Zoochory on/off: A field experiment and our new paper in Journal of Vegetation Science

We have recently published a paper about the relative importance of zoochory compared to other effects of grazing livestock.

The citation of the paper is

Kiss, R., Deák, B., Tóthmérész, B., Miglécz, T., Tóth, K., Török, P., Lukács, K., Godó, L., Körmöczi, Z., Radócz, S., Borza, S., Kelemen, A., Sonkoly, J., Kirmer, A., Tischew, S., Valkó, O. (2021): Zoochory on and off: A field experiment for trait-based analysis of establishment success of grassland species. Journal of Vegetation Science 32: e13051. doi: 10.1111/JVS.13051 [IF2020: 2.685]

The paper is open access and can be downloaded from here. 

Cattle are very important drivers of vegetation dynamics.

Grazing livestock play a central role in the vegetation dynamics of grasslands. They alter microsite availability by grazing, trampling and manuring and they are important zoochorous vectors for the propagules of many plant species. These complex effects of livestock on the vegetation are seldom studied separately, so our knowledge on the relative importance of the processes is still incomplete.

In our controlled field experiment, our aim was to study the process of zoochorous dispersal separately from all other potential effects of livestock. You can see below our experimental design: we introduced propagules of 35 grassland species into source plots located in six species-poor restored grasslands (where the sown species were absent). One of the source plots were fenced, while the other one and the whole are of the pastures was grazed by cattle. We monitored the dispersal of the sown species from the source plots to the surroundings for three years in a total of 960 plots. From the fenced plots, we could exclude the possibility that the propagules of sown species can be dispersed by cattle ('Zoochory Off' setting), while from the grazed source plots, the propagules could be dispersed by the livestock ('Zoochory On' setting). All the other effects of livestock (trampling, grazing, manuring) were rather uniformly distributed accross the pasture, so we could assume that the presence or abscence of a sown species in the dispersal plots were most probably driven by the type of the source plot, i.e. whether zoochory was on or off.

Our sampling design showing the grazed areas (the whole pasture + the grazed source plot), the fenced source plot and the dispersal plots organized in transects.

Species- and flower-rich source plot located in the species-poor restored grassland.

Although grazing reduced the cover and flowering success of sown species in the source plots, the number of successful establishment events was higher in dispersal plots next to grazed source plots. The sown species were the most abundant in plots adjacent to source plots, but occurred in all monitored distances. Zoochory favoured perennial plants with high specific leaf area, low leaf dry matter content, short stature, light seeds, early flowering period, high clonal index and anemochory index.

The differences in trait composition of the vegetation under the ‘zoochory on’ and ’zoochory off’ settings highlight the importance of grazing in our study system. We showed that depending on the presence or absence of zoochory plant species with contrasting traits can colonize the surrounding homogeneous matrix. Communities that developed under zoochory were characterized by traits that are adaptive under grazed conditions, while communities that could not communicate with the source plots via zoochory were functionally different. This suggests a strong link of traits favouring zoochory and those supporting the survival of plants under grazed conditions.

In grazing-adapted ecosystems, fencing source populations of target species does not always seem to be a good option. We found that fencing increased the cover and flowering success of the sown species in the short run, but it significantly decreased their chance to colonize the surrounding area. Another negative effect of fencing in the long run is the accumulation of litter and related decrease in species richness. These problems might be overcome by targeted management of the fenced patches by mowing or by using mobile fences that can be temporarily removed, however, these practices should be tested in future studies. We suggest that in conservation and restoration projects fencing should be applied when the priority is the protection of a source population, however, when the goal is to facilitate the spread of target species, fencing is probably not a favourable option.

Abstract

Aims: We tested the establishment success of grassland species in the presence or absence of zoochory by livestock and identified the traits associated with successful establishment.

Location: Hortobágy National Park, Hungary.

Methods: In six restored species-poor grasslands we established two species-rich 16 m2-sized source plots per site in 2013. One source plot was managed by extensive cattle grazing (’zoochory on’), the other one was fenced and protected from grazers (’zoochory off’). We monitored the vegetation development in the source plots (2014-2018), and the establishment success of sown species (2016-2018) in adjacent dispersal plots in four, 20-m-long strips per source plot; in a total of 960 dispersal plots. We calculated community weighted means of thirteen plant traits related to regeneration and competitive ability. The effect of grazing, year, distance from source plots, grazing:year and grazing:distance interactions on population and trait-dynamics in the source and dispersal plots were analysed with generalized linear mixed-effect models.

Results: Although grazing reduced the cover and flowering success of sown species in the source plots, the number of successful establishment events was higher in dispersal plots next to grazed source plots. The sown species were the most abundant in plots adjacent to source plots, but occurred in all monitored distances. Zoochory favoured perennial plants with high SLA, low LDMC, short stature, light seeds, early flowering period, high clonal index and anemochory index.

Conclusions: We showed that species that can colonize the matrix with and without zoochory have contrasting trait syndromes. In grazing-adapted ecosystems, fencing source populations of target species does not always seem to be a good option. It was a good tool for increasing the cover and flowering success of the sown species in the short run, but it significantly decreased their chance to colonize the surrounding area in the long run.