Our Liviiii; Re.soiirce.\ — hilerinr West 



in 



alpine tree invasions are isolated events or part 

 of a broad pattern in western North Ameriea. 

 There are insufficient data from locations other 

 than the Pacific Northwest to speculate about 

 the geographic extent of this phenomenon. 



Future Changes 



Data on subalpine tree growth for western 

 North America are too sparse to infer that 

 growth increases are a broad regional phenom- 

 enon. Additional data from other sites are need- 

 ed to quantify growth trends in subalpine 

 species. Furthermore, consistent sampling and 

 analytical methods should be applied so that 

 different data sets can be compared. 



Sufficient information exists, however, about 

 long-term growth trends and shorter-term 

 response of growth to climate to make some 

 general predictions about potential growth 

 under future climate scenarios. If the climate 

 becomes warmer and drier, as predicted by gen- 

 eral circulation models, growth rates of sub- 

 alpine conifers will probably increase. This 

 growth increase would depend on the seasonal- 

 ity of precipitation. A decrease in snowfall 

 would be particularly beneficial to species such 

 as subalpine fir and Engelmann spruce (Ettl and 

 Peterson 1991; Peterson 1993), although 

 warmer summer temperatures could cause sum- 

 mer soil moisture deficits that would be detri- 

 mental to growth. It is unknown how future 

 growth patterns will be influenced by increased 

 concentrations of carbon dioxide. Any potential 

 growth changes must, of course, be considered 

 with respect to the effects of climate change on 

 interspecific competition and disturbance, as 

 well as deposition of nitrogen or other nutrients. 



References 



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