144
J . ROGER BRAY AND EVILLE GORHAM
B. SEASONAL CHANGES - EXTRINSIC
Estimates of the percentage utilization of attached leaves of forest
trees by primary consumers range from 5.9% for an Acer saccharum -
Betula lutea - Fagus grandifolia swamp forest to 10.6y0 for an upland Quercus forest (Bray, 1964). The mean of leaf co&.umption values
in Lindquist (1938), Rothacher et al. (1954) and Bray is 7.5%.
The rate of consumption, decomposition and respiration occurring
in leaves immediately after leaf-fall has seldom been studied. Lindquist
(1938) estimated that 15% of Fraxinus leaf litter and 10% of Ulmus
leaf litter were eaten by earthworms within 1 week after completion of
leaf-fall. Loss of weight by respiration may also be high, especially before
the leaf becomes desiccated. Studies of weight loss with various techniques of litter collection are badly needed, since such weight loss may
be higher than is usually realized, especially when collections are made
from the ground. There, leaves are subject to animal consumption, and
also, if they remain moist, to microbial decay. Bocock et al. (1960) found
that Quercus petraea leaves on a highly acid moder humus layer lost only
about 10% of their dry weight in two months. The loss was about 13%
on a faintly acid mull. Leaves of Fraxinus excelsior, much more susceptible to decay, lost about 26% of their dry weight in one month on
the moder and about 43% on the mull. On the mull earthworms removed
many whole Fraxinus leaflets from the nylon nets in which they were
held. Lunt (1935) observed that in 7 weeks after leaf-fall the dry weight
loss of some eastern North American Angiosperm tree leaves ranged
from 3 to 12%, being low for Quercus alba and Fagus grandifolia, and
high for Acer rubrum and Cornus jiorida. Earthworms were excluded
from the samples by the fine cloth mesh beneath the flat boxes in which
the leaves were placed.
c. MAGNITUDE OF LEAF CROPS
Table XIX shows weights of all attached leaves in various forests,
collections being made during the period of maturity but preceding the
phase of defoliation. Data are on an annual production basis, to allow
comparison of Angiosperms and Gymnosperms. The magnitude of these
values for yearly leaf production is similar to that of the cold temperate
leaf litter data in Table IV, but variability in site conditions, plant
populations and growing season climate makes direct comparison
dificult. In view of the extrinsic and intrinsic losses between the period
of petiole attachment and of collection in litter traps, it is likely that the
leaf crop values in Table XIX are somewhat higher than litter values
for the same community. Direct studies of leaf production and leaf litter
within one forest are needed.
J . ROGER BRAY AND EVILLE GORHAM
B. SEASONAL CHANGES - EXTRINSIC
Estimates of the percentage utilization of attached leaves of forest
trees by primary consumers range from 5.9% for an Acer saccharum -
Betula lutea - Fagus grandifolia swamp forest to 10.6y0 for an upland Quercus forest (Bray, 1964). The mean of leaf co&.umption values
in Lindquist (1938), Rothacher et al. (1954) and Bray is 7.5%.
The rate of consumption, decomposition and respiration occurring
in leaves immediately after leaf-fall has seldom been studied. Lindquist
(1938) estimated that 15% of Fraxinus leaf litter and 10% of Ulmus
leaf litter were eaten by earthworms within 1 week after completion of
leaf-fall. Loss of weight by respiration may also be high, especially before
the leaf becomes desiccated. Studies of weight loss with various techniques of litter collection are badly needed, since such weight loss may
be higher than is usually realized, especially when collections are made
from the ground. There, leaves are subject to animal consumption, and
also, if they remain moist, to microbial decay. Bocock et al. (1960) found
that Quercus petraea leaves on a highly acid moder humus layer lost only
about 10% of their dry weight in two months. The loss was about 13%
on a faintly acid mull. Leaves of Fraxinus excelsior, much more susceptible to decay, lost about 26% of their dry weight in one month on
the moder and about 43% on the mull. On the mull earthworms removed
many whole Fraxinus leaflets from the nylon nets in which they were
held. Lunt (1935) observed that in 7 weeks after leaf-fall the dry weight
loss of some eastern North American Angiosperm tree leaves ranged
from 3 to 12%, being low for Quercus alba and Fagus grandifolia, and
high for Acer rubrum and Cornus jiorida. Earthworms were excluded
from the samples by the fine cloth mesh beneath the flat boxes in which
the leaves were placed.
c. MAGNITUDE OF LEAF CROPS
Table XIX shows weights of all attached leaves in various forests,
collections being made during the period of maturity but preceding the
phase of defoliation. Data are on an annual production basis, to allow
comparison of Angiosperms and Gymnosperms. The magnitude of these
values for yearly leaf production is similar to that of the cold temperate
leaf litter data in Table IV, but variability in site conditions, plant
populations and growing season climate makes direct comparison
dificult. In view of the extrinsic and intrinsic losses between the period
of petiole attachment and of collection in litter traps, it is likely that the
leaf crop values in Table XIX are somewhat higher than litter values
for the same community. Direct studies of leaf production and leaf litter
within one forest are needed.