K.—BOTANY 203 
further deterioration in soil conditions and risk of storm damage to the 
seed trees which were isolated so late in life. ‘The only alternative in 
such cases is to complete the process by clear cutting and artificial planting, 
and this is what generally occurs. If, as sometimes happens, by good 
luck the regeneration is sufficiently complete to provide a new crop, 
then the old trees are gradually removed in a series of falls, called the 
final fellings. But the whole process known as the uniform or compart- 
mental system is slow, uncertain and risky. 'To lessen the risks of failure 
and loss by opening up large areas at one time, numerous modifications 
have been introduced into the practice of forestry. ‘The underlying idea 
was to confine natural regeneration to smaller areas, in the shape of groups 
or strips, with peripheral extensions of these as they became regenerated. 
By selecting the shape, breadth, line and direction and sequence in time 
of the strips, a considerable amount of success has been achieved. Strips 
or groups may be clear felled or a certain number of trees may be left 
to provide seed and to protect the young seedlings. In the former case, 
protection is supplied by the adjacent stand of mature trees, and seeding 
takes place from the side. Various and numerous combinations of the 
uniform, group and strip methods have been tried, with more or less 
success, under certain favourable locality conditions. 
The main trouble is that in the past the woods have not been managed 
with a view to natural regeneration; under light increment treatment, 
the more open canopy and crown room enables the trees to respond almost 
immediately to the influence of the seed felling. The under planting 
which has kept the soil in a favourable condition for seed reception can 
be dealt with easily, and after the seedlings have appeared, the old trees 
may be removed at one felling instead of gradual removal over a protracted 
series of years, as a certain amount of undergrowth can be left to provide 
shelter and protection to the young trees. 
The biology of the large pure stands of timber must obviously differ 
from that of large mixed stands, consisting of two or more species, as 
generally prevail in the primeval forest. ‘To establish artificially or to 
regenerate naturally a mixed stand of timber which will have the desired 
ratio of species at maturity, involves much labour and cost, and the attempt 
is not always certain of success, except perhaps under the selection method 
of treatment. To get over the difficulties associated with single stem 
mixture, other forms have been tried, such as planting the different species 
in alternate rows, bands, strips, clumps and groups, but still this does not 
quite solve the problem. It is all right for the trees in the centre of the 
group or strip, but those on either side at the contact margins are apt to 
become bent and branchy ; further, each of these numerous units requires 
individual attention, and this is not compatible with economic manage- 
ment. It is possible with certain light-demanding and shade-bearing trees 
to form mixtures in which the crowns of the light demanders form a kind 
of upper storey, with those of the shade bearers beneath; but such 
_mixtures are very difficult to bring through the pole stage of growth 
unless the light demander happens to find itself in its optimum conditions. 
The problem may now be stated : How are we to manage and develop 
our woods so that the demands for different species of timber, sorts and 
