THE AUTHOR 



GERALD E. REHFELDT is a plant geneticist at the Inter- 

 mountain Research Station's Forestry Sciences Laboratory 

 in Moscow, ID. 



RESEARCH SUMMARY 



Seedlings representing 138 populations of ponderosa 

 pine from drainages of the middle Columbia River system 

 were grown and compared in common environments. Field 

 studies of 3-year-old trees on mesic and xeric test sites 

 detected population differentiation for traits reflecting 

 growth and development. Populations that expressed the 

 greatest growth potential under mesic culture suffered the 

 greatest reduction in height under xeric culture. Conse- 

 quently, a different set of populations was performing the 

 best on the two sites when 3-year height was expressed as 

 the growth from a common height at age 2. 



Greenhouse studies of the periodicity of shoot elongation 

 revealed that populations of high growth potential achieved 

 a large stature by means of a long duration, late cessation, 

 rapid rate, and large amount of elongation. 



Multiple regression models accounted for as much as 

 60 percent of the variance between populations and 

 described adaptive landscapes in which populations from 

 low elevation have a high growth potential while those from 

 high elevations have a low growth potential. Geographic 

 variation at a common elevation indicated that populations 

 of high growth potential come from areas where the frost- 

 free period is long and precipitation is relatively high. Thus, 

 growth potential is directly related to the length of the 

 growing season, which can be truncated by either frost or 

 moisture stress. 



Adaptive landscapes are used to construct guidelines for 

 limiting seed transfer in artificial reforestation. In general, 

 seed from a single source should not be transferred more 

 than +200 m in elevation. 



Intermountain Research Station 

 324 25th Street 

 Ogden, UT 84401 



