126
J. D. OVINGTON
at the time of maximum production would be the most meaningful, but
at present the available data are too scanty for this. Volume yield
tables give some indication of the differences in maximum productivity
that might be anticipated although they only refer t o tree boles. Both
the current and mean annual volume increments for tree boles, t o a top
diameter of 3 in and including tree trunks removed as thinnings, are
given in standard British yield tables. The volume figures from these
tables converted t o oven-dry weights for quality class I sites for the
following species, Abies grandis, Pseudotsuga taxifolia, Pinus nigra,
Picea abies, Pinus sylvestris, Larix leptolepis, Fagus sylvatica, Larix
deciduu and Quercus robur, give maximum current annual increment
figures for the tree boles, expressed as lo3 kg per ha, as 17, 15, 12, 11,
9, 9, 8, 7 and 6, whilst the maximum mean values are 12, 10, 8, 8, 7, 7,
6, 5 and 4 respectively. The age at which maximum bole production is
achieved varies greatly, the' peak current annual increment value
usually occurs between 15 t o 45 years, and the peak mean annual
increment value usually occurs between 45 t o 80 years. The total annual
net primary productivity of the woodlands for all types of plant
material would be expected to be much greater than these bole increments, the increases varying for different tree species.
Whittaker (1961) working in the Great Smoky Mountains, U.S.A.
gives an annual net primary productivity for Rhododendron maximum
of 2 x lo3 kg per ha and for a mixed shrub community of 10 x lo3 kg
per ha. Moller et al. (1954) have estimated the current annual net
primary productivity of beech growing on a second quality site in Denmark t o be about 14 x 103 kg per ha at 25 and 46 years of age, but this
does not include any allowance for seed production, nor for the ground
flora. Ogawa et al. (1961) obtained net primary productivities of 19 and
25 x lo3 kg per ha per annum for semi-natural temperate evergreen and
evergreen gallery forests respectively in Thailand, but point out thak
these are under-estimates and suggest that the real annual net primary
productivity of the tropical forest is probably nearer 40 x lo3 kg per ha.
They refer to investigations in Japanese forests of Distylium racemosum.
and Abies sachalinensis which gave net primary productivities of about
22 x lo3 kg per ha per annum and t o a thicket of Arundo donax, a
bamboo-like grass, of the humid tropics with an extraordinarily high
annual value of 52 x lo3 kg per ha.
iv. Seasonal Pattern of Net Primary Productivity. The rate of net
primary production in a woodland ecosystem is not constant throughout the year but exhibits a well-defined seasonal rhythm which may be
different for the various plant strata. An extreme example of this is
seen in the deciduous woodlands of southern England where bluebell,
Endymion nonscriptus frequently dominates the ground flora. In March,
J. D. OVINGTON
at the time of maximum production would be the most meaningful, but
at present the available data are too scanty for this. Volume yield
tables give some indication of the differences in maximum productivity
that might be anticipated although they only refer t o tree boles. Both
the current and mean annual volume increments for tree boles, t o a top
diameter of 3 in and including tree trunks removed as thinnings, are
given in standard British yield tables. The volume figures from these
tables converted t o oven-dry weights for quality class I sites for the
following species, Abies grandis, Pseudotsuga taxifolia, Pinus nigra,
Picea abies, Pinus sylvestris, Larix leptolepis, Fagus sylvatica, Larix
deciduu and Quercus robur, give maximum current annual increment
figures for the tree boles, expressed as lo3 kg per ha, as 17, 15, 12, 11,
9, 9, 8, 7 and 6, whilst the maximum mean values are 12, 10, 8, 8, 7, 7,
6, 5 and 4 respectively. The age at which maximum bole production is
achieved varies greatly, the' peak current annual increment value
usually occurs between 15 t o 45 years, and the peak mean annual
increment value usually occurs between 45 t o 80 years. The total annual
net primary productivity of the woodlands for all types of plant
material would be expected to be much greater than these bole increments, the increases varying for different tree species.
Whittaker (1961) working in the Great Smoky Mountains, U.S.A.
gives an annual net primary productivity for Rhododendron maximum
of 2 x lo3 kg per ha and for a mixed shrub community of 10 x lo3 kg
per ha. Moller et al. (1954) have estimated the current annual net
primary productivity of beech growing on a second quality site in Denmark t o be about 14 x 103 kg per ha at 25 and 46 years of age, but this
does not include any allowance for seed production, nor for the ground
flora. Ogawa et al. (1961) obtained net primary productivities of 19 and
25 x lo3 kg per ha per annum for semi-natural temperate evergreen and
evergreen gallery forests respectively in Thailand, but point out thak
these are under-estimates and suggest that the real annual net primary
productivity of the tropical forest is probably nearer 40 x lo3 kg per ha.
They refer to investigations in Japanese forests of Distylium racemosum.
and Abies sachalinensis which gave net primary productivities of about
22 x lo3 kg per ha per annum and t o a thicket of Arundo donax, a
bamboo-like grass, of the humid tropics with an extraordinarily high
annual value of 52 x lo3 kg per ha.
iv. Seasonal Pattern of Net Primary Productivity. The rate of net
primary production in a woodland ecosystem is not constant throughout the year but exhibits a well-defined seasonal rhythm which may be
different for the various plant strata. An extreme example of this is
seen in the deciduous woodlands of southern England where bluebell,
Endymion nonscriptus frequently dominates the ground flora. In March,