Processing of pine (Pinus sylvestris) and birch (Betula pubescens) leaf material in a small river system in the northern Cairngorms, Scotland

Abstract. Processing rates, and macroinvertebrate colonisation, of pine needles and birch leaves were studied at eight sites on the river Nethy, a small river system in the Cairngorm region of north-eastern Scotland. Throughout this river system, processing rates were slow for pine (k values 0.0015-0.0034 day^-1) and medium to fast for birch (k values 0.0085-0.0331 day^-1). Plecopteran shredders dominated both pine and birch leaf packs during the early part of the experiment while chironomids were more important in the latter stages. It is suggested that the slow processing rate of pine needles could adversely affect the productivity of streams, particularly where needles provide the major allochthonous energy source and retentive features are limited. Forest managers should consider this when creating new pinewoods in treeless areas as it will take many years for the trees to reach a size at which they can effectively contribute retentive features, in the form of woody debris, to streams.

Keywords: leaf processing, pine needles, shredders, Pinus sylvestris, Betula pubescens, Scotland.