Do hornworts in Switzerland benefit from a more environmentally-friendly arable farming during the last decade?
Survey of hornwort populations in selected arable fields in the Swiss Plateau
Irene Bisang¹, Luc Lienhard² und Ariel Bergamini³
download the complete report here (in German only)
Typical arable landscape in the Swiss Plateau,
the most common habitat
for hornworts in Central Europe
Background
Hornworts, a systematically isolated lineage of bryophytes comprising
c. 100 to 150 species, belong to the most ancient land plants (Goffinet
2000). They exhibit their highest diversity in tropical regions. Only
a few species are part of the European flora, of which three (Anthoceros
punctatus, A.
agrestis, Phaeoceros carolinianus) occur also
in Switzerland (see http://www.nism.unizh.ch/map/map.htm for their distribution
in Switzerland). The Swiss localities of A. punctatus are confined to
Ticino south of the Alps (Bisang & Urmi 2006).
In the northern part of the country, A. agrestis
(Fig.) and the more rare P. carolinianus
(Fig.) grow on sub-neutral, loamy or sandy soils on open ground, mainly
in arable environments, and more rarely along paths and ditches. Hornworts
are usually annual in Northern Switzerland and other parts of Central
Europe due to climatic reasons. They complete their life cycles from spore
germination to spore maturation within a few months during summer and
autumn (Bisang 1995, 2004). In contrast to the ephemeral gametophytic
populations, spores can survive for several years in the diaspore bank
(Bisang 1996). During the 20th century populations of the two species,
in particular of P. carolinianus¸
declined in different European regions (Bisang 1992, Hofmann et al. 2007).
The latter is considered "endangered" in the in the Red List
of Swiss bryophytes (Schnyder N et al. 2004), and likewise included in
Red Data Books of several European countries.
Initial study and questions addressed
The repeated survey of 28 arable fields in the Swiss Plateau from 1989
to 1995 revealed that the type of crop and associated arable farming practices
were critical in determining hornwort occurrences (Bisang 1998, 1999).
Gametophytic populations developed best in stubble-fields that were abandoned
or only extensively managed after harvest, and preferably lacked cover-crop.
)
Anthoceros agrestis
(diameter of the plant in the foreground c. 1 cm)
From 2005 to 2007, we re-investigated the selected fields. We asked if measures towards a more environmentally-friendly agriculture since the completion of the previous investigation, and the onset of agri-environment schemes (1999) and linked changes in soil conservation measures favour the occurrence and performance of hornwort populations, or whether the latter need to be promoted more specifically. In addition, we were interested if the study fields harboured a diaspore bank from which gametophytic populations may regenerate if cultivation conditions allow.
Results and Recommendations
Our results show that the occurrences of the two
species have tendentially decreased at the study sites during the passed
10 to 13 years. The decline in our data is explained by a reduction of
the number of unmanaged stubble-fields present in late summer and autumn.
Soil conservation measures, mandatory since 2005, require that all fields
that are harvested before 31 August are either cultivated with an autumn
crop, or latest by 15 September until 15 November by intercropping (Bundesrat
2007). The fraction of fields among our study sites used as pasture, on
the other hand, has increased. Animal Welfare directives raised the demand
for grazing land during the past decade (Anonymous 2007). These changes
are reflected at our study sites and lead to fewer optimal habitats available
for hornworts in the agricultural landscape of the Swiss Plateau.
)
Phaeoceros carolinianus
with yellow ripe spores in the capsules
(thallus diameter c. 1.5 cm)
The cool and wet summer 2007 appeared to have a beneficial
effect on hornwort occurrences. Hornwort spores survived unfavourable
cultivation conditions at least two (P. carolinianus),
or three years, respectively (A. agrestis),
in the diaspore bank in the soil. Suitable cultivation, however, was more
critical than the diaspore reservoir for the development of gametophytic
population at the surface.
If hornworts should be maintained in Swiss agro-ecosystems in the long-term,
in particular the red-listed P. carolinianus,
specific measures are required. Since spores are long-lived, changes in
the current arable management practices at a relatively small scale are
expected to be sufficient to promote their population development. We
propose the following measures:
-> Arable field margins ("Ackerschonstreifen") remain unmanaged
and without intercropping until late autumn
-> Selected fields with known occurrences of hornworts are ploughed
only in late autumn
-> Arable field margins cultivated with annual herbs, s. c. "Segetalflorastreifen".
There is evidence that such margins have a positive effect on annual species
of the arable phanerogam flora, and we expect that the ephemeral hornwort
populations will benefit from them as well.
References see downloadable report
We thank the Federal Office for the Environment (FOEN)
for financial support, MeteoSchweiz for providing weather data, and Ferdi
Bisang, Lisa Eggenschwiler (ART), Peter Litfors and Ingela Lundwall (Universität
Stockholm) and Edi Urmi (Universität Zürich) for information
and various input.
¹Naturhistoriska riksmuseet,
Kryptogambotanik, Box 50007, SE-104 05 Stockholm, Sverige, irene.bisang"at"nrm.se;
pers.
homepage, more
about hornworts (in swedish)
²Waldrain 16, 2503 Biel, luc.lienhard"at"bluewin.ch
³ WSL, Biodiversity & Conservation Biology, Zürcherstrasse 111, 8903 Birmensdorf, ariel.bergamini"at"wsl.ch; pers. homepage
Photos: Irene Bisang
July 2008
