228 NATURALISATION OF FOREST TREES. 



intensities of light in different climates must be remembered. 

 The light under a forest here may be equally intense with full light 

 in, say, England, so that a light-demanding species from the latter 

 would be apparently shade-bearing here. 



Soil, 



The second chief factor of locality is the soil, which though not 

 so important by itself as climate, must be by no means neglected, 

 with regard both to its mineral composition and also to its relation 

 to the factors of climate, especially to moisture. 



It is generally recognised that the mineral composition of soils 

 is of comparatively little importance, but this generalisation is apt 

 to lead to too much neglect of it. It is sometimes the only factor 

 which causes a change in tree distribution and an excess or 

 deficiency of a certain mineral food will prohibit the growth of a 

 species. Consequently a locality may be quite unsuited to a 

 certain exotic even though the climate is entirely suitable. Pinns 

 pinaster fails owing to a quantity of lime in the soil in which Piniis 

 halepensis delights, while the latter will fail if a certain minimum 

 of lime is not present. Most species cannot endure more than a 

 small amount of " brak," whereas others, such as Red Gum, can 

 stand a comparatively large quantity. 



Some species show much natural adaptability in this respect, 

 and others show little and much remains to be learnt on the ques- 

 tion. 



The influence of depth, permeability, retentive capacity of soil, 

 the level of the water table, and the degree of slope, on the available 

 moisture supply under any given climatic conditions, and conse- 

 quently on the distribution of species, is well known, and when 

 introducing an exotic careful judgment must be used in deciding 

 what difference in these factors will compensate for a difference in 

 the climatic factors, and vice versa. Generally speaking, a deeper 

 or more rententive soil, may compensate for a drier climate. 



These factors of soil may, however, be of consequence by them- 

 selves. For instance, some species demand a loose soil and will 

 not thrive in a compact one whatever the moisture of the latter 

 may be. 



Again, the relation of a soil to temperature is of importance in 

 compensating for a difference in climate. Species from a warmer 

 climate may thrive in a colder one when planted on warm soils, 

 but will succumb on cold soils. 



Aspect, elevation and latitude need not be considered here because 

 they are only of importance in controlling the climate, but we are 

 warned that they must never be neglected when comparing locali- 

 ties, by the very distinct effect we know them to have upon the 

 local distribution of species. 



Climatic Varieties. 



In the above considerations, I have only referred to the selection 

 of the suitable species, but the same considerations apply to the 

 selectioh of the suitable " Climatic variety " of a given species. 

 The difference between these climatic varieties, as regards quality 



