The implications of red deer grazing to ground vegetation and invertebrate communities of Scottish native pinewoods.

Abstract

1. The effect of grazing by red deer was assessed in eight native pinewoods in the Scottish Highlands in 1991 and 1992 by comparing ground vegetation and invertebrate communities in grazed forest with adjacent ungrazed deer exclosures.
2. Grazing was associated with less heather cover and more grass. Bilberry cover remained the same, but grazed bilberry was half the height of ungrazed bilberry and had almost twice as many of its apical tips removed by grazing.
3. Lepidopterous larvae formed 60% of all invertebrates. Four species comprised 96% of larvae, those of Hydriomena furcata were most numerous (39%).
4. Forests in the West (Argyll) had, on average, more than seven times fewer lepidopterous larvae than those in the East (Deeside). Rates of decrease towards the West differed between species.
5. On average, numbers of lepidopterous larvae in grazing exclosures were almost 4-fold higher, Hymenoptera, chiefly ants Formica rufa 3-fold higher, and Coleoptera, Aranaea, Diptera and Plecoptera all 2-fold higher than in grazed forest.
6. The importance of deer grazing and tree density in determining larval abundance and their subsequent potential for affecting insectivorous birds in pinewoods are discussed.