The response of male and female black poplar (Populus nigra L. subspecies betulifolia (Pursh) W. Wettst,) cuttings to different water table depths and sediment types: implications for flow management and river corridor biodiversity

Management of river flows has altered the pattern of flood arrival times an d reduced their frequency and duration on many European floodplains. Floodp lain toe species depend on floods both to provide new sites for their regen eration and to recharge water tables at various depths in the rooting zone. A reduction in floods is one factor that has led to loss of river corridor biodiversity, with early successional tree species from the Salicaceae bei ng particularly adversely affected. Members of the Salicaceae are dioecious and it is possible that the males and females of these species have measur ably different water table requirements, which might lead to spatial segreg ation of the sexes on a floodplain. This paper describes an investigation t hat was carried out into the response of male and female black poplar (Popu lus nigra L. subspecies betulifolia (Pursh) W. Wettst.) to different soil m oisture conditions. An experiment was set up on an alluvial island in the R iver Great Ouse (UK) in which cuttings of male and female black poplar were grown in different sediment types with different water table levels. The e xperiment was carried out over two held seasons in 1997 and 1998. Results s howed that females tended to prefer wetter and more nutrient-rich sites tha n males but that there was considerable overlap in their requirements. A co mplementary genetic study showed very little genetic variation in the exper imental population, which may also partially explain the relatively low lev el of variation between the two sexes found in the study. It is suggested t hat some limited spatial segregation of the sexes does occur in response to soil moisture availability and that river flow management which aims to ma intain or increase river corridor biodiversity may need to take this into a ccount. Copyright (C) 2000 John Wiley & Sons, Ltd.