Fig 1.
Map of the study area showing Eastern Arc mountains, Amani and Nilo nature forest reserve sites.
The Eastern Arc layer source is from [35].
Table 1.
The environmental and disturbance factors (Mean ± SD) within the tropical sub -montane forests of East Usambara, Tanzania.
The bolded factors significantly explained species composition.
Fig 2.
Canonical correspondence analysis diagram showing the ordination of dominant species represented and their correlation with environmental and disturbance variables in the sub-tropical montane forest plots.
Canonical correspondence analysis biplot of Amani and Nilo FR species distribution (blue dots) based on tree species abundance. The gray axes vectors indicate the significant explanatory variables in their abbreviated form: El = Elevation, TS = Temperature seasonality, MAP = Mean Annual precipitation, P = Soil phosphorus, Rd = Distance to the road and Vl = Distance to the villages. We also used abbreviated species scientific names of each tree by using first two letters each from genus and species; Al.ch = Alangium chinense (Lour.) Harms, Al.gu = Albizia gummifera (J.F.Gmel.) C.A.Sm., Al.me = Allophylus melliodorus Gilg ex Radlk., Al.st = Allanblackia stuhlmannii (Engl.) Engl., Al.sc = Alsodeiopsis schumannii (Engl.) Engl., An.ku = Annickia kummeriae (Engl. & Diels) Setten & Maas, An.gr = Anthocleista grandiflora Gilg, An.me = Antidesma membranaceum Müll.Arg. An.to = Antiaris toxicaria Lesch., Ar.he = Artocarpus heterophyllus Lam, Bl.un = Blighia unijugata Baker, Ce.go = Celtis gomphophylla Baker, Ce.mi = Celtis mildbraedii Engl., Ce.us = Cephalosphaera usambarensis (Warb.) Warb., Ch.pe = Chrysophyllum perpulchrum Mildbr. ex Hutch. & Dalziel, Dr.ge = Drypetes gerrardii Hutch., En.us = Englerodendron usambarense Harms, Er.su = Erythrophleum suaveolens (Guill. & Perr.) Brenan, Fi.ex = Ficus exasperata Vahl, Fi.su = Ficus sur Forssk., Fu.af = Funtumia africana (Benth.) Stapf, Gr.su = Greenwayodendron suaveolens (Engl. & Diels) Verdc., Is.sc = Isoberlinia scheffleri (Harms) Greenway, Le.fr = Lecaniodiscus fraxinifolia Baker, Le.us = Leptonychia usambarensis K. Schum. Ma.ca = Macaranga capensis (Baill.) Sim, Ma.em = Maesopsis eminii Engl., Ma.lu = Markhamia lutea (Benth.) K.Schum., Me.in = Mesogyne insignis Engl., My.ho = Myrianthus holstii Engl., Ne.bu = Newtonia buchananii (Baker) G.C.C.Gilbert & Boutiqu, Pa.ex = Parinari excelsa Sabine, Po.al = Pouteria alnifolia (Baker) Roberty, Qu.un = Quassia undulata (Guill. & Perr.) D.Dietr. Ri.he = Ricinodendron heudelotii (Baill.) Heckel, Ro.ma = Rothmannia manganjae (Hiern) Keay, Sh.el = Shirakiopsis elliptica (Hochst.) Esser, So.ma = Sorindeia madagascariensis Thouars ex DC., St.sc = Strombosia scheffleri Engl., Sy.ce = Synsepalum cerasiferum (Welw.) T.D.Penn., Sy.ms = Synsepalum msolo (Engl.) T.D.Penn., Ta.pa = Tabernaemontana pachysiphon Stapf, Ta.ve = Tabernaemontana ventricosa Hochst. ex A.DC., Ta.ni = Tarenna nigrescens (Hook.f.) Hiern, Tr.dr = Trichilia dregeana Sond., Tr.ma = Trilepisium madagascariense DC., Tr.my = Tricalysia myrtifolia S.Moore, Xy.mo = Xymalos monospora (Harv.) Baill.
Fig 3.
Dendrogram of hierarchical clustering using similarity ratio showing four community types in different sites (plot 1–59) of the study area (Ward’s method, Bray-Curtis distance) across Amani and Nilo nature forest reserve in sub-tropical East Usambara montane forest of Eastern Arc.
The communities are named by using number of communities denoted as (Cn) and they are named after by two dominant species: C1 = Tabernaemontana ventricosa-Leptonychia usambarensis, C2 = Ficus sur- Myrianthus holstii, C3 = Artocarpus heterophyllus-Lecaniodiscus fraxinifolia and C4 = Isoberlinia schefflera- Sorindeia madagascariensis communities (S1 Appendix).
Fig 4.
Canonical correspondence analysis diagram displaying the ordination of community types represented and their correlation with environmental and disturbance variables, indicating abundance relationships in sub-tropical East Usambara montane forest of Eastern Arc mountains.
Communities: Tave.Leus = Tabernaemontana ventricosa- Leptonychia usambarensis, Arhe.Lefr = Artocarpus heterophyllus-Lecaniodiscus fraxinifolia, Fisu.Myho = Ficus sur- Myrianthus holstii and Isoberlinia schefflera- Sorindeia madagascariensis communities (S1 Appendix).
Fig 5.
Boxplot showing difference among individual communities with respect to environmental and disturbance factors.
The horizontal line crossing the box in the center represents the median; the box represents the 25th and the 75th percentiles. The vertical line outside the box represents the minimum and maximum values. Difference in letters (a, b, c, d) signifies that the communities are different in the specified factor. Communities: 1 = Tabernaemontana ventricosa-Leptonychia usambarensis, 2 = Ficus sur- Myrianthus holstii, 3 = Artocarpus heterophyllus-Lecaniodiscus fraxinifolia, 4 = Isoberlinia schefflera- Sorindeia madagascariensis.
Fig 6.
The Venn diagram showing variation partitioning results (partial CCA model) and the contribution of the four studied environmental and disturbance variable groups (i.e., climatic, soil, topography, and disturbance) that drive the plant species distribution.
The proportion of variance in tree species composition explained by environmental and disturbance factors. The values represent adjusted R2 (%) of independent and shared effects by 4 the factors.
Table 2.
CCA variation partitioning (%) on overall plant species composition of Tropical sub- montane forests of East Usambara, Northern Tanzania.