De Nederlandse akkerflora, een geschiedenis van toenemende rijkdom

The loss of diversity in the Dutch arable weed flora due to modern farming methods is considerable and the disappearance of a former rich flora embellishing the fields is much deplored. It led to the creation of arable flora reserves. But since when were crops accompanied by so many species? This contribution explores the history through time, from the earliest agriculture in the Netherlands, 5300 BC, to relatively modern times. The data originate from archaeological sources, as written texts are not suited to the purpose. The study focuses on the character species of the phyto-sociological class Stellarietea mediae Tüxen, Lohmeyer et Preising in Tüxen 1950. Such plants arrived in human settlements together with crops. Considered are charred remains. Plants may have arrived in archaeological sites in different ways, but remains affected by fire are related to human actions. The intentional burning of crop processing waste, or the store struck by lightning, have an anthropogenic background. Therefore, charred remains are the most reliable source. Forty species were suited to the purpose, because their remnants can be identified to species level. From 37 species archaeological remains were reported. For an additional check, waterlogged remains are considered to assess whether this approach does not end in an erroneous result. The black cells of Table 2 refer to charred conditions and the red cells to the earliest appearance in waterlogged records. Time is expressed in archaeological periods, ranging from Early Neolithic to Middle Ages and later (Table 1). The outcome of the check is that some species were present earlier, possibly even as field weeds, than deduced from their appearance as charred specimens. The result of the analysis is that the number of species increases in the course of the millennia, even when corrected for changes in harvesting methods. Over time harvesting with sickles changed into harvesting with scythes, involving a change in cutting height. Cutting relatively high on the stalk with a sickle results in leaving low-growing plants behind on the field. Table 3 presents the share of three height classes in the periods before and after the introduction of scythe-like implements in the second part of the Iron Age. The switch to another harvesting implement may have had an effect, but does not account for the appearance of the entire set of low-growing herbs. Therefore, the increase in species must be real. A striking observation is that the earliest Dutch crop weeds (Table 4) are also those that survive modern farming. These are, for instance, Cockspur grass (Echinochloa crus-galli (L.) P.Beauv.), Fat hen (Chenopodium album L.) and Chickweed (Stellaria media L.).