STATISTICAL ANALYSES
Although the growth curves show that there is a difference in growth patterns of Pinus contorta from other local species in Germany and Sweden, testing the statistical difference in mean heights is important in determining the significance of these observations. Mean height data of Pinus contorta, Pinus sylvestris and Picea abies from two age groups were isolated (ages 7 and 17) and compared using multiple one-way ANOVA analyses (Figure 25-26). The mean estimates and respective standard errors (and 95% confidence intervals) were calculated from the ANOVA outputs. The mean estimates as well as post-hoc analyses using Tukey's pairwise tests were then used to explore any significant results. From these results, it can be concluded that the null hypothesis was rejected: Pinus contorta has significantly lower relative growth than other local trees species in areas of low SDM suitability. Also, Pinus contorta is a strong competitor relative to other local tree species in areas of high SDM suitability.
Germany
Similarly to the growth curves, the ANOVA showed a difference in mean heights for Germany in both age groups. Mean heights in Germany were significantly different at age 7 [F(2,13)= 193.95, p=2.093e-10] as well as at age 17 [F(2,15)= 19.082, p=7.56e-05]. At age 7, the post-hoc analysis inferred that all three species had significantly different means, with the largest difference in mean height between Picea abies and Pinus contorta. At age 17, the post-hoc analysis inferred that Pinus contorta was significantly lower than the other two species. |
Sweden
In Sweden, the frame of reference used to compare the growth curves was an important factor to consider. As Figure 23 shows, the growth curves in Sweden begin to diverge after year 10. The older the stand, the greater the difference in mean height among species. This observation was reflected in the results of the ANOVA as well. At age 7, there was no significant difference in mean heights among the three species [F(2,13)= 0.0437 p=79574]. However, at age 17, the results of the ANOVA became significant [F(2,15)= 5.5684 p=0.01553]. A post-hoc analysis determined that Pinus sylvestris was significantly lower than Picea abies and Pinus contorta. |