Richard
Both dormant and adventitious buds may be referred to as epicormic buds.
Dormant buds being produced before the formation of secondary xylem and
remaining semi-dormant, growing only at the rate of parent stem/branch
radial growth. It appears that auxin depletion is the most likely
trigger for dormant buds developing to form shoots. Adventitious shoots
develop from the differentiation of any living cells into bud initials.
Oak (Q. robur and Q. petraea) do not produce adventitious buds (Harmer.
R, 199?) but produce all epicormic shoots from dormant buds. Simon is
correct in so far as some species can produce new initials on old wood
(adventitious buds) but there are some that do not. Dormant buds are
produced at nodes at the same time as buds that subsequently develop
into shoots. In some species, dormant buds divide whilst remaining
suppressed, sometimes resulting in such a proliferation of buds that the
parent branch or stem appears swollen.
With regard to your hypothetical oak, shoots are most likely to develop
if the apical control asserted by the distal shoots is severely limited
by hard pruning, whereas light pruning and therefore persistence of
apical control would probably result in little epicormic shoot
development. If my memory serves me correctly, in experiments with Q.
robur, Harmer found that partial stem girdling above branch nodes
reliably stimulated epicormic shoot development during April and May.
Reliance upon epicormic shoots when cutting oak at any other time in UK
would be unwise.
I hope this helps. I can fax Harmer (199?) and other related papers if
you wish.
Mike Ellison
--
Mike Ellison
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