Context. Climate and economic changes promote the encroachment of woody plants on marginal mountain pastures. In the Alps, the main woody invader is the nitrogen-fixing shrub Alnus viridis (green alder). Robust breeds of different ruminant species may perform well on these shrub-encroached pastures. Aims. To assess the effects of A. viridis encroachment levels of mountain pastures on the growth performance and carcass and meat characteristics of cattle and sheep. Methods. For 8–9 weeks, 22 15-month-old growing Dexter cattle and 20 7-month-old weaned Engadine sheep were grazed rotationally on pastures in a subalpine zone with four different levels of A. viridis encroachment (average: 0.8%, 28.7%, 50.3% and 67.8%). Following slaughter, the assessed carcass and meat characteristics (longissimus thoracis and biceps femoris) included physicochemical meat quality, muscle fibre typing, fatty acid profiling (intramuscular and perirenal fat) and the sensory properties of patties. Key results. The shrub encroachment levels had only minor effects on the animals. Interactions with the animal species influenced some sensory and fatty acid characteristics. The average daily gains were 201 g in the Dexter cattle and 104 g in the Engadine sheep. Both species achieved satisfactory carcass and meat quality and favourably low n-6/n-3 fatty acid ratios (0.63 and 0.68 in the intramuscular fat of the cattle and sheep, respectively). The meat from the Dexter cattle had a slightly higher cooking loss and shear force and a slightly lower proportion of fatty acids relevant to human health. Flavour appreciation was in favour of the burgers prepared from the beef. Conclusions. Both robust breeds were suitable for producing meat on extensive pastures with A. viridis encroachment of up to 70%. Based on indirect evidence, it seems that neither species consumed significant quantities of leaves or bark from the trees. Implications. Our study provides detailed information on rare robust breeds of two animal species in the context of meat production according to customer preferences. To better explain the differences between the two animal species, particularly in terms of fatty acid profiles, the role of the A. viridis understory needs to be clarified.