182
T.T. Veblen and P.B. Alaback
higher latitudes than in South America, with peak rainfall typically
occurring in the fall. An equally significant and more consistent gradient
of temperature characterizes this north-south transect , as shown in Figure
9.3. This gradient in temperature encompasses a wider range than in
South America and is closely related to forest yield and productivity (Farr
& Harris , 1979). Seasonal variation of temperature is greatest in the
north , whereas diurnal variation is greate st in the south. Fog plays a key
role in depressing spring and summer temperatures, particularly in the
seasonal rainforest zone. Along the Oregon coast, the moderating
influence of the ocean is most constricted , often to within only 1 km of the
coast, and is most pervasive in southeast Alaska , where moderated temperatures may extend 150km inland.
Patterns of Stand Development
Patterns of stand development in North and South American rainforests
are the consequence of both coarse-scale disturbances producing wholestand replacement patterns and small tree falls resulting in fine-scale gap
dynamics. In landscapes dominated by a high rate of coarse-scale disturbance, patterns of stand development are well described by Oliver's
(1981) general model of whole-stand replacement, consisting of the
following four stages: stand initiation , stem exclusion, understory reinitiation , and old growth.
In South American temperate rainforests , coarse-scale disturbances are
particularly important , and stand development patterns conform with
Oliver's (1981) model of whole-stand replacement. Following coarse-scale
disturbances such as landslides, fire, glacial activity, and volcanic ash
deposition, shade-intolerant tree species such as Nothofagus species,
Weinmannia trichosperma , and/or Eucryphia cordifolia form even-aged
cohorts. Over extensive areas , relatively old (>300 years) forests are
dominated by these same shade-intolerant species, but young or small
trees of these shade-intolerant species are absent or scarce in these old
stands. In contrast, shade-tolerant tree species (such as Laurelia sempervirens, Laureliopsis philippiana, Persea lingue, A extoxicon punctatum,
and numerous myrtaceous trees) are typically abundant and occur as allaged populations in the old stands (Armesto & Figueroa, 1987; Donoso,
Escobar, & Urrutia , 1985; Donoso, Grez, Escobar, & Real 1984; Veblen,
1985b; Veblen & Ashton , 1978; Veblen, Donoso, Schlegel, & Escobar,
1981). In the absence of disturbance, there is a gradual successional trend
toward dominance by these shade-tolerant species. In landscapes with a
high frequency of coarse-scale disturbances , this successional trend,
however, is not completed , and the shade-intolerant tree s (especially
Nothofagus) remain as the dominants of the oldest stands. In other
landscapes with lower rates of coarse-scale disturbance , such as the coastal
T.T. Veblen and P.B. Alaback
higher latitudes than in South America, with peak rainfall typically
occurring in the fall. An equally significant and more consistent gradient
of temperature characterizes this north-south transect , as shown in Figure
9.3. This gradient in temperature encompasses a wider range than in
South America and is closely related to forest yield and productivity (Farr
& Harris , 1979). Seasonal variation of temperature is greatest in the
north , whereas diurnal variation is greate st in the south. Fog plays a key
role in depressing spring and summer temperatures, particularly in the
seasonal rainforest zone. Along the Oregon coast, the moderating
influence of the ocean is most constricted , often to within only 1 km of the
coast, and is most pervasive in southeast Alaska , where moderated temperatures may extend 150km inland.
Patterns of Stand Development
Patterns of stand development in North and South American rainforests
are the consequence of both coarse-scale disturbances producing wholestand replacement patterns and small tree falls resulting in fine-scale gap
dynamics. In landscapes dominated by a high rate of coarse-scale disturbance, patterns of stand development are well described by Oliver's
(1981) general model of whole-stand replacement, consisting of the
following four stages: stand initiation , stem exclusion, understory reinitiation , and old growth.
In South American temperate rainforests , coarse-scale disturbances are
particularly important , and stand development patterns conform with
Oliver's (1981) model of whole-stand replacement. Following coarse-scale
disturbances such as landslides, fire, glacial activity, and volcanic ash
deposition, shade-intolerant tree species such as Nothofagus species,
Weinmannia trichosperma , and/or Eucryphia cordifolia form even-aged
cohorts. Over extensive areas , relatively old (>300 years) forests are
dominated by these same shade-intolerant species, but young or small
trees of these shade-intolerant species are absent or scarce in these old
stands. In contrast, shade-tolerant tree species (such as Laurelia sempervirens, Laureliopsis philippiana, Persea lingue, A extoxicon punctatum,
and numerous myrtaceous trees) are typically abundant and occur as allaged populations in the old stands (Armesto & Figueroa, 1987; Donoso,
Escobar, & Urrutia , 1985; Donoso, Grez, Escobar, & Real 1984; Veblen,
1985b; Veblen & Ashton , 1978; Veblen, Donoso, Schlegel, & Escobar,
1981). In the absence of disturbance, there is a gradual successional trend
toward dominance by these shade-tolerant species. In landscapes with a
high frequency of coarse-scale disturbances , this successional trend,
however, is not completed , and the shade-intolerant tree s (especially
Nothofagus) remain as the dominants of the oldest stands. In other
landscapes with lower rates of coarse-scale disturbance , such as the coastal