LITTER PRODUCTION I N FORESTS O F THE WORLD
107
We are especially indebted to the librarians in the reference room of
the University of Toronto Library for their expert and unfailing
bibliographic assistance.
111. SELECTION AND PRESENTATION O F DATA
A. CRITERIA FOR ACCEPTANCE
Despite wide variation in methods of litter collection (e.g., raking of
cleared surface, cloth or wire screen at soil surface, box or bucket with
screen bottom above soil surface) and adequacy of sampling, most of
the data examined have been included in this review, in order to obtain
maximum coverage. Owing t o the difficulty of equating number, area
and type of litter traps, length of exposure, etc., studies of very unequal
value have had to be given equal weight. I n the case of Japanese
forests (Ohmasa and Mori, 1937) the few data based on less than five
plots were omitted. A study by Tarrant et ul. (1951) has been excluded
because the data refer mainly to one year's growth of leaves or needles
sampled from the lower portion of the crown (G. S. Meagher, private
communication). All values based on complete or representative sampling of forest tree canopy have been segregated for separate examination
of the yearly standing crop of tree foliage (see Table XIX).
No attempt has been made to convert air-dry to oven-dry weights,
partly because it has not always been possible to ascertain the method
of drying, but also for other reasons. There appears to be considerable
variation in weight loss upon further drying. Table I11 shows between
7 and 18% loss in weight by air-dry litter after drying either at an
elevated temperature or in vucuo. Ebermayer (1876) reported losses
TABLE I11
Loss of Weight by Air-dried Litter upon Further Drying
Material
% weight loss Drying method
Authority
Fagus sihatica litter
18
100" c
Ebermayer, 1876
Picea abies litter
15
looo c
Ebermayer, 1876
Pinus silvestris litter
14
100" c
Ebermayer, 1876
Fagus silvatica leaves
9.4
-
Burger, 1925
Picea abies needles
10.0
-
Burger, 1925
Picea abies needles
8.1
In vacuo, P,O,
Lindberg and Norming, 1943
Picea abies needles
6.8
I n vacuo, P,O,
Lindberg and Norming, 1943
Picea ubiecr needles
6.9
100-105" C, 5 h. Lindberg and Norming, 1943
Populus leaves
7.8
I n vucuo, P,O,
AnderssonandEnander, 1948
Bet& litter
10.5
I n vacuo, 20" C Knudsen and
Betub litter
10.8
10@-103° C, 2.6 h. Knudsen and
Angiosperm tree litter
8.7
105' C
Bray, unpublished
Heath and moss litter
9.5
In vacuo, P,O,
AndrB, 1947
Mauritz-Hansson, 1939
Mauritz-Hansson, 1939
107
We are especially indebted to the librarians in the reference room of
the University of Toronto Library for their expert and unfailing
bibliographic assistance.
111. SELECTION AND PRESENTATION O F DATA
A. CRITERIA FOR ACCEPTANCE
Despite wide variation in methods of litter collection (e.g., raking of
cleared surface, cloth or wire screen at soil surface, box or bucket with
screen bottom above soil surface) and adequacy of sampling, most of
the data examined have been included in this review, in order to obtain
maximum coverage. Owing t o the difficulty of equating number, area
and type of litter traps, length of exposure, etc., studies of very unequal
value have had to be given equal weight. I n the case of Japanese
forests (Ohmasa and Mori, 1937) the few data based on less than five
plots were omitted. A study by Tarrant et ul. (1951) has been excluded
because the data refer mainly to one year's growth of leaves or needles
sampled from the lower portion of the crown (G. S. Meagher, private
communication). All values based on complete or representative sampling of forest tree canopy have been segregated for separate examination
of the yearly standing crop of tree foliage (see Table XIX).
No attempt has been made to convert air-dry to oven-dry weights,
partly because it has not always been possible to ascertain the method
of drying, but also for other reasons. There appears to be considerable
variation in weight loss upon further drying. Table I11 shows between
7 and 18% loss in weight by air-dry litter after drying either at an
elevated temperature or in vucuo. Ebermayer (1876) reported losses
TABLE I11
Loss of Weight by Air-dried Litter upon Further Drying
Material
% weight loss Drying method
Authority
Fagus sihatica litter
18
100" c
Ebermayer, 1876
Picea abies litter
15
looo c
Ebermayer, 1876
Pinus silvestris litter
14
100" c
Ebermayer, 1876
Fagus silvatica leaves
9.4
-
Burger, 1925
Picea abies needles
10.0
-
Burger, 1925
Picea abies needles
8.1
In vacuo, P,O,
Lindberg and Norming, 1943
Picea abies needles
6.8
I n vacuo, P,O,
Lindberg and Norming, 1943
Picea ubiecr needles
6.9
100-105" C, 5 h. Lindberg and Norming, 1943
Populus leaves
7.8
I n vucuo, P,O,
AnderssonandEnander, 1948
Bet& litter
10.5
I n vacuo, 20" C Knudsen and
Betub litter
10.8
10@-103° C, 2.6 h. Knudsen and
Angiosperm tree litter
8.7
105' C
Bray, unpublished
Heath and moss litter
9.5
In vacuo, P,O,
AndrB, 1947
Mauritz-Hansson, 1939
Mauritz-Hansson, 1939