E D I N B U R G H J O U R N A L O F B O T A N Y 68 (2): 301–319 (2011)
301
Ó Trustees of the Royal Botanic Garden Edinburgh (2011)
doi:10.1017/S0960428611000217
THE THEMEDA QUADRIVALVIS TALL-GRASS
SAVANNAH OF OMAN AT THE CROSSROAD
BETWEEN AFRICA AND ASIA
A. PATZELT
Vegetation analysis reveals that the Themeda quadrivalvis tall-grass savannah in Oman,
southern Arabia, forms a clearly defined belt with strong edaphic and geomorphological
characteristics. The newly described association Desmodio gangetico-Themedetum
quadrivalvis ass. nov. is interpreted as an impoverished easternmost outlier of the East
African savannah.
Keywords. Arabia, endemism, fog-oasis, Oman, phytogeography, phytosociology,
southwest monsoon, tall-grass savannah, Themedo-Hyparrhenietea.
Introduction
The mountains of southern Oman are influenced by the southwest monsoon which
creates a tropical fog-oasis in an arid environment. The area is an outstanding
example of an island-like refugium: a seasonal cloud-forest in an otherwise arid
environment (Kürschner, 1998; Hildebrandt, 2005). The mountain chain in southern
Oman and adjacent Yemen has a unique climate which is reflected in a high plant
species diversity with high levels of endemism.
These local climatic and geographic factors allow for the survival of subtropical
elements in an otherwise unfavourable arid environment. Isolation in space, time and
climate has led to the independent development of many taxa, resulting in a high
number of endemics (Miller & Nyberg, 1991; White & Léonard, 1991; Patzelt, 2008).
The mountains of southern Arabia have recently been added to the list of worldwide
biodiversity hotspots as part of the ‘Horn of Africa’ hotspot (Mittermeier et al.,
2005).
Plate tectonics and climate, recent and historic, are the driving forces behind
diversity and floristic composition of the Themeda quadrivalvis (L.) Kuntze tall-grass
savannah in southern Arabia. The relatively late separation of Arabia from Africa
and Asia, during the Oligocene, some 10–15 million years BP, allowed for the
migration of plants between tropical Africa, southern Arabia and the Indo-Malayan
region (Raven & Axelrod, 1974; Mandaville, 1984; Delany, 1989; White & Léonard,
1991; Kürschner, 1998). During the Miocene, when today’s separate landmasses
Oman Botanic Garden, Diwan of Royal Court, PO Box 808, Muscat 122, Sultanate of Oman. E-mail:
annette.patzelt@omanbotanicgarden.com
302
A. PATZELT
were still connected, Arabia supported palaeotropical vegetation with swamps and
open savannah grassland (Hamilton et al., 1978; Whybrow & McClure, 1981;
Mandaville, 1984). During the late Tertiary this vegetation was progressively
replaced by more drought-adapted vegetation. Mesic elements of the palaeo-African
and palaeo-Indo-Malayan stock could only survive in climatically favourable refugia
(Lioubimtseva, 1995; Kürschner, 1998). These refugia in southern Arabia developed
during the late Tertiary and early Quaternary through a strong enhancement of the
monsoon (Mandaville, 1984; Jolly et al., 1998).
Although the unique vegetation of the ‘Dhofar Fog Oasis’ (Miller, 1994) has been
acknowledged by many authors (e.g. Mandaville, 1977; Radcliffe-Smith, 1980;
Miller & Morris, 1988; Miller, 1994), plant community aspects have only recently
been investigated (Kürschner et al., 2004). These recent results highlight the
significance of this mountain chain where endemic palaeo-African relict plant forest
communities, dominated by the endemic Anogeissus dhofarica A.J.Scott, are found.
In Oman Themeda savannahs replace Anogeissus forest on plateaus at medium
altitudes. They are the tallest grasslands in the country and are restricted to the
refugium provided by the southern mountains.
The aims of this study are (i) to identify habitat characteristics, structure, diversity
of life forms, biogeographical relationships and the phytosociological classification
of the Themeda quadrivalvis tall-grass savannah in southern Oman, (ii) to relate
species composition to the tall-grass savannah of Yemen and East Africa, and (iii) to
correlate biogeographical relationships to Tertiary and Quaternary events.
The study area is located in the fog-affected mountains of southern Oman (Fig. 1).
