Patterns of variation in vascular plant species richness and composition in SE Norwegian agricultural landscapes

Agriculture, Ecosystems and Environment 114 (2006) 270–286 www.elsevier.com/locate/agee

Patterns of variation in vascular plant species richness and composition in SE Norwegian agricultural landscapes Harald Bratli a,*, Tonje Økland a, Rune Halvorsen Økland b, Wenche E. Dramstad a, Reidar Elven b, Gunnar Engan a, Wendy Fjellstad a, Einar Heegaard c,d, Oddvar Pedersen b, Heidi Solstad b b

a Norwegian Institute of Land Inventory, P.O. Box 115, N-1431 A˚s, Norway Department of Botany, Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, N-0318 Oslo, Norway c Bjerknes Centre for Climate Research, University of Bergen, Alle´gt. 55, N-5007 Bergen, Norway d Biological Institute, University of Bergen, Alle´gt. 41, N-5007 Bergen, Norway

Received 18 March 2005; received in revised form 10 October 2005; accepted 31 October 2005 Available online 18 January 2006

Abstract Plant species richness and composition were studied in 16 1 km2 agricultural landscape plots in SE Norway, in which a total of 2201 patches of 18 types (built-up areas omitted) were identified and mapped. Plots differed with respect to area covered by ploughed land (6–93, mean 47%) and woodland (1–90, mean 41%), while the area of boundary transitions, pastures and semi-natural land was low to moderate in all plots (2–22, mean 12%). Landscape complexity varied considerably among plots (from 31 to 285 discrete patches). A total of 738 species were recorded in the total studied area of 14.02 km2, more than twice as many as in comparable studies with plot-based sampling. The frequency distribution of species in patches were strongly right-skewed with a median frequency of 1%, showing that in the modern agricultural landscape species are patchily distributed and that it is very common to be rare. Species frequencies in plots were bimodally distributed, demonstrating existence of a large group of regionally widespread, landscape-scale core species. Two major floristic gradients were identified by ordination of patch species composition: (1) a gradient from species with preference for open sites and fertile soils to species with tolerance for shaded sites and infertile soils, reflecting variation from intensively used areas (ploughed land, with prominence of weeds) via boundary transitions, extensively used (pastures) and abandoned (semi-natural) land, to woodland. Within ploughed land this gradient reflected variation in intensity of use, within abandoned land it reflected time since abandonment and the re-growth succession under closing canopies. (2) A gradient related to preference for dry versus moist sites. Strong between patch variation in species composition within patch types suggested that factors other than those used to delimitate land type were also important determinants of the species composition. Patterns of variation in species composition and species richness were found to differ among scales and the implications of this result are discussed. # 2005 Elsevier B.V. All rights reserved. Keywords: Agricultural landscapes; Intensification; Land-use; Land-cover types; Ordination; Soil fertility; Species composition; Vegetation gradients

1. Introduction During recent decades there has been a broad-scale polarisation within the agricultural landscape (McInerney, 1994; Robinson and Sutherland, 2002), with increasingly intensified use of already intensively managed land, * Corresponding author. Tel.: +47 64947880. E-mail address: [email protected] (H. Bratli). 0167-8809/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2005.10.022

accompanied by abandonment of more extensively managed land (Meeus, 1993; Ska˚nes and Bunce, 1997; Haines-Young et al., 2003). Intensification has involved extensive use of agrochemicals, increasing the size of intensively managed patches, levelling and draining, closing open ditches, and removal of a wide variety of landscape features considered to represent obstacles to production, such as remnant islets of semi-natural vegetation and grassy banks that mark field or ownership boundaries (Agger and Brandt, 1988; Hamre

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and Austad, 1999). Reduced agricultural activity has usually been accompanied by reforestation of grasslands or land abandonment, over most of north-western Europe initiating a succession that has closed woodland as its natural endpoint (Svenning, 2002). Land-use changes are constant threats to agricultural landscape biological diversity (Korneck et al., 1998; Daily et al., 2001; Waldhardt et al., 2003), and the extent of species losses from agricultural landscapes is likely to accelerate in the future (Tilman et al., 2001). Norway differs from most European countries in the low proportion of farmland: 3.4% of the total land area (Anonymous, 2004), e.g. contrasted with 75% for Great Britain (Robinson and Sutherland, 2002). Although Norwegian concerns for biodiversity loss have mainly been directed at natural ecosystems there is now a growing awareness that agricultural landscapes are important for biodiversity conservation (Framstad and Lid, 1998; Dramstad et al., 2002). Ecological studies of vascular plants in agricultural ecosystems have mostly focused on selected species groups (Austrheim and Eriksson, 2003), detailed analyses of specific land types, such as hedgerows (Aude et al., 2003, 2004), hay-making meadows (Losvik, 1993; Bratli and Myhre, 1999; Myklestad and Sætersdal, 2003) or abandoned fields (Degn, 2001; Ejrnæs et al., 2003; Waldhardt and Otte, 2003), and have mostly been carried out in study areas of small geographic extent by use of small sample plots (but see Moser et al., 2002). In general, these studies have demonstrated the importance of small patches with low-intensity land-use for landscape-scale species richness (Austad and Losvik, 1999; Norderhaug et al., 2000; von Arx et al., 2002) and boundary transitions, e.g. between ploughed land and road, ploughed land and woodland, and ploughed land and water (Norderhaug et al., 2000; Cousins and Eriksson, 2001; Marshall and Moonen, 2002; Smart et al., 2002). However, the extent to which recurrent patterns of variation in species composition occur in agricultural landscapes, the scales on which such recurrent patterns occur, and their relationships with environmental and land-use factors, are insufficiently known (cf. Wagner et al., 2000; Jeanneret et al., 2003; Whittaker et al., 2005). Recurrent patterns of variation in species composition are recognisable as pronounced gradients in species composition (coenoclines; Whittaker, 1967), with clear relationships to environmental or historical complexgradients (Økland, 1990). Knowledge of the gradient structure of agricultural landscape vascular plant species composition is an important prerequisite for management: (1) by aiding identification of landscape elements with a species composition that is deviant or otherwise of particular interest (cf. Faith, 2003); (2) for monitoring (Økland et al., 2004), e.g. for providing estimates of rates of floristic change in response to land-use change and (3) for development of realistic scenarios and robust predictions of effects of financial and other policy instruments affecting the structure

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of agricultural landscapes (Ernoult et al., 2003, Faith et al., 2004). Contrasting opinions have been forwarded on the strength of relationships between biodiversity and landscape structure at broad-scales (e.g. Moser et al., 2002; Jeanneret et al., 2003; Fe´doroff et al., 2005). The notion that the magnitude of biotic effects is predictable as a function of landscape structural change is challenged by the sparsely available empirical data (Heikkinen and Neuvonen, 1997; Wagner et al., 2000; Luoto et al., 2002; von Arx et al., 2002) and problems with selecting appropriate scale (grain and extent; Dungan et al., 2002) for the study (Waldhardt et al., 2004; Whittaker et al., 2005). It has, though, been argued (Wu and Levin, 1994; Waldhardt et al., 2004) that patches of the landscape mosaic with more or less uniform environmental conditions and land-use history are the most appropriate units for studies of patterns of variation in agricultural landscapes. The present study is part of a larger programme, with the ultimate aim of assessing the extent to which landscape-scale vascular plant species richness and species composition can be predicted from landscape structural features. To approach this aim, the vascular plant species composition was recorded in 2201 mapped landscape patches within 16 1 km2 plots that were selected to be representative for the variation in SE Norwegian agricultural landscapes. The aim of this study is to provide a baseline description of: (1) landscape structural variability; (2) distribution of vascular plant species richness and, in particular; (3) variation in vascular plant species composition, among the individual patches and patch types that make up the SE Norwegian agricultural landscape. This third and main aim of the present study is accomplished by identifying the main gradients of compositional variation in the data set and by relating these gradients to patch geometric, geographic, land-use and environmental characteristics, and thus to the ongoing dynamic processes in the agricultural landscape.

