Q U A N T I T A T I V E ECOLOGY A N D WOODLAND E C O S Y S T E M 119
weight distribution within the various woodland strata but from a comparison of Tables I and I11 it seems that the total biomass of the fauna
is likely t o be much less than that of the plants. However, animal biomass figures give little indication of the functional activity of the
organisms within the ecosystem and are probably of much more limited
value than plant biomass figures in relation t o ecosystem dynamics.
Nevertheless their determination is a necessary first stage in evaluating
the quantitative role of the fauna in forest processes.
3. Changes in Biomass
Changes in the weight of organic matter in woodland ecosystems
occur both during the year and on a longer term basis. In relatively
stable, mature, natural forests the weight of plant organic matter
present is presumably fairly constant from year t o year, there being an
overall equilibrium bet ween production and decomposition, a1 th ough
an intricate patchwork of accretion or loss may exist as old trees die and
are replaced by new ones. In present-day woodlands this situation occurs
only rarely, for in addition t o natural events such as windblow or fire,
the widespread effects of man have upset any natural equilibrium over
large areas.
When new woodlands become established a continuous build up of
organic matter takes place, and this can be seen best where new forests
are successfully planted on areas deficient in organic matter, such as
sand dunes or abandoned fields. The rate at which plant organic matter
accumulates depends upon many factors but the highly productive,
intensively managed woodlands of Table I contain approximately
350 x lo3 kg per ha of plant organic material when about 50 years old
giving an average annual rate of accretion of about 7 x lo3 kg per ha.
In some years the annual build up of plant organic matter greatly exceeds the average figure which includes the early stages when true woodland conditions do not exist and the older stages when large amounts of
timber are being harvested.
Current annual changes in the weights of trees, ground flora and the
organic matter over the surface of the mineral soil in plantations of
Pinus sylvestris growing at a good pine site in the English Breckland
are illustrated in Fig. 2 (Ovington, 1957a, 1959b). When the pine
plantations are at the dense pole stage, i.e. from 12 to 20 years of age,
there is a rapid build up of organic matter in the trees and on the forest
floor whilst the ground vegetation becomes sparser, until it is only
present in a few small patches. Afterwards, with the advent of thinning,
gaps are created in the tree canopy, the ground vegetation begins t o
spread and increase in veight and, although organic matter continues
to accumulate on the forest floor, it does so at a slower rate. The rate
weight distribution within the various woodland strata but from a comparison of Tables I and I11 it seems that the total biomass of the fauna
is likely t o be much less than that of the plants. However, animal biomass figures give little indication of the functional activity of the
organisms within the ecosystem and are probably of much more limited
value than plant biomass figures in relation t o ecosystem dynamics.
Nevertheless their determination is a necessary first stage in evaluating
the quantitative role of the fauna in forest processes.
3. Changes in Biomass
Changes in the weight of organic matter in woodland ecosystems
occur both during the year and on a longer term basis. In relatively
stable, mature, natural forests the weight of plant organic matter
present is presumably fairly constant from year t o year, there being an
overall equilibrium bet ween production and decomposition, a1 th ough
an intricate patchwork of accretion or loss may exist as old trees die and
are replaced by new ones. In present-day woodlands this situation occurs
only rarely, for in addition t o natural events such as windblow or fire,
the widespread effects of man have upset any natural equilibrium over
large areas.
When new woodlands become established a continuous build up of
organic matter takes place, and this can be seen best where new forests
are successfully planted on areas deficient in organic matter, such as
sand dunes or abandoned fields. The rate at which plant organic matter
accumulates depends upon many factors but the highly productive,
intensively managed woodlands of Table I contain approximately
350 x lo3 kg per ha of plant organic material when about 50 years old
giving an average annual rate of accretion of about 7 x lo3 kg per ha.
In some years the annual build up of plant organic matter greatly exceeds the average figure which includes the early stages when true woodland conditions do not exist and the older stages when large amounts of
timber are being harvested.
Current annual changes in the weights of trees, ground flora and the
organic matter over the surface of the mineral soil in plantations of
Pinus sylvestris growing at a good pine site in the English Breckland
are illustrated in Fig. 2 (Ovington, 1957a, 1959b). When the pine
plantations are at the dense pole stage, i.e. from 12 to 20 years of age,
there is a rapid build up of organic matter in the trees and on the forest
floor whilst the ground vegetation becomes sparser, until it is only
present in a few small patches. Afterwards, with the advent of thinning,
gaps are created in the tree canopy, the ground vegetation begins t o
spread and increase in veight and, although organic matter continues
to accumulate on the forest floor, it does so at a slower rate. The rate