LITTER PRODUCTION IN FORESTS OF THE -WORLD
147
The mean leaf crop in t/ha/yr for closed canopy Angiosperm forests
in Table XIX is 3.7 for eleven Quercus sites, 3.0 for three Fagus sites,
2.9 for two Salix sites, 2.6 for two Alnus sites, 2.5 for two Fraxinus
sites, 2-5 for three Populus sites, and 2-4 for eight Betula sites. The high
values for Quercus sites, which range from 2.6 to 5.3 t/ha and include
four studies with values of 4-0 t/ha or more, are noteworthy. The
Quercus leaf is usually thick and leathery, with a high lignin content
(see Handley, 1954, Table XII). It is possible that Quercus forests are
among the highest pPoducers of leaf litter within the Temperate regions;
and the thick soil litter layers frequently found in Quercus forests may
be related to high production of leaves as well as to the slow rate of leaf
decay of many species in this genus. Some of the Betula and Populus
data &re taken from more northerly areas of the Temperate zone, and
are not directly comparable with the Quercus values.
Leaf crops of Gymnosperms in Table XIX are similar to those of
Angiosperms, with means in t/ha/yr of 2.8 for five Pinus sites and of
3.0 for two Larix sites. Of the nine Angiosperm and Gymnosperm
genera with two or more sites, seven genera, including both Gymnosperm genera, have leaf crops between 2.5 and 3-0 t/ha/yr. Mean Angiosperm leaf production by genera is 2.8 t/ha/yr which is similar to the
Gymnosperm mean of 2.9 t/ha/yr.
VII. LEAF LITTER AS AN INDEX TO NET PRODUCTION
Although leaf litter represents an amount somewhat less than leaf
production, owing to intrinsic and extrinsic weight losses prior to and
probably also following abscission, it may still be useful as a guide to
minimum levels of total net production. There is a logarithmic relationship between the foliage weight of some needle-leaved and a few broadleaved trees and tree stem diameter (Kittredge, 1944; Cable, 1958;
Satoo, 1962). It is doubtful if this relationship is of much use in predicting net total production since (1) the constants in the regression
equation obtained for a given stand will not, because of varying modes
of competition, necessarily apply to other stands of the same species
(Satoo, 1962) and (2) the relationship does not apply over the entire
life-span of a tree since it is common for many Gymnosperms, including
Pinus banksiana and P. contorta, to have a reduced, scraggly, broomshaped crown in later years, which is much smaller than the crown in
the earlier part of the life span. Cooper (1960) demonstrated a linear
relationship between needle air-dry weight and growth of stem basal
area from stump sections in two plots of young (30 yr and 49 yr) Pinus
ponderosa. There was no statistical difference in the regression equation
for the two plots. Other studies of foliage in relation t o net production
are desirable to determine whether a general regression equation can be
147
The mean leaf crop in t/ha/yr for closed canopy Angiosperm forests
in Table XIX is 3.7 for eleven Quercus sites, 3.0 for three Fagus sites,
2.9 for two Salix sites, 2.6 for two Alnus sites, 2.5 for two Fraxinus
sites, 2-5 for three Populus sites, and 2-4 for eight Betula sites. The high
values for Quercus sites, which range from 2.6 to 5.3 t/ha and include
four studies with values of 4-0 t/ha or more, are noteworthy. The
Quercus leaf is usually thick and leathery, with a high lignin content
(see Handley, 1954, Table XII). It is possible that Quercus forests are
among the highest pPoducers of leaf litter within the Temperate regions;
and the thick soil litter layers frequently found in Quercus forests may
be related to high production of leaves as well as to the slow rate of leaf
decay of many species in this genus. Some of the Betula and Populus
data &re taken from more northerly areas of the Temperate zone, and
are not directly comparable with the Quercus values.
Leaf crops of Gymnosperms in Table XIX are similar to those of
Angiosperms, with means in t/ha/yr of 2.8 for five Pinus sites and of
3.0 for two Larix sites. Of the nine Angiosperm and Gymnosperm
genera with two or more sites, seven genera, including both Gymnosperm genera, have leaf crops between 2.5 and 3-0 t/ha/yr. Mean Angiosperm leaf production by genera is 2.8 t/ha/yr which is similar to the
Gymnosperm mean of 2.9 t/ha/yr.
VII. LEAF LITTER AS AN INDEX TO NET PRODUCTION
Although leaf litter represents an amount somewhat less than leaf
production, owing to intrinsic and extrinsic weight losses prior to and
probably also following abscission, it may still be useful as a guide to
minimum levels of total net production. There is a logarithmic relationship between the foliage weight of some needle-leaved and a few broadleaved trees and tree stem diameter (Kittredge, 1944; Cable, 1958;
Satoo, 1962). It is doubtful if this relationship is of much use in predicting net total production since (1) the constants in the regression
equation obtained for a given stand will not, because of varying modes
of competition, necessarily apply to other stands of the same species
(Satoo, 1962) and (2) the relationship does not apply over the entire
life-span of a tree since it is common for many Gymnosperms, including
Pinus banksiana and P. contorta, to have a reduced, scraggly, broomshaped crown in later years, which is much smaller than the crown in
the earlier part of the life span. Cooper (1960) demonstrated a linear
relationship between needle air-dry weight and growth of stem basal
area from stump sections in two plots of young (30 yr and 49 yr) Pinus
ponderosa. There was no statistical difference in the regression equation
for the two plots. Other studies of foliage in relation t o net production
are desirable to determine whether a general regression equation can be