Relationships between climate and flowering of eight herbs in a Swedish deciduous forest

Effects of annual Variation in rainfall, temperature and humidity on flower ing abundance of eight temperate woodland plants (Anemone nemorosa, Cardami ne bulbifera, Lamiastrum galeobdolon, Oxalis acetosella, Ranunculus ficaria , Stellaria holostea, Viola reichenbachiana and Viola riviniana) were studi ed during 12 consecutive years (1989-2000) in a hornbeam (Carpinus betulus) forest in southeast Sweden. Above-average rainfall:humidity in late summer to early autumn of the preceding year increased flowering abundance in L. galeobdolon, O. acetosella, V. reichenbachiana, V. riviniana and, especiall y, in R. ficaria, but not in S. holostea and A. nemorosa. Moreover, floweri ng of R. ficaria and O. acetosella was positively related to rainfall/humid ity during several parts of, or the entire, preceding year. On the contrary , flowering of S. holostea and A. nemorosa was closely related to low value s of rainfall/humidity in autumn and/or winter of the preceding year and al so to low humidity in the current year in A. nemorosa. Two long periods (3- 4 years) of increasing rainfall deficit coincided with decreasing flowering abundance in most of the species, but not with decreasing vegetative devel opment. Temperature variability was less consistently related to flowering. A cool period during the preceding summer or autumn seemed important for f lowering in L. galeobdolon, O. acetosella and the Viola species, although t hese relations were, at least partly, caused by interactions with rainfall/ humidity. No significant (P < 0.05) correlations were found between floweri ng and the conditions prevailing in April to May-the main flowering season- of the current year. (C) 2001 Annals of Botany Company.