8. Phytogeographic Relationships and Regional Richness Pattern s
149
paragraphs is that the net balance of Tertiary and Quaternary events has
favored greater richness in the southern forests .
Diversity Patterns and Life Forms
As many authors have pointed out (e.g. , Cowling, Holmes , & Rebels ,
1992; Diamond, 1988) species diversity is a complex phenomenon because
of difficulties in differentiating between historical and ecological processes .
Evolutionary events, such as speciation and extinction , are affected both
by history and ecological dynamics. Ideally, moreover, data on alpha ,
beta , and gamma diversity are needed . For meaningful assessments of
biodiversity, as opposed to species richness per se, attention must also be
given to the number of phylogenetic lineages contained among the species
present (Arroyo , Raven , & Sarukhan, 1992). Most current methods
designed to address this problem (e.g., Williams, Humphries, & VaneWright, 1991) depend on the existence of cladistic data and are applicable
only for well-studied groups of organisms. The nearest estimate of phylogenetic diversity for regional comparisons involving large numbers of
species at the moment is the number of families and genera present. The
data available for southern South American cool temperate rainforest
is presently too sketch y and too variable methodwise to consider the
individual diversity components outlined above. Thus , basically, we will
consider the broad regional product of alpha , beta, and gamma diversity,
along with some limited data for equal-sized plots.
A consideration of diversity in the rainforest habitat immediately raises
the question of what should be considered a rainforest species. We
considered a rainforest species as that reported to grow in or under the
influence of a tall-to-moderately tall forest canopy. This definition was
adopted in view of the v, ery open canop ies of several rainfore st types in
southern South America (e.g. , Fitzroya cup ressoides, Araucaria araucana
forest). The definition admits natural gap species, which may also be
frequently found with manmad e cutting of the forest canopy (e.g .,
Fuchsia magellanica and Gaultheria spp.), and species of flush and bog
areas occurring under the forest canopy in Magellanic rainforest. However , weedy herbaceous species found occasionally on the forest edge
and in disturbed secondary forest habitats have been excluded. True
Magellanic moorland and krummholz are not included. We have also
excluded nadis , on account of their openness, and distribution mainly in
the central depression (Ramirez, San Martin , Figueroa , MacDonald, &
Ferrada, 1991).
Tables 8.2 and 8.3 show the tot al number of species found in the
rainfore st habitat. Ongoing work suggests that, including all habitat types,
there are more than 1300 vascular plant species south of latitude 40°S in
Chile (Arroyo et aI., unpublished data) . For the larger area south of
149
paragraphs is that the net balance of Tertiary and Quaternary events has
favored greater richness in the southern forests .
Diversity Patterns and Life Forms
As many authors have pointed out (e.g. , Cowling, Holmes , & Rebels ,
1992; Diamond, 1988) species diversity is a complex phenomenon because
of difficulties in differentiating between historical and ecological processes .
Evolutionary events, such as speciation and extinction , are affected both
by history and ecological dynamics. Ideally, moreover, data on alpha ,
beta , and gamma diversity are needed . For meaningful assessments of
biodiversity, as opposed to species richness per se, attention must also be
given to the number of phylogenetic lineages contained among the species
present (Arroyo , Raven , & Sarukhan, 1992). Most current methods
designed to address this problem (e.g., Williams, Humphries, & VaneWright, 1991) depend on the existence of cladistic data and are applicable
only for well-studied groups of organisms. The nearest estimate of phylogenetic diversity for regional comparisons involving large numbers of
species at the moment is the number of families and genera present. The
data available for southern South American cool temperate rainforest
is presently too sketch y and too variable methodwise to consider the
individual diversity components outlined above. Thus , basically, we will
consider the broad regional product of alpha , beta, and gamma diversity,
along with some limited data for equal-sized plots.
A consideration of diversity in the rainforest habitat immediately raises
the question of what should be considered a rainforest species. We
considered a rainforest species as that reported to grow in or under the
influence of a tall-to-moderately tall forest canopy. This definition was
adopted in view of the v, ery open canop ies of several rainfore st types in
southern South America (e.g. , Fitzroya cup ressoides, Araucaria araucana
forest). The definition admits natural gap species, which may also be
frequently found with manmad e cutting of the forest canopy (e.g .,
Fuchsia magellanica and Gaultheria spp.), and species of flush and bog
areas occurring under the forest canopy in Magellanic rainforest. However , weedy herbaceous species found occasionally on the forest edge
and in disturbed secondary forest habitats have been excluded. True
Magellanic moorland and krummholz are not included. We have also
excluded nadis , on account of their openness, and distribution mainly in
the central depression (Ramirez, San Martin , Figueroa , MacDonald, &
Ferrada, 1991).
Tables 8.2 and 8.3 show the tot al number of species found in the
rainfore st habitat. Ongoing work suggests that, including all habitat types,
there are more than 1300 vascular plant species south of latitude 40°S in
Chile (Arroyo et aI., unpublished data) . For the larger area south of