Saudi Journal of Biological Sciences (2016) 23, 687–697
King Saud University
Saudi Journal of Biological Sciences
www.ksu.edu.sa
www.sciencedirect.com
ORIGINAL ARTICLE
Main vegetation types and plant species diversity
along an altitudinal gradient of Al Baha region,
Saudi Arabia
Abdullah Al-Aklabi a,*, Abdul Wali Al-Khulaidi b, Akram Hussain c,
Nageeb Al-Sagheer d
a
Department of Biology, College of Science and Arts, Albaha University (BU), Baljurashi, Saudi Arabia
Faculty of Applied Studies and Continuous Education, Saudi Arabia
c
Al Baha University, Saudi Arabia
d
Food and Agriculture Organization of the United Nation, Saudi Arabia
b
Received 8 November 2015; revised 2 February 2016; accepted 4 February 2016
Available online 3 March 2016
KEYWORDS
Vegetation types;
Al Baha;
Saudi Arabia;
MVSP;
Plant density
Abstract Plant species composition patterns and vegetation types were investigated along Elevational Gradients in Al Baha region, Saudi Arabia. Sandy plain, wadis, drainage lines, rocky outcrops, hills and fallow lands occur over a wide geographic range encompassing variation in plant
species and communities among these different ecological sites. To provide a quantitatively based
classification of the vegetation we used Multi Variant Statistical Package (MVSP) software, followed by the re-arrangement of a matrix of the similar plant species in rows and similar sample sites
in columns. Plant density and environmental variables were measured and recorded in each quadrat. Two-way indicator species analysis and Canonical Correspondence Analysis (CCA) were used
to analyze the relationships between vegetation and environmental variables, while Arc Map was
used to analyze the pattern of plant species density. A total of 59 sample plots (25 25 m), stratified, randomly-placed relevés were collected in Al Baha region, along a cross section running from
south-west to north-west. About 190 plant species belonging to 59 families were recognized. This
study showed that these plant species formed 15 vegetation types that primarily correspond mainly
to different combinations of elevation, and topography. The study concluded that this research has
provided the first quantitative and systematic survey of the vegetation in Al Baha region.
Ó 2016 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University. This is
an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
* Corresponding author.
E-mail address: alaklabia@yahoo.com (A. Al-Aklabi).
Peer review under responsibility of King Saud University.
Production and hosting by Elsevier
1. Introduction
The vegetation types of Al Baha region have not been studied
in detail before, and this study is the first comprehensive one
on the entire vegetation communities across altitudinal gradient in Al Baha region. A few studies have been carried out
http://dx.doi.org/10.1016/j.sjbs.2016.02.007
1319-562X Ó 2016 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
688
A. Al-Aklabi et al.
on the vegetation of Al Baha and focused on the recording of
few or individual plant species and vegetation (Alaklabi et al.,
2014; Al-Zahrani and Elhag, 2005; Collenette, 1985;
El-Karemy and Zayed, 1996; Hajar, 1993; Hassan and
Al-Hemaid, 1995; Zayed and Fayed, 1987).
Al Baha region characterized by high diverse vegetation,
Juniperus procera woodland and forest found there in abundance beside other communities. The high mountains of Al
Baha are considered as one of most significant plant diversity
zones in Saudi Arabia. Although Al-Baha is a small area in
Kingdom of Saudi Arabia, recent studies estimated about
230 plant species (about 12% of the total plant species of the
Kingdom). The flora of Al Baha is a mixture of the tropical
African, Sudanian plant geographical region (Paleotropical
origin) and the with very few of Saharo-Sindian or SaharoArabian region (Holarctic origin) and Mediterranean regions
(Al-Khulaidi, 2013). Most of Al Baha’s flora belongs to Sudanian region of Eritreo-Arabian province of Sudanian region
(Zohary, 1973) or Somalia-Masai region center of endemism,
(White, 1983). The Sudanian element dominates the western
mountains and parts of the high land plains which are characterized by relatively high rain fall. The Mediterranean region
element dominates the high mountain areas. The SaharoArabian element dominates the coastal plains, eastern mountain and the eastern and northern desert plains.
Much of the work on vegetation classification comes from
European and North American ecologists (Van Der Maarel,
2004; Feldmeyer-Christie et al., 2005). They have fundamentally different approaches. In North America, vegetation types
are based on a combination of the following criteria: climate
pattern, plant habit, phenology and/or growth form, and dominant species. In the current US standard (adopted by the Federal Geographic Data Committee (FGDC), and originally
developed by UNESCO and the Nature Conservancy, the
classification is hierarchical and incorporates the non-floristic
Figure 1
criteria into the upper (most general) five levels and limited
floristic criteria only into the lower (most specific) two levels
(Van Der Maarel, 2004). In Europe, classification often relies
much more heavily, sometimes entirely, on floristic (species)
composition alone, without explicit reference to climate, phenology or growth forms (Feldmeyer-Christie et al., 2005). It
often emphasizes indicator or diagnostic species which may
distinguish one classification from another.
