142
J. ROGER BRAY AND EVILLE GORHAM
7.2 and 7.2 t/ha for these three ages, and leaf litter to 3.2, 3.7 and
3.7 t/ha. Litter-fall was thus the same under the 55- and 200-year
forests, despite a more than four-fold difference in density. However,
undergrowth litter contributed about a quarter of the total litter collected beneath the 200-year forest and only about a tenth of that
beneath the 55-year stand.
VI. STANDING CROP OF LEAVES
A. SEASONAL CHANGES -INTRINSIC
Olsen (1948) found no consistent dry weight change in leaves of Fagus
silvatica after the rapid increase accompanying foliage maturation in
May. The terminal value for yellow leaves prior t o defoliation was a
trifle low, but cannot be specified accurately from his graph. Mitchell
(1936) reported rather marked increases in leaf dry weight of six eastern
American Angiosperm trees until the beginning of July (and in the two
Quercus species until the beginning of August). Carya (Hicoria) ovata
leaves in full autumn color weighed only a littlk less than green leaves
sampled a month before.
Tamm (1955) observed a spring phase of rapid dry weight increase
in needles of Swedish Pinus silvestris and Picea abies, followed by a dry
weight loss of about 20% in June and July. Viro (1955) sampled different
age groups of needles of the same species in Finland during August,
and found the dry weight of 1000 Pinus silvestris needles to be 28.6 g
in the first year, 28.9 g in the second, 29.5 g in the third, and 34.4 g in
older needles ranging up to eight years in age. For Picea abies needles
the corresponding weights were 3.51,4-76,4*58 and 5.02 g.
Weight changes upon and immediately prior to abscission have been
investigated by Viro (1955) in a comparison of dry weights of 1000
green leaves or needles collected in August with dry weights of 1000
yellow leaves or needles collected partly from the tree and partly from
the ground at the end of September. Weight loss associated with yellowing averaged 21% (range 19 to 23%) for the deciduous Angiosperms
Betula (pubescens and verrucosa), Populus tremula, Alnus incana and
Salix caprea. If yellow Pinus silvestris needles are compared with needles
older than three years, the yellow ones weigh 44% less. For Picea abies
the difference is 39%. However, it cannot be assumed that all yellow
needles are more than three years old. If yellow and three-year needles
are compared, the weight loss on yellowing would appear to be only 34%
for both Pinus and Picea. Such a weight loss would still be very high,
about one-third of the total dry matter. A much lower difference between brownish and green Picea pungens needles was observed at
Minneapolis, U.S.A., on 29 May 1963. Sixty-eight brownish needles were
J. ROGER BRAY AND EVILLE GORHAM
7.2 and 7.2 t/ha for these three ages, and leaf litter to 3.2, 3.7 and
3.7 t/ha. Litter-fall was thus the same under the 55- and 200-year
forests, despite a more than four-fold difference in density. However,
undergrowth litter contributed about a quarter of the total litter collected beneath the 200-year forest and only about a tenth of that
beneath the 55-year stand.
VI. STANDING CROP OF LEAVES
A. SEASONAL CHANGES -INTRINSIC
Olsen (1948) found no consistent dry weight change in leaves of Fagus
silvatica after the rapid increase accompanying foliage maturation in
May. The terminal value for yellow leaves prior t o defoliation was a
trifle low, but cannot be specified accurately from his graph. Mitchell
(1936) reported rather marked increases in leaf dry weight of six eastern
American Angiosperm trees until the beginning of July (and in the two
Quercus species until the beginning of August). Carya (Hicoria) ovata
leaves in full autumn color weighed only a littlk less than green leaves
sampled a month before.
Tamm (1955) observed a spring phase of rapid dry weight increase
in needles of Swedish Pinus silvestris and Picea abies, followed by a dry
weight loss of about 20% in June and July. Viro (1955) sampled different
age groups of needles of the same species in Finland during August,
and found the dry weight of 1000 Pinus silvestris needles to be 28.6 g
in the first year, 28.9 g in the second, 29.5 g in the third, and 34.4 g in
older needles ranging up to eight years in age. For Picea abies needles
the corresponding weights were 3.51,4-76,4*58 and 5.02 g.
Weight changes upon and immediately prior to abscission have been
investigated by Viro (1955) in a comparison of dry weights of 1000
green leaves or needles collected in August with dry weights of 1000
yellow leaves or needles collected partly from the tree and partly from
the ground at the end of September. Weight loss associated with yellowing averaged 21% (range 19 to 23%) for the deciduous Angiosperms
Betula (pubescens and verrucosa), Populus tremula, Alnus incana and
Salix caprea. If yellow Pinus silvestris needles are compared with needles
older than three years, the yellow ones weigh 44% less. For Picea abies
the difference is 39%. However, it cannot be assumed that all yellow
needles are more than three years old. If yellow and three-year needles
are compared, the weight loss on yellowing would appear to be only 34%
for both Pinus and Picea. Such a weight loss would still be very high,
about one-third of the total dry matter. A much lower difference between brownish and green Picea pungens needles was observed at
Minneapolis, U.S.A., on 29 May 1963. Sixty-eight brownish needles were