QUANTITATIVE ECOLOUY A N D WOODLAND ECOSYSTEM
143
plants. This is over twice the annual energy released per capita in
Britain from all kinds of industrial fuel. Tentative estimates of the
energy content of the woodland fauna and heterotrophic plants, from
the fauna weights in Table I11 and microflora numbers, indicate that
their maximum possible energy content is in the order of 0.2 x 1O’O cal
per ha, about one-twentieth of the annual energy release. Since the
biomass figures for the fauna and heterotrophic plants are based on the
maximum values, the total is probably too high and the true ratio of
energy content to annual flow is probably nearer one two-hundredth
(Macfadyen, 1 96 1).
The preparation of energy-balance tables showing the detailed
accounting of energy flows of this magnitude by the consumer organisms in different types of woodland ecosystems is not possible at present
but represents one of the most important and challenging problems t o
woodland ecologists. A recent investigation by Golley (1960) illustrates
the need t o combine closely both botanical and zoological studies in
order t o understand the functioning of terrestrial ecosystems in relation
to energy dynamics.
V. WATER CIRCULATION
On a world scale, the hydrologic cycle involves the interchange of
water between the oceans and the land via the atmosphere. Sutcliffe
(1956) has pointed out that the amount of precipitable water contained
in the world’s atmosphere only amounts t o 2.5 cm of rain, i.e. 25 x lo4
kg of water per ha of the earth’s surface, so that a huge and rapid
transfer of water takes place continually. Normally, precipitation, as
rain or snow, constitutes the main source of water for forest ecosystems,
although in some circumstances this may be supplemented by the
upward movement of subterranean water and by the lateral flow of soil
water from neighbouring ecosystems. Woodlands rarely occur in
regions where the annual input of water is less than 300 x lo4 kg per ha.
Whilst it is unlikely that forests materially modify the mass global
circulation of water, it has been implied that they may increase precipitation locally by inducing condensation through a reduction of air
temperature and an increase of humidity, both a result of transpiration,
and by collecting water droplets from low-lying cloud and fog (Oberlander, 1956; Bleasdale, 1957). Apart from areas where cloud- and
fog-drip take place, it seems doubtful that the presence of woodland
significantly changes the total precipitation, but once precipitation
occurs, the nature of the forest cover greatly affects the passage of
water through the ecosystem.
The pattern of water circulation in woodland ecosystems does not
follow the organic system so closely as does energy flow or mineral cir-
143
plants. This is over twice the annual energy released per capita in
Britain from all kinds of industrial fuel. Tentative estimates of the
energy content of the woodland fauna and heterotrophic plants, from
the fauna weights in Table I11 and microflora numbers, indicate that
their maximum possible energy content is in the order of 0.2 x 1O’O cal
per ha, about one-twentieth of the annual energy release. Since the
biomass figures for the fauna and heterotrophic plants are based on the
maximum values, the total is probably too high and the true ratio of
energy content to annual flow is probably nearer one two-hundredth
(Macfadyen, 1 96 1).
The preparation of energy-balance tables showing the detailed
accounting of energy flows of this magnitude by the consumer organisms in different types of woodland ecosystems is not possible at present
but represents one of the most important and challenging problems t o
woodland ecologists. A recent investigation by Golley (1960) illustrates
the need t o combine closely both botanical and zoological studies in
order t o understand the functioning of terrestrial ecosystems in relation
to energy dynamics.
V. WATER CIRCULATION
On a world scale, the hydrologic cycle involves the interchange of
water between the oceans and the land via the atmosphere. Sutcliffe
(1956) has pointed out that the amount of precipitable water contained
in the world’s atmosphere only amounts t o 2.5 cm of rain, i.e. 25 x lo4
kg of water per ha of the earth’s surface, so that a huge and rapid
transfer of water takes place continually. Normally, precipitation, as
rain or snow, constitutes the main source of water for forest ecosystems,
although in some circumstances this may be supplemented by the
upward movement of subterranean water and by the lateral flow of soil
water from neighbouring ecosystems. Woodlands rarely occur in
regions where the annual input of water is less than 300 x lo4 kg per ha.
Whilst it is unlikely that forests materially modify the mass global
circulation of water, it has been implied that they may increase precipitation locally by inducing condensation through a reduction of air
temperature and an increase of humidity, both a result of transpiration,
and by collecting water droplets from low-lying cloud and fog (Oberlander, 1956; Bleasdale, 1957). Apart from areas where cloud- and
fog-drip take place, it seems doubtful that the presence of woodland
significantly changes the total precipitation, but once precipitation
occurs, the nature of the forest cover greatly affects the passage of
water through the ecosystem.
The pattern of water circulation in woodland ecosystems does not
follow the organic system so closely as does energy flow or mineral cir-