The effect of crown position and tree age on resin-canal density in Scots pine (Pinus sylvestris L.) needles

Resin canals are an important taxonomic characteristic in conifers. In this paper we examined within- and between-needle variation of the cross-sectio nal number of resin canals in Scots pine (Pinus sylvestris L.). Variation w ithin needles was determined from 12 free-hand sections taken along the who le length of foliage collected from a common crown position. The effect of crown location and tree age on resin-canal density was also examined from t he midpoint cross sections of 450 Scots pine needles collected from interio r and exterior locations from the top, middle, and bottom of 25 crowns of t rees ranging in age from 8 to 70 years. Within-needle resin-canal density v aried with needle length. Two resin canals were typical for the basal and t he terminal needle cross sections. There were 3.2 and 8.6 resin canals for cross sections taken from 10 and 30% of the needle length from the basal sh eath, respectively. Resin-canal density was largest, and relatively constan t, between 30 and 80% of the needle length. We found significant difference s in the cross-sectional number of needle resin canals, as influenced by cr own positions and tree age. Resin-canal density increased with foliage heig ht. Foliage from the top one-third of crowns had significantly more resin c anals than foliage from the bottom. Foliage collected from the crown interi or (proximal to the stem) had fewer resin canals than samples from the crow n edge. Resin-canal density increased from 7.1 to 10.3 as tree age increase d from 8 to 70 years. These results suggest that crown position and tree ag e need to be incorporated into the sampling protocols used to establish spe cies standards in resin-canal density, at least for Scots pine, if meaningf ul comparisons are to be made.