Ecology and Development Series No. 10, 2003 - ZEF

Impacts of human use on the forest vegetationTable 5.5. Summary of PCA analysis resultsAxes I II III IV Total inertiaEigenvalues 0.489 0.165 0.113 0.073 1.000Cumulative % variance of species data 48.9 65.3 76.7 84.0Sum of all eigenvalues 1.00The first axis of both PCA and RDA represent the gradient in human impact ordisturbance. In the PCA species-site biplot (Figure 5.1), the gradient in human impactincreases toward the left. All sites representing managed forest categories for coffeeproduction are located in the left half of the ordination space. For sake of clarity, onlyselected species were shown in the biplot. Coffea arabica is strongly correlated with thefirst PCA axis and its relative abundance increases towards the direction in whichhuman impact increases (Figure 5.1.). Many small trees (Dracaena fragrans, Veprisdainelli), climbers (Landolphia buchananii, Hippocratea africana), and canopy treeslike Prunus africana, Olea capensis ssp. welwitschi are also strongly correlated with thefirst PCA Axis, but their relative abundance increases in the direction in which humanimpact decreases. Maytenus gracilipes was strongly correlated with the second axis, andappears to be less affected by human impact. Maytenus gracilipes is not correlated withthe human impact gradient at all, because it can regenerate vigorously both from seedsand from stumps by coppicing even in the managed forests.81