Variation in seedling abnormalities and 2- and 4-year growth were studied in a trial in north-westem
Tasmania established from 594 open-pollinated families from throughout the geographical range of
Eucalyptus globulus Labill. ssp, globulus and populations intergrading with other subspecies. Most
(77-80%) of the total (phenotypic) variation in growth traits occurred within families. The genetic
variation between families within localities (within c. 10 krn; 13-15% of the total variation), between
localities within regions (within c. 100-150 km; c: 4%) and between regions (3-8%) was generally
highly significant. However, regional and locality components together accounted for only a small
proportion of the total phenotypic variation. Little differentiation was detected between separate
sampling sites within localities. Estimates of individual narrow-sense heritabilities were markedly
higher than previous reports and were 0.38 for conic volume and 0.41 for height at 4 years, assuming a
coefficient of relatedness of 0.4 amongst open-pollinated sibs. On average, progenies from the Otway
Ranges region were the fastest growing at the test site, followed by those from King Island. Parent trees
with high breeding values were concentrated in the Otway Ranges, Strzelecki Ranges and far southeastem
Tasmania with the Bass Strait island localities having intermediate frequencies.
Forest fragmentation through clearing for agriculture appears to have had a deleterious effect on the
quantitative genetic structure of intergrade populations consistent with high levels of inbreeding.
Remnant populations tended to have higher levels of severely abnormal seedlings, higher mortality and
poorer growth, and higher heritability estimates and variability both within and between families.
Advanced generation hybridisation and inbreeding due to long periods of isolation in small, relict
populations may also have had similar effects. Populations sampled are, therefore, likely to have
markedly different levels of inbreeding which may have inflated differences between localities and may
have important consequences for the exploitation of this material for breeding.
Heritability of early growth traits and their plasticity in 14 woody species of Chinese subtropical forest
