Figure 1 — Geographic distribution of ponderosa pine (siiading) 

 within the major drainages of the middle Columbia River system 

 and location of sampled populations. Letters A to G locate the 

 elevational dines presented in figure 2. 



5. Drought mortality, the proportion of trees within 

 each plot that died from drought under xeric conditions. 



Analyses of variance were performed on each variable 

 according to a model in which the effects of populations, 

 planting sites, and blocks within sites were considered as 

 random variates. A harmonic mean of 7.31 reflected the 

 number of seedlings in each block. 



Periodicity of Shoot Elongation 



Seedlings from 98 of the populations were grown for 

 2 years in plastic containers (740 cm^) in a shadehouse at 

 Moscow. Each population was represented by nine seed- 

 lings in each of three blocks. In mid-March of the second 

 growing season, seedlings were moved into a greenhouse 

 before shoot elongation had begun. Greenhouses were 

 maintained under natural photoperiods and light inten- 

 sities. Temperatures were held at about 24 ±3 °C during 

 the day and were allowed to cool to a minimum 13 °C at 

 night. All seedlings were measured three times each week 

 until elongation was well under way. Thereafter, measure- 

 ments were made twice each week until elongation of the 

 preformed shoot had ceased. 



As described by Rehfeldt and Wykoff (1981), shoot 

 elongation of individual trees was expressed by a modified 

 logistic function with a hyperbolic time term: 



where Y is the proportion of total increment attained by 

 day X; b, r, and c are regression coefficients; and e is the 

 base for natural logarithms. 



Regression statistics allowed calculation of the following 

 variables for describing the periodicity of shoot elongation 

 of individual seedlings: (1) initiation of elongation: the day 

 on which 2 mm of growth had occurred; (2) cessation of 

 elongation: the day on which all but 2 mm of growth had 

 occurred; (3) duration of elongation: the number of days 

 between initiation and cessation; (4) rate of elongation: 

 elongation (millimeters) per day during the period of max- 

 imum elongation; and (5) total elongation (millimeters). 



Population differentiation was assessed according to an 

 analysis of variance in which the effects of populations and 

 blocks were considered to be random. A harmonic mean of 

 8.83 reflected the number of seedlings from each popula- 

 tion in each block. 



2 