The aim of vegetation classification in this study is to
group the plant species together on the basis of their floristic
composition into vegetation types (communities) generally
known as plant phytosociological units using MVSP software and following the method of Braun-Blanquet ordination methods.
2. Site description
Al Baha region (Fig. 1) is located in the south western part of
Saudi Arabia. It is situated between longitude 41/42E and latitude 16/20N. The study area is located along environmental
gradients with an elevation of 130–2450 m above sea level. It
is a transition zone between dry coastal plain, Rocky mountains that face west and semi desert mountains that face east.
It has a wide variety of woodland, shrubland, grassland, and
forest habitats accompanied by many plant species.
2.1. Topography
Al Baha region composes of three main ecosystems as in
Fig. 2. Tihama plain: it is a sandy flat to undulating plain,
ranging from 50 to 150 (200 m) and narrowing toward northwest slopes and touching the foothills at 350 m. The plain is
intersected by many valleys mainly wadi Nawan, wadi Al
Hasaba, wadi Malal, wadi Nabira and wadi Uleib.
Location of the Al Baha region.
Main vegetation types and plant species diversity
689
Aref et al., 2011). Records from 7 stations show that annual
average rainfall of the Al Baha area ranges from 142 mm to
316 mm. The annual rainfall reaches 142 mm at Al Aqiq
(1650 m), 300 mm at Baljurashi (2062 m), 316 mm at Al Mandaq (1948 m), and 200 mm at Al Mikhwah (600 m)
(Aboulabbes, 2013).
3. Materials and methods
After preliminary reconnaissance, transects were located along
Elevational Gradients in Al Baha region, Saudi Arabia, consistently correlated mainly with elevation and topography. Transects were chosen to cross the region and identify major
vegetation communities in the different landforms (Fig. 3). A
total of 59 plant species which stratified, randomly-placed
quadrats (25 25 m) were sampled along this transect. With
the use of vegetation data sheet, the following variables were
measured and recorded in the field: Terrain (land form by field
observation according to the categories, slope direction; latitude and longitude using Geographical Positioning System
(GPS) and vegetation cover, expressed as number of each species in the sample site.
The following methods were used to survey the plant cover
based on the Zurich–Montpellier (Kent and Coker, 1992) or
Braun-Blanquet school (Zonneveld, 1989):
Figure 2
Topography of Al Baha region.
The foothills facing Tihama: it is a medium to steep slope
intersected by valley gullies, descending gradually toward the
west, the altitude ranges from 200 (400) to 2001 and 2200 west
of Al Baha city and Uwera and between 2000 and 2100 m west
of Baljurashi.
High-altitude mountains: in some parts with almost flat and
undulating plateaus, the altitude ranges between 1700 to the east
and from 2000 to 2500 m toward the west at Jabal Alzzrayeb, rising up to 2565 m at Al Hamd (north-east of Al Baha city).
The eastern mountains and plateaus: gradually descend
toward the east and north-east, dissected by several valleys
such as the wadi Jazab and wadi Ayna. The altitude ranges
between 1300 and 1700 m.
(1) Plant species were identified and entered in rows and sample plots were entered in columns of an initial matrix.
(2) Number for each plant species and environmental data
such as altitude, topography, exposure for each sample
plot was added.
2.2. Climate
The Orographic rise of air masses from the onshore wind provides an effective cooling mechanism, which causes rainfall.
For example, areas exposed to the sea such as the southern
slopes, receive more rainfall than the zones facing the interior
plateau. Local topographic features cause similar effects, at
correspondingly smaller scales. According to Koppen’s climate
classification system (1936), dry and semiarid climates (BWh)
predominate in Arabian Peninsula. Almost the entire area of
Al Baha belongs to the climate class BWh of tropical/subtropical desert (Ayele and Al Shadily, 2000).
The climate of Al Baha region is influenced by its varying
topography. It is generally moderate in summer and cold in
winter, with average temperature ranging between 12 and
23 °C. The climate is comparatively cold in winter (10–22 °C)
and mild in summer (22–32 °C). Average rainfall in Al-Aqiq
and Al-Mikhwah areas is 100–200 mm, temperature is 20–
37 °C in winter and 36–51 °C in hot summer (Ibrahim, 2010;
Figure 3
Cross section along the study area.
