138
J. ROGER BRAY AND EVILLE OORHAM
The difference in leaf-fall periodicity of different species within mixed
forest has been shown clearly by Blow (1955), working in upland oak
forest of eastern Tennessee in the U.S.A. Table XVII shows the percentage of leaf-fall during the year 1948-49 which was collected by
late August, mid-October and early December. From this table it
appears that the overstory species lose their leaves later than the understory species, and that even within these groups there are distinct
specific differences. The only species in this forest which retains many
leaves (10%) through the winter is Quercus alba, although a few remain
REF
ANISOPTERA
SHOREA
. . I
MALAYAN FOREST
40
40
u.
LK
4 0 -
W
It 2 0 -
MALAYAN FOREST, SHOREA L A E V I S
- 40
. 2 0
1 1 )
-3
I
+ 6 0
z
0
* 40
20
0
N E T H E R L A N D S FOREST
QUERCUS
T R E M U L A
20
JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT OCT. NOV. DEC.
FIG. 5. Seasonal litter-fall of individual species in mixed forests. (1) Mitchell (P.c.);
(2) Witkamp and van der Drift, 1961.
on Quercus stelbta. Apparently overstory species may lose their leaves
earlier than understory species, or even understory individuals of the
same species, in other areas, as for example in mixed savannah forest
of NW Thailand (Ogawa et al., 1961).
Pig. 5 shows the marked variation in litter-fall periodicity among
mixed Angiosperms in the Netherlands (Witkamp and van der Drift,
1961). Populus tremula and Quercus robur show distinct peaks of litterfall in October and November respectively. Betula verrucosa also reaches
a peak in October, but litter-fall is quite heavy in August and September
as well. Alnus glutinosa is unusual in exhibiting a bimodal pattern, with
many green leaves being shed in July in addition to the major fall of
brown leaves in October. Tadaki and Shidei (1960) found that in a