Bosrelikten in de Gelderse Vallei

The starting point for this publication was the observation that in the „Gelderse Vallei” eastward of Amersfoort Anemone nemorosa is a very common plant, whilst southward and northward of this town the anemones are totally lacking even on those soils which are obvious of nearly the same nature. A detailed comparison of the flora of both regions showed that a number of plants: Adoxa Moschatellina, Asperula odorata, Chrysosplenium alternifolium, Circaea lutetiana, Galeobdolon luteum, Geum rivale, Listera ovata, Oxalis acetosella. Polygonum Bistorta, Primula elatior, Viola silvestris (Riviniana), which are also lacking southward and northward of Amersfoort, are still to be found eastward of it, or have only vanished recently. Now all these plants are characteristic of those deciduous woods, which grow on a more or less moist soil and the above mentioned facts point towards the conclusion, that in past centuries the region that is at present characterised by the presence of the anemones, formed one complex of such deciduous woods. The study of the historical data confirmed: as late as the 14th century the Sylva Renhem extended over all these regions, than began the clearing of the forest, which started the process whose final stage was a flat moor covered with heather where only dispersed woodlets on the higher parts and on the lower ones meadows were to be found. By means of a sociological survey of these woodlets I tried to get a more detailed notion of this forest. A great difficulty is, that in the Netherlands undisturbed climaxstages of the forest associations concerned, are no longer to be found, and in consequence when we want to consider other forest associations for the sake of comparison it only remains for us to study those of Northwestern Germany, which have developed in somewhat different edaphic and climatic circumstances. This drawback is the more important because as was shown by quotations from Tüxen’s publication „Ueber einige nordwestdeutsche Waldassoziationen in regionaler Verbreitung” a hard and fast separation of the Querceto-carpinetum roboretosum and alnetosum from the Querceto-betuletum on the hand and the Alnetum glutinosae typicum on the other will cause difficulties. A detailed sociological survey of small copses in the „Gelderse Vallei” near Amersfoort showed, that in this case such mixtures of the aforesaid plant communities occurred; the height of the waterlevel in the soil and the pH appeared to be the determining factors. Adoxa Moschatellina, Anemone nemorosa, Galeobdolon luteum, Hedera Helix, Moehringia trinervia, Rubus Idaeus, Rumex sanguineus, Stellaria Holostea, Viola silvestris, all characteristic Fagion-plants were sufficient evidence that the Stellaria Holostea subassociation or Querceto-carpinetum roboretosum was present. Surveys taken in different parts of the „Gelderse Vallei” yielded the same result. A difference from the surveys made bij Tüxen in Northwestern Germany lies however in the absence of the hornbeam, Carpinus Betulus, a tree which has with the exception of some planted specimen been totally lacking for many years and has perhaps in historical times never grown wild here; consequently a variant of the above mentioned subassociation seems to be present. This Querceto-carpinetum roboretosum is found on a soil which geologically is described as sandy low terrace. It was evident that Anemone nemorosa which mostly characterises the somewhat higher grounds occupied by the Querceto-carpinetum roboretosum is in the regions eastward of Amersfoort nearly as common on some lower grounds with a higher waterlevel and stagnant water and Vithin a plant community to which among others the Stachys silvatica subassociation, the Querceto-carpinetum alnetosum bears the closest resemblance. The tree layer is composed of alders; among the herbs Anemone nemorosa predominates. This Querceto-carpinetum alnetosum is only to be found on a soil which geologically is described as an upland moor ¹) of which the top-layer is said to have been taken away. In those parts of the „Gelserse Vallei” which in former times were covered with woods and where resp. Anemone nemorosa and Stellaria Holostea are present now, these woods belonged to the Querceto-carpinetum roboretosum or alnetosum, whilst in those regions where both plants are the lacking the extinct woods belonged to the Quercetobetuletum or to the true Alnetum. The forest which till 1870 existed between Apeldoorn and Zutphen in Guelderland „het Beekbergerwoud” was also used for a sociological comparison. J. Wttewaal has a hundred years ago given us a brief description of this forest, which in a measure could be used for sociological work. Although the edaphic condition pointed to an Alnetum glutinosae and the tree layer was almost wholly composed of very old alders, the herbaceous layer contained besides many characteristic plants of the Alnion, a great number of species, which are characteristic species of the Fagion especially of the Querceto-carpinetum alnetosum. In Wttewaals list are for instance mentioned the characteristic Fagion species: Circaea lutetiana, Galeobdolon luteum, Hedera Helix, Impatiens Noli tangere, Luzula multiflorum, Lysimachia nemorum, Milium effusum, Paris quadrifolia, Phyteuma nigrum, Poa nemoralis. Primula elatior. Viburnum Opulus, which make it very probable that this wood showed a great resemblance to the Querceto-carpinetum alnetosum associations described in the neighbourhood of Amersfoort. It is not impossible that this too should be only a fragment of an association and not a climax stage, although we can say that if anywhere in our country, then certainly here the opportunity of reaching the climax stage was given. The observations in these forestrelics point towards the conclusion that edaphic factors e.g. the height of the water level in the soil, the pH etc., determine the prevailing of one of these woodassociations. True species in a sociological sense are those which in regard of these factors are able to maintain themselves in the struggle for existence only between the limits which are characteristic for these associations. It may however be possible that this holds good for one climate, but not for a somewhat different one and so the degree of fidelity to a certain association may not be the same everywhere. Although the notion of plant communities forms the foundation of sociology, it should be borne in mind that the line of division between one community and another is not a natural but an artificial and arbitrary one.