690
(3) Sample plots with a high similarity of plant species composition were placed side by side.
(4) Plant species with similar patterns in quadrat plots were
aggregated.
Using MVSP Two-way indicator species analysis and
Canonical Correspondence Analysis (CCA) were used to analyze the relationships between vegetation and environmental
variables.
The number of plant species in each quadrat, as well as the
number of individuals of each species was recorded to calculate
plant density per hectare. ArcGis (Arc Map) was used to create
a raster plant density map along the cross section (Silverman,
1986).
4. Results and discussion
4.1. Plant species density
The 190 plant species belonging to 59 families were recorded
along the cross section. These plant species formed 15 vegetation
types that primarily correspond mainly to different combinations of elevation, and topography. These types are representative of the vegetation in different ecosystems. Each type had a
different vegetation structure, topography and environment
(Table 1). The variation types were significantly related to elevation, topography, and aspect. The highest species diversity
appeared in the fog affected mountain slopes facing Tihama
coastal area under medium disturbance intensity. Factors such
as fogs, elevation, slope, aspect, moisture, soil and topography
were strongly correlated with species composition.
Plant species density is the number of plant species and
abundance of each species that are found in the study area.
ArcGis (Arc Map) was used to create a raster plant density
map along the cross section. Plant density appears to peak at
high altitude areas (around Aqabat Hizna and Baljurashi)
and declines gradually toward south west (coastal plains)
and north east (around Al Aqiq) as rainfall decreases and temperature increases (Fig. 4).
Using MVSP software and following the method of BraunBlanquet ordination methods (Braun-Blanquet, 1932), the
sample plots were arranged to similarities and then combined
with 15 vegetation types (Fig. 6 and Table S1). A Number of
each plant species were entered in the matrix. Species with similar distributions were grouped together in the table and
association-analysis final groups were re-arranged to consolidate patterns in the table as much as possible. The matrix
shows a diagonal clusters where the boundaries of vegetation
types in rows and sociological species groups in columns can
be detected visually through the absence or presence of different plant species. Vegetation types are labeled by the dominant
species (the second name) and by the species almost exclusively
occurring in the vegetation type (the first name) (see Figs. 5
and 7).
4.2. Description of main vegetation types
4.2.1. Tamarix aphylla – Salvadora persica type
This type forms woodland and is restricted to wadis. The vegetation cover ranges between 30% and 36%. The topography
is composed of flat wadis. The altitude ranges from 150 to
A. Al-Aklabi et al.
160 m above sea level. The most common species are T. aphylla
and S. persica.
4.2.2. Acacia ehrenbergiana – Acacia tortilis type
This type forms sparse woodland and is found on rocky slopes
adjacent to wadis and fallow lands. The altitude ranges from
136 to 275 m above sea level.
The vegetation cover is very poor ranging between 2% and
9%. The average tree cover is 20%, the average shrub cover is
1%, and the average herbaceous cover is 1%. Association
plant species are S. persica, Calotropis procera and Abutilon
pannosum.
4.2.3. Commiphora myrrha – Maerua crassifolia – Acacia asak
type
This type forms woodland to shrubland and grassland. The
vegetation cover ranges between 8% and 110%. The average
tree cover is 13%, the average shrub cover is 9%, and the average herbaceous cover is 25%.
The topography is composed of steep to moderate steep
slope and rock outcrops. The altitude ranges from 700 to
990 m above sea level. The dominant species is A. asak. The
most common species that always occur are A. asak, Anisotes
trisulcus. The following species are rare and found only in this
type: Barleria acanthoides, Barleria hochstetteri, Boscia angustifolia, Commelina forsskalaei, Commicarpus sp., Commiphora
kua, Dobera glabra, Ecbolium viride, Euphorbia cuneata, Indigofera spiniflora, Portulaca oleracea, Pulicaria sp., Salsola
sp., Sarcostemma viminale, Suaeda aegyptiaca.
4.2.4. Nicotiana glauca – A. asak type
This type represents the degraded sites of type 3 that occur in
the same ecological zone and in the same type of land formation but at a higher altitude. The vegetation cover ranges
between 5% and 24%. The average tree cover is 5%, the average shrub cover is 2%, and the average herbaceous cover is
4%. The most common species that always occur are A. asak
and N. glauca. The following species are rare and found only in
this type Forsskaolea tenacissima and Acacia hamulosa.
The topography is composed of a moderate steep slope.
The altitude ranges from 1127 to 1756 m above sea level.
4.2.5. Flueggea virosa – A. asak type
This type forms woodland. The vegetation cover ranges
between 70% and 80%. The topography is composed of a
steep to moderate steep rocky drainage line. The altitude
ranges from 1700 to 1750 m above sea level.
