Year-to-year oscillations in demography of the strictly biennial Pedicularis sylvatica and effects of experimental disturbances

Published source details Petrů M. (2005) Year-to-year oscillations in demography of the strictly biennial Pedicularis sylvatica and effects of experimental disturbances. Plant Ecology, 181, 289-298.
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Summary

Traditionally, many semi-natural European grasslands have been mown and/or grazed, forming often nitrogen-limited and species-rich habitats. However, floristic quality of many has declined where traditional management is reduced or abandoned, or replaced by less sympathetic intensive management. Management may especially affect shorter-lived herbs. An example is the biennial, lousewort Pedicularis sylvatica, in the Czech Republic a herb of wet meadows where it is endangered. These meadows were traditionally mown or grazed for centuries, but in the last 30-40 years grazing has been widely abandoned, or former manual mowing has been mechanized and intensified. As a result, many lousewort populations have declined or become extinct. In this study the effect of disturbance regimes (clipping with small gap creation or mowing) vs. no management, on lousewort populations in two wet meadows in the southern Czech Republic were studied.

Study areas: Two Pedicularis populations in oligotrophic wet meadows were selected:

i) Javornik (49º07’N, 13º39’E) with a large population (several hundred to thousands of individuals). The meadow is mown once a year (June-July), with medium intensity late season sheep grazing (August–September). Vegetation height ranged from 5 to 20 cm.

ii) Ruda (49º08’N, 14º43’E), with a few hundreds individuals, mown twice a year, in June–July and August–September; 15–30 cm vegetation height before the first mowing.

Experimental design: In August 1997, 15, 0.25 m² plots (excluded from ongoing meadow management) were subject to the following treatments:

i) gap (mimicking grazing/trampling) - above ground vegetation cut to 5 cm height and removed from all 0.25 m² plots; belowground biomass and soil removed from five random circular gaps (5 cm diameter, 3 cm deep) within each plot;

ii) mowing - aboveground vegetation cut to 5 cm height and removed (mimicking traditional mowing);

iii) vegetation left unmown.

Each of the treatments had five replicates at each site, repeated in October 1998, 1999 and 2000.

Plant monitoring: In 1998-2001 counts of adults and seedlings were made in April/May, and juveniles in September/October in all plots. Disturbance effects were evaluated by:

i) monthly (April–September) seedling recruitment in the first cohort in 1998;

ii) survival of a cohort in the first year (within-year) and their survival from the first to the second year (between year) in 1998-2001.

The relationship between plant survival and bud size was investigated by measuring the diameter of the overwintering buds of 160 plants in September 2000, and recording their survival in April 2001.

The two Pedicularis populations both varied greatly over the four years in relative numbers of seedlings, juveniles and adults (partly a consequence of the biennial life history not related to the treatments). In 2000 the populations consisted of many seedlings and only few adults, in other years, there were low seedling and high adult numbers.

Average year-to-year seedling number varied hugely (3 to 103/0.25 m²). Inversely in the same years and plots, average adult numbers varied (0.7 to 12). Disturbance effects were only important for seedling recruitment in spring in all years. Mowing promoted initial recruitment, but these effects were not statistically significantly different from undisturbed plots. Within- and between-year survival fluctuated greatly among years but was not affected by disturbance regime. Between-year survival increased with increasing size of the overwintering bud and was higher in disturbance treatments.

However, disturbances promoted seedling recruitment, thus grazing or mowing regimes are recommended as they create regeneration opportunities and maintain habitat quality. Undoubtedly, longer term abandonment (i.e. no management) would lead to declines due to successional processes.

Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www.springerlink.com/content/y522l3775m455277/fulltext.pdf