176
J. D. OVINOTON
ties of woodland soils have been recorded (Day, 1940; Zinecker, 1950;
Dimbleby, 1952 ; Giulimondi et al., 1956; Duchaufour and Guinaudeau,
1957; Wittich, 1961). Generally, comparisons are made of the soils of
woodlands of different tree species and of wooded and treeless areas
established in close proximity on originally similar soils. The published
results show a very wide range of rates of change and in some cases it
appears that soil changes attributed to the growth of trees may in
reality be due to initial differences in the sites being compared. The
most obvious and well-documented pedological differences recorded
are in the type, weight, percentage and total chemical compositionr;l of
the litter layers formed over the surface of the mineral soil. Changes in
the underlying mineral soil resulting from woodland growth are more
difficult to determine precisely and vary according to the inherent soil
properties. For example, in nutrient-deficient acid soils or base-rich
alkaline soils the soil pH is not likely to be changed greatly by a single
generation of trees. Whilst there is evidence that woodlands may cause
a redistribution of chemical elements within the soil profile, few data
are available of changes in the weights of nutrients in the whole Roil
mass. An increase in the amount of a particular chemical element in the
organic matter equalled by a corresponding decrease in the mineral
soil has not been demonstrated. In fact, the amounts of exchangeable
nutrients and total nitrogen in the mineral soil may be increased in
high-producing woodlands having a large nutrient uptake. Long-term
changes in woodland soils cannot be interpreted solely in terms of
nutrient incorporation within the organic mass and loss from the soil, but
account must be taken of the complete ecosystem dynamics, particularly the external flow of nutrients into and out of the woodland ecosystem. Any evaluation of the effect of woodlands on the soil resources
must also embrace the complete crop rotation, from establishment to
felling, since, when the tree trunks are harvested, the breakdown of the
tree crowns, roots and litter left in the ecosystem would partly compensate for any depletion of the soil reserves that has occurred.
E. INPUT
Nutrients contained in the precipitation constitute an important
addition to woodland ecosystems (Table XVIII) and, except for nitrogen and phosphorus, and to a lesser extent calcium, the amounts are
not much less than the annual removal in tree trunks. When precipitation is intercepted by vegetation some of the contained nutrients may
be absorbed directly by the vegetation. On balance, it seems that there
is a greater leaching out of nutrients from the plants, since the amount
contained in the precipitation is increased by interception, even though
only a proportion of the rain-water reaches ground level (Madgwick and
J. D. OVINOTON
ties of woodland soils have been recorded (Day, 1940; Zinecker, 1950;
Dimbleby, 1952 ; Giulimondi et al., 1956; Duchaufour and Guinaudeau,
1957; Wittich, 1961). Generally, comparisons are made of the soils of
woodlands of different tree species and of wooded and treeless areas
established in close proximity on originally similar soils. The published
results show a very wide range of rates of change and in some cases it
appears that soil changes attributed to the growth of trees may in
reality be due to initial differences in the sites being compared. The
most obvious and well-documented pedological differences recorded
are in the type, weight, percentage and total chemical compositionr;l of
the litter layers formed over the surface of the mineral soil. Changes in
the underlying mineral soil resulting from woodland growth are more
difficult to determine precisely and vary according to the inherent soil
properties. For example, in nutrient-deficient acid soils or base-rich
alkaline soils the soil pH is not likely to be changed greatly by a single
generation of trees. Whilst there is evidence that woodlands may cause
a redistribution of chemical elements within the soil profile, few data
are available of changes in the weights of nutrients in the whole Roil
mass. An increase in the amount of a particular chemical element in the
organic matter equalled by a corresponding decrease in the mineral
soil has not been demonstrated. In fact, the amounts of exchangeable
nutrients and total nitrogen in the mineral soil may be increased in
high-producing woodlands having a large nutrient uptake. Long-term
changes in woodland soils cannot be interpreted solely in terms of
nutrient incorporation within the organic mass and loss from the soil, but
account must be taken of the complete ecosystem dynamics, particularly the external flow of nutrients into and out of the woodland ecosystem. Any evaluation of the effect of woodlands on the soil resources
must also embrace the complete crop rotation, from establishment to
felling, since, when the tree trunks are harvested, the breakdown of the
tree crowns, roots and litter left in the ecosystem would partly compensate for any depletion of the soil reserves that has occurred.
E. INPUT
Nutrients contained in the precipitation constitute an important
addition to woodland ecosystems (Table XVIII) and, except for nitrogen and phosphorus, and to a lesser extent calcium, the amounts are
not much less than the annual removal in tree trunks. When precipitation is intercepted by vegetation some of the contained nutrients may
be absorbed directly by the vegetation. On balance, it seems that there
is a greater leaching out of nutrients from the plants, since the amount
contained in the precipitation is increased by interception, even though
only a proportion of the rain-water reaches ground level (Madgwick and