Tabel I: DNAme clocks vs. Epimutation-based aging clocks.

The CG epimutation-based aging clock described for trees differ fundamentally from the DNA methylation-based (DNAme) clocks used in the mammalian field. This table summarizes theri differences along several key dimensions. Current data on CG epimutation-based aging clocks in trees is still limited, and an assessment of their properties is therefore somewhat hypothetical. To indicate this uncertainty, we use parentheses, “( )”, in places. The properties of DNAme clocks have been reviewed by Horvath and Raj [62]. Their summary has informed the construction of the “DNAme clocks in mammals” column. When necessary, additional references were used as indicated.

Clock properties and data requirements	DNAme clocks, in mammals	Epimuialion clocks in Uses
Minimum Nb. of input CGs for clock	few (1 to 513 target CGs)	Many (> 1C°, but depends on epimutation rates)
Quantification	Weighted mean CG methylation levels + model	CG methyiatior divergence f model
Nature of age-rela;ed mCG change	Systematic (reproducible, directional change from hypo- to typermetiiylaton. or vice versa, as function of age)	Random (stochastic CG gains and losses throughout agng)
Dependence on Nb. oi mHotic divisions	No	Yes
Clock at equilibrium	No (follows from the Uirectonalry of die changes)	(Yes)
Clock reset at every generation	Yes	(No)
Accurate across genotypes	Yes (by construction)	unknown
Acturate across species	Yes (by construction) Refs: [90. 91]	unlikely
Minimum # of samples required	1 sample (individual)	>> 1 sample (individual) (precise number is still undear)
Tissue requirement	Wide range of tissues possible	Leaves, stems, buds