Geography Reference
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the pine forests ( Pinus hartwegii ) of central Mexico (20°N), at elevations up to 4,000
m (13,200 ft) (Lauer 1973), and the stunted Polylepis forest ( Polylepis tomentella ) in
northern Chile and western Bolivia (18°S), where upper treeline elevations reach 4,600
to >4,800 m (15,100 to 15,800 ft) (Hoch and Körner 2005) and isolated trees occur at
elevations exceeding 5,000 m (16,400 ft) (Navarro et al. 2005).
Northern versus Southern Hemisphere Mountain Forests
Mountain forests in the southern hemisphere are composed primarily of broadleaf ever-
green trees and include more species of trees, shrubs, lianas, epiphytes, and herbs than
those of the northern hemisphere. Tree ferns are common understory plants in many
temperate southern hemisphere forests, even near the timberline. Although some spe-
cies interchange has taken place between the northern and southern hemispheres, the
floras on either side of the equator evolved independently and are distinct.
The humid tropics show little difference in species composition north and south
of the equator. This pattern changes dramatically by 15° to 20°S latitude, where the
seasonal contrasts become more strongly expressed, particularly at higher elevations.
Montane forests extending from Bolivia to Mexico have similar genera, with Wein-
mannia, Podocarpus, and Fuchsia being widely distributed. Above 2,000 m (6,600 ft),
however, forest composition north of the equator becomes distinctly boreal, while
forests south of the equator are dominated by southern hemisphere species. This pat-
tern is an artifact of geological history and plant evolution, rather than a result of cur-
rent climatic differences. The situation changes rapidly beyond the Tropics of Cancer
and Capricorn because of the contrast in the landmasses of the northern and southern
hemispheres and a greater marine influence in the southern hemisphere.
The cool lowland temperate forests of Patagonia and New Zealand are similar to the
upper-montane forests of tropical Malaysia, East Africa, and the Andes, suggesting that
the southern hemisphere exhibits elevation and latitude zonation patterns similar to
the northern hemisphere, and that many tree species and genera found in the southern
hemisphere midlatitudes are also found in tropical mountains (Troll 1960). For example,
both the equatorial mountain forests of New Guinea and the forests of New Zealand,
40° farther south, are co-dominated by the evergreen beech Nothofagus and conifers
such as Podocarpus spp. and Phyllocladus spp. The major differences between these
forests are the greater number of species in New Guinea and the predominance of pure
Nothofagus stands in New Zealand (Wardle 1973a). The tendency toward single-species
dominance at higher latitudes also occurs in Australia, where evergreen gums, espe-
cially the snow gum ( Eucalyptus niphophila ), dominate higher-elevation forests (Costin
1957, 1959). In southern Chile, the genus Nothofagus, including deciduous species in
Patagonia, is again important (Veblen et al. 1996), as is Araucaria and the species alerce
( Fitzroya cupressoides ) and cordilleran cypress ( Austrocedrus chilensis ). Similar to the
northern hemisphere, (1) there is a distinct decrease in timberline elevations with in-
creasing latitude; (2) there is a marked decrease in species with distance from the
equator; and (3) there are lower midlatitude treelines on the lee side of the southern
Andes (Daniels and Veblen 2003).
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