Ecology and Development Series No. 10, 2003 - ZEF

Impacts of human use on the forest vegetationIn all height classes, the three managed forest categories (SEMIFOR-NEW,SEMIFOR-OLD, and SEMIFOR-PLAN) were significantly different from both NATFORand SECFOR in terms of the abundance of stems per plot of 400 m 2 (Table 5.10.). Thedifference was very highly significant in height classes 1 and 2 (HC1 and HC2). The meanabundances in HC 2 and HC 3 of undisturbed forests, NATFOR and SECFOR, were almostten-fold of the abundance of similar height classes in the three managed forest categories(Table 5.10). Likewise, abundances in HC 4 of the undisturbed forests were also at leastfour-fold of the abundances in the managed forests of the same height class.Table 5.10. Test of differences in abundance of stems in different height classes, usingMann-Whitney U-test. The levels of significance indicated by asterix, as * = P< 0.05; ** = P < 0.01; *** = P < 0.001, and NS = not significant. Meanabundance is the average number of stems per 400 m 2 sample plot.12345HC 1 HC 2 HC 3 HC 41 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5Mean abundance 2927 2766 1908 1419 837 425 563 42 36 97 32 21 3 2 3 8 8 2 2 0.1NATFORSECFOR NS NS NS NSSEMIFOR-NEW * * *** *** *** *** * **SEMIFOR-OLD *** *** NS *** *** NS *** *** * * *** NSSEMIFOR-PLAN *** *** ** NS *** *** NS NS *** *** NS NS *** *** *** **On the other hand, there was no significant difference between NATFOR andSECFOR in all height classes (Table 5.13.). The three managed forest categories weresimilar to each other in the abundances of HC 2. The SEMIFOR-NEW differs significantlyfrom the SEMIFOR-PLAN in HC 1 and HC 4. The SEMIFOR-NEW and SEMIFOR-OLDdiffered from each other in HC 3 only. The SEMIFOR-PLAN differed significantly fromSEMIFOR-NEW and SEMIFOR-OLD in HC 4.5.3.5 Changes in basal areaThe comparisons of the basal areas (BA) of the five forest categories are presented in Table5.11 below. The test static used in this case is the paired t-test, since the BA is a continuousmeasured variable as compared to abundance, which is count data. The forest categoriesdiffered significantly in their BA (F 4,45 = 3.78; P < 0.01; Appendix 6).89