Effects of undergrowth removal and edge proximity on ground beetles and vascular plants in urban boreal forests

Urban forests are regularly managed for human safety and esthetic reasons, but they are crucial habitat for many species. Removals of undergrowth occur commonly in these forests, yet the ecological consequences of these operations are poorly understood. We sampled ground beetles (Coleoptera, Carabidae) and vascular plants along 20-m edge gradients in Finnish urban forests, in five stands treated 0.5–2.5 years earlier with undergrowth removal and in five untreated stands. We hypothesized that undergrowth removal and edge proximity would benefit opportunistic and open-habitat species, whereas shady-habitat species would be affected negatively. (1) Regarding carabids, diversity and evenness indices, open-habitat species and Carabus nemoralis responded positively, and forest species, Leistus terminatus and Pterostichus oblongopunctatus responded negatively, to the undergrowth removal. Regarding plants, generalists, Maianthemum bifolium, Rubus saxatilis and Sorbus aucuparia responded positively, and forest species, Geranium sylvaticum, Oxalis acetocella and Vaccinium myrtillus responded negatively, to the undergrowth removal. (2) Edge proximity had little effect on both plants and carabids. However, open-habitat carabids were less abundant and less speciose, and the plants Oxalis acetocella, Trientalis europaea and Rubus saxatilis had higher cover, 10–20 m from than right at the edge. (3) Plant (but not carabid) community responded to the undergrowth removal but not to the edge proximity. When managing urban forests, we recommend an avoidance of undergrowth removals at sites that host rare or threatened forest-associated flora and fauna.