QUANTITATIVE ECOLOGY A N D WOODLAND ECOSYSTEM
131
radiation show that, for the 6 months, April to September, the maximum
possible net primary production for a closed green crop in the Netherlands is about 36 x lo3 kg per ha, so that West European forest production is considerably less than the potential production indicated by incoming solar radiation. Restrictions on production may be imposed by
factors such as water and nutrient shortage. The high level of production
of woodlands is achieved with remarkably little input of human energy
since forest soils are not normally ploughed or fertilized regularly and
the growing crop receives comparatively little attention. In addition,
the stability of the forest ecosystem is such that harvesting of large
amounts of organic matter as wood is possible without greatly affecting
the overall woodland productivity, at least over several generations
of trees. NiChiporoviEh and Strogonova (1957) have suggested that
good economic yields are dependent upon large biological production
and this is the case for woodlands. The chemical composition of the
organic matter produced by different ecosystems varies greatly, the
forest production being essentially bulk carbohydrate rather than
protein. It seems pertinent t o consider what the factors are that limit
primary production in woodland ecosystems.
ii. Factors A.ffecting Primary Production in Woodlands. Organic
matter production by woodlands may be considered from three interrelated viewpoints, ( a ) the environmental limits t o productivity, ( b ) the
features of woodland ecosystems enabling them t o attain a relatively
high level of efficiency in exploiting the environment, and ( c ) the possibilities of improving productivity by aylvicultural operations.
Several environmental factors are known t o limit woodland productivity and there is an extensive literature describing the circumstances
in which a particular factor becomes limiting. Kramer (1958) has
recently reported on the present status of research relating t o photosynthesis by trees with particular reference t o the influence of the more
important environmental factors namely, light, temperature, moisture,
mineral nutrition, atmospheric carbon dioxide, defoliating insects,
pathogenic fungi and toxic gases released by industry. Since photosynthesis is the plant metabolic process most directly concerned in the production of organic matter, the same factors, with the addition of wind
essentially control the upper limit of productivity, i.e. the site capacity.
Within the limits set by the environment, the rate of organic matter
production by woodland and other terrestrial ecosystems varies enormously but attention has been drawn t o the relative efficiency of some
woodlands. Working with agricultural crops Watson (1958) concluded
that with an adequate supply of moisture and minerals, the rate of
organic matter production depends upon the efficiency and more particularly the size of the photosynthetic system. $0 far as size is con-
131
radiation show that, for the 6 months, April to September, the maximum
possible net primary production for a closed green crop in the Netherlands is about 36 x lo3 kg per ha, so that West European forest production is considerably less than the potential production indicated by incoming solar radiation. Restrictions on production may be imposed by
factors such as water and nutrient shortage. The high level of production
of woodlands is achieved with remarkably little input of human energy
since forest soils are not normally ploughed or fertilized regularly and
the growing crop receives comparatively little attention. In addition,
the stability of the forest ecosystem is such that harvesting of large
amounts of organic matter as wood is possible without greatly affecting
the overall woodland productivity, at least over several generations
of trees. NiChiporoviEh and Strogonova (1957) have suggested that
good economic yields are dependent upon large biological production
and this is the case for woodlands. The chemical composition of the
organic matter produced by different ecosystems varies greatly, the
forest production being essentially bulk carbohydrate rather than
protein. It seems pertinent t o consider what the factors are that limit
primary production in woodland ecosystems.
ii. Factors A.ffecting Primary Production in Woodlands. Organic
matter production by woodlands may be considered from three interrelated viewpoints, ( a ) the environmental limits t o productivity, ( b ) the
features of woodland ecosystems enabling them t o attain a relatively
high level of efficiency in exploiting the environment, and ( c ) the possibilities of improving productivity by aylvicultural operations.
Several environmental factors are known t o limit woodland productivity and there is an extensive literature describing the circumstances
in which a particular factor becomes limiting. Kramer (1958) has
recently reported on the present status of research relating t o photosynthesis by trees with particular reference t o the influence of the more
important environmental factors namely, light, temperature, moisture,
mineral nutrition, atmospheric carbon dioxide, defoliating insects,
pathogenic fungi and toxic gases released by industry. Since photosynthesis is the plant metabolic process most directly concerned in the production of organic matter, the same factors, with the addition of wind
essentially control the upper limit of productivity, i.e. the site capacity.
Within the limits set by the environment, the rate of organic matter
production by woodland and other terrestrial ecosystems varies enormously but attention has been drawn t o the relative efficiency of some
woodlands. Working with agricultural crops Watson (1958) concluded
that with an adequate supply of moisture and minerals, the rate of
organic matter production depends upon the efficiency and more particularly the size of the photosynthetic system. $0 far as size is con-