19 
LOW TEMPERATURES. 
uncongenial conditions. Depressed vitality or attacks by insect enemies have 
followed to disappoint us of the good results we hoped to realize. The amount 
of loss due to planting trees where the general climatic conditions are too mild 
for them is serious, as may be seen in the familiar case of E. globulus and the less 
familiar case of E. Gunnii when planted on the warm lowlands of the North 
Island; or amongst the conifers in the case of larch and spruce. But much the 
larger percentage of our losses with the eucalypts has been due to planting our 
selected species where they could not endure the ordinary or occasional degrees of 
cold. In Australia, as we have seen, the main restrictive factor for the large- 
growing eucalypts is rainfall; in New Zealand it is temperature. 
EFFECTS OF LOW TEMPERATURE. 
There are several ways in which eucalypts may be injured by low 
temperatures. 
(a) An occasional heavy frost may cut back the growing tips of young trees 
without hurting the main mass of their foliage. The injury in such case will be 
slight and the trees will soon recover. 
( b ) Still severer cold may freeze the cambium tissue round the stems of the 
younger trees. The bark will then be forced away from the wood by the expansion 
of the frozen tissue. In a short time the trees will die back to the injured part; but 
the stumps will sprout again and throw up other stems that may survive and 
become large trees. In this case the dead stems should be cut away and the new 
sprouts reduced in each case to one or two of the strongest. 
(c) If the temperature falls phenomenally low and remains low for a con¬ 
siderable time, tender species may be killed to the root and the area lecpiiie to 
be replanted. 
( d) The annual average warmth in a locality may be too low for a species. 
In this case the trees may live on for many years; but they will make no adequate 
growth. Instead of attaining normal girth and height they will remain mere 
stunted shrubs of dwarfy dimensions. The meaning of the evidence will be that 
the species must have a larger percentage of sunny days and a higher general 
average of warmth. 
Many species that are exceedingly tender in the seedling and sapling stages 
become strongly frost-resistant after they have clothed their stems with a thick 
bark and lifted their heads high above the ground. On the other hand, seedlings 
of some sub-tropical species are reported to have endured 10° of frost m localities 
where the mean annual temperature is hopelessly too low for the successful 
cultivation of such species. Adult trees have sometimes been killed by frost; but 
in nearly all cases when eucalypts have passed the seedling and sapling stages and 
are growing vigorously they may be regarded as assured against even an extreme 
fall of the thermometer. 
MODIFYING INFLUENCES. 
It is impossible to state definitely and positively how many degrees of frost 
any particular species can endure, for the reason that many mfluences come m 
to modify the effect of a low temperature. It has been observed that within the 
