Transcript Effects of topography and altitude on floristic diversity

Effects of environmental factors on floristic diversity
and composition of vascular plants in the remnant
moist Afromontane forest in Wondo Genet, South
Central Ethiopia
Mamo Kebede1, Eshetu Yirdaw, Olavi Luukkanen,
Mulugeta Lemenih
1Viikki
Tropical Resources Institute (VITRI), Department of
Forest Sciences, University of Helsinki
Introduction
Ethiopia is endowed with diverse vegetation types ranging
from Afroalpine vegetation in the central highlands to arid
lowlands in the east, and rainforests in the west (Friis et al.,
2010)
The country has the fifth largest flora in Africa (EPA, 1997)
Wondo Genet forest in the south central highlands, where
this study was conducted, is classified as Moist evergreen
Afromontane Forest (Friis et al., 2010)
The forest cover of the area declined from 16% to 2.8% in
three decades (Dessie, 2007).
Objectives of the study
 To examine the floristic diversity and composition
of vascular plants
 To assess the structural diversity and population
structure of the forest
 to analyze regeneration characteristics and soil
seedbank pool in the forest and compare with the
standing stock
To study reproductive phenology of selected four
native tree species with population structure at risk
Study questions
What is the extent of the vascular plant species diversity
in this remnant forest as influenced by environmental
gradients ?
 what is the current status of structural diversity of tree
and / or shrub species ?
Which species maintained regeneration and soil seed
bank pool for potential replacement of the standing crop ?
Do the selected native tree species have adequate
reproductive phenology in terms of the presence of
flowering mature trees, flower visitors and seed
production ?
Introduction …
Generating information to assist planning for conservation and restoration
of this forest is crucially important.
The aim of this study was to:
(i)
Describe species richness, abundance and plant community types of
Wondo Genet Afromontane forest
(ii) Ascertain the pattern of species richness and abundance with
elevation, slope and aspect, and
(iii) Carry out floristic similarity (Sørensen’s) comparison of the Wondo
Genet forest with other Afromontane forests of Ethiopia and with
some Eastern African countries.
Materials and Methods
Wondo Genet is situated in the south-eastern central highlands of
Ethiopia, about 263 km from Addis Ababa, at 7o 5’N latitude and 38o 36’ E
longitude on the eastern slope of the Rift Valley escarpment
The altitude ranges from 1800 m to 2500 m. The mean annual rainfall is
about 1200 mm and it is bimodal.
Rain can be expected from March to April and June to August. The period
from November to February is relatively dry.
The soils are young and of volcanic origin, characterized by well-drained
loam or sandy loam, and it is shallow at steep convex slopes but deeper
at lower altitudes (Eriksson and Stern, 1987).
The current land use is predominantly smallholder agriculture with an
average landholding size of less than one hectare per household
Materials and Methods …
Systematic plot sampling was conducted in four transects and seventy-five
20 x 20 meter quadrats
The first quadrat was located randomly, and after that the quadrats were
established at 100 m intervals along transects.
Transects were spaced 350 m apart. In each quadrat, all species with DBH
(Diameter at Breast Height) ≥ 2 cm and height ≥ 2 m were identified and
counted.
The presence of epiphytes, herbs, grasses, sedges and ferns was recorded
for floristic compilation. Herbarium vouchers were collected and Plant
identification was done in the National Herbarium, Addis Ababa University.
Environmental parameters including slope, elevation, exposition, and
coordinates were measured on plot basis.
Data Analysis
Diversity Analysis
Species diversity was measured using Shannon diversity (H’), H’max, and
Shannon evenness (J’), Simpson index (D) ((Magurran, 2004 )
Cluster Analysis
Hierarchical cluster analysis of the data was done using PC-ORD for Windows
version 5 (McCune and Mefford, 2006).
Ordinations
Ordination was also computed using a Nonmetric Multidimensional Scaling
(NMDS) (McCune and Grace, 2002). The species abundance and environmental
matrices containing elevation (meter a.s.l), slope (%), and aspect were used for
the ordination
Phytogeographic comparison
A similarity analysis was carried out to evaluate the relationship between the
forest based on the presence of trees and shrubs. Sørensen’s similarity was
used for comparison with Mafi in Tanzania (Lyaruu et al., 2000) and Mt. Elgon in
Kenya, (Hitimana et al., 2004) and other Ethiopian Afromontane forests.