2. Materials and methods 2.1. Study region and data collection The study was restricted to the lowland boreo-nemoral and the southern boreal vegetation zones (Moen, 1998) of five neighbouring counties (Vestfold, Østfold, Akershus, Hedmark and Oppland) in SE Norway (Fig. 1) in order to avoid extensive biogeographic variation within the data set. The region extended approximately 200 km in the northsouth and 100 km in the east-west directions, and from 0 to 440 m above sea level. The bedrock varied among plots; siliceous granites and gneisses were most common, but calcareous schists and limestone (Sigmond et al., 1984) also occurred. Mean annual precipitation ranged from 550 to 900 mm (Førland, 1993) and the length of the growing

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Fig. 1. Map of SE Norway showing the geographic position of the 16 studied plots.

season (basal temperature 5 8C) was between 7 and 8 months (Aune, 1993). The study region is situated in the part of Norway most favourable for crop production. The main agricultural crops were grain cereals (wheat, oats, barley), and rape for oilseed production. Grass crops and pastures were also common while vegetables were cultivated more sporadically. The 16 1 km
1 km plots used in this study were drawn by a stratified random procedure from the national monitoring network for agricultural landscapes (3Q; Dramstad et al., 2002). This network is based on a systematic 3 km
3 km grid of points covering the entire country. Since agricultural landscapes are focused, only the 1474 plots with agricultural land in their centre were

included in the 3Q network. Three hundred and seventy-five of these 3Q plots were located in the study region. Plots for the present study were chosen among the 43 plots selected at random for field control of the 3Q land-type mapping in years 1998 and 1999. These 43 plots were divided into quartiles for two variables: (1) percentage cover of ploughed land, and (2) spatial heterogeneity of land-type patches (the HiX index which ranges from 0 to 1; see Fjellstad et al. (2001) for details). These two variables were used for stratification because they were expected to span landscapescale gradients in the importance of major land types and, hence, the range of variation in land-use intensity and vascular plant species composition (cf. Fe´doroff et al., 2005) in SE Norwegian agricultural landscapes. One plot was selected at random from each cell in the 4
4 quartile grid for the two variables. A non-hierarchical classification of the terrestrial land area in the 16 studied plots was performed, into nine basic patch types (plus discarded land area) and nine boundary transition patch types (see Table 1 for definitions). Boundary transitions were included as separate types because they are often assumed to be particularly rich in vascular plant species (Marshall and Moonen, 2002).The classification into basic patch types was a modification of the classification used by the 3Q programme (with 8, 24, and 104 types at the three hierarchical levels; Dramstad et al., 2002). The basic patch types were ploughed land (four types according to current year’s crop: cereals, vegetables, grass, and fallow), midfield islet, pasture, semi-natural land, woodland (treated collectively, also including regular forests) and wasteland. All other kinds of built-up areas (including private gardens), wetland areas (mires, swamps, rivers and lakes), and maritime shores, were defined outside the scope of the present study. Areas were classified as ploughed land if fully cultivated (cultivated to normal plough depth) or surface cultivated

Table 1 Classification of the land area into nine basic and nine boundary transition patch types Patch type

No of patches

Definition

PloughedVegetab PloughedCereals PloughedGrass PloughedFallow Midfield islet Pasture SemiNat Wasteland Woodland B-Ploughed.Ploughed B-Ploughed.Pasture B-Ploughed.Semi B-Ploughed.Road B-Ploughed.Built B-Road.Other B-Ploughed.Woodland B-Ploughed.Water B-Ploughed.Pond

33 181 91 18 144 50 160 19 245 108 56 118 238 177 276 254 24 9

Ploughed land with annual crops of leafy and root vegetables Ploughed land with annual crops of cereals or oilseeds Ploughed land with grass crops, fully cultivated or surface cultivated Fallow ploughed land, recently abandoned Patch surrounded by ploughed land, area <5000 m2 Grazed pasture; fertilised or unfertilised, improved or unimproved Semi-natural open land (see woodland), not in agricultural use Outdoor storage areas, including dumps and rubbish tips Land with crown cover >25% of trees >3 m tall Boundary with ploughed land on both sides Boundary with ploughed land on one side and pasture on the other Transition between ploughed land and semi-natural land Road verge bordering ploughed land Transition between ploughed land and built-up area Road verge not bordering ploughed land Transition between ploughed land and woodland Transition between ploughed land and water (except farm ponds) Transition between ploughed land and farm pond

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(cleared and levelled, so that mechanised harvesting is possible) and as pasture if clearly and regularly influenced by grazing. The remaining land was classified as woodland if having a cover >25% of crowns of trees more than 3 m tall or if derived from woodland by clear-felling, etc.; wasteland if the ground was extensively influenced by human outdoor storage (e.g. machinery) or used as rubbish tips or for dumping and as semi-natural land otherwise. Midfield islets were recognised as a separate patch type if smaller than 5000 m2, otherwise classified as open semi-natural land or woodland. Boundary transition zones (B; nine types, see Table 1 for definitions) were delineated along all edges of ploughed land, around farm ponds, and along all roads. A land-type map was constructed for each plot using aerial photographs followed by careful inspection in the field, prior to recording of vascular plants. For land-type patches (other than boundary transitions; see below) to be delineated a minimum size of 1000 m2 was required, 100 m2 when bordering ploughed land or pasture. For landtype patches not wholly included in a plot, the part contained in the plot was analysed if larger than the minimum size required for the type. Patches of semi-natural land were included in boundary transition zones if <15 m broad. By definition, the borderline of a patch of ploughed land was drawn where plough furrows or tracks of agricultural vehicles disappeared. The borderline of woodland patches towards adjacent land types was drawn between the trunks of the outermost trees, more than 3 m tall and with a maximum inter-stem distance of 7.5 m. Pastures and patches of open semi-natural land were allowed to include isolated tree groups <1000 m2. By definition, road verges bordering ploughed land (B-Ploughed.Road) and woodland (B-Road.Other, in part) extended from the middle of the road to the borderline of the adjacent land type. Whenever present, fences or other obvious borders were used to delimit built-up areas. By definition, the transition between ploughed land and water (B-Ploughed.Water) extended from the border of ploughed land to one m horizontal distance beyond the normal shoreline, into the water. Small streams and ditches <2 m wide were included in the adjacent land type. For each of the 2201 land-type patches recognised in the 16 1 km2 plots, presence of vascular plant species (nomenclature follows Elven (2005)) was recorded in the field by a team of four experienced botanists (Palmer et al., 2002) that used standardised procedures to ensure that the species list were comparable and as complete as possible. This was done by allocating to each patch an amount of time that depended on patch type, area and shape, and by use of a customised checklist. Eight plots were investigated each of the years 2001 and 2002. Specimens were collected for later identification by experts whenever necessary (voucher specimens were deposited in the herbarium of the University of Oslo (O)). Species of some critical genera were treated collectively. A pilot study (Bratli et al., unpublished data)

