The plots at DCEF were fertilized in fall 1972. At that 

 time the stand had a mean diameter of 1.4 inches and a 

 mean height of 10.7 feet. 



The DCEF study was designed as a randomized com- 

 plete block with five blocks, each having three treat- 

 ments. The treatments were randomly assigned to 

 0.5-acre treatment units as: 



Treatment 1: no fertilization 



Treatment 2: urea applied by hand spreader at the 

 rate of 200 lb of N per acre 



Treatment 3: urea applied by hand spreader at the 

 rate of 400 lb of N per acre 



Subplots of 0.04 acre were established within the treat- 

 ment units, and trees within the subplots were tagged 

 and measured. 



The PREF study was on 3 acres in the lower part of 

 the Benton Creek Drainage. The stand originated in 

 1955 after cutting of the previous stand and dozer clear- 

 ing of the area. Slope angles ranged from 25 to 35 per- 

 cent. The stand is growing on soils classified as typic 

 cryochrept and derived from gneiss parent material. 

 After a cleaning in fall 1971 to a 12-foot-square spacing, 

 a uniform stand of the following species was left: 



western white pine 

 western larch 

 Douglas-fir 



lodgepole pine (Pinus contorta Dougl. ex Loud.) 

 western hemlock 



western redcedar {Thuja plicata Donn ex D. Don) 

 Engelmann spruce 



ponderosa pine (Pinus ponderosa Dougl. ex Laws. var. 

 ponderosa) 



FertiHzation at PREF took place early in spring 1973. 

 At that time, the mean stand diameter was 3.3 inches 

 and the mean height was 21.7 feet. 



At PREF a randomized complete block design was 

 used with three blocks each having two treatments. In 

 contrast to the DCEF study, only two treatments were 



randomly assigned to 0.5-acre treatment units, as 

 follows: 



Treatment 1: no fertilization 



Treatment 2: urea appHed by hand spreader at the 

 rate of 200 lb of N per acre 



Subplots of 0.1 acre were established within the treat- 

 ment and the trees within them tagged and measured. 



At both areas, diameter at breast height (d.b.h.) and 

 total height of the tagged trees were measured in 1973, 

 1974, 1977, and 1982. Periodic mean annual diameter 

 growths and periodic mean annual height growths for 

 1973 to 1977 and 1977 to 1982 were computed for the 

 trees remaining in 1977 and 1982, respectively. 



An analysis of covariance was used to analyze the 

 data for each study area. Because tree size at the time 

 of treatment influences subsequent growth, individual 

 tree d.b.h. at the time of establishment was used as a 

 covariate for analyses involving diameter, and individual 

 tree height at the time of establishment was used as a 

 covariate in the analyses involving heights. The depen- 

 dent variables used in the analyses included d.b.h., 

 height, and periodic mean annual height growth and 

 periodic mean annual diameter growth for to 5 and 5 

 to 10 years after treatment. Those species that had ade- 

 quate observations to analyze alone included grand fir at 

 DCEF and western white pine, western larch, and 

 Douglas-fir at PREF. Various analysis of covariance 

 tables were created (table 1). In all cases, if the F test in 

 the analysis detected significant differences (p < 0.05) 

 between the treatment means, the least squares mean 

 separation procedure was used to locate the differences 

 (SAS Institute 1982). 



RESULTS 



The results of this study reveal how mixed-species 

 stands of conifers respond to the application of nitrogen 

 fertilizer in northern Idaho, and how nitrogen fertilizer 

 affects the diameter and height growth of four species. 

 In addition, these results show the inconsistent growth 

 responses that can be expected when applying fertilizer 

 to forest stands. 



Table 1.— Analysis of covariance 



Degrees of freedom 



Deception Creek 

 Experimental Forest Priest River Experimental Forest 



Western 





All 



Grand 



All 



white 



Western 



Douglas- 





Source 



trees 



fir 



trees 



pine 



larch 



fir 



Expected mean squares 



Treatments 



2 



2 



1 



1 



1 



1 



a2 + Sfff + sr E r?/(t-1) 



Blocks 



4 



4 



2 



2 



2 



2 



a2 + Sa2 + St L )3?/(r-1) 



Block * treatment 



8 



8 



2 



2 



2 



2 



ff2 + Sff2 



(experimental error) 

















Sampling error 



200 



96 



170 



16 



28 



69 





Covariate (initial 



1 



1 



1 



1 



1 



" 1 





height or initial 

















d.b.h.) 

















Total 



215 



111 



176 



22 



34 



75 





2 



