Counteracting Green Alder Shrub Expansion by Low-Input Grazing

Counteracting Green Alder Shrub Expansion by Low-Input Grazing

In the past decades, the decline of traditional agriculture has caused an abandonment of marginal pastures in many mountain areas of Europe. In the Swiss Alps, green alder (Alnus viridis) is the most abundant successional shrub. A survey of 24 pasture-shrub gradients showed that the encroachment by green alder, in contrast to other shrubs, is associated with a substantial decline in plant species richness. The understorey of alder is primarily populated by very few, broad-leaved herbaceous species benefitting from the atmospheric nitrogen fixed by actinomycetes in symbiosis with green alder. However, the understory vegetation also provides an underestimated forage, rich in protein and comparable in productivity and digestibility to nearby open pastures. A two-year grazing experiment with cattle (Dexter), sheep (local Engadine sheep) and mixed-breed goats in the Eastern Swiss Alps demonstrated that robust breeds were able to exploit these resources as they readily penetrated the thickets. The Engadine sheep and the goats consumed green alder bark and thus actively counteracted shrub encroachment. Dexter cattle did not forage on alder bark but on leaves and opened the thickets by their movement through them. Since goats preferred other woody species to green alder and depleted them before the alder, they may impair the regeneration of late-successional forest. Dexter heifers and Engadine lambs performed equally well on pastures with high shrub cover and on open pastures in terms of average daily weight gain, carcass and meat quality. This was facilitated by the comparatively low productivity of these breeds. In this way, low-input grazing systems utilizing adapted breeds, especially sheep, can add to conservation goals and sustain a viable meat production in marginal areas.