The most common plant species are: A. asak, Cissus rotundifolia, Crotalaria sp., Ficus cordata, Ficus ingens, F. virosa,
Grewia trichocarpa, Grewia villosa, Lantana sp., Triumfetta
flavescens.
4.2.6. Panicum turgidum – Acacia tortilis type
This type forms woodland and shrubland. The vegetation
cover ranges between 18% and 65%. The average tree cover
is 19%, the average shrub cover is 13%, and the average
herbaceous cover is 9%. The topography is composed of
wadis. The altitude ranges from 415 to 736 m above sea level.
The most common species and always occur are A. tortilis,
Aerva javanica, Indigofera spinosa. The following species are
Relationship between the vegetation types and different environmental factors.
1
2
5
6
Way point (WP)
101
88
100
3
69
71
70
27
111
86
222
112
6
4
26
68
5
4
25
92
232
72
230
227
231
91
87
220
44
194
195
Plant density
Richness
Exposure
land form
Rainfall
Trees %
Shrub %
Herb %
Total
Altitude m
42
3
S
W
90
35
1
0
36
158
3
3
SW
fa
90
2
0
0
2
136
17
4
SW
s
90
7
0
2
9
275
128
23
SE
RO
250
7
5
40
52
990
72
13
SW
S
250
25
10
5
40
805
14
8
NW
S
250
5
3
0
8
870
11
8
W
S
250
5
2
0
7
762
103
16
W
S
250
10
5
50
65
875
71
12
SW
RS
250
20
20
10
50
700
292
20
W
RS
250
20
5
15
40
735
138
23
SW
S
250
10
20
80
110
815
11
5
W
S
250
7
1
0
8
1167
9
7
NW
S
250
10
1
0
11
1127
40
6
SW
S
250
4
5
15
24
1287
21
6
W
S
250
4
1
5
10
1233
24
4
SW
S
250
1
2
5
8
1426
13
4
W
S
250
4
1
0
5
1756
54
11
W
dr
250
50
20
10
80
1720
155
18
SW
W
150
10
30
20
60
440
31
13
W
W/P
200
10
7
1
18
736
126
17
SW
W
150
10
20
5
35
472
223
19
SW
W
150
15
5
10
30
440
147
21
SE
W
150
50
5
10
65
417
101
14
SW
S
250
30
15
10
55
1488
54
9
W
RO
250
10
10
15
35
1463
68
18
W
RS
250
4
2
20
26
1440
147
8
S
Fa
300
10
2
80
92
2025
107
7
S
Fa
300
50
2
80
132
2032
282
20
S
Fa
300
20
15
50
85
2040
Vegetation type
9
Way point (WP)
175
176
43
3
219
177
178
179
110
90
89
85
109
75
73
107
79
81
80
82
77
83
78
105
106
108
84
76
74
Plant density
Richness
Exposure
land form
Rainfall
Trees %
Shrub %
Herb %
Total
Altitude m
123
17
SW
RO
300
7
25
5
37
2020
136
16
S
RO
300
3
5
30
38
2084
591
13
NW
W
300
60
40
70
170
2036
14
3
SW
s
200
7
0
5
12
2031
174
10
S
RS
200
1
8
10
19
1902
306
17
N
S
300
30
2
35
67
2260
149
16
E
S
300
15
2
35
52
2360
209
23
S
S
300
10
5
50
65
2383
107
21
SW
SS
200
15
2
30
47
1979
52
12
W
S
200
8
10
20
38
1718
67
16
W
S
200
5
40
30
75
1700
131
16
S
W
250
10
60
20
90
2085
111
15
S
W
250
15
30
40
85
1906
91
11
SE
S
250
60
2
10
72
1835
58
9
SE
S
250
2
40
5
47
1840
29
5
W
S
250
4
2
20
26
1865
20
7
E
h
100
7
2
5
14
1565
24
6
NE
P
100
20
1
1
22
1410
50
7
SE
W
100
3
20
2
25
1472
43
6
S
P
100
50
15
1
66
1378
44
5
S
S
140
10
2
25
37
1746
14
7
E
S
100
2
3
1
6
1691
41
12
S
S
140
2
15
5
22
1621
123
15
W
W
200
5
25
30
60
2020
95
13
W
W
200
20
3
5
28
1905
94
19
N
S down
200
7
2
25
34
1921
112
14
E
W
140
7
20
1
28
1867
82
14
N
W
100
15
5
2
22
1805
198
14
E
Riv
250
5
1
80
86
1810
10
11
12
7
13
8
14
Main vegetation types and plant species diversity
Table 1
Vegetation type
15
691
692
A. Al-Aklabi et al.
This type is found on fallow lands that been previously cultivated and severely in danger because of expanding the
buildings.
