Thanks Guy for the email earlier this morning. And if any Buzzers are interested, that paper is available here.
I would expect that the biggest effect of a Ca drench would be an increase in pH (= reduction in acidity) at the treated surfaces. Calcium and trees have an interesting relationship. Calcium is the soil element that trees need the most....with most all of it in the cell wall system. Yes, Ca is essential in tiny quantities within the symplast but far more is in the apoplast. In plants, Ca pumps are always pointed out!
As with field crops, calcium treatments (as in liming) is not so much about alleviating Ca-deficiency but reducing acidity that can interfere with uptake of other essential elements.
That research paper suggested that in our naturally acidic northeastern soils, naturally occurring aluminum can become mobilized and interfere with Ca uptake, even if Ca is available in the soil.
I'll restrain my inclination to lay out more of the Ca story. My publication list has a fair bit on Ca (check profile and Researchgate (for the older stuff)).