Use of Molasses-Based Blocks to Modify Grazing Patterns and Increase Highland Cattle Impacts on Alnus viridis-Encroached Pastures

Abstract

Alnus viridis is a pioneer species that has expanded in Central Europe in the last decades, causing a series of negative agro-environmental impacts. Robust livestock grazing could be used as a targeted tool to reduce its encroachment, but more information is needed to find the best approach to achieve this goal. In this study, we assessed the potential of molasses-based blocks (MB) to lure Highland cattle into A. viridis-encroached areas and monitored impacts on the vegetation after grazing. In 2019 and 2020, two Highland cattle herds equipped with GPS collars were placed in three paddocks in the Swiss and Italian Alps, differing in the degree of A. viridis encroachment. In 2020, MB were added to highly encroached areas within each paddock to attract the herds to feed on A. viridis. Botanical surveys were carried out before and after grazing, around MB and control areas. Highland cattle grazed significantly more around MB (up to 50 m from the MB) compared to the previous year (i.e., same area without MB) and compared to control areas. The increased targeted grazing around MB led to a significant decrease in herbaceous cover and an increase in bare soil compared to control areas. Livestock grazing and trampling significantly reduced the cover of ferns, tall herbs, medium and small herbs, and woody species around MB compared to control areas. A. viridis leaves and branches were significantly removed and damaged up to 10 m from the MB, due to the more intense livestock grazing. Such results highlight the potential of this management regime to effectively reduce A. viridis encroachment in montane grasslands.

Nitrogen translocation by Highland cattle grazing in Alnus viridis-encroached pastures

“…To avoid such negative impacts and preserve nutrient capital, it is advised to adopt a rotational management, as it allows more homogeneous utilization of the pasture compared to free-grazing systems. Previous studies have shown that the presence of fences, shaded zones, attractive points (such as salty or molasses blocks), and a water trough may also impact the spatial distribution of dung and urine pats (Jewell et al 2007 ; Buttler et al 2008 ; Auerswald et al 2010 ; Pittarello et al 2016 ; Carnevalli et al 2019 ; Svensk et al 2022 ). Thus, these features should be included in the management of cattle grazing to better redistribute nutrients across the pastures.…”

“…A water trough was installed in paddocks 2, 3 and 4, while natural streams were present in paddock 1 for the entire grazing period. As described in Svensk et al ( 2022 ), in the second year of the project (2020), five molasses-based blocks were installed in small highly encroached areas of paddocks 1, 2, and 3, as part of another experiment set, to attract Highland herds into these areas. In each herd and during both years, six to ten cows were equipped with GPS collars (Followit AB ©, Tellus GPS System collars, Sweden) that recorded their position every ten minutes during the whole grazing period, with an accuracy of two to five meters.…”

“…Three samples of A. viridis leaves (1750 g of fresh leaves each) were collected in both sites of Bovonne and Val Vogna, in June, July and August of both years to represent the changes in leaf N content during the summer season. For each sample, A. viridis leaves (including petioles) were hand-harvested all around the canopy of five different trees up at a maximum above-ground height of 1.80 m to simulate the potential grazing by Highland cattle (Svensk et al 2022 ). In each paddock, 12 to 66 vegetation patches of 0.47 ± 0.05 ha (0.01 ha to 1.7 ha) were defined prior to Highland cattle grazing, representing areas with homogeneous botanical composition and vegetation structure.…”

“…Previous studies have shown that robust cattle breeds, such as Highland cattle, are able to feed on shrub species foliage with low forage quality (Pauler et al 2020b ; Svensk et al 2021 ). The exploitation of woody species-encroached areas by Highland cattle can help controlling shrub and tree cover over time, by combining the effect of direct foliage consumption, trampling, and the mechanical breaking of branches, thanks to their long horns, and could potentially lead to the slow opening of the canopy, allowing the recolonization of typical pasture species in the long-term (Probo et al 2016 ; Pauler et al 2019 , 2020a ; Svensk et al 2022 ).…”

Foraging behavior of Highland cattle in silvopastoral systems in the Alps

“…For instance, Alberes cattle can feed year-round with a predominantly woody diet in Mediterranean forests of the Pyrenees (Bartolomé et al 2011 ). In the Alps, Dexter (Pauler et al 2022b ) and Highland (Pauler et al 2020 ; Svensk et al 2022 ) cattle are acknowledged to feed on woody species as well. The ability of certain livestock species and breeds to consume woody plants is linked with microbial populations in their rumen able to detoxify secondary metabolites and degrade lignin.…”