142
M.T .K. Arroyo et al.
above 1000m on Volcan Llaima and Parque Nacional Conguillio, and at
around Puerto Dominguez (38°54' S; 1580mm annual precipitation, 9.6%
in summer) north of Valdivia on the coast. The central depression (mainly
summer-deciduous forest) is excluded to 41°S because of a mean January
temperature exceeding 16°C. The northeastern limit crosses into Argentina
to include the arc west of Lago Espejo, Isla Victoria, and the western
part of Lago Menendez. Isla Victoria receives more than 1600mm precipitation (Dimitri, 1972) of which an estimated 9.3% is received in the
summer interval (defined here as 20 December to 20 March). The more
southerly eastern limit of the rainforest is seen as running west of Aysen to
meet the western borders of the North Patagonian and South Patagonian
ice fields.
The southern limit of rainforest, however, is still problematical. The
Cape Horn Islands are tentatively included. Recorded precipitation at
Bahia Orange (55°27' S, 68°06' W), just north of the islands over the years
1982 to 1983 was 1483mm (Pisano, 1980a), while the Diego Ramirez
Islands to the southwest receive an average of 1218 mm precipitation
annually. The Cape Horn Islands might receive less than 1400mm precipitation, but given that they are limiting and provide the only good
floristic data (Dollenz, 1980, 1981, 1982a,b; Pisano , 1980a, 1980b) for the
southern extreme of the rainforest, their inclusion seems justified.
The rainforest can be further divided into seasonal and nonseasonal
types, and the latter into perhumid and boreal sections (Weigand,
Mitchell, & Morgan 1992). The first limit sits around 42°S, but with all of
the island of Chiloe included in nonseasonal rainforest (Figure 8.4). The
limit of the boreal rainforest is around 51°30' S. The three major rainforest
zones as defined by Veblen et al. (1983) are also useful for regional
comparisons (Figure 8.4) . These comprise the Valdivian rainforest zone,
to 43°20' S, the North Patagonian rainforest zone, to 47°30' S, and the
Magellanic rainforest zone to 55°30' S.
It should be noted that climatically defined rainforest partially includes
high-elevation deciduous Nothofagus pumilio and N. antarctica forest
and Araucaria araucana forest , generally not considered rainforest on
floristic grounds (c.f., Oberdorfer 1960; Schmithiisen 1958) . On the other
hand, excluded are the northern extremes of the Valdivian rainforest
and southeastern extreme of the Magellanic rainforest as defined by
Oberdorfer (1960).
Origins of the Rainforest Flora
Knowledge of the origins of the present-day rainforest flora can provide
important clues to understanding ecological dynamics. Many rainforest
trees are long lived and must evolve slowly. Ecophysiological constraints
conditioned by past evolutionary history can be expected (Arroyo,
Armesto, Squeo, & Gutierrez, 1993). If the origins of taxa can be traced,
M.T .K. Arroyo et al.
above 1000m on Volcan Llaima and Parque Nacional Conguillio, and at
around Puerto Dominguez (38°54' S; 1580mm annual precipitation, 9.6%
in summer) north of Valdivia on the coast. The central depression (mainly
summer-deciduous forest) is excluded to 41°S because of a mean January
temperature exceeding 16°C. The northeastern limit crosses into Argentina
to include the arc west of Lago Espejo, Isla Victoria, and the western
part of Lago Menendez. Isla Victoria receives more than 1600mm precipitation (Dimitri, 1972) of which an estimated 9.3% is received in the
summer interval (defined here as 20 December to 20 March). The more
southerly eastern limit of the rainforest is seen as running west of Aysen to
meet the western borders of the North Patagonian and South Patagonian
ice fields.
The southern limit of rainforest, however, is still problematical. The
Cape Horn Islands are tentatively included. Recorded precipitation at
Bahia Orange (55°27' S, 68°06' W), just north of the islands over the years
1982 to 1983 was 1483mm (Pisano, 1980a), while the Diego Ramirez
Islands to the southwest receive an average of 1218 mm precipitation
annually. The Cape Horn Islands might receive less than 1400mm precipitation, but given that they are limiting and provide the only good
floristic data (Dollenz, 1980, 1981, 1982a,b; Pisano , 1980a, 1980b) for the
southern extreme of the rainforest, their inclusion seems justified.
The rainforest can be further divided into seasonal and nonseasonal
types, and the latter into perhumid and boreal sections (Weigand,
Mitchell, & Morgan 1992). The first limit sits around 42°S, but with all of
the island of Chiloe included in nonseasonal rainforest (Figure 8.4). The
limit of the boreal rainforest is around 51°30' S. The three major rainforest
zones as defined by Veblen et al. (1983) are also useful for regional
comparisons (Figure 8.4) . These comprise the Valdivian rainforest zone,
to 43°20' S, the North Patagonian rainforest zone, to 47°30' S, and the
Magellanic rainforest zone to 55°30' S.
It should be noted that climatically defined rainforest partially includes
high-elevation deciduous Nothofagus pumilio and N. antarctica forest
and Araucaria araucana forest , generally not considered rainforest on
floristic grounds (c.f., Oberdorfer 1960; Schmithiisen 1958) . On the other
hand, excluded are the northern extremes of the Valdivian rainforest
and southeastern extreme of the Magellanic rainforest as defined by
Oberdorfer (1960).
Origins of the Rainforest Flora
Knowledge of the origins of the present-day rainforest flora can provide
important clues to understanding ecological dynamics. Many rainforest
trees are long lived and must evolve slowly. Ecophysiological constraints
conditioned by past evolutionary history can be expected (Arroyo,
Armesto, Squeo, & Gutierrez, 1993). If the origins of taxa can be traced,