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showed good comparability of species lists among botanists and land types. Normally, 80–95% of the total number of species present in a patch in a given year was recorded, which is comparable to other studies (e.g. Scott and Hallam, 2003). Species are most likely to be lost by overlooking, misidentification, seasonality, and shortage of time for complete survey. Maps for each of the 16 1 km2 plots were digitised and stored in a GIS database, using the software ArcView GIS Version 3.2a (Anonymous, 1992–2000). The GIS database was used to derive, for each patch (and hence, for each plot by aggregation over all patches), geographical co-ordinates (easting, northing, altitude, and warmth sum) and patch geometric properties (size and perimeter). One habitat diversity variable was also recorded for all patches (see Table 2 for full account). Ploughed land and woodland, end-points along a gradient of intensity of agricultural use, differed so widely with respect to ecological conditions that these were to a large extent incommensurable (Fe´doroff et al., 2005). A data subset with the 1633 out the total 2201 patches that were classified to the 13 patch types other than ploughed land and woodland was therefore defined, for which several additional ecological and land-use variables were recorded (see Table 2 for full account) for interpretation of relationships between species composition and explanatory variables. The Ellenberg indicator value system was used to obtain surrogate variables for four important ecological variables that, for practical and economic reasons, could not be sampled in every patch: light, moisture, soil reaction, and soil fertility. Ellenberg indicator index values (Ellenberg et al., 2001) are ordinal scores assigned to Central European plants on the basis of accumulated field and other experience (1–9 scale; moisture: 1–12 scale; high values indicate preference for open, moist, basic and nitrogen-rich sites, respectively). Index values should be interpreted as best guesses for the ecological optima (Ernst, 1978) of the species along a gradient, i.e. under field conditions. Although single index values did not fully account for the complexity of real ecological factors and the species’ responses to them (Schaffers and Sy´kora, 2000; Lawesson, 2003), and simple indices might be biased geographically and otherwise (e.g. Wamelink et al., 2002; Witte and von Asmuth, 2003), Ellenberg indicator values provided a reliable basis for calculating indicator variables for sampling units of different sizes, to demonstrate shifts along compositional gradients in the ecological preferences of the species present (Diekmann, 1995, 2003). It should be noted, however, that strict use of species characteristics for characterising sites in principle would involve a circular argument. Furthermore, Ellenberg N values indicated relationships to general soil fertility rather than nitrogen availability per se (Hill and Carey, 1997; Myklestad, 2004). The average Ellenberg index value for all taxa present in the patch and for which Ellenberg et al. (2001)

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Table 2 Explanatory variables observed in all 2201 patches or in (entire or part of) the 1633 patch subset without ploughed land and woodland: name and short description (name used in text in bold letters), number of observations n in the 1633 patch subset (n = 2201 for variables recorded in the full data set; otherwise n  1633), type (C, continuous; B, binary; O1 and O2, ordinal with six classes) and summary statistics for the subset: number of non-zero values, minimum, maximum, mean and S.D. Variable

n

Type

Non-zero values

Minimum

Maximum

Mean

S.D.

2201 2201 2201 2201

C C C C

2201 2201 2201 2201

64733 130026 0 815

52994 322988 441 1444

18553 235418 183 1116

21863 62981 102 150

2201 2201 2201

C C C

2201 2201 2201

3 8 1.00

Habitat diversity The number of vegetation types (see Fremstad, 1997)

2201

C

2201

0

Ecology (including land-use and human impact) Grazed (the year, in which field recording was performed) Mown (the current year) Previously grazed or mown Fertilised (the current year) Sprayed with pesticide (the current year) Area of patch afwoodlanded Area of patch covered by stone tip Area of patch covered by soil tip Canopy height Area of patch tree covered Area of patch shrub covered Presence of stone heap Presence of telegraph pole Number of buildings Length (m) of footpath Length (m) of stone fence Length (m) of other permanent fence Length (m) of temporary fence Length (m) of tree lines Length (m) of shrub lines Length (m) of water ditch (ditch filled with water) Length (m) of dry ditch (ditch without water) Length (m) of streams Average Ellenberg light (L) index Average Ellenberg moisture (M) index Average Ellenberg reaction (R) index Average Ellenberg nitrogen (N) index

2201 1793 1878 1633 1956 2182 1583 1583 1633 1633 1633 1937 467 1878 1878 1878 1878 1633 1583 1583 1878 1878 1878 2201 2201 2201 2201

B B B B B O1 O1 O1 O2 O1 O1 B B C C C C C C C C C C C C C C

172 351 339 789 885 48 57 75 953 534 576 60 89 45 95 26 164 76 53 16 103 229 149 2201 2200 2196 2201

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5.17 3.83 2.00 1.75

Geographical Easting (m) Northing (m) Altitude (above sea level; m) Warmth sum: effective temperature sum with basal temperature 5 8C (Laaksonen, 1979); obtained by interpolation of data for annual mean temperatures 1961–1990 (Aune, 1993) for the centre-point of each 1 km2 plot (Norwegian Meteorological Institute, unpublished data) and patch-wise correction for altitude Patch geometry Area Perimeter Shape index; the ratio of the patch perimeter (P) and the perimeter of a circular patch with the same size (A): index of shape complexity ¼ 2pffiffipPffipffiffiAffi ¼ 0:282PA0:5

801048 7031 14.62

6370 382 2.74

29525 518 1.75

11

1.75

1.13

1 1 1 1 1 5 5 5 5 5 5 1 1 20 4000 500 1300 900 130 200 1000 1000 1500 7.50 8.72 8.00 7.50

0.08 0.20 0.18 0.48 0.45 0.07 0.11 0.13 1.40 0.82 0.69 0.03 0.19 0.07 10.88 1.15 10.35 6.48 1.64 0.49 5.05 12.93 10.75 6.72 5.59 5.87 5.61

0.27 0.40 0.38 0.50 0.50 0.50 0.62 0.67 1.50 1.43 1.09 0.17 0.39 0.81 131.12 15.19 58.36 45.16 10.28 6.88 37.65 55.81 76.18 0.35 0.54 0.75 0.80

The two ordinal scales are: O1: 0, no canopy; 1 cover <6.25% but not zero; 2, 6.25–12.5%; 3, 12.5–25%; 4, 25–50% and 5, cover >50%. O2: 0, no shrub layer; 1, shrubs 1–3 m; 2, trees 3–5 m; 3, trees 5–10 m; 4, trees 10–15 m; 5, trees >15 m.

provided an indicator value with respect to the factor in question was assigned to every patch: 604 (of a total of 738) for Ellenberg L, 562 for Ellenberg M, 448 for Ellenberg R and 555 for Ellenberg N.

