A comparison of needle retention on Japanese black pine and Japanese red pine

Needle retention (number of needle sets), needle density, height increment and radial increment were surveyed on seven Japanese black pines (Pinus thunbergii Parl.) and seven Japanese red pines (Pinus densiflora Sieb. et Zucc.) growing on the same site. Number of needle sets on branches with respect to whorl position was estimated visually. In 1999, maximum summer needle retention was observed on the fifth and sixth whorl from the top, with values of 3.4 needle sets for the black pines and 2.4 needle sets for the red pines, respectively. The needle trace method (NTM) was used to determine needle retention and needle density along the main stems retrospectively for the years 1968–1998. The long-term mean summer needle retention along the main stem was 3.7 needle sets for the black pines and 2.2 needle sets for the red pines. In both pine species, the number of needle sets varied from year to year. However, the long-term budget between newly born and annually shed needle sets was in equilibrium. The long-term average of needle density per cm of stem shoot was 9.4 needle pairs for the black pines and 7.4 needle pairs for the red pines. The results showed clear intra-specific and inter-specific similarities in needle retention, height increment and radial increment trends. The values for number of needle sets, height increment and radial increment positively increased with favorable growing conditions, whereas the value of needle density had an opposite tendency.