Hydrobiologia 389: 115–130, 1998. © 1998 Kluwer Academic Publishers. Printed in the Netherlands. 115 The faunal communities of upland streams in the eastern region of Ireland with reference to afforestation impacts D. Tierney 1 , M. Kelly-Quinn & J.J. Bracken Zoology Department, University College Dublin, Belfield, Dublin 4, Ireland 1 Present address: Central Fisheries Board, Balnagowan House, Mobhi Boreen, Glasnevin, Dublin 9, Ireland Received 19 December 1997; in revised form 28 October 1998; accepted 17 November 1998 Key words: upland, faunal communities, afforestation, TWINSPAN, ordination Abstract Macroinvertebrates were sampled from forty-seven sites on upland soft water streams in eastern Ireland. Clas- sification generated four recognisable faunal communities or site groups which differed in biological, physical and chemical character; these patterns were supported by ordination analyses. The environmental gradients which probably influenced water quality were broadly categorised into geology, distance from source or elevation and forestry. Faunal diversity and abundance were reduced in both high altitude and extensively afforested sites com- pared to moorland sites. Whereas, Plecoptera dominated the fauna at most sites, many taxonomic groups such as the Ephemeroptera and members of the family Elmidae were absent from high altitude and forested areas. The impact of afforestation was most evident at those sites which were located in forest plantations or were on catchments with extensive (>25%) closed canopy (>12 yr) afforestation. Low levels (<25%) of forestry in the absence of acid waters did not lead to impoverishment. This work reveals how plantation forestry in areas receiving only moderately polluted rain can be linked with acid waters and impoverished invertebrate communities. Introduction Extensive research has been carried out in the U.K., Europe and North America, on the effects of acidifi- cation and afforestation on aquatic systems (Overrein, 1976; Haines, 1981; Mason, 1990). The implication of forestry, particularly conifers, as an exacerbating fac- tor in the acidification of both soil and aquatic systems is now widely accepted (Harriman & Morrison, 1980; Burns et al., 1984; Hornung et al., 1986; Wells & Har- riman, 1987; Grieve, 1990; Kresier et al., 1990; Miller et al., 1991; Adamson et al., 1993). Studies involving chemical analyses of throughfall and stemflow reveal increased concentrations of sulphate, hydrogen, chlo- ride, sodium, magnesium, potassium and calcium ions and a decline in pH under conifer canopies compared to the ambient precipitation (Clesceri & Vasudevan, 1980; Chappell et al., 1990; Neal et al., 1992; Miller op. cit.). The underlying soil and soil water are acid- ified (Benecke, 1988; Tamm & Hallbäcken, 1988) resulting in the mobilisation of iron and more im- portantly of aluminium (Cronin & Schofield, 1979; Driscoll, 1980; Driscoll Jr. et al., 1980). These ions, along with hydrogen and other acidifiers such as ni- trate and sulphate ions are transported in soil solution to the aquatic environment. Macroinvertebrates are commonly used as biolog- ical indicators (Rosenberg & Resh, 1993), and have been used to elucidate the impact of afforestation on aquatic systems elsewhere. The typical faunal commu- nity of afforested streams is often impoverished and dominated by Plecoptera. Ephemeroptera, in particu- lar, are adversely affected and are known to be acid sensitive. Their density and richness have been cor- related with pH values (Fiance, 1978; Engblom & Lingdell, 1984; Willoughby & Mappin, 1988; Smith et al., 1990). Many studies have found a correlation between low pH values and a reduction in taxon diver- sity (Friberg et al., 1980; Harriman & Morrison, 1980; Stoner et al., 1984; Sutcliffe & Hildrew, 1989). Dia- mond et al. (1987) concluded that fauna are restricted by low pH and associated parameters such as calcium,