QUANTITATIVE ECOLOGY AND WOODLAND ECOSYSTEM
1%)
of gross productivity, so that net primary productivity seems the
most suitable basis for comparison. A distinction can be made between
primary biological productivity and the production of plant matter of
economic value (NiEiporoviE, 1960). Of these the economic yield is the
least satisfactory value for fundamental comparisons, since the intensity
of harvesting and type of plant material cropped are liable t o change
with changing social conditions. Valid reasons can be given for presenting net primary biological productivity as either the greatest values for
the mean or current annual production and doubt may be expressed
about the use of both values. It can be argued that the period of maximum biological production is a relatively short phase in a forest rotation
and cannot be maintained on a long-term basis so that the true measure
of forest productivity is the seasonal turnover of organic matter at the
equilibrium stage when no significant change in biomass is taking place
from year t o year. An alternative basis for comparison is the rate of
accretion of organic matter into woodland ecosystems, possibly with
some addition for the wood harvested. Tentative figures for some of
these different measures are given in Table V ; it should be emphasized
that these tend t o approximate to the maximum values for temperate
regions since they are based on the available figures for high production
woodlands growing on good sites.
There are few determinations of the net primary productivity of
other types of uncultivated terrestrial ecosystems. Billings and Bliss
(1959) have examined various characteristic alpine ecosystems and
record the following rates of net primary production of dry matter
exclusive of roots, expressed as 103 kg per ha: alpine snowbank communities 0.3 t o 1.3, alpine meadows 0.2 t o 1-1, an herbaceous community in North Alaska 0.6, heath Juncus field 1.3, heath Juncus
TABLE V
Approximate Maximum Primary Production of Organic
Matter by High-producing Woodlands in West Europe
Oven-dry weight
10' kg per ha
_ _
Current gross production
40
Current net production (Biological)
22
Current accretion of organic matter
Mean gross production
20
Mean net production (Economic-tree boles)
Mean accretion of organic matter
Current net production (Economic-tree boles)
17
10
Mean net production (Bioiogical)
15
12
7
E
E.R.-I
1%)
of gross productivity, so that net primary productivity seems the
most suitable basis for comparison. A distinction can be made between
primary biological productivity and the production of plant matter of
economic value (NiEiporoviE, 1960). Of these the economic yield is the
least satisfactory value for fundamental comparisons, since the intensity
of harvesting and type of plant material cropped are liable t o change
with changing social conditions. Valid reasons can be given for presenting net primary biological productivity as either the greatest values for
the mean or current annual production and doubt may be expressed
about the use of both values. It can be argued that the period of maximum biological production is a relatively short phase in a forest rotation
and cannot be maintained on a long-term basis so that the true measure
of forest productivity is the seasonal turnover of organic matter at the
equilibrium stage when no significant change in biomass is taking place
from year t o year. An alternative basis for comparison is the rate of
accretion of organic matter into woodland ecosystems, possibly with
some addition for the wood harvested. Tentative figures for some of
these different measures are given in Table V ; it should be emphasized
that these tend t o approximate to the maximum values for temperate
regions since they are based on the available figures for high production
woodlands growing on good sites.
There are few determinations of the net primary productivity of
other types of uncultivated terrestrial ecosystems. Billings and Bliss
(1959) have examined various characteristic alpine ecosystems and
record the following rates of net primary production of dry matter
exclusive of roots, expressed as 103 kg per ha: alpine snowbank communities 0.3 t o 1.3, alpine meadows 0.2 t o 1-1, an herbaceous community in North Alaska 0.6, heath Juncus field 1.3, heath Juncus
TABLE V
Approximate Maximum Primary Production of Organic
Matter by High-producing Woodlands in West Europe
Oven-dry weight
10' kg per ha
_ _
Current gross production
40
Current net production (Biological)
22
Current accretion of organic matter
Mean gross production
20
Mean net production (Economic-tree boles)
Mean accretion of organic matter
Current net production (Economic-tree boles)
17
10
Mean net production (Bioiogical)
15
12
7
E
E.R.-I