4.2.9. Maytenus parviflora – Hyparrhenia hirta – J. procera type
This type forms forest, shrubland and grassland. The vegetation cover ranges between 12% and 170%. The average tree
cover is 16%, the average shrub cover is 16%, and the average
herbaceous cover is 24%. The topography is composed of rock
outcrops, wadis and rocky slopes. The altitude ranges from
1900 to 2085 m above sea level.
The most common plant species of this type are: J. procera,
H. bottae, H. hirta, A. origena. The following plant species are
rare and only found in this type: Periploca somalensis, Farsetia
longisiliqua, Celtis africana, Phyllanthus sp., Astragalus atropilosulus and Centaurothamnus maximus.
4.2.10. Lavandula dentata – Themeda triandra – J. procera type
Figure 4
Plant density along the cross section.
found only in this type: A. pannosum, Aloe sp., Boerhavia
diffusa, Cissus quadrangular, Citrullus colocynthis, Cleome
scaposa, Datura inoxia, Euphorbia inarticulata, Indigofera sp.,
Jatropha glauca, Jatropha pelargoniifolia, P. turgidum, Senna
alexandrina, Senna italica, Tribulus terrestris.
4.2.7. Combretum molle – Cyphostemma digitatum type
This type forms woodland to grassland. The vegetation cover
ranges between 25% and 55%. The average tree cover is 15%,
the average shrub cover is 2%, and the average herbaceous
cover is 20%. The topography is composed of rocky slopes
and rock outcrops. The altitude ranges from 1440 to 1490 m
above sea level.
The most common species and always occur are Abutilon
fruticosum and C. molle. The following species are rare and
found only in this type: C. molle, Coptosperma graveolens,
C. digitatum, Psydrax schimperiana, Talinum portulacifolium,
Ecbolium gymnostachyum, Ocimum filamentosum, Rhynchosia
sp., Aerva lanata.
4.2.8. Achillea biebersteinii – Acacia origena type
This type forms woodland to grassland. The vegetation cover
ranges between 40% and 132%. The average tree cover is
33%, the average shrub cover is 5%, and the average herbaceous cover is 70%. The topography is composed of fallow
lands and wadis. The altitude ranges from 2025 to 2177 m
above sea level.
The most common plant species are of this type are: A.
origena, A. biebersteinii, Asphodelus fistulosus, Halothamnus
bottae, Onopordum heteracanthum, Verbesina encelioides. The
following species are rare and found only in this type: Chenopodium ambrosioides, Marrubium vulgare, Mirabilis jalapa,
Phragmanthera austroarabica, Rumex steudelii, Ruta chalepensis, Xanthium spinosum.
This type forms forest, woodland and grassland. The vegetation cover ranges between 52% and 67%. The average tree
cover is 18%, the average shrub cover is 3%, and the average
herbaceous cover is 40%. The topography is composed of
rocky slopes. The altitude ranges from 2015 to 2383 m above
sea level.
The most common plant species of this type are: J. procera,
T. triandra, Micromeria imbricata, Sageretia thea. The following plant species are only found in this type: Clutia lanceolata,
Lavandula dentate and rarely Gomphocarpus fruticosus,
Hypoestes forskalei, Meriandra bengalensis, Salvia aegyptiaca,
Conyza pyrrhopappa, Cymbopogon sp., Ephedra aphylla.
4.2.11. Barbeya oleoides – Olea europaea – J. procera type
This type forms shrubland and grassland. The vegetation cover
ranges between 38% and 90%. The average tree cover is 10%,
the average shrub cover is 28%, and the average herbaceous
cover is 25%. The topography is composed of steep to moderate steep rocky slopes and rocky wadis. The altitude ranges
from 1700 to 2065 m above sea level.
The most common plant species of this type are: Jasminum
grandiflorum, J. procera, Lavandula pubescens, O. europaea,
Psiadia punctulata. The following plant species are rare and
only found in this type: Opuntia ficus-indica, Pentas lanceolata.
4.2.12. Ochradenus baccatus – Dodonaea viscosa type
This type forms forest, shrubland and grassland. The vegetation cover ranges between 38% and 90%. The average tree
cover is 10%, the average shrub cover is 28%, and the average
herbaceous cover is 25%. The topography is composed of
steep to moderate steep rocky slopes and rocky wadis. The altitude ranges from 1700 to 2085 m above sea level.
The most common plant species of this type are: Acacia
etbaica, D. viscosa, O. europaea, P. punctulata. The following
plant species are rare and only found in this type: Phoenix
caespitosa, S. aegyptiaca.