This mountain chain extends some 320 km from the southeastern part of the Al
Mahra, Yemen, to southwestern Dhofar, the southern region of the Sultanate of
Oman. In Dhofar the mountain chain is built up of three ranges: Jebel Qamar, Jebel
Qara and Jebel Samhan. The present study was carried out on Jebel Qamar, situated
in the centre of the monsoon-affected area. Jebel Qamar reaches an altitude of
1350 m and forms a steep escarpment to the south, with smaller plateaus between
500 and 800 m. The rock is formed by Cretaceous and Tertiary limestone material,
overlaid in many areas with Quaternary scree (Guba & Glennie, 1998). From midJune to mid-September the area comes under the influence of the southwest
monsoon (locally called ‘khareef’). During these three months dense fogs build up
against the seaward-facing mountains, reaching only a few kilometres inland
(Stanley-Price et al., 1988). The low cloudbank cannot rise because of a temperature
inversion created by the flow of warm dry air from the inland desert north of the
mountain chain. This combination of topography and temperature inversion thus
creates a stable fog bank clinging to the sea-exposed slopes. Measurements indicate
that fog precipitation during the monsoon amounts to 13 litres/m2 per day at 0.9 m
above the ground and 34–35 litres/m2 at 4.2 m (Stanley-Price et al., 1988), amounting
to two-thirds of the annual precipitation (Hildebrandt, 2005). Unfortunately no
long-term climatic data of the study area are available. Climatic data at Qairoon
Hariti, situated in the drier part of the mountains, are used for comparison (Fig. 1B).
THEMEDA QUADRIVALVIS SAVANNAH IN OMAN
303
F I G . 1. Location of the mountain chain of southern Oman (A & C) and climatic conditions
(B). In B, the left-hand axis is temperature (°C) and the right-hand axis is rainfall (mm).
Materials and Methods
The description of the Themeda grassland of Oman is based on the traditional
Braun-Blanquet cover-abundance scale (Braun-Blanquet, 1964), using the modified
scales of Barkman et al. (1964) representing the following values: r 5 solitary, cover
, 5%; + 5 few, less than 1% cover; 1 5 few and 1–5% cover; 2m 5 numerous and
cover , 5%; 2a 5 6–12% cover; 2b 5 13–25% cover; 3 5 25–50% cover; 4 5 51–75%
cover; 5 5 76–100% cover. Cover-abundance values are relatively broad subjective
classes, and were determined by estimating cover of every single species within the
area of the stand. A standard 5-point scale was used to indicate the degree of
clumping or gregariousness (sociability) of an individual plant species, obtained as
a visual impression, represented by the following values: ‘1’ indicates a shoot
growing singly, ‘2’ indicates plants growing in small groups of a few individuals or in
small tussocks, ‘3’ indicates small patches, cushions or large tussocks, ‘4’ refers to
304
A. PATZELT
growing in extensive patches, carpets or broken mats, and ‘5’ indicates plants
growing in large mats or pure populations.
The areas of relevés were selected with respect to floristic homogeneity and
representation of typical stands. In each relevé and stratum a plant list was established
and cover-abundances and sociability were estimated. Fieldwork was carried out in
September and November 2003 and September/October 2004 and 2005. The size of the
sampling stands varied but was usually 100–200 m2. The vegetation was sampled in 15
relevés (Table 1). For each relevé a habitat description was recorded which included
geographic coordinates, altitude, slope inclination, aspect, height of different strata,
plant cover, topographic position and soil characteristics. The study area is located
between 16°419N, 53°069E and 16°499N, 53°409E.
After fieldwork the next stage in this method involved the tabulation of data from
similar stands and the synthesis of vegetation units. The final table (Table 1) displays
vegetation units which are defined by the presence of particular characteristic species.
Finally, the vegetation units under investigation are positioned in the hierarchical
floristic system of Braun-Blanquet which requires consideration of the sociological
rank and ecological amplitude of each species.
The classification of plant communities at higher syntaxonomic levels in southern
Arabia remains difficult as higher levels are not yet known. Therefore, further
investigation is needed into which synsystematic rank each species belongs to and
how to segregate the higher syntaxa. The syntaxonomic classifications follow the
International Code of Phytosociological Nomenclature (Weber et al., 2000).
Family concepts follow APG II (Angiosperm Phylogeny Group, 2003). The
taxonomy and nomenclature of the taxa recorded follows Thulin (1993, 1995, 1999,
2006), Miller & Cope (1996), Cope (2007) and Ghazanfar (2003, 2007). Otherwise the
most recent taxonomic publications were consulted. Distribution data and chorotypes were mainly compiled from Cope (1985), Miller & Morris (1988), Thulin (1993,
1995, 1999, 2006), Miller & Cope (1996), Ghazanfar (2003, 2007) and Pickering &
Patzelt (2008).
For the purposes of this study, an ‘endemic species’ is defined as a species that
occurs in only one country and a ‘near-endemic’ or ‘limited range species’ is defined
as ‘a species which occurs in limited numbers in no more than three countries in
Arabia’. For the physiognomic classification, the vegetation structure classification
as described in Scholte (2000) has been followed.
