Is Campanula glomerata threatened by competition from expanding grasses? Results from a 5-year pot-experiment

Abstract

The disappearance of low-intensity types of agricultural land use such as mowing and grazing is a global phenomenon which leads to changes in species composition and interactions in plant communities. In central Germany, formerly species-rich, semi-natural dry grasslands have been converted into species-poor communities dominated by Festuca rupicola or Poa angustifolia. As a consequence, several forbs have become endangered, and biodiversity has decreased. In a 5-year competition experiment (replacement design; pots were placed outdoors at Halle Botanical Garden), we evaluated the performance of plant-plant interactions between the rare forb Campanula glomerata, F. rupicola and P. angustifolia, respectively. The response of C. glomerata to the presence of the two grass species were measured by stem length, number of flowers and above-ground biomass annually harvested. We did not find significant differences in C. glomerata stem lengths between years and treatments, but flower production, which was highest in the first year, strongly decreased in the subsequent years. Moreover, flower production was lower in combination with P. angustifolia than with F. rupicola. Biomass production showed significant differences between years, but not between treatments. The positive and negative interactions between C. glomerata and the two grass species was estimated by calculating Relative Neighbour Effect Index (RNE). In combination with F. rupicola, interactions switched between facilitation and competition from year to year. In the presence of P. angustifolia, competitive effects on C. glomerata were highest in the second year, but declined from year to year. Curiously, there were no significant correlations between positive and negative interactions with climatic conditions (annual temperature, precipitation and relative air humidity). Our results showed that the response of the rare forb C. glomerata varies with neighbour species, and that fecundity is more prominently affected by competition than stem height or biomass. Our data indicate that biomass removal by traditional land use methods would facilitate the restoration of species-rich dry grassland communities.

Does land use change affect the interactions between two dry grassland species?

“…Similar results were found in competition experiments between the grass species F. rupicola and the rare and low-growing Alyssum montanum (Partzsch et al, 2011), and with the endangered and declining dry grassland species Campanula glomerata (Bachmann et al, 2005;Partzsch and Bachmann, 2010). These results support the assertion of Aarssen and Keogh (2002), and of Freckleton et al (2009) who argue that most studies of plant competition have the risk being incorrect in that they tend to only focus on the measurement of growth responses to competition and ignore fecundity.…”

Does competition with wind‐pollinated species alter Echium plantagineum's attractiveness to a common pollinator Bombus terrestris?

“…Working with species mixtures of insect-pollinated plants, Baude et al (2011) found that the presence of a strong plant competitor led to a decrease in the total amount of sugar allocated to nectar in the less competitive one, probably through soil resource depletion. Likewise, the presence of a neighbouring wind-pollinated competitor reduced the flower production of an insect-pollinated one, C. glomerata (Partzsch & Bachmann, 2011), and Flacher et al (2015) found that competition induced by wind-pollinated plants led to a decrease in floral display size and flower size, but also total flower production and total sugar allocated to nectar in two annual insect-pollinated species. In this last experiment, the stronger the competitor, the stronger the effect on attractiveness traits.…”

“…competition for abiotic resources between plants), could thus play a key role in plant-pollinator networks. However, to our knowledge, while the effect of plant competition for abiotic resources on floral traits has been studied (Baude et al, 2011;Partzsch & Bachmann, 2011;Flacher et al, 2015), the indirect role of such competition on pollinator behaviour, through modifications of floral traits involved in plant attractiveness, has never been investigated. In addition, wind-pollinated species are almost never taken into account in plant-pollinator studies.…”

“…In addition, wind-pollinated species are almost never taken into account in plant-pollinator studies. However, they can affect floral traits in insect-pollinated plants through competitive interactions (Partzsch & Bachmann, 2011;Flacher et al, 2015), and they may influence the attractiveness of an insect-pollinated focal plant through competition for abiotic resources while insect-pollinated competitors would influence the attractiveness of the focal plant through an additional process, competition for pollinators. In this context, to better understand pollinators' response to plant competition for abiotic resources, we set up a pot experiment in which a common pollinator, Bombus terrestris, could visit focal insect-pollinated plants (Echium plantagineum).…”

The effect of management on productivity, litter accumulation and seedling recruitment in a Carpathian mountain grassland

“…Smaller, less competitive species usually benefit from mowing because they are harmed less by cutting and they are often able to recover quickly because of a release from competition pressure. Removal of biomass, which usually follows mowing, also prevents accumulation of dead biomass (Ruprecht et al 2010;Partzsch and Bachmann 2011).…”