6. Constraints on Terrestrial Primary Productivity
in Temperate Forests Along the Pacific Coast of
North and South America
R.H. Waring and W.E. Winner
When residents of the temperate forest regions along the Pacific Ocean of
North and South America exchange places, their first impression is that
the climates of the two continents are similar but out of phase. The
second impression is that the forests, although predominantly evergreen
in both places, differ in form. Broadleaf, broad-crowned trees are
common in the south; whereas narrowleaf, narrow-crowned trees occur in
the north. In both regions , the climates are moderated by the Pacific
Ocean. This maritime influence allows considerable photosynthesis by
evergreen species beyond the normal growing season (Alaback, 1991 ;
Waring & Franklin, 1979).
To assess the implications of current or changing climate in either
region requires a model that accounts for how various climatic factors
affect growth-related processes . To generalize for the myriad combinations of topography, climate, and soils present , we attempt to interpret
environmental factors in an operational sense (Mason & Lagenheim,
1957) as they directly initiate a response that impairs or improves a
plant's ability to: 1) capture light and carbon dioxide for photosynthesis;
2) maintain favorable water relations; 3) sequester nutrients; and 4) grow
and maintain structure.
A general ecosystem model developed by Running and colleagues at
the University of Montana incorporates these operational principles and
allows reliable predictions of the growth of coniferous forests throughout
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