POOL-AND-HUMMOCK PATTERNING IN A SOUTHERN PENNINE BLANKET MIRE .2. THE FORMATION AND EROSION OF THE POOL SYSTEM

1 Inferences about the processes leading to surface patterning, pool f ormation and gully erosion in a Southern Pennine blanket mire are draw n from the 15-m stratigraphic profile from Alport Moor described in Pa rt I. 2 Four successive stages in the development of the present mire surface are recognized: a topographically differentiated dry bog veget ation c. 2800 years ago, which then developed into a wet rather featur eless mire surface by c. 200 Cal BC; an extended phase between c. 200 Cal BC and 1250 Cal AD when hummock-hollow differentiation was taking place over the mire surface; and drier bog vegetation since c. 1250 Ca l AD, probably following incision of the main drainage gullies. 3 Pres erved remains of Sphangnum occurred in 52% of the peat samples analyse d for macrofossils. In the peat profile the Sphagnum remains were conc entrated into five essentially continuous and nearly horizontal bands, separated by intervening regions where Sphagnum was scarce or absent. 4 The temporary discontinuous distribution of Sphagnum in the stratig raphic profile is shown to be an overall response to climate change (S phagna increasing in abundance during periods of wetter climate), modi fied by site-specific responses to ongoing topographic differentiation and the incidence of erosion. 5 It is suggested that high pollen valu es of Cyperaceae found in the pollen record from Alport Moor and some other Southern Pennine sites might record the local spread of Eriophor um angustifolium across bare wet peat, and might thus indicate times w hen the mire surface was under stress. 6 Site-specific differences in the patterns of Sphagnum abundance over the last 1200 years in the stu dy area and on the nearby Featherbed Moss are used to follow the devel opment of the erosion system on Alport Moor. 7 The currently eroded mi re surface on much of Alport Moor has arisen from at least three proce sses acting on the pool-and-hummock system: (a) the drawing-off of wat er from the pools by endotelmic streams extending headwards from the m ain streams of the catchment area, probably at least 1000 years ago; ( b) extensive drying-out of pools and hummocks during the drier climati c conditions between c. AD 1150 and 1300; (c) subsequent human modific ation of the mire vegetation by burning, grazing and, latterly, air po llution. 8 Sphagnum was lost from the mire surface generally on Alport Moor by 400-500 years ago. Only the disappearance of the moss Racomit rium lanuginosum from the hummocks might be attributed to the deleteri ous effects of air pollution.