Effects of land use practices on arable bryopytes in the Swiss lowlands - a 30-year monitoring study using hornworts a model organisms

Irene Bisang¹, Luc Lienhard² und Ariel Bergamini³

Background and previous results

In the Swiss lowlands north of the Alps, the two hornworts Phaeoceros carolinianus and Anthoceros agrestis (Figs 1, 2) are largely confined to arable environments, where they are a characteristic element of the traditional agricultural landscape. They are representatives of the systematically isolated hornwort lineage that belongs to the most ancient land plants, comprises globally 200 to 250 species and exhibits its highest diversity in tropical regions (Villarreal et al., 2010). Eight species are known to occur in Europe (Hodgetts, 2014), and three in Switzerland: The two species mentioned above and a third species, A. punctatus, found at localities south of the Alps (see “Online-Atlas der Schweizer Moose” for the distribution of hornworts in Switzerland).

Fig. 1 Anthoceros agrestis, Phaeoceros carolinianus and Riccia sorocarpa at the margin of an arable field.

Hornworts are frost-sensitive and their gametophytic populations are therefore generally short-lived in Central Europe. However, spores can survive below the surface in the spore bank for several years (Bisang 1996, Bisang et al., 2009). We have shown that arable farming practices are critical in determining hornwort occurrences (Bisang, 1998). Gametophytic populations develop best in autumn stubble-fields that are left untreated after harvest, and preferably lack cover-crops (Fig. 3). During recent years, gametophytic hornwort populations have occasionally been observed in spring, after having survived mild winters.

Phaeoceros carolinianus and A. agrestis are highly significant for the implementation of the Swiss federal conservation goals in agricultural areas. Both species are to be promoted by specific measures in the realisation of a sustainable agricultural production ("Umweltziele Landwirtschaft"; BAFU & BLW, 2008; BAFU, 2013a). During the 20th century, hornwort populations, especially those of P. carolinianus (Fig. 2), have decreased in many parts of Europe as a result of the enormous intensification of agriculture (Bisang, 1992; Hodgetts, 2014). Phaeoceros carolinianus is thus classified as “Endangered” (EN) in the Swiss Red List of Bryophytes (Schnyder et al., 2004), and it is also protected in Switzerland (NHV, 2015).

Fig. 2. Phaeoceros carolinianus with young sporophytes and antheridial chambers.

Since 1989, we monitor selected arable fields in the Swiss lowlands for hornwort occurrences and –performance at regular intervals of 10 years. At the latest monitoring 2005-2007, we revealed a further decline of hornworts, which was mainly explained by a decrease in unmanaged stubble-fields in late summer and autumn (Bisang et al., 2009). This in turn was due to modified soil conservation measures in 2005, as part of the Swiss agri-environmental schemes (AES), which require cultivation of harvested fields before mid-September to prevent nitrate leaching. Hornwort populations fluctuate strongly among years, which partly depends on weather conditions: High humidity during the summer promotes hornwort development under suitable management. Elements of current AES, finally, such as rotational fallows or flower strips, may locally benefit hornwort occurrences (Studer, 2016, Valentini, 2014).

Current questions addressed

We currently survey the selected populations for the third time to assess whether the observed negative trend continues under the current AES. The AES undergo regular modifications in order to respond to evaluations of their effects on biodiversity and sustainable production (BAFU & BLW, 2016; Bundesrat, 2017). We will examine potential changes of hornwort populations and their habitats in the Swiss lowlands during the past almost 30 years (first observations 1989, last survey planned 2018) to uncover the relative role of arable management, specific AES measures and weather conditions on the performance of these populations. We will propose management practices to promote hornwort populations and thus contribute to the Species Action Plans in the agricultural landscape (BAFU, 2013b). They will be aligned with the actions implemented in a project for the preservation of arable weeds („Ressourcen-Projektes zur Erhaltung und Förderung gefährdeter Schweizer Ackerbegleitflora“). These measures will thus also benefit other typically ephemeral arable mosses, as well as other organisms of arable land.

Fig. 3. Cereal stubble fields which last at least until late October are favourite habitats for hornworts.

Cited references download here

We thank the Federal Office for the Environment (FOEN) for financial support, and Ferdi Bisang and Norbert Schnyder for information and valuable discussions.

¹Naturhistoriska riksmuseet, Box 50007, SE-104 05 Stockholm, Sverige, irene.bisang"at"nrm.se;

² Natur&Geschichte, Waldrain 16, 2503 Biel, luc.lienhard“at“bluewin.ch;

³ WSL, Biodiversity & Conservation Biology, Zürcherstrasse 111, 8903 Birmensdorf, ariel.bergamini"at"wsl.ch.

Photos: Irene Bisang; Lars Hedenäs (Phaeoceros carolinianus)
April 2017

© Bryolich17.06.2017 - Member of the Swiss Academy of Sciences SCNAT