4.2.13. Rhazya stricta – Lycium shawii type
This type forms woodland and shrubland. The vegetation
cover ranges between 6% and 66%. The average tree cover
is 13%, the average shrub cover is 8%, and the average herbaceous cover is 6%. The topography is composed of steep to
Main vegetation types and plant species diversity
Figure 5
693
Maps showing the location of each vegetation type.
moderate steep rocky slopes plains, hills and wadis. The altitude ranges from 1378 to 1746 m above sea level.
The most common plant species of this type are: A. ehrenbergiana, A. etbaica, A. tortilis, L. shawii, Ziziphus spinachristi. The following plant species are rare and only found
in this type: Aizoon canariensis, Desmidorchis penicillata
(=Caralluma penicillata), Caralluma quadrangula (=Monolluma quadrangular), Chrozophora oblongifolia, Euphorbia granulate, Hibiscus micranthus.
is 11%, the average shrub cover is 11%, and the average
herbaceous cover is 13%. The topography is composed of
wadis and foot slopes. The altitude ranges from 1805 to
2020 m above sea level.
The most common plant species of this type are: A. etbaica,
Acacia gerrardii, D. viscosa, Fagonia indica, Solanum incanum,
Ziziphus spina-christi. The following plant species are rare and
only found in this type: K. odora, Boerhavia elegans, Asparagus
africanus.
4.2.14. Kleinia odora – Acacia etbaica type
4.2.15. Kanahia laniflora – Bacopa monnieri type
This type forms woodland and shrubland. The vegetation
cover ranges between 22% and 60%. The average tree cover
This type forms grassland. The vegetation cover reaches 86%.
The average tree cover is 5%, the average shrub cover is 1%,
694
A. Al-Aklabi et al.
Figure 6
MVSP similarity result data.
and the average herbaceous cover is 80%. The topography is
composed of springs. The altitude ranges from 1800 to
1810 m above sea level.
The most common plant species of this type are: Argemone
ochroleuca, B. monnieri, K. laniflora, Pluchea sp.
4.3. Environmental data analysis
4.3.1. The sampling plots
Altitude and rainfall are the most important environmental
variables and increase along a gradient from the right to the
left. There is a strong relationship between the distribution
of sample plots of vegetation types 8–12 (left) with altitude
and rainfall and between the sample plots of eastern mountain
slopes, Tihama foothills and coastal plains (right) with landform. The sample plots of wadis and fallow lands (types 1, 2
and 6) are negatively correlated with altitude and moisture,
while the sample plots of vegetation types 8–10, are positively
correlated with altitude and rainfall. Sample sites of vegetation
type 13 with variable landforms are negatively correlated with
rainfall Sample sites of wadis (type 6) are negatively correlated
with rainfall and altitude.
4.3.2. Plant species
The CCA axis (Fig. 8) shows that altitude and rainfall increase
along a gradient from the right to left and are strongly correlated with ordination axis 1. The CCA axis represents the following orders:
Species more commonly associated with high altitude areas
and high rainfall (bottom left) and more commonly associated
with fallow lands e.g. A. origena, A. biebersteinii, A. fistulosus,
Withania somnifera, or commonly associated with rocky slopes
e.g. Echinops sp., Ficus palmata, H. bottae, M. parviflora,
Nepeta deflersiana, O. heteracanthum, Osteospermum vaillantii,
Polygala abyssinica, V. encelioides.
Species more commonly associated with high altitude areas
and relatively high rainfall and rocky areas (top left) e.g.
Anagyris foetida, Anarrhinum forsskaolii, Caylusea hexagyna,
Centaurea pseudosinaica, H. hirta, J. procera, M. parviflora,
M. imbricate, O. vaillantii, Periploca aphylla, P. abyssinica,
Rumex nervosus, S. thea, T. triandra.
Species negatively correlated with rainfall and altitude
(bottom right) and more commonly associated with wadis
e.g. A. ehrenbergiana, C. colocynthis, P. turgidum, Desmidorchis
retrospiciens, C. quadrangular, S. persica, E. inarticulata, J.
glauca, T. aphylla or more commonly associated with rocky
slopes e.g. Acacia johnwoodii, Adenium obesum, A. trisulcus,
A. asak, M. crassifolia, Commiphora gileadensis, C. myrrha,
Cadaba farinosa, Cadaba glandulosa, Grewia erythraea, Grewia
tenax, I. spinosa, Premna resinosa, Pennisetum setaceum,
Sarcostemma sp.
