RESPONSE OF CALLITRICHE AND POTAMOGETON TO CUTTING, DREDGING AND SHADE IN ENGLISH DRAINAGE CHANNELS

Populations of two submersed species, common water-starwort (Callitric he stagnalis Scop.) and curled pondweed (Potamogeton crispus L.), grow ing in drainage channels in the Solway Drainage Area of northwestern E ngland, responded differently to stress and disturbance produced by cu tting, dredging and shade in a field experiment. Although the survival strategy of both plants is essentially similar (competitive-disturban ce tolerator), the results suggested that starwort was the more compet itive of the two species, while curled pondweed tolerated disturbance better. Shade stress was also better tolerated by curled pondweed. Sub merged weed management regimes in use in the Solway Drainage Area-depe nd heavily on cutting and dredging: these disturbance-based control me thods probably have a low efficacy against disturbance-tolerant specie s, and may promote their dominance in the channel system.