The relationship between leaf longevity and growth ring markedness in modern conifer woods and its implications for palaeoclimatic studies

Growth rings in modern conifer woods were quantitatively analysed to investigate the relationship between leaf longevity and the markedness of the growth ring boundary. Five conifer species exhibiting a wide range of Leaf Retention Times (LRTs) were examined in anatomical sections stored in the Jodrell Laboratory, Royal Botanic Gardens, Kew, Surrey, UK. The species studied were Larix decidua Mill. (deciduous), Pinus sylvestris L. (LRT=1–3 years), Picea abies (L.) H. Karst. (LRT=3–5 years), Cedrus libani A. Rich. (LRT=3–6 years), and Araucaria araucana (Molina) K. Koch (LRT=3–15 years). Two aspects of ring markedness were quantified: (1) the percentage of latewood in each growth ring increment and (2) the difference between the maximum and minimum radial cell diameters in the growth ring increment expressed as a percentage of the maximum cell diameter (percentage diminution). The product of these two parameters was calculated to give a Ring Markedness Index (RMI). Five growth ring increments were measured for each species from poorly provenanced specimens grown in southern England. Statistical analysis of these data shows that there is a significant inverse linear relationship between median LRT and percentage latewood (R2=0.86), percentage diminution (R2=0.77), and RMI (R2=0.91), at P<0.001. These data suggest that leaf longevity exerts an important control on growth ring markedness, in addition to the influence exerted by the growing environment (climatic and edaphic conditions). The significance of these results for the palaeoclimatic analysis of growth rings in fossil woods is discussed with reference to two case-studies: (1) the Early Carboniferous tropical climate of the British Isles and (2) the Early Cretaceous polar climate of the Antarctic Peninsula.