QUANTITATIVE ECOLOQY AND WOODLAND ECOSYSTEM
109
Table does not suggest that the woodland shrub layer is typically very
luxuriant. The dry weight of the herbaceous layer varies considerably,
the understorey vegetation being absent in dense woodlands and very
luxuriant in open sheltered woodlands where it may exceed the tree
leaves in weight. Pase and Hurd (1957) found that the biomass of the
air-dry herbage increased from 25 t o 1 857 kg per ha when the basal
area of the trees decreased from 50 m2 per ha to 0 on clear-cut areas.
From evidence obtained with trenched plots, Ellison and Houston
(1958) suggest that root competition between the trees and understorey
plants is an important factor, perhaps more important than shading,
in limiting the growth of the understorey vegetation. Tamm (1953)
found that in an open spruce forest with a mossy ground flora, mainly
of Hylocomium splendens, the living moss biomass was about 2 080 kg
per ha. The annual production of about 1 2 9 8 kg per ha by the moss
was closely related t o the light supply when this was low, and at high
light intensities t o the nutrient supply contained in the rain-water
dripping from the tree canopies.
Numerous weight determinations have been reported for the layer
of organic matter formed over the mineral soil; in temperate regions
little organic matter accumulates under most hardwood tree species,
beech can be a notable exception, whilst in coniferous stands a large
weight of surface crganic matter may persist. Metz (1954) comparing
hardwood and pine stands in South Carolina, U.S.A., found the ovendry weight of organic matter, calculated as lo3 kg per ha, ranged from
6 to 12 in hardwood stands, from 13 t o 18 in mixed hardwood and pine
stands, and from 17 t o 23 in pine stands. Further north, greater amounts
of organic matter tend to accumulate over the mineral soil. Alway and
various associates (Alway, 1930; Alway and Harmer, 1927; Alway and
Rost, 1927) give a range of 18 to 76 x lo3 kg per ha for the weight of
surface organic matter in nine virgin forest stands in Minnesota,
U.S.A., 16 to 58, for 21 forests in north eastern Minnesota, and 18 t o
38 for five pine stands in North Minnesota. Ovington (1954a) in England
found the weight of the surface organic matter varied hetween 4 t o
6 x lo3 kg per ha in nine hardwood stands and from 7 t o 35 in 19 plantations of coniferous trees. The 33-year-old stand of Scots pine in Table I
has an unusually huge amount of surface organic matter, but this
plantation is particularly dense, has been neglected and never thinned
so that the soil organic layer contains a large proportion of fallen trees
and branches. I n this respect it closely resembles the natural Douglas
fir stands, the differences in weight of the organic matter of the forest
floor in managed and natural st,ands being well-shown by the Douglas
fir series. No biomass figures for natural populations of forest fungi and
bacteria are known but bacteria and fungi are included in the organic
109
Table does not suggest that the woodland shrub layer is typically very
luxuriant. The dry weight of the herbaceous layer varies considerably,
the understorey vegetation being absent in dense woodlands and very
luxuriant in open sheltered woodlands where it may exceed the tree
leaves in weight. Pase and Hurd (1957) found that the biomass of the
air-dry herbage increased from 25 t o 1 857 kg per ha when the basal
area of the trees decreased from 50 m2 per ha to 0 on clear-cut areas.
From evidence obtained with trenched plots, Ellison and Houston
(1958) suggest that root competition between the trees and understorey
plants is an important factor, perhaps more important than shading,
in limiting the growth of the understorey vegetation. Tamm (1953)
found that in an open spruce forest with a mossy ground flora, mainly
of Hylocomium splendens, the living moss biomass was about 2 080 kg
per ha. The annual production of about 1 2 9 8 kg per ha by the moss
was closely related t o the light supply when this was low, and at high
light intensities t o the nutrient supply contained in the rain-water
dripping from the tree canopies.
Numerous weight determinations have been reported for the layer
of organic matter formed over the mineral soil; in temperate regions
little organic matter accumulates under most hardwood tree species,
beech can be a notable exception, whilst in coniferous stands a large
weight of surface crganic matter may persist. Metz (1954) comparing
hardwood and pine stands in South Carolina, U.S.A., found the ovendry weight of organic matter, calculated as lo3 kg per ha, ranged from
6 to 12 in hardwood stands, from 13 t o 18 in mixed hardwood and pine
stands, and from 17 t o 23 in pine stands. Further north, greater amounts
of organic matter tend to accumulate over the mineral soil. Alway and
various associates (Alway, 1930; Alway and Harmer, 1927; Alway and
Rost, 1927) give a range of 18 to 76 x lo3 kg per ha for the weight of
surface organic matter in nine virgin forest stands in Minnesota,
U.S.A., 16 to 58, for 21 forests in north eastern Minnesota, and 18 t o
38 for five pine stands in North Minnesota. Ovington (1954a) in England
found the weight of the surface organic matter varied hetween 4 t o
6 x lo3 kg per ha in nine hardwood stands and from 7 t o 35 in 19 plantations of coniferous trees. The 33-year-old stand of Scots pine in Table I
has an unusually huge amount of surface organic matter, but this
plantation is particularly dense, has been neglected and never thinned
so that the soil organic layer contains a large proportion of fallen trees
and branches. I n this respect it closely resembles the natural Douglas
fir stands, the differences in weight of the organic matter of the forest
floor in managed and natural st,ands being well-shown by the Douglas
fir series. No biomass figures for natural populations of forest fungi and
bacteria are known but bacteria and fungi are included in the organic