2.2. Data analysis Detrended correspondence analysis (DCA; Hill, 1979; Hill and Gauch, 1980) was used to identify main gradients in

H. Bratli et al. / Agriculture, Ecosystems and Environment 114 (2006) 270–286

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Table 3 Characteristics of 1 km2 plots, ordered from north to south Plot ID

1652 1680 1710 1711 1738 1785 1817 1833 1932 1995 2037 2086 2127 2130 2171 2239

Patch types (No., of 18) 16 17 13 16 13 15 16 9 15 14 13 14 15 14 15 10

Patches (No.) 171 146 51 104 158 180 285 31 178 131 122 147 126 125 172 83

Area (km2) 0.954 0.939 0.967 0.973 0.911 0.929 0.715 0.944 0.939 0.970 0.969 0.618 0.969 0.862 0.724 0.636

Areal cover (% of plot total)

Land-use (% of patches)

Ploughed

Woodland

Pasture

SemiNat

Border

Grazed

Mown

Fertilised

Sprayed

Taxa plot (No.)

66.29 76.64 6.48 83.08 92.95 12.28 68.63 13.21 57.33 35.38 30.19 45.56 59.90 26.62 66.07 8.88

14.56 7.88 89.48 5.99 1.28 79.43 4.95 84.82 28.95 43.26 64.45 40.07 33.21 60.78 16.47 81.04

11.82 7.01 1.04 3.81 0.00 0.93 0.32 0.00 5.27 9.95 0.00 0.00 2.25 4.48 9.01 0.00

0.70 2.20 0.32 2.40 0.51 2.68 8.43 0.21 2.15 7.11 0.27 3.94 0.42 1.39 2.31 3.16

6.62 5.56 2.57 4.39 5.02 4.46 12.39 1.75 6.26 4.28 4.84 8.31 4.19 4.98 5.61 6.91

9.4 8.2 41.2 13.5 0.0 22.8 0.7 0.0 2.2 8.4 0.0 0.0 8.7 7.2 18.0 0.0

12.9 7.5 17.6 7.7 24.1 18.9 24.2 3.2 18.5 6.9 1.6 24.5 16.7 12.0 18.0 14.5

14.6 31.5 5.9 45.2 28.5 19.4 22.1 54.8 54.5 54.2 46.7 46.9 39.7 40.0 57.6 18.1

22.8 36.3 0.0 51.0 48.7 14.4 31.9 74.2 60.1 58.8 50.8 49.7 23.8 40.0 61.0 22.9

377 315 284 229 322 339 438 264 287 303 331 307 303 390 347 486

Taxa patch (No.) 43.3 41.3 56.9 32.4 42.2 45.2 48.4 56.5 38.2 46.0 52.2 57.2 40.1 57.4 45.2 78.2

Area refers to the total area included in this study (built-up areas, wetlands, etc., excluded). Taxa plot and taxa patch refer to the total number of taxa recorded in the plot and the mean number of taxa per patch in a given plot, respectively.

species composition at the grain size (Legendre and Legendre, 1998; Dungan et al., 2002) of land patches. DCA was applied to the total data set (2201 patches) and the subset without ploughed land and woodland (1633 patches). DCA was run with the following options: detrending by segments, non-linear rescaling of axes, and no downweighting of rare species. Our attention was restricted to the first two, ecologically interpretable, DCA ordination axes. Patch-type mean ordination scores and their S.D. were plotted to assist interpretation of the major ordination axes. The Wilcoxon (Mann–Whitney) two-sample test for unpaired observations (Sokal and Rohlf, 1995) was used to test patch pairs for significance of difference in scores, axis by axis. Further interpretation of ordination axes for the subset without ploughed land and woodland was accomplished by calculating Kendall’s non-parametric correlation coefficients t (Sokal and Rohlf, 1995) between plot scores and the continuous and ordinal explanatory variables of Table 2, and by using the Wilcoxon (Mann–Whitney) twosample test for unpaired observations to test for differences between scores for the 0 and 1 levels of binary variables. Contour plots for selected patch properties in the ordination diagram, created by the loess function in S-plus for nonparametric smoothing (Crawley, 2002), were used to assist the interpretation of axes visually. Because species number is generally strongly related to area (Arrhenius, 1921; Palmer and White, 1994), partial Kendall’s correlation coefficients (in which the effect of area was partialled out) was used to test relationships between species number and the ordination axes (Sokal and Rohlf, 1995). CANOCO, Version 4.5 (ter Braak and Sˇmilauer, 2002), was used for ordination analyses. All other statistical analyses were made using SPSS Version 11.5.1

(Anonymous, 2002), and S-PLUS version 6.0 for Windows (Anonymous, 2001).

3. Results From 3 to 38% of the total area of 1 km2 plots was discarded due to presence of land types not considered in this study (Table 3), resulting in a total investigated area of 14.0 km2 (87.6% of the total plot land area in 16 plots). Of the 2201 mapped patches, 14.7% were ploughed land, 11.1% were woodland, 7.3% were semi-natural land, 6.5% were midfield islets, and 57.3% were boundary transitions (nine patch types); see Table 4. By area, ploughed land made up 47.1%, woodlands 41.1%, all boundary transition types together 5.3%, pastures 3.6%, semi-natural land 2.3%, and midfield islets only 0.1% (Table 4). The plots spanned the full range of variation from intensively managed agricultural landscapes with large cereal (and oilseed) fields (maximum area of ploughed land = 93.0% coinciding with minimum area of woodland = 1.3 %; maximum percentage of patches fertilised = 58 and sprayed = 74; Table 3) to landscapes with more fine-grained patch structure, predominantly used for grass crops and pastures (maximum area of pasture = 11.8%), or that were dominated by woodlands (minimum area of ploughed land = 6.5% coinciding with maximum area of woodland = 89.5%). Landscape complexity varied considerably among plots. The number of patches per plot varied between 31and 285. Semi-natural land (range: 0.2–8.4% of area) and boundary transitions (range: 1.8–12.4% of area) occupied small fractions of the total area. The area of semi-natural land was not clearly related to the balance between ploughed land and woodland but generally

276

Patch type

Presence in 1 km2 plots

No. of patches

% of total area (14.02 km2)

Average area (m2)

Total

Mean

Minimum

PloughedVegetab PloughedCereals PloughedGrass PloughedFallow Midfield islet Pasture Semi-Natural Wasteland Woodland

7 14 12 7 15 11 16 9 16

33 181 91 18 144 50 160 19 245

3.08 35.54 7.30 1.14 0.11 3.63 2.25 0.43 41.13

13094 27532 11252 8897 109 10166 1972 3200 23534

129 250 245 189 249 369 532 278 625

25.21 31.65 28.69 34.67 20.19 67.20 50.26 55.11 61.47

14 7 9 16 2 30 11 17 7

B-Ploughed. Ploughed B-Ploughed.Pasture B-Ploughed.Semi B-Ploughed.Road B-Ploughed.Built B-Road.Other B-Ploughed. Woodland B-Ploughed.Water B-Ploughed.Pond

15

108

0.64

826

345

43.00

11 15 16 16 16 16

56 118 238 177 276 254

0.21 0.18 1.28 0.51 1.41 0.94

515 216 753 404 716 521

270 326 459 440 615 437

7 6

24 9

0.20 0.02

1174 296

225 185

For abbreviations, see Table 1.