Species commonly associated with middle to low altitude,
relatively low rainfall and rocky areas or wadis and drainage
lines (middle right) e.g. C. molle, C. graveolens, C. digitatum,
Ehretia obtusifolia, F. ingens, F. virosa, Grewia tembensis,
G. trichocarpa, G. villosa, Hibiscus deflersii, P. schimperiana.
The species A. etbaica, Acacia gerrardii, B. oleoides,
Main vegetation types and plant species diversity
695
Figure 7 Canonical Correspondence Analysis (CCA) ordination biplot of sampling points on main landforms and environmental
variables (altitude, rainfall and land form). Arrows represent the environmental data and point in the direction of maximum change of the
environmental variable across the diagram. Altitude and rainfall are the most important environmental variables. Altitude and landform
are strongly correlated with ordination axis 2. There is a very clear segregation between vegetation types 8 to 12 (left) and of the other
vegetation types (right). The first group is strongly correlated with altitude and rainfall, and the second group is strongly correlated with
the landforms.
CCA variable scores
2.6
Lycium shawii
PistaciaAcacia
falcata etbaica
2.0
land form
Micromeria imbricata
Otostegia fruticosa
Barbeya oleoides
Solanum incanum
Rhus retinorrhoea
1.5
Jasminum grandiflorum
Segeretia thea
Themeda triandra
Kleinia odora
Lavandula pubescens
Argemone ochroleuca
Clutia lanceolata
Anagyris foetida
Juniperus
procera
Ziziphus spina-christi
1.0
altitude
Axis 2
Ochradenus
baccatus
Psiadia
punctulata
Nicotiana glauca
Fagonia indica
Acacia gerrardii
Lavandula
dentata viscosa
Dodonaea
Periploca aphylla
Anarrhinum forskahlii
Ehretia obtusifolia
Olea europaea
Pulicaria crispa
Centaurea pseudosinaica
0.5
Hyparrhenia hirta
Rhazia stricta
Grewia trichocarpa
Psydrax schimperianum
Hibiscus deflersii
tembensis
FicusGrewia
cordata
Coptosperma
graveolens
Acacia tortilis
Maerua crassifolia
Calotropis procera
Polygalla abyssinica
Aerva javanica
Blepharis edulis
Combretum molle
Ficus ingens
-4.06
-3.25
-2.44
-1.62
Bacopa
Kanahiamonnieria
laniflora Cyphostemma digitatum
Andropogon sp.
-0.81
Maytenus parviflora
Echinops sp.
Grewia villosa
Osteospermum vaillantii
Rumex nervosus
Caylusea hexagyna
Halothamnus bottae
-0.5
Ficus palmata
Flueggea virosa
1.62
3
Citrullus colocynthis
Grewia erythrea
Acacia asak
Acacia johnwoodii
Commiphora gileadensis
Euphorbiaturgidum
inarticulata
Panicum
Pennisetum setaceum
Cadaba glandulosa
Cissus rotundifolia
Senna alexandrina
Indigofera spinosa
-1.0
Cadaba Adenium
farinosa obesum
Rainfall
Acacia ehrenbergiana 2.44
Tamarix aphylla
Salvadora persica
Sarcostemma sp.
Acacia origena
Asphodelus fistulosus
Nepeta deflersiana
Onopordon heteracanthum
0.81
Commiphora
myrrha
Jatropha
glauca
Premna
resinosa
Anisotes trisulcus
Withania somnifera
Verbesina encelioides
Grewia tenax
Achillea biebersteinii
-1.5
Cissus
quadrangula
Caralluma
russeliana
-2.0
Axis 1
Figure 8 Canonical Correspondence Analysis (CCA) ordination biplot of plant species and 3 environmental variables. Altitude and
moisture (rainfall) are the most important environmental variables.
696
J. grandiflorum, K. odora, L. pubescens, L. shawii, Otostegia
fruticosa, Pistacia falcata (top right) are associated with rocky
areas, relatively low altitude and low rainfall.
The life form spectrum in Tihama and eastern part of the
study area reflects a typical desert flora, the majority of species
being therophytes and Chamaephytes. These results agree with
the spectra of vegetation in desert habitats in other parts of
Saudi Arabia (El-Demerdash et al., 1995; Collenette, 1999;
Chaudhary, 1999, 2000, 2001; Al-Turki and Al-Qlayan, 2003;
Fahmy and Hassan, 2005; El-Ghanem et al., 2010). It may also
be stated that the Saharo Arabian species which are restricted
in their distribution to the south western strip of Saudi Arabia
are more abundant in habitats of more favorable microenvironmental conditions and those providing better protection (Zohary, 1973; Ghazanfar and Fisher, 1998; El-Ghanem
et al., 2010).
