8. Phytogeographic Relationships and Regional Richness Patterns
135
comprising the vast boreal zone and forests of the Rocky Mountains
(Elliot-Fisk, 1988; Peet, 1988).
Although much phytosociological work has been carried out in the cool
temperate rainforests of southern South America (e.g., Dimitri & Correa,
1966-1967; Dollenz, 1980; Oberdorfer, 1960; Pisano, 1977, 1989; Ramirez
& Figueroa , 1985, 1987; Schmithiisen, 1958; Villagran, Soto, & Serey,
1974) and forest dynamics has been a strong focus (e.g., Armesto &
Figueroa, 1987; Donoso , 1984a, 1993; Donoso, Escobar, & Urrutia,
1985; Veblen, 1982, 1985; Veblen et aI., 1991), the overall regional
diversity patterns have only been touched upon (e.g., Alaback , 1991;
Dimitri , 1972). The insular nature of the South America rainforest zone,
a condition in place since the late Tertiary, and therefore prior to the
Pleistocene, could lead to the prediction of lower diversity than in western
North American rainforests . This paper will show, however, that complex
historical and climatic factors seem to have led to an opposite effect,
insofar as vascular plant diversity is concerned. While the Tertiary and
Quaternary left North American rainforests gymnosperm-dominated, with
angiosperms becoming prominent only in specialized habitats and at the
early stages of succession (Franklin , 1988), those of South America
comprise an intergrading series of angiosperm-dominated, gymnospermdominated, and mixed gymnosperm-angiosperm forests (Armesto &
Figueroa , 1987; Armesto, Mitchell, & Villagran, 1985; Donoso et aI.,
1985; Veblen, Schlegel, & Oltremari, 1983) of strikingly different aspect
and diversity.
After outlining the major climatic trends, in order to lay a background
to present diversity patterns, we first show that the temperate rainforest
constitutes an extraordinarily rich floristic assemblage, linking ancient
continents, and as such is quite distinct from western North America
temperate rainforest . Second, we address the life-form composition and
the overall richness of the rainforest flora. Finally, the latitudinal gradient
in species richness is focused on. In the northern hemisphere , mean
latitudinal range increases significantly with latitude in several groups of
organisms (Rapoport, 1975; Stevens, 1989). Stevens (1989) related this
trend to adaptation to greater annual temperature extremes at higher
latitudes . In this paper we show that there is no latitudinal increase in
annual temperature range throughout the entire cool temperate rainforest
zone in southern South America . It is of theoretical interest, thus to
determine whether Rapoport's rule is a feature of this southern hemisphere vegetation type.
The Broad Climatic Patterns
Conditions for existence of rainforest in southern South America derive
from a maritime climate with strong westerly flow along the Pacific coast
during the summer and winter months, an intense rainshadow effect of
135
comprising the vast boreal zone and forests of the Rocky Mountains
(Elliot-Fisk, 1988; Peet, 1988).
Although much phytosociological work has been carried out in the cool
temperate rainforests of southern South America (e.g., Dimitri & Correa,
1966-1967; Dollenz, 1980; Oberdorfer, 1960; Pisano, 1977, 1989; Ramirez
& Figueroa , 1985, 1987; Schmithiisen, 1958; Villagran, Soto, & Serey,
1974) and forest dynamics has been a strong focus (e.g., Armesto &
Figueroa, 1987; Donoso , 1984a, 1993; Donoso, Escobar, & Urrutia,
1985; Veblen, 1982, 1985; Veblen et aI., 1991), the overall regional
diversity patterns have only been touched upon (e.g., Alaback , 1991;
Dimitri , 1972). The insular nature of the South America rainforest zone,
a condition in place since the late Tertiary, and therefore prior to the
Pleistocene, could lead to the prediction of lower diversity than in western
North American rainforests . This paper will show, however, that complex
historical and climatic factors seem to have led to an opposite effect,
insofar as vascular plant diversity is concerned. While the Tertiary and
Quaternary left North American rainforests gymnosperm-dominated, with
angiosperms becoming prominent only in specialized habitats and at the
early stages of succession (Franklin , 1988), those of South America
comprise an intergrading series of angiosperm-dominated, gymnospermdominated, and mixed gymnosperm-angiosperm forests (Armesto &
Figueroa , 1987; Armesto, Mitchell, & Villagran, 1985; Donoso et aI.,
1985; Veblen, Schlegel, & Oltremari, 1983) of strikingly different aspect
and diversity.
After outlining the major climatic trends, in order to lay a background
to present diversity patterns, we first show that the temperate rainforest
constitutes an extraordinarily rich floristic assemblage, linking ancient
continents, and as such is quite distinct from western North America
temperate rainforest . Second, we address the life-form composition and
the overall richness of the rainforest flora. Finally, the latitudinal gradient
in species richness is focused on. In the northern hemisphere , mean
latitudinal range increases significantly with latitude in several groups of
organisms (Rapoport, 1975; Stevens, 1989). Stevens (1989) related this
trend to adaptation to greater annual temperature extremes at higher
latitudes . In this paper we show that there is no latitudinal increase in
annual temperature range throughout the entire cool temperate rainforest
zone in southern South America . It is of theoretical interest, thus to
determine whether Rapoport's rule is a feature of this southern hemisphere vegetation type.
The Broad Climatic Patterns
Conditions for existence of rainforest in southern South America derive
from a maritime climate with strong westerly flow along the Pacific coast
during the summer and winter months, an intense rainshadow effect of