72 
E. A. CHESTERFIELD ET AL. 
DISCUSSION 
Although the effect of low root temperatures has 
been widely researched in horticulture (e.g. 
Cooper 1973, Nielsen & Humphries 1966), the 
implications of low soil temperatures on growth 
have received little consideration in the study of 
natural ecosystems. Low soil temperatures influ¬ 
ence the formation of mycorrhizal associations 
(Theodorou Sc Bowen 1970) and increase the 
resistance to the uptake of nutrients (Kramer 
1969). In particular, phosphorus is absorbed 
much more slowly at low than at high tempera¬ 
tures (Sutton 1969). Paton etal. (1979) observed 
the effect of root temperature on dehardening of 
four species of eucalypts and found that root 
temperature in the range 0.5-1.0°C delayed the 
dehardening response of warm shoots. In gen¬ 
eral, below the optimum temperature, height 
growth, root length and dry weight production 
show a broad sigmoidal increase with increasing 
temperature to an optimum, beyond which 
further temperature increase causes a decline in 
productivity. In most trials of horticultural or 
agricultural species, the optimum band of root 
temperature differed between species but was 
between 20-30°C. In this trial, root tempera¬ 
tures were probably well below optima for all 
species. 
The significant interaction between species 
and temperature for height growth in this trial 
was not evident for the other variables tested. 
Eucalypts that compete with vigorous shrub 
growth in the early stages of establishment must 
make rapid, early height growth if they are to 
survive. In contrast, diameter growth changes 
little, particularly during the seedling stages. 
Thus height growth of seedlings may be more 
sensitive to the different root temperature 
regimes than the other variables tested. A simi¬ 
lar discrepancy between height growth and dry 
weight production was recorded for Pinus radi- 
ata and Pinus contorta by Sweet & Wareing 
(1968). Dry weight of their second year seedlings 
was almost identical for the first eight months, 
despite more than 30% difference in height 
growth. In the following months, when the 
height growth of both species was negligible, dry 
weight production continued at a reduced rate 
and clear differences were finally evident in the 
partitioning of dry weight between root and 
stem. For the eucalypts tested in this trial, soil 
temperature appeared to influence this ratio 
with the response of £. regnans and E. nitens 
differing from that of E.fastigata and E. delega- 
tensis. 
The height growth of the southern New South 
Wales form (EE and ET), which was signifi¬ 
cantly better than the West Gippsland form (CR 
and CT), emphasises the difficulties associated 
with using seedlings as a guide to growth in later 
stages (Table 5). Pederick (1979) found ranking 
of provenances according to height growth 
changed after planting in the field. The Errinun- 
dra provenance which was initially the tallest 
had become the shortest within three years. 
Thus the growth of seedlings in containers is at 
best a poor guide to the response of mature to 
over mature trees growing in the natural en¬ 
vironment. 
Major Victorian occurrences of E. nitens m 
on plateaus. At the time of European settlement 
the most extensive populations of E . nitens oc¬ 
curred on Errinundra Plateau and Toorongo 
Plateau. Where the species occurs amongst more 
steeply dissected land forms, it is often confined 
to depressions, gully heads or on moderate 
slopes, in contrast to forests of surrounding 
species, eg. Connors Plains, Mt Useful Spur, 
headwaters of Snobs Creek, Moroka, Royston, 
Rubicon, Little and Taggerty Rivers, Torbreck 
Range (Pederick 1977) and slopes below the Baw 
Baw Plateau, e.g. Christmas Creek. 
Plateau topography affects at least two factors 
that influence the vegetation. The undulating 
landform may increase the severity of frosts 
through cold air drainage, and by influencing the 
rate of fire spread, plateaus may reduce fire in¬ 
tensity and frequency. 
Where the effect of frost is regular and pro¬ 
nounced it may delimit the tree line (Moore & 
Williams 1976). Rare but exceptionally severe 
frosts may influence the segregation of species 
(Davidson Sc Reid 1985), particularly amongst 
lower growing species. For tall growing eu¬ 
calypts, frost effects are likely to be most severe 
during early establishment stages. Superiorfrost 
resistance combined with good growth rate has 
led to the increasing significance of E. nitensm 
plantation species in Tasmania (Tibbits 1986) 
and in other countries (Tibbits & Reid 1987). 
High frost frequency on Errinundra Plateau 
could be at least partly responsible for that ex¬ 
tensive occurrence of E. nitens (Featherstone et 
al. 1987), although a comprehensive study of 
variation in frost resistance indicated that the 
southern New South Wales and Errinundra 
provenances of E. nitens were least frost hardy 
(Tibbits & Reid 1987). Damage due to frost 
would be most pronounced during early re¬ 
generation stages, particularly if regeneration 
occurred as even aged stands without the pro- 
