178
T.T. Veblen and P.B. Alaback
of approximately 42°S the seasonal distribution of precipitation is relatively uniform, with stormy conditions prevailing year-round. Along this
north-to-south gradient of decreased precipitation seasonality, there also
is a trend toward lower mean annual temperatures. In the far south , at
approximately 52°S-55° S, cool, windy conditions prevail for most of the
year. Soils are often derived from volcanic ash in the northern part of the
perhumid and seasonal rainforest zones, but locally they may be developed
from a broad variety of parent materials ranging from metamorphic rocks
to glaciofluvial deposits. Farther south (approximately 42°S), glaciofluvial
deposits predominate as soil parent materials.
The coarse-scale vegetation patterns of southern Chile and Argentina
mirror the north-to-south and west-to-east climatic gradients (see Figure
9.1). Central Chile is characterized by evergreen sclerophyll shrublands
and low forests. Bordering this zone on the south is the district of warm
temperate deciduous Nothofagus forest. Toward the south, as conditions
become more humid, temperate rainforests prevail south of approximately
37°45'S.
The temperate rainforests of South America are a mixture of evergreen
conifer and broadleaf tree species. Among the conifers, two Cupressids
(Fitzroya cupressoides and Pilgerodendron uviferum) and three Podocarps
(Podocarpus nubigena, Podocarpus saligna, and Saxegothaea conspicua)
are important species in the rainforests, as noted in Table 9.1. Among the
broadleaf elements, Nothofagus species are the most important trees in
the rainforests. Although the three evergreen Nothofagus species are
most typical of rainforest (occurring primarily in the subpolar and perhumid types), deciduous Nothofagus species also occur in areas with
mean annual precipitation well over the 1400mm threshold. The
deciduous N. obliqua and N. alpina occur in the northern seasonal rainforests characterized by relatively dry summers. The deciduous N.
antarctica occurs in poorly drained areas throughout the rainforest district.
The deciduous N. pumilio occurs at high elevation, typically forming
upper timberline on both the western and eastern sides of the Andes
within the rainforest district. This belt of deciduous N. pumilio includes
sites with mean annual precipitation >4000 mm (Veblen, Ashton , Schlegel,
& Veblen, 1977); the same species as well as N. antarctica also dominate
dry forests farther east of the Andes , where mean annual precipitation is
less than 1000mm. The occurrence of deciduous trees within the temperate
rainforest district at high elevation and the occurrence of these same
species outside the rainforest region at low elevations in a cold, dry
climate is a pattern best developed in South America, but it does occur to
a limited extent for one species in North America. Larix lyallii is the only
deciduous tree species that can be a canopy dominant in mature forests
within the seasonal rainforest zone in North America. It occurs at high
elevations (>1500 m) within the rainforest zone in southwest British
Columbia and adjacent Washington state and in moist subalpine sites in
T.T. Veblen and P.B. Alaback
of approximately 42°S the seasonal distribution of precipitation is relatively uniform, with stormy conditions prevailing year-round. Along this
north-to-south gradient of decreased precipitation seasonality, there also
is a trend toward lower mean annual temperatures. In the far south , at
approximately 52°S-55° S, cool, windy conditions prevail for most of the
year. Soils are often derived from volcanic ash in the northern part of the
perhumid and seasonal rainforest zones, but locally they may be developed
from a broad variety of parent materials ranging from metamorphic rocks
to glaciofluvial deposits. Farther south (approximately 42°S), glaciofluvial
deposits predominate as soil parent materials.
The coarse-scale vegetation patterns of southern Chile and Argentina
mirror the north-to-south and west-to-east climatic gradients (see Figure
9.1). Central Chile is characterized by evergreen sclerophyll shrublands
and low forests. Bordering this zone on the south is the district of warm
temperate deciduous Nothofagus forest. Toward the south, as conditions
become more humid, temperate rainforests prevail south of approximately
37°45'S.
The temperate rainforests of South America are a mixture of evergreen
conifer and broadleaf tree species. Among the conifers, two Cupressids
(Fitzroya cupressoides and Pilgerodendron uviferum) and three Podocarps
(Podocarpus nubigena, Podocarpus saligna, and Saxegothaea conspicua)
are important species in the rainforests, as noted in Table 9.1. Among the
broadleaf elements, Nothofagus species are the most important trees in
the rainforests. Although the three evergreen Nothofagus species are
most typical of rainforest (occurring primarily in the subpolar and perhumid types), deciduous Nothofagus species also occur in areas with
mean annual precipitation well over the 1400mm threshold. The
deciduous N. obliqua and N. alpina occur in the northern seasonal rainforests characterized by relatively dry summers. The deciduous N.
antarctica occurs in poorly drained areas throughout the rainforest district.
The deciduous N. pumilio occurs at high elevation, typically forming
upper timberline on both the western and eastern sides of the Andes
within the rainforest district. This belt of deciduous N. pumilio includes
sites with mean annual precipitation >4000 mm (Veblen, Ashton , Schlegel,
& Veblen, 1977); the same species as well as N. antarctica also dominate
dry forests farther east of the Andes , where mean annual precipitation is
less than 1000mm. The occurrence of deciduous trees within the temperate
rainforest district at high elevation and the occurrence of these same
species outside the rainforest region at low elevations in a cold, dry
climate is a pattern best developed in South America, but it does occur to
a limited extent for one species in North America. Larix lyallii is the only
deciduous tree species that can be a canopy dominant in mature forests
within the seasonal rainforest zone in North America. It occurs at high
elevations (>1500 m) within the rainforest zone in southwest British
Columbia and adjacent Washington state and in moist subalpine sites in