Q U A N T I T A T I V E ECOLOGY A N D W O O D L A N D ECOSYSTEM
139
IV. ENERGY DYNAMICS
The woodland plants capable of photosynthesis transform part of the
solar energy reaching woodland ecosystems t o chemical energy, which
is stored in the plant organs. Some of the energy may be dissipated
later through the metabolism of the producer plants, the rest acts as a
source of energy for the other living organisms of the ecosystem. Whilst
the overall pattern of the energy system broadly parallels that of the
organic system, the two donot correspond exactly since theenergy content
of organic material is variable. Golley (1961) has stressed the relative
constancy of the calorific value of animal tissue at about 5 000 cal per g
dry weight compared with that of plant material which shows considerable variation with an average of about 4 500 cal per g dry weight.
As organic matter is broken down by animals and heterotrophic
plants, the energy it contains is either released or transferred along
the food chain in the consuming organisms, each organism depending
upon the preceding living organisms for a supply of energy. Because of
the respiration of the consumer organisms, the amount of energy transferred along the food chain becomes progressively smaller as comminiition proceeds. When organic matter accumulates within woodland ecosystems, such as young plantations, the annual fixation of energy
exceeds energy release so that there is a carry over of energy from year
t o year and eventually, a large store of energy may be built up in the
ecosystem. The detailed pattern of energy fixation, storage, 00w and
release in woodlands is extremely complicated and is incompletely
understood but it is possible t o prepare energy budgets for the plant
material showing in a general way the magnitude of the major features
of the energy system in woodlands (Fig. 6).
A. E N E R G Y FIXATION
Whilst certain micro-organisms are capable of chemosynthesis and
may contribute energy t o woodland ecosystems, chlorophyll-bearing
plants are virtually the sole agents of energy fixation and the primary
organic matter produced by the trees, shrubs and ground flora is the
principal source of energy on which the rest of the living organisms
ultimately depend. Consequently, the photosynthetic efficiency of the
green woodland plants places an upper limit t o the potential metabolism
of the entire ecosystem. It has been suggested that woodland ecosystems
are efficient producers of organic matter compared with other types of
terrestrial ecosystems and attention has been drawn t o the low light
intensity at ground level in dense canopied woodlands, so that comparatively high levels of energy fixation by woodland ecosystems may be
anticipated.
139
IV. ENERGY DYNAMICS
The woodland plants capable of photosynthesis transform part of the
solar energy reaching woodland ecosystems t o chemical energy, which
is stored in the plant organs. Some of the energy may be dissipated
later through the metabolism of the producer plants, the rest acts as a
source of energy for the other living organisms of the ecosystem. Whilst
the overall pattern of the energy system broadly parallels that of the
organic system, the two donot correspond exactly since theenergy content
of organic material is variable. Golley (1961) has stressed the relative
constancy of the calorific value of animal tissue at about 5 000 cal per g
dry weight compared with that of plant material which shows considerable variation with an average of about 4 500 cal per g dry weight.
As organic matter is broken down by animals and heterotrophic
plants, the energy it contains is either released or transferred along
the food chain in the consuming organisms, each organism depending
upon the preceding living organisms for a supply of energy. Because of
the respiration of the consumer organisms, the amount of energy transferred along the food chain becomes progressively smaller as comminiition proceeds. When organic matter accumulates within woodland ecosystems, such as young plantations, the annual fixation of energy
exceeds energy release so that there is a carry over of energy from year
t o year and eventually, a large store of energy may be built up in the
ecosystem. The detailed pattern of energy fixation, storage, 00w and
release in woodlands is extremely complicated and is incompletely
understood but it is possible t o prepare energy budgets for the plant
material showing in a general way the magnitude of the major features
of the energy system in woodlands (Fig. 6).
A. E N E R G Y FIXATION
Whilst certain micro-organisms are capable of chemosynthesis and
may contribute energy t o woodland ecosystems, chlorophyll-bearing
plants are virtually the sole agents of energy fixation and the primary
organic matter produced by the trees, shrubs and ground flora is the
principal source of energy on which the rest of the living organisms
ultimately depend. Consequently, the photosynthetic efficiency of the
green woodland plants places an upper limit t o the potential metabolism
of the entire ecosystem. It has been suggested that woodland ecosystems
are efficient producers of organic matter compared with other types of
terrestrial ecosystems and attention has been drawn t o the low light
intensity at ground level in dense canopied woodlands, so that comparatively high levels of energy fixation by woodland ecosystems may be
anticipated.