Ecology and Development Series No. 10, 2003 - ZEF

Floristic analysis of the undisturbed forest4.3.4 Relationships between environmental variables and community typeThe three groups identified by cluster analysis are distinct and show a clear distributionpattern with respect to the axes in the PCA species-plots biplot (Figure 4.2). Group 1 ismainly positively correlated with the first axis, while some plots in the group are positivelyand others negatively correlated with the second axis. Group 2 is negatively correlated withboth the first and the second axis. On the other hand, Group 3 is mainly positivelycorrelated with second axis, and slightly negatively correlated with first axis (Figure 4.2).The first axis is the strongest gradient, accounting for 40.8% of the variation, while thesecond axis accounts for 23.3% of the variation species distribution (Table 4.3). Thegradients in the PCA axes can be attributed to some environmental variables (Table 4.5).The gradient in first axis increases with decreasing slope, silt and pH, and with increasingdistance from Geba river. On the other hand, the gradient in the second axis increases withaltitude, silt, soil moisture, CEC, distance from Geba river and C-N ratio.Table 4.5. Correlations between environmental variables and PCA axesEnvironmental variable Axis I Axis IIAltitude 0.269 0.696Slope-percent -0.506 -0.084Sand 0.323 -0.314Silt -0.535 0.327Soil moisture -0.351 0.093pH -0.519 -0.208CEC -0.340 0.243Distance from Geba river 0.625 0.458C : N ratio 0.170 0.718The mean difference in these environmental variables was tested using the onewayanalysis of variance and Duncan’s multiple range tests. The three groups differsignificantly from each other with regard to three environmental variables, namely: altitude(F 2,54 = 5.671, P < 0.01), slope (F 2,54 = 3.510, P < 0.05) and distance from the Geba river(F 2,54 = 10.841, P < 0.001). The summary of the mean difference between groups withregard to the significantly varying environmental variables is presented in Table 4.6.56