Density and species diversity of trees in four - Makerere University

G. Eilu et al.
Family
No. of
Genera
No. of
Species Family
gradient (Ter Braak & Smilauer, 1998). The first four axes of
CCA and DCA, respectively, explained 16.2 and 19.1% of the
cumulative variance in species data (Table 4). The third and
fourth axes with eigenvalues < 0.250 were less important in ecological
terms and are not considered further. The sample scores
on the first CCA axis were most strongly correlated with pH and
those of the second axis with altitude. Correlations between
environmental variables and DCA ordination axes confirmed
No. of
Genera
Euphorbiaceae 16 25 Ochnaceae 2 2
Rubiaceae 12 16 Olacaceae 2 2
Meliaceae 8 16 Verbenaceae 2 2
Fabaceae 12 13 Icacinaceae 1 2
Sapotaceae 6 11 Agavaceae 1 1
Sapindaceae 7 8 Alangiaceae 1 1
Apocynaceae 5 8 Aquifoliaceae 1 1
Moraceae 5 8 Araliaceae 1 1
Ulmaceae 4 8 Arecaceae 1 1
Flacourtiaceae 6 7 Asteraceae 1 1
Sterculiaceae 5 7 Balanitaceae 1 1
Annonaceae 4 6 Canellaceae 1 1
Unknown 1 5 Chrysobalanaceae 1 1
Anacardiaceae 4 4 Cyatheaceae 1 1
Clusiaceae 4 4 Dichapetalaceae 1 1
Simarubaceae 4 4 Ebenaceae 1 1
Rutaceae 3 4 Hypericaceae 1 1
Tiliaceae 3 4 Loganiaceae 1 1
Rhizophoraceae 1 4 Melastomataceae 1 1
Bignoniaceae 3 3 Melianthaceae 1 1
Capparidaceae 3 3 Monimiaceae 1 1
Oleaceae 3 3 Myristicaceae 1 1
Rhamnaceae 3 3 Myrtaceae 1 1
Boraginaceae 2 2 Rosaceae 1 1
Cecropiaceae 2 2 Theaceae 1 1
Celastraceae 2 2 Violaceae 1 1
Lauraceae 2 2 — — —
No. of
Species
Table 3 Tree families, numbers of genera and
species recorded from Bwindi, Kasyoha, Kibale
and Budongo forests of the Albertine Rift
Table 4 Eigenvalues of the first four axes of canonical correspondence analysis (CCA) and Detrended correspondence analysis (DCA) of all
plots and the amount of variance explained of the species data and of the species-environment relation by the CCA axes. The length of gradient
is shown for DCA
Axes 1 2 3 4 Total inertia
Eigenvalues (CCA) 0.480 0.259 0.228 0.128 6.757
(DCA) 0.709 0.251 0.207 0.149 6.879
Lengths of gradient (DCA) 5.259 2.772 2.700 2.191 —
Species-environment correlations (CCA) 0.861 0.820 0.950 0.755 —
Cumulative percentage variance of species data (CCA) 7.1 10.9 14.3 16.2 —
(DCA) 10.3 14.0 17.0 19.1 —
Cumulative percentage variance of the species-environment
relation (CCA)
30.1 46.4 60.7 68.7 —
Sum of all unconstrained eigenvalues (CCA) — — — — 6.757
(DCA) — — — — 6.757
Sum of all canonical eigenvalues (CCA) — — — — 1.593
results of CCA analysis with axis 1 most strongly correlated with
pH (r = 0.565).
Automatic forward selection of environmental variables by
canoco (Table 6) showed that pH explained the most variance
(0.39) while silt explained the least (0.08%). After selecting pH,
altitude, rainfall, loss of organic matter on Ignition, potassium
(K), available phosphorus and slope contributed significantly (at
5% level) to the model of already included variables.
306 Diversity and Distributions, 10, 303–312, © 2004 Blackwell Publishing Ltd