provides a flexible, explicit method of subdividing a study area to any level of generalisation. This is particularly useful for landscape management when exploring local differences or highlighting regional similarities.
Acknowledgements Work was funded by the Environment Service of the Department of the Environment for Northern lreland. Ronald Murray (Research Officer) and Thomas McCann (Research Assistant) of the Department of Environmental Studies, University of Ulster are both thanked for their invaluable contributions.
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A. Cooper / Landscapeand Urban Planning 31 (1995) 11-19
(Editor), Ecological Mapping from Ground, Air and Space, Institute of Terrestrial Ecology, Symposium Number 10. Institute of Terrestrial Ecology, Cambridge, pp. 39-46. Chipperfield, E., Pilling, R., Gibson, R., Brown, A., Smith, R.S. and Bunce, R.G.H., 1978. An ecological survey of the Sedburgh region of the Yorkshire Dales National Park and of the ArnsidefSilverdale Area of Outstanding Natural Beauty. Report to the County Planning Officer, Cumbria County Council, Kendal. Cooper, A., 1986. The Northern Ireland Land Classification. Department of Environmental Studies, University of Ulster, Jordanstown. Cooper, A. and Murray, R., 1992. A structured method of landscape assessment and countryside management. Appl. Geogr., 12: 319-338. Edwards, S.J., Thomson, A.E., Hughes, M.G.B. and Porteous, A.E., 1982. An Ecological Classification of Strathclyde Region. Nature Conservancy Council, South West (Scotland) Region, Balloch.
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Gardiner, M.J. and Radford, T., 1980. Soil Associations of Ireland and their Land Use Potential. National Soil Survey ofIreland, Dublin. Gauch, H. and Whittaker, R.H., 1981. Hierarchical classification of community data. J. Ecol., 69: 537-557. Hill, M.O., 1979a. TWINSPAN: a FORTRAN program for arranging multivariate data in an ordered two-way table by classification of the individuals and attributes. Cornell University, New York. Hill, M.O., 1979b. DECORANA: a FORTRAN program for detrended correspondence analysis and reciprocal averaging. Cornell University, New York. Meteorological Office, 1983. The climate of Northern Ireland. Meteorological Office, Belfast. Murray, R., McCann, T. and Cooper, A., 1992. A land classification and landscape ecological study ofNorthern Ireland. Report to the Environment Service, Department of the Environment for Northern Ireland, University ofUlster, Coleraine.