9. A Comparative Review of Forest Dynamics
195
Canal (in the Skagway and Haines region north of Juneau ; Noste, 1969).
Pinus contorta subs. contorta and Betula papyrifera occur where fires are
frequent (and nowhere else within the rainforest zone). In the perhumid
zone, continuously wet and thick organic horizons prevent effective heat
penetration from forest fires into the soil layer. As a result, fires often do
not lead to dramatic changes in plant species composition. Thuja and
Picea appears to regenerate better and outcompete Tsuga more effectively
following fire. Much of the effect appears to be more one of eliminating
advance regeneration of Tsuga than creating more favorable growth conditions for Thuja or Picea.
In the seasonal rainforest zone in North America fire is infrequent (100
to 300 years), but often catastrophic in scale. The widespread occurrence
of Pseudotsuga menziesii, in the southern portion of this region, for
example, is usually attributable to catastrophic fire (Agee, 1991;
Harcombe, 1986; Juday, 1976). Formerly extensive even-aged old-growth
forests of Pseudotsuga covered large portions of the Oregon Coast Range
and are attributable to just a few catastrophic fires. In the Olympic
Mountains of Washington, fire is a critical factor on the eastern slope of
the mountains (east of the Bailey Range) where Pseudotsuga forest may
also dominate (Fonda & Bliss, 1969). Likewise fire frequencies in the
Cascades are generally much higher than along the coast both because of
increased lightning frequencies and lower fuel moisture. From the
western Olympics northwards to the northern limit of the seasonal rainforest type, stands originated by fire become progressively more localized
or infrequent , and are usually associated with excessively drained, rocky
sites, exposed southern slopes, or other anomalously warm or dry microsites (Gagnon & Bradfield, 1987).
Disturbance by Native Herbivores
Although South American temperate rainforests are generally depauperate
of large mammalian herbivores , in pre-European times native guanacos
(Lama guanicoe) were common along the ecotone between Nothofagus
forests and the Patagonian steppe. Guanacos were the principal game
animal of Patagonian aboriginals and were described by nineteenth century
explorers as occurring in immense herds (Musters, 1871; Prichard, 1902).
Today, in some N . pumilio stands on Tierra del Fuego, guanacos are
abundant and seriously impede Nothofagus regeneration (A. Rebertus ,
personal communication). Other large herbivores that may have affected
forest composition include huemul deer (Hippocamelus bisulcus) and
small pudu deer (Pudu pudu), both hunted by Indian populations (Cox,
1863; Machoni, 1732). Pudu deer occur principally in the rainforests of
southern Chile and adjacent areas of Argentina, while huemul deer favor
ecotonal areas near alpine timberline or the Patagonia steppe (Povilitis,
1978).
195
Canal (in the Skagway and Haines region north of Juneau ; Noste, 1969).
Pinus contorta subs. contorta and Betula papyrifera occur where fires are
frequent (and nowhere else within the rainforest zone). In the perhumid
zone, continuously wet and thick organic horizons prevent effective heat
penetration from forest fires into the soil layer. As a result, fires often do
not lead to dramatic changes in plant species composition. Thuja and
Picea appears to regenerate better and outcompete Tsuga more effectively
following fire. Much of the effect appears to be more one of eliminating
advance regeneration of Tsuga than creating more favorable growth conditions for Thuja or Picea.
In the seasonal rainforest zone in North America fire is infrequent (100
to 300 years), but often catastrophic in scale. The widespread occurrence
of Pseudotsuga menziesii, in the southern portion of this region, for
example, is usually attributable to catastrophic fire (Agee, 1991;
Harcombe, 1986; Juday, 1976). Formerly extensive even-aged old-growth
forests of Pseudotsuga covered large portions of the Oregon Coast Range
and are attributable to just a few catastrophic fires. In the Olympic
Mountains of Washington, fire is a critical factor on the eastern slope of
the mountains (east of the Bailey Range) where Pseudotsuga forest may
also dominate (Fonda & Bliss, 1969). Likewise fire frequencies in the
Cascades are generally much higher than along the coast both because of
increased lightning frequencies and lower fuel moisture. From the
western Olympics northwards to the northern limit of the seasonal rainforest type, stands originated by fire become progressively more localized
or infrequent , and are usually associated with excessively drained, rocky
sites, exposed southern slopes, or other anomalously warm or dry microsites (Gagnon & Bradfield, 1987).
Disturbance by Native Herbivores
Although South American temperate rainforests are generally depauperate
of large mammalian herbivores , in pre-European times native guanacos
(Lama guanicoe) were common along the ecotone between Nothofagus
forests and the Patagonian steppe. Guanacos were the principal game
animal of Patagonian aboriginals and were described by nineteenth century
explorers as occurring in immense herds (Musters, 1871; Prichard, 1902).
Today, in some N . pumilio stands on Tierra del Fuego, guanacos are
abundant and seriously impede Nothofagus regeneration (A. Rebertus ,
personal communication). Other large herbivores that may have affected
forest composition include huemul deer (Hippocamelus bisulcus) and
small pudu deer (Pudu pudu), both hunted by Indian populations (Cox,
1863; Machoni, 1732). Pudu deer occur principally in the rainforests of
southern Chile and adjacent areas of Argentina, while huemul deer favor
ecotonal areas near alpine timberline or the Patagonia steppe (Povilitis,
1978).