Number of taxa Maximum

Ellenberg L mean

Ellenberg F mean

Ellenberg R mean

Ellenberg N mean

Mean no. of habitats

44 64 60 63 67 136 122 135 200

6.92 6.91 7.02 6.94 6.88 6.73 6.71 6.86 6.16

5.08 5.43 5.42 5.78 5.38 5.88 5.84 5.41 5.90

6.60 6.32 6.23 5.77 5.95 5.60 5.73 5.96 5.22

6.77 6.44 6.17 5.90 6.06 5.26 5.33 5.76 4.83

1.03 1.02 1.02 1.06 1.39 1.94 1.84 1.84 2.90

12

87

6.74

5.66

6.05

5.86

1.64

43.20 36.96 55.89 46.99 60.21 50.19

11 11 10 14 10 13

70 85 134 98 200 129

6.76 6.81 6.88 6.83 6.76 6.57

5.70 5.60 5.46 5.36 5.44 5.70

6.13 6.01 6.06 6.13 5.72 5.66

5.82 5.83 5.60 5.90 5.19 5.39

1.29 1.50 1.80 1.56 1.92 1.80

47.58 42.67

20 15

88 58

6.71 6.76

6.67 6.51

5.95 5.36

5.65 5.14

1.88 1.89

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Table 4 Characteristics of the 18 patch types

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Fig. 2. Distribution of species on all 2201 patches. Inserts provide successive magnification of the left part of the graph (species with low frequency).

occupied smaller fractions of the total investigated area in less complex landscapes (Table 4). From 9 to 17 patch types were represented in each plot (Table 3). Patches classified as ploughed land (at least one type), woodland and semi-natural land occurred in all plots, pasture occurred in 11 plots (Tables 3 and 4). A total of 738 taxa were encountered in the 2201 landtype patches. Species frequencies were very strongly rightskewed, showing that a majority of species were rare in the sense that they occurred in few patches (Fig. 2). Only 13 species were present in more than 50% of the patches, of which most were associated with open, intensively used agricultural land: Elymus repens (1679 patches), Taraxacum ruderalia agg. (1586), Ranunculus repens (1574), Rubus idaeus (1483), Anthriscus sylvestris (1472), Urtica dioica (1439), Vicia cracca (1439), Achillea millefolium (1376), Galeopsis bifida/tetrahit (1356), Trifolium repens (1320), Phleum pratense (1314), Trifolium pratense (1309), and Cirsium arvense (1293), Dactylis glomerata (1167), Stellaria graminea (1162), Poa annua (1159), Ranunculus acris (1152), Poa pratensis (1134), and Deschampsia cespitosa (1106). A total of 109 species (14.8%) occurred in 12.5% or more of the patches. As many as 107 species (14.5%) occurred in one patch only, 237 species (32.1%) occurred in 5 patches and 306 species (41.5%) occurred in 10 patches (Fig. 2). The median frequency was 1% (22 of 2201 patches). A total of 674 species occurred in the 1633 patch subset without ploughed land and woodland. Eight of 315 species recorded in ploughed land were unique to ploughed land while 56 of 559 species recorded in woodland patches were unique to woodland. Species frequencies in 1 km2 plots were bimodally distributed, although with a higher peak for low plot numbers: 158 species occurred in one plot, while 99 species were found in 16 plots (21.4% and 13.4%, respectively).

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Fig. 3. Distribution of species on the 16 1 km2 plots.

This showed that at plot grain size, being rare and being common were both common (Fig. 3). Eigenvalues and gradient lengths of the two first DCA ordination axes for all 2201 patches were 0.360 and 0.207, and 4.76 and 4.05 S.D. units, respectively. The total inertia was 11.33. The patch cloud was continuous with highest density near mid-points of axes, slightly tongue-shaped and with largest variation along axis 2 for high axis 1 scores (Fig. 4A). Patches segregated along axis 1 along a sequence from ploughed land via the 13 patch types of the 1633 patch data subset to woodland (Fig. 4B). Within ploughed land, vegetable crop patches had significantly lower mean DCA-1 scores than patches with cereals, and midfield islets obtained lower mean scores than grass and fallow ploughed land. Midfield islets spanned a wide range along DCA-1 (Fig. 4A and B), and midfield islet patch scores along DCA-axis 1 were significantly correlated with area (Kendall’s t = 0.331, P < 0.0001, n = 144). Mean scores for pasture and seminatural patches along DCA-axis 1 were closer to those of woodland than means for most boundary transition types (boundaries between ploughed land and woodland excepted; Fig. 4B). Boundary transition types greatly overlapped in the middle part of DCA-axis 1 (Fig. 4A) and segregated only to a minor extent (Fig. 4B). Many types such as pasture, seminatural land and woodland spanned the entire range of the axis (Fig. 4A) while others were to some extent restricted to lower (boundaries of ploughed land with road and built-up areas, and of road with other types of land) or higher scores (ploughed land-water boundaries). The successional sequence from ploughed land with cereals via fallow ploughed land and semi-natural land to woodland described a trajectory from the (upper) left towards the (lower) right in the two-dimensional ordination diagram. Eigenvalues and gradient lengths of the two first DCA ordination axes for the 1633 patch subset without ploughed

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lower end of axis 2 of the total ordination) and midfield islets were separated from other patch types along axis 2 rather than along axis 1 (Fig. 5). Midfield islet scores along both axes were strongly correlated with area (DCA-1: Kendall’s t = 0.257; DCA-2: t = 0.329; both P < 0.0001, n = 144). The 13 patch types made up two main groups with means well separated along DCA-axis 1. The first main group contained seven patch types with low mean scores and, hence, with a species composition more similar to that of ploughed land than to woodlands, mostly containing grassland patches bordering built-up land and ploughed land. The second main group contained six patch types with relatively higher mean scores, more similar to woodlands than ploughed land, mostly containing other road verges (not bordering ploughed land) and other open land. Within each main group, three groups of patch-types could be recognised, with patch-type means more or less significantly separated from adjacent groups along the second DCA-axis (Fig. 5). Within the first main group of patch types, built-up areas (roads and wasteland) and their boundaries onto ploughed land (B-Ploughed.Road and B-Ploughed.Built) made up one group; boundaries with ploughed land on both sides, between ploughed land and pasture or semi-natural land made up a second group and midfield islets made up a third group. Within the second main group, road verges not bordering ploughed land took an isolated position at low DCA-2 scores; pasture, semi-natural land and boundary transitions between ploughed land and woodland made up a

