Genetic variation of the bud and leaf phenology of seventeen poplar clones in a short rotation coppice culture

Leaf phenology of 17 poplar (Populus spp.) clones, encompassing spring phenology, length of growth period and end-of-year phenology, was examined over several years of different rotations. The 17 poplar clones differed in their latitude of origin (45degrees30'N to 51degreesN) and were studied on a short rotation experimental field plantation, situated in Boom (province of Antwerpen, Belgium; 51degrees05'N, 04degrees22'E). A similar, clear pattern of bud burst was observed during the different years of study for all clones. Clones Columbia River, Fritzi Pauley, Trichobel (Populus trichocarpa) and Balsam Spire (Populus trichocarpa x Populus balsamfera) from 45degrees30'N to 49degreesN reached bud burst (expressed as day of the year or degree day sums) almost every year earlier than clones Wolterson (Populus nigra), Gaver, Gibecq and Prim (Populus deltoides x Populus nigra) (50degreesN to 51degreesN). This observation could not be generalised to end-of-season phenology, for which a yearly returning pattern for all clones was lacking. Late bud burst and early leaf fall of some clones (Beaupre, Boelare, IBW1, IBW2, IBW3) was brought about by increasing rust incidence during the years of observation. For these clones, the variability in leaf phenology was reflected in high coefficients of variation among years. The patterns of genetic variation in leaf phenology have implications for short rotation intensive culture forestry and management of natural populations. Moreover, the variation in phenology reported here is relevant with regard to the genetic mapping of poplar.