382
R.G. Lawford and P.B. Alaback
Physical Processes
The interconnections between elements of the physical environment have
been clearly documented in the first section of this book . At mid- and
high latitudes, the atmospheric circulation serves as a driving force,
producing distinct precipitation and temperature patterns along the western
coasts of both North and South America and leading to well-defined
patterns of runoff and ecosystem productivity as the rain falling on the
surface is redistributed by the local topography . These same atmospheric
circulation patterns control the coastal patterns of upwelling and, in turn,
are influenced by the larger oceanic forcing effects such as EI Nino. In
spite of the common influence of the large-scale oceanic thermal forcing
in each hemisphere, the presence of an ice-covered continent at the South
Pole, the smaller land mass in the Southern Hemisphere, and the greater
disruption to the flow introduced by the higher Andes mountains combine
to produce some significant deviations in the hydroclimatic patterns along
the western coasts of the two continents.
Regional-scale effects are important in atmosphere-ocean and
atmosphere-hydrosphere linkages. Upwelling and marine biological
activity are linked to the atmosphere through the production of dimethylated sulphur and ammonia. These gases are transported by wind and
precipitation to forest areas, where they play an important role in supplying chemicals and nutrients to plants and soils. These inputs vary
between North and South America because the atmospheric inputs are
either supplemented by the geological inputs (common in the glaciated
seasonal rainforests of North America) or are modified very little by
geological inputs (more common in the unglaciated perhumid rainforest
zone of South America). Clearly, forest productivity and type are strongly
influenced by both the direct variability of temperature and precipitation
patterns and the indirect effects such as geochemical and nutrient cycling.
Biota
The biota associated with the high- and temperate-latitude rainforests of
North and South America are widely divergent, reflecting fundamental
differences in evolutionary history and biogeography. The long history of
separation from other temperate forests has allowed Chilean forests to
develop many unique species and families, and its more equitable climate
appears to have been a key factor in allowing the development of a high
level of plant species richness. The connection of southern temperate
rainforests to the tropics in early geological history appears to have key
significance in explaining many of today's plant and animal community
structures. While the southern rainforest flora are relatively species rich
R.G. Lawford and P.B. Alaback
Physical Processes
The interconnections between elements of the physical environment have
been clearly documented in the first section of this book . At mid- and
high latitudes, the atmospheric circulation serves as a driving force,
producing distinct precipitation and temperature patterns along the western
coasts of both North and South America and leading to well-defined
patterns of runoff and ecosystem productivity as the rain falling on the
surface is redistributed by the local topography . These same atmospheric
circulation patterns control the coastal patterns of upwelling and, in turn,
are influenced by the larger oceanic forcing effects such as EI Nino. In
spite of the common influence of the large-scale oceanic thermal forcing
in each hemisphere, the presence of an ice-covered continent at the South
Pole, the smaller land mass in the Southern Hemisphere, and the greater
disruption to the flow introduced by the higher Andes mountains combine
to produce some significant deviations in the hydroclimatic patterns along
the western coasts of the two continents.
Regional-scale effects are important in atmosphere-ocean and
atmosphere-hydrosphere linkages. Upwelling and marine biological
activity are linked to the atmosphere through the production of dimethylated sulphur and ammonia. These gases are transported by wind and
precipitation to forest areas, where they play an important role in supplying chemicals and nutrients to plants and soils. These inputs vary
between North and South America because the atmospheric inputs are
either supplemented by the geological inputs (common in the glaciated
seasonal rainforests of North America) or are modified very little by
geological inputs (more common in the unglaciated perhumid rainforest
zone of South America). Clearly, forest productivity and type are strongly
influenced by both the direct variability of temperature and precipitation
patterns and the indirect effects such as geochemical and nutrient cycling.
Biota
The biota associated with the high- and temperate-latitude rainforests of
North and South America are widely divergent, reflecting fundamental
differences in evolutionary history and biogeography. The long history of
separation from other temperate forests has allowed Chilean forests to
develop many unique species and families, and its more equitable climate
appears to have been a key factor in allowing the development of a high
level of plant species richness. The connection of southern temperate
rainforests to the tropics in early geological history appears to have key
significance in explaining many of today's plant and animal community
structures. While the southern rainforest flora are relatively species rich