8. Phytogeographic Relationships and Regional Richness Patterns
165
zygosity (Arroyo et aI. , 1993) . Under the fairly high population densities
in temperate rainforest; local inbreeding, as may occur in tropical forests ,
is probably uncommon, leading to a tendency for clinal variation along
the major environmental gradients. Such clinal variation is evident in
several species of Nothofagus (Donoso 1979, 1987; Ramirez, 1987), a
genus in which three tested species ar~ now known to be genetically selfincompatible (M. Riveros, unpublished data). This may explain why
even Nothofagus, a genus that experienced large latitudinal shifts in the
Pleistocene (Heusser, 1983) ; has not undergone much local speciation in
the rainforest habitat. Hypotheses for low speciation rates in the southern
South America temperate rainforest, clearly, can only be resolved with
detailed genetic analyses. Detection of levels of genetic variation and
minimum viable population size are not only paramount to understanding
these problems, but for understanding how the rainforest will respond in
relation to the enormous pressures presently inflicted on it.
Here, we have undertaken the first attempt to determine the entire
vascular flora of south South American cool temperate rainforest. Without
doubt, there will be additions to the rainforest flora as more detailed
floristic work comes to hand. We have not referred to the extraordinarily
abundant lichen flora (e. g., Galloway, 1992) and mosses of the se fore sts,
because of our lack of experience in these groups and their many systematic difficulties. What is becoming clear, however , is that the functional
actors in North American and South American rainforests are turning out
to belong to different taxonomic groups. Alaback (this volume) draws
attention to the lack of vascular epiphytes in the north, suggesting that
this niche is only filled by mosses and lichens. We have suggested here
that saplings of shade-tolerant angio sperms in the undergrowth in South
America and Chusquea will often replace the angio sperm shru bs of North
American forest. There are , of course , man y other functional differences
related to tendencies for biotic pollination (Riveros, 1991; Rivero s,
Humafia, & Lanfranco , 1992) and biotic dispersal (Armesto & Rozzi ,
1989) in southern South America, which have not been referred to here.
Use and conservation of any cool temperate rainforest clearly requires
an intim ate knowledge of the basic biology , ecological dynamics, and
population genetics of the component species in a framework of climate
change. Research in the future must go beyond a basic descriptive level,
yet not fall into a spira l of broad generalities. Topics need to be chosen
with gre at care in order to maximiz e the practical and theoretical advances
that comparative studies will bring.
Acknowledgments. The original data in this paper were assembled thanks
to MacArthur Foundation Grant No. 90-9929, BSPIWWF Grant No.
7506, and FONDECYT Grant No. 92-1135. We thank Donald Bran for
supplying his unpublished phytosociological data for Argentina.
165
zygosity (Arroyo et aI. , 1993) . Under the fairly high population densities
in temperate rainforest; local inbreeding, as may occur in tropical forests ,
is probably uncommon, leading to a tendency for clinal variation along
the major environmental gradients. Such clinal variation is evident in
several species of Nothofagus (Donoso 1979, 1987; Ramirez, 1987), a
genus in which three tested species ar~ now known to be genetically selfincompatible (M. Riveros, unpublished data). This may explain why
even Nothofagus, a genus that experienced large latitudinal shifts in the
Pleistocene (Heusser, 1983) ; has not undergone much local speciation in
the rainforest habitat. Hypotheses for low speciation rates in the southern
South America temperate rainforest, clearly, can only be resolved with
detailed genetic analyses. Detection of levels of genetic variation and
minimum viable population size are not only paramount to understanding
these problems, but for understanding how the rainforest will respond in
relation to the enormous pressures presently inflicted on it.
Here, we have undertaken the first attempt to determine the entire
vascular flora of south South American cool temperate rainforest. Without
doubt, there will be additions to the rainforest flora as more detailed
floristic work comes to hand. We have not referred to the extraordinarily
abundant lichen flora (e. g., Galloway, 1992) and mosses of the se fore sts,
because of our lack of experience in these groups and their many systematic difficulties. What is becoming clear, however , is that the functional
actors in North American and South American rainforests are turning out
to belong to different taxonomic groups. Alaback (this volume) draws
attention to the lack of vascular epiphytes in the north, suggesting that
this niche is only filled by mosses and lichens. We have suggested here
that saplings of shade-tolerant angio sperms in the undergrowth in South
America and Chusquea will often replace the angio sperm shru bs of North
American forest. There are , of course , man y other functional differences
related to tendencies for biotic pollination (Riveros, 1991; Rivero s,
Humafia, & Lanfranco , 1992) and biotic dispersal (Armesto & Rozzi ,
1989) in southern South America, which have not been referred to here.
Use and conservation of any cool temperate rainforest clearly requires
an intim ate knowledge of the basic biology , ecological dynamics, and
population genetics of the component species in a framework of climate
change. Research in the future must go beyond a basic descriptive level,
yet not fall into a spira l of broad generalities. Topics need to be chosen
with gre at care in order to maximiz e the practical and theoretical advances
that comparative studies will bring.
Acknowledgments. The original data in this paper were assembled thanks
to MacArthur Foundation Grant No. 90-9929, BSPIWWF Grant No.
7506, and FONDECYT Grant No. 92-1135. We thank Donald Bran for
supplying his unpublished phytosociological data for Argentina.