TITLE:
Assessing Tree Species Dominance along an Agro Ecological Gradient in the Mau Forest Complex, Kenya
AUTHORS:
Mwangi James Kinyanjui, Chris A. Shisanya, Ondimu Ken Nyabuti, Wargute Patrick Waqo, Merceline Awuor Ojwala
KEYWORDS:
Species Dominance, Basal Area, Agro Ecological Zoning
JOURNAL NAME:
Open Journal of Ecology,
Vol.4 No.11,
August
19,
2014
ABSTRACT: Species relative dominance by basal area was assessed along an agro ecological
gradient in the Mau Forest Complex (MFC). Trees were recorded per species and
diameter at breast height (D1.3) for size class D1.3 ≥ 10
cm in 60 quarter hectare plots distributed in 7 agro ecological zones (AEZ)
namely LH1, LH2, LH3, LH4, UH0, UH1 and UH2. Basal area per species was used to
calculate species relative dominance i.e. the proportion of basal area by a species to the total basal area of the
AEZ. Species associations were analysed as the group of highly ranked species
in each AEZ. Sorensons similarity index was used to calculate the proportion of
similar species among AEZ. Analysis of variance compared basal area among AEZ
and Tukey’s multiple comparison test used to identify specific AEZ with differences. Tabernaemontana stapfiana (Britten)
was ranked first in LH1, UH1 and UH0 with relative dominance values of 22.66%,
22.89% and 30.73% respectively. It was however not recorded in any other AEZs. Dombeya goetzenii (K. Schum) occurred in
6 of the 7 AEZs but had moderate dominance values in each of the 6 AEZs. The
sum of dominance values per species in all AEZs indicated no species
mono-dominance and different species dominated at different AEZs. Co-dominance
resulted in species associations like Tabernaemontana-Allophylus-Eke-bergia-Albizia in
LH1, Juniperus-Dombeya-Casearia-Prunus in LH2, Acokanthera-Cussonia-Olea-Teclea in LH4 and Tabernaemontana-Syzygium-Podocarpus-Neoboutonia in
UH1. Species richness was highest in UH1 and had the highest similarity indices
with those of other AEZs. The UH1 had a species similarity of 67% with LH1, 63%
with LH2 and 56% with LH4. However, species in the very humid zone UH0 differed
with those of the drier lower highland zones (UH0 vs LH3 and vs LH4 = 31% and
37% respectively). Basal area differed significantly among AEZ ( = 3.76) showing that they differ in stocking levels. Tukeys test showed
that high potential zones of LH1, LH2, UH0, UH1 did not differ and similarly
the lower potential zones; LH3 and LH4. The results show that the variation of
species and forest stocking in the MFC is strongly influenced by AEZ and
proposes future biomass mapping to be done along AEZ.