128
J. D. OVINGTON
carbon dioxide absorption. Using such a technique Saeki and Nomoto
(1958) found that the photosynthetic activity of a deciduous tree
Zelkowa serrata reached its maximum in April and this was maintained
for about 24 months before decreasing slowly until defoliation occurred in
November. Coniferous trees showed a similar seasonal pattern of photosynthesis to Zelkowa except that some net photosynthesis occurred
in winter although a t a much lower rate than during the summer
months. There has been some controversy about whether the amount of
net photosynthesis of evergreen trees in winter is significant (Bourdeau,
1959). The extent of winter curtailment of net photosynthesis depends
upon the severity of the cold weather and the cold-hardiness of the
trees (Parker, 1961) so that when climatic conditions are favourable,
evergreen trees give small but positive winter net photosynthesis rates.
Pearson and Lawrence (1958) have shown that large amounts o i chlorophyll are contained in the bark of the quaking aspen Populus tremuloides and suggest that in early spring, before leaf emergence, photosynthesis may occur in the tree bark of deciduous hardwoods.
2. Gross P ~ i m r y
Production
Since pert of the photosynthate produced by woodland plants is used
in their respiration, the gross primary productivity is in excess of the
net values. The rate of respiration varies greatly for different plant
parts, being high for leaves and relatively low for woody material such
as tree trunks, and also shows marked seasonal changes (Johansson,
1933). Moller et al. (1954) have calculated the annual loss of photosynthate by respiration for beech stands in Denmark, expressed as lo3
kg per ha, t o be about 6 at 8 years of age and increasing to 10 at 85
years, equal t o 85% and 89% of the net primary productivity. Ogawa
et al. (1961) using data for Japanese forests give respiration losses of
243% and 124% of the net primary productivity for Disfylium racemosum and Abies sachalin,ensis forest, whilst Tranquillini (1959a,b)
found that for 5- to 8-year-old trees of Pinus cembra, the loss of photosynthate by respiration was about 62% of the annual dry matter
increment.
3. Woodland Ecosystems as Productive Units
i . Woodlands Compared with other Terrestrial Ecosystems. Natural and
artificial ecosystems containing green plants all have the ability t o
synthesize and accumulate organic matter and it is of interest to contrast woodlands with other ecosystems for the efficiency with which site
conditions are utilized for the annual production of organic matter. The
main difficulty is to decide on the most appropriate basis on which to
assess woodland productivity. At present there are few data available
J. D. OVINGTON
carbon dioxide absorption. Using such a technique Saeki and Nomoto
(1958) found that the photosynthetic activity of a deciduous tree
Zelkowa serrata reached its maximum in April and this was maintained
for about 24 months before decreasing slowly until defoliation occurred in
November. Coniferous trees showed a similar seasonal pattern of photosynthesis to Zelkowa except that some net photosynthesis occurred
in winter although a t a much lower rate than during the summer
months. There has been some controversy about whether the amount of
net photosynthesis of evergreen trees in winter is significant (Bourdeau,
1959). The extent of winter curtailment of net photosynthesis depends
upon the severity of the cold weather and the cold-hardiness of the
trees (Parker, 1961) so that when climatic conditions are favourable,
evergreen trees give small but positive winter net photosynthesis rates.
Pearson and Lawrence (1958) have shown that large amounts o i chlorophyll are contained in the bark of the quaking aspen Populus tremuloides and suggest that in early spring, before leaf emergence, photosynthesis may occur in the tree bark of deciduous hardwoods.
2. Gross P ~ i m r y
Production
Since pert of the photosynthate produced by woodland plants is used
in their respiration, the gross primary productivity is in excess of the
net values. The rate of respiration varies greatly for different plant
parts, being high for leaves and relatively low for woody material such
as tree trunks, and also shows marked seasonal changes (Johansson,
1933). Moller et al. (1954) have calculated the annual loss of photosynthate by respiration for beech stands in Denmark, expressed as lo3
kg per ha, t o be about 6 at 8 years of age and increasing to 10 at 85
years, equal t o 85% and 89% of the net primary productivity. Ogawa
et al. (1961) using data for Japanese forests give respiration losses of
243% and 124% of the net primary productivity for Disfylium racemosum and Abies sachalin,ensis forest, whilst Tranquillini (1959a,b)
found that for 5- to 8-year-old trees of Pinus cembra, the loss of photosynthate by respiration was about 62% of the annual dry matter
increment.
3. Woodland Ecosystems as Productive Units
i . Woodlands Compared with other Terrestrial Ecosystems. Natural and
artificial ecosystems containing green plants all have the ability t o
synthesize and accumulate organic matter and it is of interest to contrast woodlands with other ecosystems for the efficiency with which site
conditions are utilized for the annual production of organic matter. The
main difficulty is to decide on the most appropriate basis on which to
assess woodland productivity. At present there are few data available