SOME CAUSES OF THE DECAY OF AUSTRALIAN FORESTS. 95 
— of investigating this myself, = I ee that about 
twenty years since, when the same thing was going on rapidly in 
parts of "this Colony, many theories were val ecwede to account 
for it. Some thought it due to grubs which got between the bark 
and wood and ate out the life of the tree, but all who have been in 
the bush know that grubs eat between the bark and woods of trees 
cut down or ringbarked, and seem only to do it when the sap has 
ceased to circulate. Another theory laid the cause to some disease 
in the roots similar to that affecting orange trees at the same time; 
this was, I believe, the view held by the late Sir William 
M‘Arthur, a very close observer of natural phenomena, and he 
had trenches cut between the healthy and dying trees, with a view 
to stopping the progress of the disease through the ground, but 
without producing the desired effect. 
Mr. MacPherson has — us very clearly that where he resided 
in Victoria opossums were the cause of death in the gum-trees, 
and I trust others sei have observed in other places will publish 
the results of their pribnoncnaneet and then we may be able to see 
if the cause is the same everywhere. It does not appear to affect. 
all the forest at the same time ; Sica patches die off while all 
round there is the usual healthy vegetation, and if we are to judge 
by the patches of bare country the same ‘thing has gone on at. 
fish et & very long time past. 
thes e bare patches of country should remain. 
sisgaiche some change in the soil which renders it unfit to. 
sieges tree life. The subject is, however, a wide one, and I am 
not prepared to enter fully into ‘the discussion of it, but I hope- 
hat Mr. MacPherson’s example will be followed by many who are 
in a position to throw light upon this important matter. 
The PRESIDENT Prof. Liversidge, F.R.S.), in conveying the 
thanks of the Society to the author for his valuable and suggestive 
paper, stated that he thought the decay and death of the trees. 
might in some cases be due to the exhaustion of the soil for those 
particular trees stg Lined mere the soil might still be able to 
support a flourishing grow other forest trees : ; and that 
obtain the best growth of omy it is necessary to have a “ rotation 
of crops” just as in farming. In fact such a rotation seems to 
have arisen naturally over various areas of the earth's surface, the 
ge 
buried remains of oak forests being met with in the Car 
shire Fen district and elsewhere. 
It is also known that the present forest vegetation of Sweden 
and Norway has been preceded by others which have died out over 
large areas; the former forests of beech, oak, &c., having been 
successively replaced by pine forests ee 
He also mentioned, although a matter not directly connected 
with the subject of the paper, that in his opinion the reason why — 
a the ears of gum-trees in cond and elsewhere -_ been a 
Fe K 
