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J. D. OVINQTON
less than in corresponding virgin stands. He suggests that there is a
maximum humus depth at which equilibrium is attained between
annual litter fall and decomposition. It is noteworthy that although
dead organic matter accumulates rapidly over the ground in young
coniferous plantations, ultimately a stage is reached at which no further
litter accretion takes place. Once the weight of the litter layers becomes
constant from year t o year, annual litter fall and decomposition must
be equal so that the annual litter fall provides a measure of organic
matter breakdown at the surface of the mineral soil.
From the limited viewpoint of the mass annual turnover of the
primary production of aerial shoots, once the equilibrium stage between
litter fall and decomposition is reached, there is little significant difference between woodlands having very different amounts of litter
accumulated on the ground so long as the amount of litter fall is equal.
Coniferous forests in Britain frequently develop a thick layer of organic
matter over the mineral soil, about three t o five times the weight of the
annual litter fall, and we can assume that on the whole, the annual
litter fall takes from 3 t o 5 years to decompose. In deciduous woodlands
at similar sites, there is frequently little carry over of litter from year
t o year so that annually complete decomposition of the litter fall is
achieved. In fact decomposition is often so rapid that it is virtually
completed within a 6- t o 9-month period. Nevertheless, since litter fall
is often much greater in softwood than hardwood forests, the annual
rate of organic matter turnover through the coniferous litter may far
exceed that of the deciduous hardwood forest.
Studies of organic mhtter turnover have been largely concerned with
the above-ground parts but the turnover of roots may be equally important. Harley (1959) has published a series of photographs of beech
roots at different times of the year and points out the seasonal loss of
roots which he attributes t o drought or animal action. Unfortunately few
quantitative data of root decomposition are available but Remezov
(1959) reports that in a 50-year-old oak stand in U.S.S.R. the mortality
of roots less than 3 mm in diameter amounted to about 0.3 x lo3 kg per
ha from June to August. Orlov (1955) has reported that the turnover
of roots in a 25-year-old conifer stand was about 50% of that of the
needles and in a 50-year-old stand about 20%.
In the older plantations of the age series of Scots pine, the annual turnover of plant material through the litter amounts to about 8 x lo3 kg per
ha and, if allowance is made for the breakdown of small roots, the annual
turnover of organic matter would be over 9 x lo3 kg per ha. Other more
productive woodlands would be expected to have a greater annual decomposition of organic matter; Ogawa et al. (1961) for example, give a range
of values increasing to 25 x lo3 kg per ha for the evergreen gallery forest.
J. D. OVINQTON
less than in corresponding virgin stands. He suggests that there is a
maximum humus depth at which equilibrium is attained between
annual litter fall and decomposition. It is noteworthy that although
dead organic matter accumulates rapidly over the ground in young
coniferous plantations, ultimately a stage is reached at which no further
litter accretion takes place. Once the weight of the litter layers becomes
constant from year t o year, annual litter fall and decomposition must
be equal so that the annual litter fall provides a measure of organic
matter breakdown at the surface of the mineral soil.
From the limited viewpoint of the mass annual turnover of the
primary production of aerial shoots, once the equilibrium stage between
litter fall and decomposition is reached, there is little significant difference between woodlands having very different amounts of litter
accumulated on the ground so long as the amount of litter fall is equal.
Coniferous forests in Britain frequently develop a thick layer of organic
matter over the mineral soil, about three t o five times the weight of the
annual litter fall, and we can assume that on the whole, the annual
litter fall takes from 3 t o 5 years to decompose. In deciduous woodlands
at similar sites, there is frequently little carry over of litter from year
t o year so that annually complete decomposition of the litter fall is
achieved. In fact decomposition is often so rapid that it is virtually
completed within a 6- t o 9-month period. Nevertheless, since litter fall
is often much greater in softwood than hardwood forests, the annual
rate of organic matter turnover through the coniferous litter may far
exceed that of the deciduous hardwood forest.
Studies of organic mhtter turnover have been largely concerned with
the above-ground parts but the turnover of roots may be equally important. Harley (1959) has published a series of photographs of beech
roots at different times of the year and points out the seasonal loss of
roots which he attributes t o drought or animal action. Unfortunately few
quantitative data of root decomposition are available but Remezov
(1959) reports that in a 50-year-old oak stand in U.S.S.R. the mortality
of roots less than 3 mm in diameter amounted to about 0.3 x lo3 kg per
ha from June to August. Orlov (1955) has reported that the turnover
of roots in a 25-year-old conifer stand was about 50% of that of the
needles and in a 50-year-old stand about 20%.
In the older plantations of the age series of Scots pine, the annual turnover of plant material through the litter amounts to about 8 x lo3 kg per
ha and, if allowance is made for the breakdown of small roots, the annual
turnover of organic matter would be over 9 x lo3 kg per ha. Other more
productive woodlands would be expected to have a greater annual decomposition of organic matter; Ogawa et al. (1961) for example, give a range
of values increasing to 25 x lo3 kg per ha for the evergreen gallery forest.