Height Growth of Planted Trees 



Height-growth data were recorded separately for individual trees planted in 1968 

 and 1969, in the likely event that the two populations were not comparable (statistical 

 analysis o£ the data verified that they were not). A standard analysis of variance was 

 conducted for each year of each data set. Results are summarized in table 2. 



There were highly significant differences in growth on the three replications in 

 both data sets for all years. Differences were caused by replication 1 which consist- 

 ently had higher growth than replications 2 and 3. Based on an overall average, 

 replication 1 had 42 percent greater growth than replications 2 and 3. Replication 1 

 was the block of plots in the upper one- fourth of the road fill; the other two replica- 

 tions were lower on the fill slope (fig. 2) . Apparently, tree growth tends to be 

 greater in the upper portions of the fill slope, possibly in direct response to greater 

 depth of fill materials and increased moisture collected on the road surface. Similar 

 trends in growth of ponderosa pine with soil depths have been noted on natural soils by 

 investigators cited earlier. 



Average annual height-growth values for all years in each data set are plotted on 

 figure 7. Curves to illustrate apparent time trends are shown to facilitate interpre- 

 tation. Notice the low growth and especially the low treatment e-Pfect during the first 

 year after planting the 1968 trees; similar results were not obtained for the 1969 

 trees. The difference might be explained by the -Pact that the 1968 trees were planted 

 about 1 month late because of the time required to construct erosion plots; the 1969 

 trees were planted on schedule. 



Figure 7 also shows that growth tends to decrease after 1970. This result differs 

 from that observed by Hall and Curtis (1970) , who reported that the rate of seedling 

 height growth increased steadily the first 10 years for plantings in the Town Creek area 

 of the Boise National Forest. However, Lynch (1958) showed that height growth of 

 ponderosa pine decreased markedly as competition between trees increased. Thus, the 

 decreasing growth trend found in this study apparently resulted from increased competi- 

 tion as closely spaced trees grew larger (fig. 3 and 4) . 



The overall treatment effects (table 2) were statistically significant for all 

 years in both data sets, mostly at the 99 percent level. In order to better define 

 treatment effects, individual treatments were compared against one another using 

 Hartley's multiple range test procedure (Snedecor 1956, p. 253). The effects of fer- 

 tilizer are immediately apparent on figure 7. Growth on fertilized plots was signifi- 

 cantly greater (95 percent level) than growth on all unfertilized plots in all data 



Table 2. --Level of significance obtained from analysis of variance tests 

 for the effects of treatments and replications on height growth 



Year 



1968 Trees 



Replication 



Treatment 



1969 Trees 



Replication 



Percent 



Treatment 



1969 

 1970 

 1971 

 1972 



99 

 99 

 99 

 99 



95 

 99 

 99 

 95 



99 

 99 

 99 



99 

 99 

 99 



11 