Results
A total of 240 plant species including nine endemic
plant species were found representing 91 families and
210 genera, of which trees constitute 23.8%, shrubs
25%, herbs 35%, lianas 11.3% and ferns 5%.
Cluster and indicator species analyses revealed five
plant communities described as:
•
•
•
•
•
C1 - Teclea nobilis-Calpurnia aurea,
C2- Erythrococca trichogyne-Millettia ferruginea,
C3 - Croton macrostachyus-Vernonia hochstetteri,
C4 - Protea gaguedi-Rhus retinorrhoea and
C5 - Dodonaea angustifolia-Hypericum quartinianum
community.
Shannon
Community
Elevation
Species richness
Evenness
diversity (H')
H'Max
Evenness (J)
Simpson
Berger
I
1800-2000
51 (6.51)
0.354 (0.18)
2.89 (0.44)
3.95
0.73(0.11)
0.90 (0.12)
0.17(0.15)
II
1850-2000
44 (4.19)
0.468 (0.13)
3.026 (0.44)
3.78
0.8 (0.10)
0.932 (0.12)
0.142 (0.16)
III
1900-2200
61 (7.67)
0.402 (0.14)
3.20(0.42)
4.11
0.778 (0.08)
0.931(0.07)
0.163 (0.11)
IV
2200-2400
45(3.64)
0.45(0.13)
3.017(0.39)
3.61
0.793(0.07)
0.926 (0.09)
0.185(0.12)
V
2050-2150
37 (4.35)
0.46 (0.18)
2.836(0.43)
3.8
0.785 (0.11)
0.897(0.09)
0.26 (0.14)
Over all
1800-2445
72 (6.04)
0.52 (0.17)
3.63 (0.43)
4.32
0.84(0.10)
0.96(0.10)
0.079(0.143)
Dendrogram
Results
Results…
The five communities identified were: A. schimperi-F. indica community, E.-M.
ferruginea community, C. macrostachyus- V. hochstetteri community, P. gaguedi- R.
retinorrhoea community ; D.angustifolia – H. quartinianum community
Ten combinations of pair-wise T-test comparisons were conducted and
showed a significant difference (P = 0.001).
From the analysis, the T- value statistic for the five groups is -27.07 (P =
0.001) and the agreement statistic A is 0.554
The test statistic T describes the separation between groups. The more
negative T values, the strongest the separation
The agreement statistics A describes chance corrected for within-group
homogeneity, compared to random expectation and lies between 0 and 1 (
when all items are identical.
150
y = -0.185x+467.4
5
50
10
15
20
25
y = -0.0317x+80.63
r = 0.5485
100
Species abundnance
30
r = 0.6936
1900
2000
2100
2200
2300
2400
1900
Elevation (m)
2000
2100
2200
2300
2400
200
35
Elevation (m)
y = -0.7397x + 120.02
150
Species abundance
50
10
15
20
25
y = -3.996x+17.292
r = 0.3529
100
30
r = 0.2081
5
Species richness
Species richness
200
35
Results….
20
40
Slope %
60
80
20
40
Slope %
60
80
Results (Sørensen’s similarity)…
Forest
N
a (common)
b (WG)
c
Ss
35
37
16
0.56
19
53
12
0.36
16
56
15
0.31
19
53
11
0.37
33
39
39
0.45
34
38
35
0.47
13
59
48
0.19
23
49
28
0.37
51
Jibat
31
Chilimo
31
Menagesha
30
Wof-washa
87
Yayu
117
Mena Angetu
61
Mafi (Tanzania)
Mt. Elgon (Kenya)
51
Conclusion and recommendations
Wondo Genet remnant forest contains a substantial amount of
Afromontane plant species composition and diversity.
The high diversity, coupled with the presence of some endemic species
calls for immediate conservation strategies with the involvement of the
government and local communities that would lead to the restoration and
rehabilitation of this remnant forest
Detailed ecological studies are vital concerning the species composition,
diversity and distribution of the possible plant community types in relation
to other environmental factors such as soil properties, moisture regime,
temperature fluctuation, frost occurrence, and the like, which were not the
subject of this study.
Ethnobotanical studies should be conducted to harness the indigenous
knowledge on the uses of plant resources contained in the forest.