8. Phytogeographic Relationships and Regional Richness Patterns
143
predictions about their responses in present day communities and to
global change can be made and tested (c.f. , Read & Hill, 1989).
The basic floristic differences between North American and South
American temperate forests, including other forest types, can be related
to their Cretaceous and Tertiary histories. Each forest area has been
assembled out of floristic elements that evolved independently on either
side of the tropics, on landmasses differing markedly in degree of continentality (Axelrod, Arroyo, & Raven, 1991). The larger North American
continent , with a more continental climate, favored deciduousness among
temperate angiosperm trees, whereas the evergreen habit was maintained
on the narrower southern South American landmass with greater overall
climatic equability .
The origin of the rainforest in southern South America has been particularly complex due to a long-standing relationship of the South American
continent with Antarctica and other southern continents throughout the
Cretaceous and early Tertiary (Dalziel, 1992). A connection across
Antarctica, then much warmer, facilitated migration of elements all the
way across from the northern part of the Australian land mass, at that
time located closer to Antarctica. Simultaneously, there was excellent
continuity into high tropical latitudes in South America (Arroyo et al.,
1993). This is in major contrast to current high-latitude areas of North
America , which throughout the late Cretaceous and early Tertiary,
although warmer, lay at the edge of a continental mass (Dalziel, 1992).
This critical period in the history of southern South American rainforest
has left strong imprints On its present day floristic composition. Table 8.1
which gives the current distributions of the woody genera recorded in
cool temperate rainforest of southern South America today, shows that
eighteen genera, including many important rainforest trees, exhibit wide
geographical disjunctions in the southern lands (e.g., Araucaria , A ristotelia,
Caldcluvia, Discaria, Eucryphia , Gevuina, Griselinia, Hebe, Laurelia,
Lomatia , Luzuriaga, Muehlenbeckia, Nothofagus , Podocarpus , Pseudopanax, Prumnopitys , Sophora section Edwardsia, and Weinmannia). This
list grows when the systematic relationships of a number of rainforest
genera endemic to the Chilean phytogeographic region are considered
(Table 8.1) . The common ancestor of Mitraria, Asteranthera, and
Sarmienta (South America), and Fieldia from southeastern Australia and
Lenbrassia of Queensland, all monotypic genera of Tribe Mitrarieae (Van
Balgooy, 1984) of Gesneriaceae , must have been centered in southern
Gondwanaland. Austrocedrus, closely related to New Zealand Libocedrus,
South America Lebetanthus, an endemic genus of climbing shrubs of the
Magellanic rainforest, closely related to endemic Prionotes of Tasmania
(Arroyo, 1975); and the dominant tree Laureliopsis of the Valdivian
rainforest , closely related to Atherosperma, restricted to Tasmania and
southeast Australia (Schodde, 1983), also belong here. Although not fully
resolved, South American Drimys seems to be fairly closely related to
143
predictions about their responses in present day communities and to
global change can be made and tested (c.f. , Read & Hill, 1989).
The basic floristic differences between North American and South
American temperate forests, including other forest types, can be related
to their Cretaceous and Tertiary histories. Each forest area has been
assembled out of floristic elements that evolved independently on either
side of the tropics, on landmasses differing markedly in degree of continentality (Axelrod, Arroyo, & Raven, 1991). The larger North American
continent , with a more continental climate, favored deciduousness among
temperate angiosperm trees, whereas the evergreen habit was maintained
on the narrower southern South American landmass with greater overall
climatic equability .
The origin of the rainforest in southern South America has been particularly complex due to a long-standing relationship of the South American
continent with Antarctica and other southern continents throughout the
Cretaceous and early Tertiary (Dalziel, 1992). A connection across
Antarctica, then much warmer, facilitated migration of elements all the
way across from the northern part of the Australian land mass, at that
time located closer to Antarctica. Simultaneously, there was excellent
continuity into high tropical latitudes in South America (Arroyo et al.,
1993). This is in major contrast to current high-latitude areas of North
America , which throughout the late Cretaceous and early Tertiary,
although warmer, lay at the edge of a continental mass (Dalziel, 1992).
This critical period in the history of southern South American rainforest
has left strong imprints On its present day floristic composition. Table 8.1
which gives the current distributions of the woody genera recorded in
cool temperate rainforest of southern South America today, shows that
eighteen genera, including many important rainforest trees, exhibit wide
geographical disjunctions in the southern lands (e.g., Araucaria , A ristotelia,
Caldcluvia, Discaria, Eucryphia , Gevuina, Griselinia, Hebe, Laurelia,
Lomatia , Luzuriaga, Muehlenbeckia, Nothofagus , Podocarpus , Pseudopanax, Prumnopitys , Sophora section Edwardsia, and Weinmannia). This
list grows when the systematic relationships of a number of rainforest
genera endemic to the Chilean phytogeographic region are considered
(Table 8.1) . The common ancestor of Mitraria, Asteranthera, and
Sarmienta (South America), and Fieldia from southeastern Australia and
Lenbrassia of Queensland, all monotypic genera of Tribe Mitrarieae (Van
Balgooy, 1984) of Gesneriaceae , must have been centered in southern
Gondwanaland. Austrocedrus, closely related to New Zealand Libocedrus,
South America Lebetanthus, an endemic genus of climbing shrubs of the
Magellanic rainforest, closely related to endemic Prionotes of Tasmania
(Arroyo, 1975); and the dominant tree Laureliopsis of the Valdivian
rainforest , closely related to Atherosperma, restricted to Tasmania and
southeast Australia (Schodde, 1983), also belong here. Although not fully
resolved, South American Drimys seems to be fairly closely related to