Fig. 4. DCA ordination of 2201 agricultural landscape patches in 16 SE Norwegian 1 km2 plots, axes 1 and 2 (scaled in S.D. units). (A) Patch positions, (B) patch-type (see Table 1 for explanation) means (symbols)  1 S.D. (lines). Legend applies to both A and B.

land and woodland were 0.269 and 0.202, and 4.31 and 3.66 S.D. units, respectively. The total inertia was 10.31. The patch cloud was continuous with highest density near midpoints of axes, almost without any tongue shape. Corresponding DCA axes for the subset and for the entire data set were strongly correlated (Kendall’s rank correlation coefficients: DCA-1, t = 0.766; DCA-2, t = 0.606; both P  0.0001). The subset ordination thus merely provided a slight ‘magnification’ of the middle part of the total ordination. Patches were better spread out along the axes of the subset ordination, but note that gradient lengths were almost equal in the two ordinations despite ploughed land and woodland patches made up end-points of the first and the

Fig. 5. DCA ordination of 1633 agricultural landscape patches (the subset without ploughed land and woodland) in 16 SE Norwegian 1 km2 plots, axes 1 and 2 (scaled in S.D. units): patch-type (see Table 1 for explanation) means (symbols)  1 S.D. (lines). Letters following patch-type name in legend sum up the results of Wilcoxon two-sample unpaired tests for all combinations of patch type and ordination axis. Types sharing at least one letter (capital letters for DCA-1 and small letters for DCA-2) are not significantly different at the a = 0.01 level.

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Table 5 Kendall’s non-parametric correlation coefficients t between patch scores along DCA axes (ordination of the subset without ploughed land and woodland, n = 1633 patches) and continuous and ordinal explanatory variables (see Table 2 for explanation) DCA-1

Easting Northing Altitude Warmth sum Area Perimeter Shape index Habitat types Afwoodlanded Stone tip Soil tip Canopy height Tree covered Shrub covered Buildings Footpath Stone fence Other fence Temporary fence Tree line Shrub line Water ditch Dry ditch Streams Ellenberg L Ellenberg M Ellenberg R Ellenberg N

DCA-2

t

P

t

P

0.210 0.183 S0.038 0.103 0.182 0.119 0.020 0.164 0.037 0.001 –0.001 0.219 0.150 0.329 0.016 0.050 0.059 0.032 0.025 0.027 0.023 0.136 0.136 0.134 S0.333 0.329 S0.641 S0.560

<0.0001 <0.0001 0.0229 <0.0001 <0.0001 <0.0001 0.2170 <0.0001 0.0708 0.9487 0.9742 <0.0001 <0.0001 <0.0001 0.4241 0.0139 0.0038 0.1110 0.2161 0.1903 0.2540 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001

0.240 S0.124 S0.365 0.266 S0.130 S0.125 S0.104 S0.135 0.053 0.039 0.001 S0.185 S0.119 S0.188 0.037 0.061 S0.100 0.022 0.008 0.077 0.062 0.050 0.004 0.013 0.258 0.321 0.223 0.441

<0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 0.0095 0.0536 0.9491 <0.0001 <0.0001 <0.0001 0.0669 0.0026 <0.0001 0.2770 0.6964 0.0002 0.0025 0.0118 0.8549 0.5233 <0.0001 <0.0001 <0.0001 <0.0001

Correlations significant at level a = 0.0001 in bold face.

second group and a third group was made up by boundaries between ploughed land and water. The explanatory variables most strongly correlated with DCA ordination axis 1 in the subset without ploughed land and woodland were Ellenberg R and Ellenberg N, both decreasing from low to high scores (Table 5, Fig. 6). Ellenberg M (and presence of ditches and streams) increased with increasing DCA-1 scores while Ellenberg L decreased Table 6 Difference (in S.D. units) between mean patch scores with respect to DCA axes (ordination of the subset without ploughed land and woodland, n = 1633 patches) for the two levels (level 1–level 0) of binary explanatory variables (see Table 2 for explanation), with P value for Wilcoxon (Mann– Whitney) two-sample test for unpaired observations Variable

Grazed Mown Previous grazed mown Fertilised Pesticide Stone Heap Pole

DCA-1

DCA-2

Difference

P

Difference

P

0.471 S0.203 0.236 S0.212 S0.274 0.083 S0.410

<0.0001 <0.0001 <0.0001 <0.0001 <0.0001 0.225 <0.0001

S0.263 0.059 S0.277 0.417 0.395 –0.269 0.327

<0.0001 0.292 <0.0001 <0.0001 <0.0001 <0.0001 0.002

Tests significant at level a = 0.0001 in bold face.

and overstorey characteristics (shrub-covered area, canopy height, tree-covered area) increased (Fig. 6). Low scores along DCA-axis 1 were associated with more intensive landuse (current mowing rather than current or previous grazing, fertilization and use of pesticides; Table 6). Some geographic differentiation of patches occurred along DCA-axis 1; scores decreased from NW to SE in the study area (Table 5). The same explanatory variables were, to a large extent, also most strongly correlated with DCA-axis 2, but partly differed in directions of variation. Thus, all four Ellenberg indices increased along the axis while tree and shrub cover decreased (Table 5). Low scores along DCA-axis 2 were associated with less intensive current land-use, previous grazing and mowing, presence of stone fences and stone heaps, while high DCA-axis 2 scores were associated with application of fertilisers and pesticides (Tables 5 and 6). A clear geographic differentiation occurred; high-altitude patches in the northwestern part of the study area obtained low scores. Two independent patterns of variation were recognised in the two-dimensional ordination diagram: (1) from midfield islets, often with telegraph pole (low scores along DCA-axis 1 and high scores along axis 2; the upper left corner in the

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Fig. 6. Contourplot for Ellenberg indicator indices in the DCA ordination of the data subset without ploughed land and woodland (1633 patches).

ordination diagram) to road verges (the lower right corner of the diagram). The gradient was associated with decreasing prominence of species with preference for open sites and fertile, high-pH soils and, towards the lower right corner, with closing canopies and increased use for grazing. (2) From patches bordering on built-up areas, road and wasteland (low scores along both axes; lower left corner in the ordination diagram) to boundary transitions between ploughed land and water (upper right corner), associated with increasing prominence of moisture-demanding species (Ellenberg M) and presence of ditches. The number of habitat types within each patch and the number of species per patch increased along DCA-1 and decreased along DCA-2, following the pattern of variation in patch size (Table 5) and the main pattern of variation described above. The relationships between patch ordination scores and species number remained significant after the effect of area had been partialled out (partial Kendall’s t: DCA-1, t = 0.168; DCA-2, t = 0.279; both P < 0.0001). The distribution of the 466 species occurring in five or more patches on the four main groups of patch types along DCA-axis 1, i.e. (1) ploughed land, (2) grassland bordering built-up land and ploughed land, (3) other road verges and other open land, and (4) woodland (Fig. 5) is tabulated in

Electronic Appendix A. A species was considered as affiliated with a main patch type group when its average frequency in the patch types belonging to this group amounted to 20% or more of the species’ average frequency summed over the four main groups. Only five species were affiliated with ploughed land of which only one, Galium aparine, had an overall frequency above 2%. Seventy-one species, mostly weeds, were affiliated with ploughed land and one or both main types of open land and boundary transition patch types. Forty species, among them weeds (e.g. Cuscuta europaea and Melilotus officinalis), introduced species (e.g. Bunias orientalis and Festuca trachyphylla) and grassland species (Carum carvi, Centaurea scabiosa and Rhinanthus minor), were affiliated with one or both main types of open land patch types. The largest species groups were those affiliated with woodland only (79 species), woodland and woodland-like open land (168 species) and woodland and both types of open land (91 species).

