Variation in Populus nigra clones: Implications for river restoration projects in the United Kingdom

Abstract

Black poplar (P. nigra ssp. betulifolia) is a tree species that is a subject of concern in the United Kingdom because of its rarity, skewed sex ratio, and apparent inability to regenerate naturally. In its natural habitat, it is an early successional tree that occurs on floodplains. It is dependent on channel movement for the provision of suitable habitats for regeneration. In the United Kingdom, there is considerable interest in using black poplar in river restoration schemes. This study was carried out to determine the importance of choice of black poplar clones in such schemes. Cuttings were collected from 11 female and 8 male black poplars from a wide geographical range in Britain. Of these, cuttings from 7 males and 6 females were rooted and grown successfully for one season in a field experiment designed to determine the difference in growth response of the range of individuals to a variety of soil moisture conditions. The propagated cuttings were described morphometrically, and measurements of growth response were recorded. The source trees were also described genetically, using analysis of AFLPs (Amplified Fragment Length Polymorphisms), in order to determine relatedness. Results showed that genetic diversity of the source trees used in this study was low. However, there were some significant differences in growth response and morphometric characteristics (mean leaf area, mean branch angle) among the plants derived from different source trees. Growth was always best in the wettest sites, and females grew better than males at these sites. The results suggest that, in riparian forest restoration schemes, choice of clone affects the balance of sex ratios, viable genetic diversity and survival of plantings on varied sites.