Bm. Potts et Gj. Jordan, THE SPATIAL PATTERN AND SCALE OF VARIATION IN EUCALYPTUS-GLOBULUS SSPGLOBULUS - VARIATION IN SEEDLING ABNORMALITIES AND EARLY GROWTH, Australian Journal of Botany, 42(4), 1994, pp. 471-492
Variation in seedling abnormalities and 2- and 4-year growth were stud
ied in a trial in north-western Tasmania established from 594 open-pol
linated 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 grow
th traits occurred within families. The genetic variation between fami
lies within localities (within c. 10 lan; 13-15% of the total variatio
n), between localities within regions (within c. 100-150 km; < 4%) and
between regions (3-8%) was generally highly significant. However, reg
ional and locality components together accounted for only a small prop
ortion of the total phenotypic variation. Little differentiation was d
etected between separate sampling sites within localities. Estimates o
f individual narrow-sense heritabilities were markedly higher than pre
vious 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-polli
nated sibs. On average, progenies from the Otway Ranges region were th
e fastest growing at the test site, followed by those from King Island
. Parent toes with high breeding values were concentrated in the Otway
Ranges, Strzelecki Ranges and far southeastern Tasmania with the Bass
Strait island localities having intermediate frequencies. Forest frag
mentation through clearing for agriculture appears to have had a delet
erious effect on the quantitative genetic structure of intergrade popu
lations consistent with high levels of inbreeding. Remnant populations
tended to have higher levels of severely abnormal seedlings, higher m
ortality and poorer growth, and higher heritability estimates and vari
ability both within and between families. Advanced generation hybridis
ation and inbreeding due to long periods of isolation in small, relict
populations may also have had similar effects. Populations sampled ar
e, therefore, likely to have markedly different levels of inbreeding w
hich may have inflated differences between localities and may have imp
ortant consequences for the exploitation of this material for breeding
.