4. Discussion Results show that the main direction of structural variation at the landscape (1 km2) scale is from land well

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suited for intensive cereal crop production, on level ground with fertile soils, often marine or glacifluvial deposits with high clay content, to land in upland districts with rugged topography, less well suited for intensified use and hence dominated by grass crops, pasture or woodland (Puschmann, 1998). Our result that the area of pastures, semi-natural land and boundary transitions, i.e. open land that is not ploughed, rarely exceeds 15% of the total land area shows that by the turn of the millennia the SE Norwegian agricultural landscape, like landscapes over most of Europe, is polarised and mostly dominated either by ploughed land or by woodland. In polarised landscapes, the balance between ploughed land and woodland indicates overall land-use intensity (Burel et al., 1998; Fjellstad and Dramstad, 1999; Hietala-Koivu et al., 2004; Fe´doroff et al., 2005). The degree of polarisation is, however, lower than reported from many other regions. For instance, only the two plots with the lowest patch complexity come close to the 2.2% reported by Howard et al. (2003) as an average for the area occupied by boundary and linear elements in agricultural landscapes in Great Britain. Our finding that the area of open but not ploughed patches is positively related to patch complexity confirms results of previous studies, showing that intensification of the already intensively managed landscape leads to an increasingly homogeneous, large-scaled landscape with fewer boundaries (Fjellstad and Dramstad, 1999; Norderhaug et al., 2000; Cousins, 2001; Luoto et al., 2003; Hietala-Koivu et al., 2004). 4.1. Species distribution A comparison between our results (738 species in 14.02 km2, of which 674 found outside ploughed land and woodland) and results of plot-based studies in open seminatural land indicates that plot-based sampling is likely to underestimate the total species richness in agricultural landscapes strongly: Wagner et al. (2000) report 179 and von Arx et al. (2002) report 180 species from 1280 and 481 Swiss 1 m2 farmland plots, respectively; Norderhaug et al. (2000) report 238 species from 2930 0.25 m2 plots in a middle boreal SE Norwegian traditional agricultural landscape (meadows and road verges; total area: 733 m2) and Cousins and Eriksson (2001) report 361 species from 146 Swedish 25 m2 plots, i.e. the full range of variation in woodland as well as open land types; total area: 3650 m2. The open semi-natural land types including pastures and boundary transitions contain 91% (674) of the recorded species on <12% of the search area and are hence of vital importance for vascular plant richness of the agricultural landscape. This agrees with results of other studies in Norway (Norderhaug et al., 2000; Myklestad and Sætersdal, 2004), Sweden (Cousins and Eriksson, 2001), Finland (Luoto et al., 2002), Denmark (Bruun, 2000), Great Britain (Smart et al., 2002) and Central Europe (e.g. Moser et al., 2002; von Arx et al., 2002). Two types of open

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patches stand out as particularly rich in species: road verges bordering other land types than ploughed land (615, or 83.3% of the species, on 1.28% of the total area) and semi-natural land (532, or 72.1% of the species, on 2.25% of the total area). Patches of these types are kept open by intermediate levels of disturbance, i.e. mowing, shrub removal and grazing, which favours high species richness, in general (Huston, 1979) and in grasslands in particular (Norderhaug et al., 2000; Dupre´ and Diekmann, 2001; Fe´doroff et al., 2005). Our result that road verges hold more species than semi-natural land on a lower total area accords with findings of Norderhaug et al. (2000) but contrasts those of Cousins and Eriksson (2001). This indicates that the relative species richness of road verges and semi-natural land is influenced by several factors that may vary among regions: local environmental factors (Ejrnæs and Bruun, 2000; Cousins and Eriksson, 2002; Waldhardt and Otte, 2003); land-use (Freemark et al., 2002; von Arx et al., 2002), historical (Lindborg and Eriksson, 2004) as well as present (Bruun et al., 2001) and intensity of fertilisation (Eriksson et al., 1995). Most likely, very fragmentary occurrence of traditionally managed meadows prevents occurrence of many habitat specialists (cf. Cousins and Eriksson, 2001; Myklestad and Sætersdal, 2004) in semi-natural land types of modern agricultural landscapes. Accordingly, the role of road verges in the modern agricultural landscape is comparable to that of semi-natural grasslands in the traditional landscape; being cut annually for traffic safety reasons road verges now comprise a major fraction of the regularly mowed area (Milberg and Persson, 1994). The frequency distribution of species on patches in the studied agricultural landscapes is extremely right-skewed, with a median frequency of 1%. This skew is far stronger than reported from plot-based studies, e.g. by Cousins and Eriksson (2001), and indicates that agricultural landscapes abound with locally rare species likely to be left unobserved with plot-based sampling. The bimodal (U-shaped) frequency distribution observed for species at landscape grain size (1 km2) accords with predictions for homogeneous data sets (Raunkiær’s law of frequencies or the core-satellite species hypothesis; Raunkiær, 1918; Hanski, 1982; Collins et al., 1993) and suggests that SE Norwegian agricultural landscapes contains a relatively homogeneous mixture of main patch types: ploughed land, woodland, seminatural land and boundary transitions. Furthermore, the bimodal frequency distribution indicates that variation in the relative importance of ploughed land versus woodland does not significantly influence landscape-scale species richness. 4.2. Species composition Ordination analyses of the full species composition of SE Norwegian agricultural landscape patches reveal a main

