Effects of increased temperature and nitrogen availability on the displacement of Calluna vulgaris by Pteridium aquilinum

Abstract. Atmospheric greenhouse gas concentrations will continue to rise for the foreseeable future, and, due to radiative forcing, surface temperatures will also increase. If soils warm sufficiently, this will result in increased litter decomposition rates, while nitrogen availability will also rise due to increased deposition. A field-based experiment manipulating air temperatures using polythene tents and nitrogen availability by adding 50 kg N ha^-1 yr^-1 has shown that this will result in further encroachment of Pteridium into Calluna moorland. Although this experiment, treating plots on and around the boundary between Pteridium and Calluna, did not show any statistically significant effect on the movement of the boundary, there were clear indications of Calluna dieback at the boundary. In addition, the frequency of Pteridium fronds increased in the Calluna-dominated areas, while Calluna became less abundant in the pure Pteridium plots. Calluna dieback was not due to litter accumulation as is frequently assumed, but the dieback is likely to be caused by shading of Calluna by the increased growth of Pteridium fronds. Botanical diversity was higher in the Pteridium plots, but considering the importance of grouse shooting for the maintenance of Calluna moorland, displacement of Calluna by Pteridium may result in a lower conservation and economic value of moorlands.     

Habitat selection and diet of the Capercaillie Tetrao urogallus in Abernethy Forest,Strathspey, Scotland

Capsule Woodland characteristics are important for fully grown birds and for broods.

Aims To describe habitat selection and diet of the Capercaillie in ancient native pinewoods and Scots Pine Pinus sylvestris plantations, in order to provide a guide for forest management.

Methods Tree selection was studied in winter by locating droppings under trees along transects, and comparing those trees used by Capercaillie with those not used. Habitat selection by broods was studied by following radiotagged chicks or females with broods. Diet was described from the analysis of droppings.

Results In winter, Capercaillie preferred Scots Pines with wide crowns and large branches, and little surrounding Heather Calluna vulgaris, but avoided forest tracks. Female Capercaillie occurred in stands with a higher density of pines compared to males. The diet of fully grown birds comprised primarily Scots Pine needles between October and April. Scots Pine pollen cones were eaten during May, June and July. Bilberry Vaccinium myrtillus leaves and fruit were eaten in summer and autumn. Habitats used by broods had a higher percentage of Vaccinium sp. and smaller Scots Pines compared with random sites. Chicks hatch at the beginning of June, and in their first two weeks, their diet comprised Formicidae, Lepidoptera larvae and Coleoptera. In July and August, Lepidoptera larvae were rarely eaten but a higher percentage of chicks took vegetable material (particularly Bilberry fruit). In June, smaller numbers of invertebrates were generally trapped in mires of wooded bogs compared with areas of Heather and Vaccinium sp. in old woodland. Areas of Vaccinium sp. had the highest numbers of Formicidae, Coleoptera and Diptera, and especially Lepidoptera larvae. Numbers of Lepidoptera larvae declined during June and July as larvae pupated, explaining the reduction of Lepidoptera larvae in the diet of older chicks.

Conclusions Habitat management for Capercaillie should aim to provide old Scots Pine forest with a Vaccinium-rich field layer. Within Scotland, this may entail increasing the tree density in ancient native pinewoods but decreasing it in pine plantations. The removal or closure of tracks might increase the amount of woodland available to Capercaillie, by reducing human disturbance.