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Traditionally managed arable fields host a specialised flora adapted to regular disturbance through tillage. Agricultural intensification during the 20th century resulted in a pronounced biodiversity decline in European agroecosystems. Anthoceros agrestis and Phaeoceros carolinianus, both largely confined to cultivated land in Central Europe and the only representatives of hornworts in northern Switzerland, are examples of species that decreased in Central Europe during the last century. A repeated survey of 28 arable fields in the Swiss Plateau from 1989 to 1995 demonstrated that crop type and associated farming routines were critical in determining hornwort occurrences. During the 10 years following the completion of this survey, agri-environment schemes were introduced aiming at a more environmental-friendly agricultural production. We re-investigated the selected sites in 2005–2007 to examine whether these programmes favoured hornworts. We found a significant decrease of untilled autumn stubble-fields, which accounted for a decline of hornworts. High relative summer air humidity positively affected hornwort occurrence. Gametophytic populations of both taxa regenerated from the persistent diaspore bank after years of unfavourable conditions. To ensure the long-term persistence of hornworts in the Swiss Plateau, we recommend three alternative modifications of current Swiss agri-environment schemes to be implemented in cereal fields with known hornwort occurrences: (1) Tailored conservation headlands, (2) Autumn stubble-fields and (3) Field margin strips sown with arable flora but without crop plants. The proposed practices will promote other typically ephemeral arable bryophytes and seed plants and are likely to be advantageous also for other organisms, such as farmland birds.

A new, resource-efficient, herbarium-based method for estimating temporal frequency changes in species, especially of non-vascular plants and fungi, is presented. It is based on a reference data set for the temporal distribution of general collecting activity for the organism group and geographical area of interest. The reference data set includes the collecting year of 650–1000 randomly selected herbarium specimens. The technique relies on the assumption that the temporal distribution of herbarium collections reflects the collecting activity in a region. The temporal distribution of collections of example species is compared with that of the reference data set to correct for the collecting intensity. Thus, cases that are explained by changes in general collecting frequency can be separated from those where other causes are likely. Species of the latter category need to be examined individually in order to assess whether the actual causes for the detected frequency variations are due to environmental changes or other factors. The present method provides a tool to assess actual increases and decreases of moderately frequent to common taxa, to aid in tracing predicted or unpredicted changes in nature.

This study investigates the status of endangered bryophytes in Switzerland, as an example of the situation in large parts of Central Europe. The decline in species and populations is quantified by examination of 522 selected literature or herbarium records. They belong to taxa classified in the Red Data List of Swiss byrophytes as endangered (E) or rare (R). In a field survey, 31% of 195 populations proved to be still present. The proportion of confirmed populations differed widely between the three main natural regions of Switzerland—50 out of 109 within the Alps, six out of 39 in the Jura mountains and only four out of 46 in the densely populated lowland area of the Mittelland. Recommendations are made for practical conservation measures for each of the populations recently confirmed or discovered.

Maps of the distribution of Anthoceros punctatus L. var. cavernosus auct. and Phaeoceros laevis (L.) Prosk. ssp. carolinianus (Michx.) Prosk. in Switzerland are presented. They are based on herbarium specimens and field studies and distinguish between records before and since 1960. According to bibliographical data from the beginning of this century, both taxa were widespread throughout Central Europe, A. punctatus being more common than P. laevis. This view is not supported by herbarium collections. Detailed field research from 1981 to 1989 in the vicinity of Berne showed that the occurrence of hornworts depends largely on the type and treatment of cultivation. P. laevis seems to be more sensitive to changes in habitat conditions caused by modern agricultural practice (mechanical stress, increase in fertilizer input and use of pesticides) than A. punctatus. In conclusion, P. laevis is classified as endangered in Switzerland.