| dc.description.abstracteng | Grazing is a well known management tool to increase and maintain species richness in grasslands. Generally, livestock grazing enhances sward structural heterogeneity due to dietary choices, trampling, nutrient cycling and propagule dispersal, resulting in a stable mosaic of grazed and avoided sward patches. This enables grassland species of different demands to establish in close proximity, hence increasing species diversity at the paddock scale. However, dealing with phytodiversity in grazed grassland, it is important to consider the type of grazing livestock. Grazer species are known to differ in their grazing behaviour, which can lead to differences in sward structure and vegetation characteristics.
In Middle and Western Europe, cattle are considered the most common grazer species in grasslands and several studies have targeted their (patch-) grazing effect for biodiversity benefits. For several decades, horses have played an increasing role as a grazer species in managed grasslands, too. However, the share of grasslands managed for horses and the horses’ effects on grassland vegetation remain unclear. Various studies address horses’ grazing effects in nature conservation projects, but only little systematic research has been conducted on their typical grazing effects on vegetation and diversity in agriculturally managed grasslands, so far. Given this background, the aim of this thesis was to estimate the share of grasslands managed in the framework of horse husbandry in Germany (Chapter 1) and to investigate the grazing effects of horses compared to those of cattle on aboveground vegetation characteristics (Chapter 2) as well as on soil seed banks (Chapter 3) in agriculturally managed grasslands.
So far, information on the share of grasslands managed with horses in Germany has been based on a rule-of-thumb estimate of approximately 10% of the grassland area. In Chapter 1, this estimate was refined following two approaches. First, in a theoretical approach, the forage demand of horse stock was calculated for each federal state in Germany. Given this information, the surface area required to meet that demand was estimated using the average productivity of grasslands in each federal state. Stepwise sensitivity analyses were performed for different demand and productivity scenarios. In a second approach, real-life data on grassland management of 700 horse keepers were collected via online survey. Joining these data with information on horse population and grassland productivity allowed a more realistic estimation. Our results point out that the grassland area managed for horses has been systematically underestimated, since we can conclude that 15-20% of the German grasslands are managed for horse husbandry. In general, stocking rates were relatively low and grassland area per farm quite small compared to typical dairy farming systems. Therefore, we conclude that horse husbandry can be considered to play an important role for maintening extensive and small scattered grasslands.
Grazer species have been observed to differ in their grazing effects on grassland vegetation. Still, surprisingly little systematic research has addressed the grazing effect of horses or compared it to that of cattle. To answer the questions whether grazer species and grazing management differ in their effects on managed grassland, an observational study (comprising Chapters 2 and 3) was conducted on farms in the Rhenish Uplands in Germany in the years 2012-2014. A stratified triplet design allowed us to directly compare grassland vegetation of paddocks grazed by cattle or horses and to distinguish effects of grazing system (cattle grazing, rotational grazing with horses, continuous grazing with horses) from those of site conditions and grassland management. Information on grassland management was obtained through standardized interviews.
In Chapter 2, aboveground vegetation was monitored on short, grazed and tall, avoided patches two times at a total of 156 paddocks arranged in 28 triplets. More species and more High-Nature-Value (HNV)-Indicator species were found on horse-grazed paddocks than on cattle-grazed paddocks in the aboveground vegetation. The vegetation composition was significantly different between continuous and rotational grazing of horses; the later being similar to that of paddocks grazed by cattle. Significant differences were found for Grime’s strategy types and grassland utilization values between continuously grazed horse paddocks and cattle-grazed paddocks. The floristic contrast between short and tall patches was shown to be stronger on horse grazed paddocks and to be the important driver of species richness on paddock scale.
For Chapter 3, a subset of 30 paddocks was chosen in 2012 to analyse the long-term effects of the different grazer species to be found in soil seed banks. Soil samples were collected in short and tall patches and seed bank analysis was performed via germination method. Since horses are known to expose swards to stronger disturbances due to their distinct grazing behaviour, we expected differences in seed bank characteristics between horse-grazed and cattle-grazed paddocks. Here, more species and more vital seeds of HNV Indicator species emerged from samples of the horse-grazed paddocks compared to the cattle-grazed paddocks. However, we found no differences between grazing systems in the seed bank’s functional traits, composition and seed bank longevity.
In conclusion, horses play an important role as grazer species in managed grasslands in Germany. They do not merely claim a significant share of agricultural surface area but are of high potential for biodiversity in agricultural landscapes. | de |