Pruning candles... We refer to JBP which has double flush of growth. Correct?
Does this phenomenon of vigorously growing candles which have needles only on their upper half but not on their lower half, also occurs on Pinus sylvestris?
That phenomenon will occur in almost any pine. Pines are apically dominant trees. Most trees are, in fact, with a few exceptions in the juniper family. There are hormones at work in trees. One hormone, in particular, Auxin, is what causes this strength differential. Essentially, Auxin is a hormone that is present at the tips of branches, and in higher concentration at the top of a tree. Auxin, in high concentrations at the tips of the branches, will suppress all growth below the tips. This is what allows trees to grow tall and stay in full sunlight. Naturally, then, a tree will give its resources to its highest points, hoping that those points will out-compete other trees and grow tall enough that they are never shaded out by others.
So, as a tree grows, its top gets stronger, as it receives full sun, and the lower branches get weaker as they are shaded out by taller ones above them. Combine that with the naturally occurinng Auxin, and you have the recipe for this "phenomenon."
How do we fix this problem? In jbp, we can candle prune when the needles harden off and get a second mature flush in the same year. Hence, the two flush pine designation. In pinus sylvestris "scots pine," you candle pinch before hardening off to remove that auxinal suppression and even candle length across the tree. Dont candle prune a single-flush pine because you will possibly kill the tree.