Deception Creek Experimental Forest 



The increased growth rates brought about by applica- 

 tion of fertilizer were short-hved. Five years after treat- 

 ment, trees of all species fertilized with nitrogen had a 

 periodic mean annual diameter growth' 24 percent larger 

 than unfertilized trees (table 2). There were no signifi- 

 cant differences (p < 0.05) in diameter growth means 

 detected between the 200- and 400-lb-per-acre fertilizer 

 treatments. In contrast, during the 5 to 10 years after 

 treatment, no significant differences in diameter growth 

 were found due to fertilization between any of the three 

 treatments (table 2). 



During the first 5 years after treatment, trees in the 

 two fertilized treatments also had significantly 

 (p < 0.05) larger periodic mean annual height growths 

 than the unfertilized treatment. An 18 percent signifi- 

 cant difference existed in the height growth means 

 observed between unfertilized and 400-lb-per-acre treat- 

 ments, but no significant difference occurred in height 

 growth means between the two levels of fertilizer. As 

 with diameter growth, no differences in height growth 

 were apparent during the 5 to 10 years following 

 treatment. 



Grand fir alone had growth patterns similar to the 

 stand as a whole. Five years after treatment, a 30 per- 

 cent difference (significant at p < 0.05) in periodic mean 

 annual diameter growth was detected between the unfer- 

 tilized and 200-lb-per-acre treatments (table 2). No sig- 

 nificant differences in the means for diameter growth 

 were observed between the two fertilizer treatments. 

 During the second 5 years, no significant differences 

 between the treatment means for diameter growth were 

 detected. 



Periodic mean annual height growth for grand fir was 

 also influenced by the application of fertilizer for only 

 the first 5 years (table 2). There was a 45 percent differ- 

 ence in height growth means between the unfertilized 

 grand firs and those treated with 400 lb per acre of 

 nitrogen. Even though there was a 17 percent difference 

 between height growth means for the two levels of fer- 



'A11 means reported are least square means adjusted by covariate 

 analysis for initial differences at the beginning of the study. 



tilizer, the difference was not statistically significant 

 (p < 0.05). No significant differences among the annual 

 height growth means could be detected 10 years after 

 treatment (table 2). 



Priest River Experimental Forest 



At PREF, the application of nitrogen fertihzer had lit- 

 tle influence on tree growth. During the first 5 years 

 after treatment, no significant differences (p < 0.05) in 

 periodic mean annual diameter growth were found with 

 application of fertilizer (table 3). Likewise, during the 

 second 5 years after treatment, no significant differences 

 were detected in diameter growth between the fertilized 

 and unfertilized trees. 



However, a significant response occurred in the ferti- 

 lized trees in periodic mean annual height growth during 

 the first 5 years after fertilization. The fertilized trees 

 had a 9 percent larger growth mean than the unfertilized 

 ones (table 3). As with treatments at DCEF, there were 

 no significant differences in annual height growth means 

 during the second 5 years after treatment. 



Western white pine did not respond positively to the 

 application of nitrogen fertilizer at PREF. Furthermore, 

 the unfertilized western white pine actually had a larger 

 periodic annual diameter growth mean than the fertilized 

 pine (table 3) during the first 5 years after treatment. 

 Neither diameter growth means nor periodic annual 

 height growth means for the two treatments were sig- 

 nificantly different during the first or second 5 years 

 after treatment. 



Western larch at PREF also had little response to fer- 

 tilizer, similar to western white pine. No significant 

 differences in periodic annual diameter growth means 

 were observed either 5 or 10 years after treatment 

 (table 3). Also, no differences in the periodic annual 

 height growth means were detected between the ferti- 

 lized and unfertilized trees. 



The only species at PREF that showed a positive 

 response to fertilization was Douglas-fir. The periodic 

 annual height growth mean 5 years after treatment for 

 200-lb-per-acre was significantly larger (17 percent) than 

 the mean for the unfertilized treatment, while 10 years 

 after treatment, no differences in height growth were 

 detected. No significant differences were detected 



Table 2.— Periodic mean' annual diameter growth and periodic mean annual height growth for all species and for 

 grand fir at Deception Creek Experimental Forest 



All species Grand fir 



Diameter Height Diameter Height 



Treatment^ O-S^ 5-10 0-5 5-10 0-5 5-10 0-5 5-10 



Inches Feet Inches Feet 



1 0.29a'' 0.28a 1.14a 1.51a 0.27a 0.26a 1.10a 1.33a 



2 .36b .28a 1.25b 1.71a .35b .27a 1.36b 1.93a 



3 .36b .31a 1.35b 1.58a .34b .31a 1.59b 1.87a 



^All means are least square means. Diameter growths are adjusted for diameter at beginning of the study and height growths 

 are adjusted for height at the beginning of the study. 

 ^Treatment 1 = no fertilizer, 2 = 200 lb N/acre, 3 = 400 lb N/acre. 



^Time since treatment in years. There are no significant differences (p s 0.05) in the means between time periods. 

 ■"Different letters following means indicate significant differences (p ■< 0.05) between treatments. 



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