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floristic gradient from species with preference for open sites and fertile soils to species with tolerance for shaded sites and infertile soils. The separate ordination of the subset without ploughed land and woodland shows that this main gradient is universally important in the agricultural landscape and not a result of polarisation between ploughed land and woodland. The main gradient reflects variation from intensively used areas, i.e. ploughed land, with prominence of weeds, via boundary transitions, extensively used land, i.e. pastures and abandoned semi-natural land, to woodland. Four sets of factors, each of them complex, contribute to the underlying complex gradient: (1) within land in active use the intensity of use, from currently intensively used land, i.e. vegetable and cereal crops with heavy application of fertiliser and pesticides, via less intensively used land, i.e. grass crops and extensively used land, such as pastures to land left unused; (2) within abandoned land, time since intensively used and stage in re-growth and reforestation succession; (3) soil fertility and acidity, natural or induced by man, from fertile, i.e. high N and P contents, base-rich soils of fertilsed or naturally base-rich or productive, open land to less fertile, more acid soils of land since long abandoned and woodlands and (4) from open grassland to woodland, associated with canopy closure. This main floristic gradient is a result of interacting gradients in topography and natural edaphic site conditions, i.e. soil fertility and acidity, relationships between natural conditions and suitability for agricultural purposes (de Blois et al., 2001; Cousins et al., 2002), and present and past land-use. Elements of this main land-use intensity – re-growth succession – soil fertility gradient from weed-dominated vegetation of ploughed land via midfield islets and boundary transitions more or less strongly impacted by man to woodland are reported in many studies of gradients in European agricultural landscapes: the full gradient (Smart et al., 2003; Wilson et al., 2003; Aude et al., 2004); successional gradients from ploughed land to grassland (Ejrnæs et al., 2003; Waldhardt and Otte, 2003); gradients of land-use intensity within grasslands (Norderhaug et al., 2000; Myklestad, 2004) and gradients from grassland to woodland (Dzwonko and Loster, 1997). This indicates that the main gradient recognised in the study area exemplifes the main between-patch floristic gradient within the modern European cultural landscape, at least in climates comparable with that of SE Norway. The segregation of ploughed land with vegetable, cereal and grass crops along this gradient, the positive relationship between gradient position and area of midfield islets, the segregation of boundary transitional patches and the general increase in patch area along this gradient, are likely to reflect generally decreasing importance of weeds relative to grassland and other species along the gradient. Prominence of weeds reflects the intensity of cultivation and fertilisation and pesticide application (Kleijn and Verbeek, 2000), as well as soil fertility in general (Hallgren et al., 1999; Lososova´ et al., 2004). Small patches are expected to be

more strongly influenced by fertiliser and pesticides than larger, and patches entirely bordering ploughed land and built-up areas more strongly than patches bordering woodland. Grassland species are sensitive to fertilisation (de Snoo, 1997; Jones and Haggar, 1997; Klein and Snoeijing, 1997) and may even be affected by pesticide drift (Marrs and Frost, 1997). The segregation of fallow ploughed land, boundary transitional patches and open semi-natural land along the main gradient partly reflects a gradient of time since abandonment, and partly reflects ecological processes associated with abandonment. The separation of fallow ploughed land from ploughed land in active use accords with observations by Degn (2001), Ejrnæs et al. (2003) and Aude et al. (2004) that the compositional turnover during initial phases of regrowth succession is high. Further segregation of semi-natural land from fallow ploughed land and woodland from semi-natural land is due to reduction along this gradient in soil P (Gough and Marrs, 1990), N (Gough and Marrs, 1990; Pywell et al., 1994), pH (Waldhardt and Otte, 2003), and increase in soil organic matter (Pywell et al., 1994), a process partly driven by littershed from closing canopies (Nihlga˚rd, 1971; Tamm and Hallba¨cken, 1988). Diminishing effects of liming of agricultural soil, a common management operation in the area (Hoel et al., 2003), with decreasing intensity of agricultural use and increasing time since abandonment may also contribute to this gradient. Ordination analyses reveal a second floristic gradient related to preference for dry versus moist sites, which is independent of the main soil fertility – land-use intensity – re-growth succession gradient. This second gradient separates boundaries of built-up areas, road verges and wasteland from pastures, semi-natural land and boundaries with ploughed land on both sides. It is associated with the presence of ditches, and has boundaries onto water as its end-point. The most important underlying factors are likely to be topographically dependent variation in soil moisture and adjacency to open water bodies, shown to be important for variation in species composition over broad spectres of variation in agricultural landscapes by Ejrnæs and Bruun (2000) and Cousins et al., (2002), and on finer scales within grasslands and boundaries onto ploughed land by Bratli and Myhre (1999) and Vandvik and Birks (2004). The strong separation of means for boundary transitional types onto water from other patch types along this gradient reflects the large element of wetland species, which only occur near open water, such as ditches, brooks, streams, ponds, and lakes, or in sites with permanently high ground-water table, in the regional species pool (cf. Dahl, 1998). The ordination analyses highlight the importance of soil nutrients, soil moisture and present land-use for the species composition of agricultural landscapes. Other factors likely to be important, although not sufficiently important to give rise to independent, interpretable, compositional gradients in SE Norway, are: distance to adjacent land and seed

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sources of different kinds, i.e. the matrix context (Marshall and Arnold, 1995; de Blois et al., 2001; but see Bruun, 2002); past land-use, that may influence soil conditions for decades (Koerner et al., 1997) and species pools for centuries or millennia (Bruun et al., 2001; Lindborg and Eriksson, 2004); presence of calcareous bedrock and soil, determining the local and regional distribution of calciphilous grassland species (Breien, 1933; Ejrnæs and Bruun, 2000) and local topography-soil depth gradients (Bratli and Myhre, 1999; Cousins and Eriksson, 2001). Demonstration in the present study of a strong vascular plant compositional gradient related to local land-use intensity and regrowth succession after abandonment shows that the patch grain size is appropriate, not only for studies of species richness patterns (Waldhardt et al., 2004), but also for studies of species composition patterns. Because the main compositional gradient directly reflects phases in the ongoing polarisation of the cultural landscape, and because the patch is the landscape sub-unit most likely to have a homogeneous land-use history (but see Lindborg and Eriksson, 2004), patch-based recording of species is well suited for quantifying biological effects of land-use changes by monitoring, using ordination and other multivariate statistical methods as research tools (cf. Økland and Eilertsen, 1996; Økland et al., 2004). Results of this study demonstrate existence of different patterns of variation in species richness and species composition on different scales, and suggest that also the most important ecological processes differ among scales (Wagner et al., 2000; Vandvik and Birks, 2002; Waldhardt et al., 2004). On the scale of tens or hundreds of metres, the species composition of single patches in the agricultural landscape is related to local environmental factors and landuse (cf. Austrheim et al., 1999; Norderhaug et al., 2000; Luoto et al., 2002; Moser et al., 2002; Vandvik and Birks, 2002). On the scale of kilometers, polarised modern agricultural landscapes differ with respect to dominance by ploughed land or woodlands but share the relatively low areal importance of boundary transitions and other seminatural open sites, they have a large group of agricultural landscape core species in common, and they display variation along the same main finer-scaled compositonal gradients. This broad-scale similarity between landscapes questions if landscape-scale species composition can be predicted from landscape structural properties. Furthermore, the very large number of rare species in the agricultural landscape questions the suggestion by Luoto et al. (2002) that landscape-scale species richness patterns may in general be predictable.

Acknowledgements We thank all land owners who kindly permitted us to survey their crop and grass fields. This work was funded by

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the Norwegian Research Council under the programme ‘Landskap i Endring’, Grant No. 140748/720.

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