Q U A N T I T A T I V E E C O L O G Y A N D WOODLAND E C O S Y S T E M
137
before the tree buds have opened, the bluebell grows rapidly so that at
peak biomass, which occurs towards the end of May, the above ground
shoots weigh about 500 kg per ha. The aerial shoots of the bluebell have
withered away by early summer when the leaves of the overstorey
vegetation are fully developed, so that primary production by bluebell
ceases completely until the following spring. During summer and winter
some loss of photosynthate through respiration occurs. The initial
growth of the bluebell shoots depends on the transference of food
reserves from subterranean bulbs and an overall increase in dry weight
only takes place from mid-April to the end of May. During this sevenweek period the total bluebell biomass trebles in weight, the increase
in bulb weight amounting t o 60% of the original (Blackman and
Rutter, 1947), even though the light intensity a t ground level progressively decreases t o about 0.3% of that in the open. The intimate
phenological synchronization between the over- and understorey vegetation effectively improves the productive capacity of these woodland
ecosystems since organic matter production by the bluebell precedes
that of the trees.
Marked differences exist in the length of the growing season of trees
of different species and in their growth when growing under similar
conditions. Kozlowski and Ward (1957a)b) have recorded the pattern
of seasonal height growth of conifers and deciduous trees; in some
cases height growth was concluded within 10 weeks but in all cases
height growth commenced in early spring, and had ended long before
the autumn frosts. Kozlowski and Ward do not record whether lammas
shoot growth occurred, but in England the production of lammas shoots
may account for a large proportion of the height growth and materially
extend the growth season (Ovington and MacRae, 1960). The radial
growth of tree stems shows a somewhat similar pattern of seasonal
growth although radial increment continues for a longer period than
height growth (Fritts, 1958; Fraser, 1952). Seasonal growth data do
not give a true measure of the seasonal fluctuations in net productivity,
thus Kozlowski and Ward suggest that early shoot growth depends on
the utilization of photosynthate produced in earlier years and that after
height growth has ceased the carbohydrate reserve continues t o
accumulate. Rutter (1957) studied the annual pattern of dry-weight
change for 2- to 5-year-old plants of Scotspine growing in south England
and found no general increase in dry weight during the early spring
period of rapid elongation of shoots and roots, the greatest weight
increments occurring from May t o September with a slight increase in
dry weight from October t o March. Regular seasonal variations in net
photosynthesis have also been recorded by field techniques such as
those developed by Huber (1950) which are based 011 measurements of
137
before the tree buds have opened, the bluebell grows rapidly so that at
peak biomass, which occurs towards the end of May, the above ground
shoots weigh about 500 kg per ha. The aerial shoots of the bluebell have
withered away by early summer when the leaves of the overstorey
vegetation are fully developed, so that primary production by bluebell
ceases completely until the following spring. During summer and winter
some loss of photosynthate through respiration occurs. The initial
growth of the bluebell shoots depends on the transference of food
reserves from subterranean bulbs and an overall increase in dry weight
only takes place from mid-April to the end of May. During this sevenweek period the total bluebell biomass trebles in weight, the increase
in bulb weight amounting t o 60% of the original (Blackman and
Rutter, 1947), even though the light intensity a t ground level progressively decreases t o about 0.3% of that in the open. The intimate
phenological synchronization between the over- and understorey vegetation effectively improves the productive capacity of these woodland
ecosystems since organic matter production by the bluebell precedes
that of the trees.
Marked differences exist in the length of the growing season of trees
of different species and in their growth when growing under similar
conditions. Kozlowski and Ward (1957a)b) have recorded the pattern
of seasonal height growth of conifers and deciduous trees; in some
cases height growth was concluded within 10 weeks but in all cases
height growth commenced in early spring, and had ended long before
the autumn frosts. Kozlowski and Ward do not record whether lammas
shoot growth occurred, but in England the production of lammas shoots
may account for a large proportion of the height growth and materially
extend the growth season (Ovington and MacRae, 1960). The radial
growth of tree stems shows a somewhat similar pattern of seasonal
growth although radial increment continues for a longer period than
height growth (Fritts, 1958; Fraser, 1952). Seasonal growth data do
not give a true measure of the seasonal fluctuations in net productivity,
thus Kozlowski and Ward suggest that early shoot growth depends on
the utilization of photosynthate produced in earlier years and that after
height growth has ceased the carbohydrate reserve continues t o
accumulate. Rutter (1957) studied the annual pattern of dry-weight
change for 2- to 5-year-old plants of Scotspine growing in south England
and found no general increase in dry weight during the early spring
period of rapid elongation of shoots and roots, the greatest weight
increments occurring from May t o September with a slight increase in
dry weight from October t o March. Regular seasonal variations in net
photosynthesis have also been recorded by field techniques such as
those developed by Huber (1950) which are based 011 measurements of