Effects of moor-draining on the hydrology and vegetation of northern Pennine blanket bog.
Water-table depths on high-level blanket bog were compared at different distances from moor-drains and with depths on nearby undrained bog. Cover-abundances of ten plant species were compared with the results for water-tables. Water-table depths fluctuated with rainfall, but less so beside drains than farther away, and less than on undrained bog. Mean water-tables near to drains were deeper than at places farther away, but the lowering was slight and confined to a zone only a few metres wide on either side of the drain. On sloping ground, the zone was narrower on the uphill side than the downhill side. Plant species dependent on high water-tables were less abundant near to drains, and species with drier heathland affinities had greater cover than at places farther away. As with water-tables, this effect was asymmetrical, but more so. Vegetation data for one site over 25 years showed that most long-term effects were confined to the downslope of drains. Cover of Calluna peaked after 8 years but declined thereafter, while decreases in cover of Sphagnum were very localized and took nearly 20 years to achieve statistical significance. It was concluded that drains mainly intercepted surface runoff, and withdrew water from the peat only alongside the drain edge. Runoff entering the drain from above reduced or nullified plant responses to the water-table on the upslope side, and the reduced runoff below the drain enhanced the response there.