Figure 2.

Biplot of the canonical correspondence analysis (CCA) model in Table 1. (a) First and second axis, species; (b) first and second axis, environmental variables. See Table 1 for details of the model, percentage variance in the fitted values explained by this figure: 34% (i.e., (λ₁ + λ₂)/Σλ_can). The plotted species are a selection of species with the highest percentage variance explained by the model, excluding tree saplings. To form a biplot, the plots A and B have to be projected over each other in equal scaling. Quantitative variables are indicated by arrows, class variables by triangles. Projecting the center of a species’ name on an arrow for a quantitative variable gives an approximation of the fitted value of the species’ optimum with respect to that variable, with scaling: origin = mean, head of the arrow = mean plus one standard deviation, mirror image of head with respect to origin = mean minus one standard deviation. Species whose names coincide with a triangle representing a class variable have their optimum in that class. Explanation of environmental variables: Lat, Lon: geographical latitude, longitude, Age: stand age, NO3(2000)EMEP: deposition of NO₃ in 2000 estimated by the EMEP model (Simpson et al., 2012), _min: mineral layer chemistry, _org: organic layer chemistry (see Appendix S5 for details), _Tr: tree species (QurM: Mediterranean oak; Qurp: temperate oak, Fags: Fagus sylvatica, Pins: Pinus sylvestris + P. nigra, Pice: Picea abies, conf: “other” coniferous, deci: “other” deciduous), _Cli: climate zones (SubAtl: subatlantic, AtlN: Atlantic North, AtlS: Atlantic South, Bor: Boreal). Number of plots: 477, number of species: 170. Explanation of abbreviated species names: Acer cam: Acer campestre, Acer pla: Acer platanoides, Alchevul: Alchemilla vulgaris, Alliapet: Alliaria petiolata, Anemonem: Anemone nemorosa, Arenamon: Arenaria montana, Aruncdio: Aruncus dioicus, Asarueur: Asarum europaeum, Astragly: Astragalus glycyphyllos, Athyrfil: Athyrium filix‐femina, Cardaama: Cardamine amara, Cardabul: Cardamine bulbifera, Cardafle: Cardamine flexuosa, Cardahep: Cardamine heptaphylla, Cardaimp: Cardamine impatiens, Cardapen: Cardamine pentaphyllos, Carpibet: Carpinus betulus, Castasat: Castanea sativa, Chrysalt: Chrysosplenium alternifolium, Clemavit: Clematis vitalba, Corylave: Corylus avellana, Cratalae: Crataegus laevigata, Cratamon: Crataegus monogyna, Dryopaff: Dryopteris affinis, Dryopcar: Dryopteris carthusiana, Dryopdil: Dryopteris dilatata, Dryopfil: Dryopteris filix‐mas, Equisarv: Equisetum arvense, Equispra: Equisetum pratense, Equissyl: Equisetum sylvaticum, Fallocon: Fallopia convolvulus, Fragaves: Fragaria vesca, Geranrob: Geranium robertianum, Geum urb: Geum urbanum, Hellefoe: Helleborus foetidus, Hepatnob: Hepatica nobilis, Ilex aqu: Ilex aquifolium, Impatnol: Impatiens noli‐tangere, Impatpar: Impatiens parviflora, Lathymon: Lathyrus montanus, Lathypra: Lathyrus pratensis, Lathyven: Lathyrus venetus, Lathyver: Lathyrus vernus, Malussyl: Malus sylvestris, Mercuper: Mercurialis perennis, Mespiger: Mespilus germanica, Oreoplim: Oreopteris limbosperma, Oxaliace: Oxalis acetosella, Phegocon: Phegopteris connectilis, Polypvul: Polypodium vulgare, Potenste: Potentilla sterilis, Prunuavi: Prunus avium, Prunupad: Prunus padus, Prunuspi: Prunus spinosa, Pteriaqu: Pteridium aquilinum, Pyruspyr: Pyrus pyraster, Querccer: Quercus cerris, Quercpyr: Quercus pyrenaica, Quercrub: Quercus rubra, Ranunaur: Ranunculus auricomus, Ranunfic: Ranunculus ficaria, Ribesalp: Ribes alpinum, Ribesspi: Ribes spicatum, Rosa arv: Rosa arvensis, Rosa can: Rosa canina, Rosa pen: Rosa pendulina, Rubuscae: Rubus caesius, Rubusfru: Rubus bifrons, Rubusida: Rubus idaeus, Rumexact: Rumex acetosella, Rumexals: Rumex alpestris, Rumexsan: Rumex sanguineus, Silendio: Silene dioica, Sorbuari: Sorbus aria, Sorbuauc: Sorbus aucuparia, Sorbudom: Sorbus domestica, Sorbutor: Sorbus torminalis, Stellhol: Stellaria holostea, Stellnem: Stellaria nemorum, Ulmusgla: Ulmus glabra, Urticdio: Urtica dioica, Viciacra: Vicia cracca, Viciasep: Vicia sepium