186
T.T. Veblen and P.B. Alaback
mass movements in the Andes. In addition on mass movements triggered
by earthquakes, many other mass movements are associated with prolonged and torrential rainfall in this region of glacially oversteepened
slopes. Bare sites created by mass movements are favorable to the establishment of shade-intolerant species , such as Nothofagus spp ., Weinmannia
trichosperma, and Fitzroya cupressoides that otherwise tend to be replaced
by the numerous shade-tolerant tree species of the Chilean rainforests
(Lara, 1991; Veblen & Ashton, 1978; Veblen et aI., 1981). On the
eastern side of the Andes in Argentina, earthquakes periodically kill
entire stands due to the intense shaking of unconsolidated debris fans and
even on stable substrates they cause increased rates of treefalls (Veblen,
Kitzberger, & Lora, 1992a).
Historical data as well as dendroecological evidence indicate that earthquakes of a magnitude similar to that of 1960 have frequently affected
tree establishment and tree growth in the rainforest district (Veblen et
aI., 1992a). In relatively species-rich Valdivian and Patagonian rainforests,
disturbance by earthquake-caused landslides can prevent the successional
replacement of shade-intolerant spp. (e.g., Nothofagus spp. , Weinmannia
trichosperma, and Fitzroya cupressoides) by more shade-tolerant species.
In the species-poor Magellanic rainforest and the pure evergreen Nothofagus forests of northern Patagonia, past earthquakes have had a significant effect on tree mortality and growth patterns, but in the absence of
the shade-tolerant tree species that are common in the Chilean rainforests,
coarse-scale disturbances are not required for the continued dominance of
stands by Nothofagus . Throughout the coastal areas of southern Chile
and in the Andes, subsidence associated with earthquakes has caused
extensive inundation and tree mortality in coastal forests (Musters, 1871;
Rothkugel;1916). Inundated coastal forests occur throughout the southern
Chilean Archipelago from just south of Chiloe to Tierra del Fuego
(Goodall, 1979).
In North America, earthquake-caused landslides and mudslides are of
less regional importance to rainforests than they are in South America.
Successional patterns on landslide or mudflow surfaces are similar to
those that occur on glacial deposits (see the next section) , with Picea and
Alnus dominating in the perhumid and subpolar zones and Pseudotsuga
or Abies dominating in the seasonal zone. Once the surfaces are stabilized,
succession is more rapid and more commonly includes trees at the early
stages than in postglacial successions (Frenzen, Krasney , & Rigney, 1988;
Halpern and Harmon, 1983). Colonization of colluvial fans at the foot of
landslides is rapid, whereas succession is slow or radically altered on steep
escarpments near the tops of landslides (Miles & Swanson, 1986; Smith &
Commandeur, 1986). In the perhumid zone, landslides are more frequent
and widespread on the mainland, but are generally localized events on
islands. Only 2 to 3% of the land are a is affected by landslides , but many
of these impacts are of regional ecological significance because they may
T.T. Veblen and P.B. Alaback
mass movements in the Andes. In addition on mass movements triggered
by earthquakes, many other mass movements are associated with prolonged and torrential rainfall in this region of glacially oversteepened
slopes. Bare sites created by mass movements are favorable to the establishment of shade-intolerant species , such as Nothofagus spp ., Weinmannia
trichosperma, and Fitzroya cupressoides that otherwise tend to be replaced
by the numerous shade-tolerant tree species of the Chilean rainforests
(Lara, 1991; Veblen & Ashton, 1978; Veblen et aI., 1981). On the
eastern side of the Andes in Argentina, earthquakes periodically kill
entire stands due to the intense shaking of unconsolidated debris fans and
even on stable substrates they cause increased rates of treefalls (Veblen,
Kitzberger, & Lora, 1992a).
Historical data as well as dendroecological evidence indicate that earthquakes of a magnitude similar to that of 1960 have frequently affected
tree establishment and tree growth in the rainforest district (Veblen et
aI., 1992a). In relatively species-rich Valdivian and Patagonian rainforests,
disturbance by earthquake-caused landslides can prevent the successional
replacement of shade-intolerant spp. (e.g., Nothofagus spp. , Weinmannia
trichosperma, and Fitzroya cupressoides) by more shade-tolerant species.
In the species-poor Magellanic rainforest and the pure evergreen Nothofagus forests of northern Patagonia, past earthquakes have had a significant effect on tree mortality and growth patterns, but in the absence of
the shade-tolerant tree species that are common in the Chilean rainforests,
coarse-scale disturbances are not required for the continued dominance of
stands by Nothofagus . Throughout the coastal areas of southern Chile
and in the Andes, subsidence associated with earthquakes has caused
extensive inundation and tree mortality in coastal forests (Musters, 1871;
Rothkugel;1916). Inundated coastal forests occur throughout the southern
Chilean Archipelago from just south of Chiloe to Tierra del Fuego
(Goodall, 1979).
In North America, earthquake-caused landslides and mudslides are of
less regional importance to rainforests than they are in South America.
Successional patterns on landslide or mudflow surfaces are similar to
those that occur on glacial deposits (see the next section) , with Picea and
Alnus dominating in the perhumid and subpolar zones and Pseudotsuga
or Abies dominating in the seasonal zone. Once the surfaces are stabilized,
succession is more rapid and more commonly includes trees at the early
stages than in postglacial successions (Frenzen, Krasney , & Rigney, 1988;
Halpern and Harmon, 1983). Colonization of colluvial fans at the foot of
landslides is rapid, whereas succession is slow or radically altered on steep
escarpments near the tops of landslides (Miles & Swanson, 1986; Smith &
Commandeur, 1986). In the perhumid zone, landslides are more frequent
and widespread on the mainland, but are generally localized events on
islands. Only 2 to 3% of the land are a is affected by landslides , but many
of these impacts are of regional ecological significance because they may