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J. ROGER BRAY AND EVILLE GIORHAM
values are not always strictly comparable, and it may be observed that
for Angiosperms sampled over 4 years the ratio of maximum to minimum annual litter-fall may be as high as 2.7 (in a New Zealand Nothofagus truncata forest). The highest ratio for Northern Hemisphere
deciduous Angiosperms is 1.8 for Acer saccharurn mixed forest. Records
over 7 years yield no higher ratios. Data for Gymnosperms include some
much longer periods of comparison, and the greatest annual variation
is recorded for a Pinus nigra stand observed over 12 years, the maximum/minimurn ratio being 5-1. I n general the longer periods of observation yield higher ratios, as expected.
Over comparable periods in the North Temperate zone, Gymnosperms tend to show high ratios a little more frequently than Angiosperms. It is well known that the longevity of evergreen Gymnosperm
leaves depends upon both internal and external conditions, so that
fluctuations from year to year in the environment might be expected
to affect the leaf-fall of such species more than that of deciduous Angiosperms whose leaves are necessarily shed every year. The single 4-year
ratio for Equatorial forest is very low, at 1.1, as might perhaps be expected where climatic fluctuations are not very severe.
The fall of non-leaf litter has not often been measured over several
years, but annual variation in the four recorded cases is relatively high,
maximum/minimum ratios over 4-6 years ranging from 1.9 for Nothofagus truncata (Miller and Hurst, 1957) to 11.9 for Quercus forest (Hole
and Nielsen, private communication). Bray recorded a ratio of 5.8 for
Acer saccharurn mixed forest and Mork (1942) a ratio of 3.7 for Betub.
Such wide variation is to be expected, since the fall of branches is a
very local phenomenon of great weight where it occurs.
Among environmental factors mentioned as associated with abnormal
litter-fall are storms (Picea abies - Bornebusch, 1937; exotic Gymnosperms in New Zealand - Will, 1959; Betula - Knudsen and MauritzHansson, 1939), which may have a very great effect on twig and branch
litter-fall. Insect attack may also be important (Picea abies - Mork,
1942). Dryness has been remarked as a factor in high Picea abies needlefall (Bornebusch, 1932), but in contrast Witkamp and van der Drift
(1961) observed that in the Netherlands three surface-rooting deciduous
species exhibited distinctly low litter-fall during a dry summer, while a
fourth deep-rooting species yielded only slightly less litter than usual.
I n New Zealand, Miller and Hurst (1957) reported that hot dry summers
favor flowering of Nothfagus truncata, and since leaf bud production
for the following year’s foliage varies inversely with flowering, a lower
subsequent leaf-fall would be expected. Cold temperatures may also
increase litter-fall, for Owen’s (1954) data on Picea sitchensis in Wales
show nearly twice as much needle deposition in 1946-47, when the
J. ROGER BRAY AND EVILLE GIORHAM
values are not always strictly comparable, and it may be observed that
for Angiosperms sampled over 4 years the ratio of maximum to minimum annual litter-fall may be as high as 2.7 (in a New Zealand Nothofagus truncata forest). The highest ratio for Northern Hemisphere
deciduous Angiosperms is 1.8 for Acer saccharurn mixed forest. Records
over 7 years yield no higher ratios. Data for Gymnosperms include some
much longer periods of comparison, and the greatest annual variation
is recorded for a Pinus nigra stand observed over 12 years, the maximum/minimurn ratio being 5-1. I n general the longer periods of observation yield higher ratios, as expected.
Over comparable periods in the North Temperate zone, Gymnosperms tend to show high ratios a little more frequently than Angiosperms. It is well known that the longevity of evergreen Gymnosperm
leaves depends upon both internal and external conditions, so that
fluctuations from year to year in the environment might be expected
to affect the leaf-fall of such species more than that of deciduous Angiosperms whose leaves are necessarily shed every year. The single 4-year
ratio for Equatorial forest is very low, at 1.1, as might perhaps be expected where climatic fluctuations are not very severe.
The fall of non-leaf litter has not often been measured over several
years, but annual variation in the four recorded cases is relatively high,
maximum/minimum ratios over 4-6 years ranging from 1.9 for Nothofagus truncata (Miller and Hurst, 1957) to 11.9 for Quercus forest (Hole
and Nielsen, private communication). Bray recorded a ratio of 5.8 for
Acer saccharurn mixed forest and Mork (1942) a ratio of 3.7 for Betub.
Such wide variation is to be expected, since the fall of branches is a
very local phenomenon of great weight where it occurs.
Among environmental factors mentioned as associated with abnormal
litter-fall are storms (Picea abies - Bornebusch, 1937; exotic Gymnosperms in New Zealand - Will, 1959; Betula - Knudsen and MauritzHansson, 1939), which may have a very great effect on twig and branch
litter-fall. Insect attack may also be important (Picea abies - Mork,
1942). Dryness has been remarked as a factor in high Picea abies needlefall (Bornebusch, 1932), but in contrast Witkamp and van der Drift
(1961) observed that in the Netherlands three surface-rooting deciduous
species exhibited distinctly low litter-fall during a dry summer, while a
fourth deep-rooting species yielded only slightly less litter than usual.
I n New Zealand, Miller and Hurst (1957) reported that hot dry summers
favor flowering of Nothfagus truncata, and since leaf bud production
for the following year’s foliage varies inversely with flowering, a lower
subsequent leaf-fall would be expected. Cold temperatures may also
increase litter-fall, for Owen’s (1954) data on Picea sitchensis in Wales
show nearly twice as much needle deposition in 1946-47, when the