Post from McNeill Trust on September 10, 2013 at 8:11AM
I cut some trees today to look for heartwood for post use. 10yr microcorys had basically no heart at all, just a hint in the lowest part of trunk. 10yr pilularis (monocalyptus) in same stand had about 60-70% of diameter as heart.
In another stand I cut down one each of 20yr maidenii, saligna and globoidea (all symphyomyrts). Maidenii had good heart at the base, but none at all by halfway up trunk. Saligna was better, with small amount of heartwood still visible about 75% of trunk height. The globoidea (monocalypt) had only a few mm of sap at ground level, and near the top of the tree a cross section about 50mm diameter under bark still had near 50% heartwood. The cross section was totally different from maidenii and saligna.
In another stand I cut down a 10yr propinqua (symphyomyrt). Only a very small amount of heartwood. Then I cut a 3yr old coppice from 10yr total age muelleriana (monocalypt). It had about 50% diameter as heartwood. Far more heartwood than the 10yr old microcorys!
Deans observations seem to hold true for this very small sample; monocalyptus have much more heartwood as young trees than the others.