The present study is the first systematic survey of the vegetation of the region. Previous studies concentrated on compiling floristic checklists or on general descriptions of the
vegetation communities found in selected habitats without following any consistent scientific methodology. It is intended
that the present research should form the basis for any future
management plants for the region.
Human activities and climate change have changed the natural environment over time; in particular they have tipped the
ecological balance resulting in a fragmentation of habitats. For
example, the increases of invasive N. glauca, rapidly can result
in detrimental effect on indigenous species. Infrastructure
around the main cities has resulted in damaging the vegetation
communities, in particular A. origena and J. procera
communities.
The study evaluated the vegetation types, the structure of
plant communities and their distribution, the plant species
composition, plant biodiversity and areas with the greatest
plant diversity.
Fog-affected seaward-facing mountain slopes occur in the
mountains above Aqabat Hizna and around Baljurashi, these
landscapes support dense deciduous woodland dominated by
the tree J. procera, together with A. origena. As the influence
of fog decreases further north-east or south-west, forest and
woodland is replaced by sparse woodland or shrubland dominated by A. asak, A. tortilis and A. ehrenbergiana. Beyond this,
the vegetation becomes sparser and finally gives way to open
semi-desert.
The main threats to the vegetation in Al Baha are from the
direct and indirect impacts of human activities. In general,
these relate to changes in the traditional land management
practices which in the past have protected the vegetation. In
particular the vegetation in the region has been directly and
indirectly changed by the recent rapid economic growth.
Direct threats of development include the taking of land for
building; this is widespread on the high altitude areas such
as around Baljurashi where it will potentially affect important
J. procera and A. origena communities.
The building of new roads affects the vegetation in various
ways: by changing watersheds and creating micro-niches along
the roadsides. Human activities in the study area, have allowed
invasive species, such as N. glauca, to rapidly spread with a
resultant detrimental effect on the abundance of native species.
This plant becomes the dominant species in many parts of the
study area forming a pure stand of open woodland. Pure
A. Al-Aklabi et al.
stands of N. glauca trees are common now in the river beds
of the main Wadi, road sides and neglected agricultural land.
5. Summary
Primarily, this study will improve the understanding of the distribution and ecology of plant taxa in the region. However, it
also emphasizes that vast areas in this remarkable region are
still botanically un-explored very well. The research is the first
detailed vegetation survey to be completed in Al Baha region
and provides data which can be used as a baseline for monitoring change. The methods and protocols developed during the
study can be used as a basis for carrying out similar studies
in other parts of Saudi Arabia and for helping to devise management and conservation programs. In the study area, the
major vegetation types, their composition and biodiversity
were identified and vegetation maps generated.
The result of Braun-Blanquet and MVSP analyses revealed
15 vegetation types and demonstrated several distinct patterns
of species distribution such as:
1.
2.
3.
4.
5.
Species
Species
Species
Species
Species
found over wide range of ecological sites.
distributed mainly on wadi beds.
only found on rocky slopes facing the Red sea.
only seen on high altitude mountains.
only seen on coastal plain and semi-desert areas.
Due to the varied topography over the study area, several
important microhabitats were identified, including runnels,
west facing mountains, wet sites, coastal plains, and semi
desert areas. Each of these microhabitats supports special
types of vegetation, each with a characteristic floristic composition and distinct physiognomy.
Human activity has exploited the plant resources of the
entire area but has preferentially targeted particular types of
vegetation. There is a clear evidence of overgrazing in the
wadis, the collection of firewood from certain trees (e.g. J. procera, A. tortilis). There has been obvious direct targeting of the
natural resources, for instance, the clearing of the forest and
woodland in high altitude areas for infrastructure.
Further study on the factors that influence the distribution
of plant species of Al Baha region and the possible effects of
climate change on the distribution patterns is needed. It would
be helpful if vegetation surveys could be combined with data
or Abiotic factors such as altitude, aspect, soil, moisture and
other environmental factors and biotic factors such as human
and other living organisms to get a better and clear idea on the
distribution, abundance and composition of plants in particular rare, endemic and near-endemic species. Detailed vegetation as well as topography and land use mapping of the
whole region of the Al Baha using the modern softwares such
as ArcGIS and ERDAS is recommended.
Acknowledgements
We like to express our gratitude to King Abdulaziz City for
Science and Technology for providing the research grant.
The researchers also express their thanks to Dr. Abdullah
Mohammed Al-Zahrani, the director of University of Al Baha
and the Dean of Applied Studies and Continuous Education,
Main vegetation types and plant species diversity
University of Al Baha for their great help and assistance to fulfill this study.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.sjbs.2016.
02.007.
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