Voucher specimens are deposited in the National Herbarium of Oman (ON), and
in the Herbarium of Sultan Qaboos University (SQUH). Some duplicates were
donated to the Royal Botanic Gardens, Kew (K) and to the Royal Botanic Garden
Edinburgh (E).
Within each relevé, 10 soil samples were taken from the surface (0–10 cm depth).
The samples were air-dried, mixed and any large stones removed. The soil was then
crushed and passed through a 2-mm sieve to remove gravel and debris. The particles
not passing the 2-mm sieve were weighed separately for determination of the content
of the coarse fragments. The fraction smaller than 2 mm was used for the soil
T A B L E 1. The Desmodio gangetico-Themedetum quadrivalvis, a newly described grassland community from southern Arabia. See Materials
and Methods for an explanation of the figures
1
552
5
SSW
300
98
–
–
98
30
2
566
10
S
400
100
–
5
95
29
3
549
20
S
100
100
–
2
100
37
Character species Desmodio gangetico-Themedetum quadrivalvis
Themeda quadrivalvis (L.) Kuntze
3.5
3.5
5.5
Setaria pumila (Poir.) Roem. & Schult.
2a.3 2a.3 2m.3
Apluda mutica L.
Desmodium gangeticum (L.) DC.
Abelmoschus esculentus (L.) Moench
Alysicarpus glumaceus (Vahl) DC.
1.3 2a.3
2m.3
1.3
2a.1
1.3
1.1 2m.3
4
574
5
W
120
100
–
2
100
29
5
741
5
S
100
85
5
2
95
28
6
730
12
S
160
90
–
2
95
32
7
720
5
S
100
90
2
2
95
29
5.5
2b.3
5.5
2b.3
5.5
2a.3
2b.3 2m.3
+.1
+.1
+.1
+.1
1.1
1.1
2a.3
1.1
+.1
+.1
2b.3
+.1
+.1
.
8
770
5
SE
100
90
2
5
90
28
9
603
8
S
200
95
–
2
95
28
5.5
5.5
2a.3 2m.3
10
770
4
SE
100
90
–
–
90
28
11
807
7
S
200
85
5
10
70
36
5.5
5.5
2a.3 2m.3
12
709
9
SSE
220
85
15
20
60
31
13
622
5
SE
200
95
5
2
90
40
14
700
9
SW
180
95
–
5
95
43
4.5
2b.3
5.5
2a.3
4.5
2a.3
3.3 2m.3 2m.3 2m.3 2m.3
1.1
1.1
1.1
1.1
.
1.1
1.1
1.1
+.1
+.1
1.1
.
1.1
1.1
.
2a.3
+.1
.
.
2a.3
1.1
1.1
.
1.1
.
.
.
.
.
2m.3
.
.
Character species Themedetalia triandrae
Bothriochloa insculpta (Hochst.) A.Camus
Eustachys paspaloides (Vahl)
Lanza & Mattei
.
.
.
.
.
2m.3
.
1.1
.
.
.
.
1.1
.
.
.
1.1
.
Character species Themedo-Hyparrhenietea
Heteropogon contortus (L.) P.Beauv.
ex Roem. & Schult.
.
.
2m.3 2m.3
.
.
2m.3
.
2m.3
1.1
.
.
.
.
2m.3
Character species Hybantho durae-Anogeissetum dhofaricae (Boscio-Commiphoretea abyssinicae)
Arthraxon pusillus Bor
2m.3 2m.3 2a.3 2a.3 2m.3 2m.3 2m.3 2m.3 2m.3 2m.3 2m.3
2m.3 2m.3
15
490
5
E
400
95
10
30
60
32
Chorotype
4.5 2m.3 Indo-Malay.
2a.3 2b.3 Palaeotrop.Palaeosubtrop.
2a.3 2b.3 Indo-Malay.
1.1
+.1 Indo-Malay.
1.1
+.1 Indo-Malay.
1.1
+.1 Somalia-Masai/
Sudano-Zamb.
2m.3
.
.
Palaeotrop.
Somalia-Masai/
Sudano-Zamb.
1.3 Pantrop.Pansubtrop.
THEMEDA QUADRIVALVIS SAVANNAH IN OMAN
Relevé no.
Altitude (m)
Inclination (°)
Orientation
Area (m2)
Total plant cover (%)
– Cover trees
– Cover shrubs
– Cover herbs
No. of species
1.1 Endemic
305
306
T A B L E 1 . (Cont’d )
+.1
.
1.3
1.3
+.1
.
1.1 2m.3
1.3
1.3
1.2
.
1.2
1.3
+.1
1.1
.
.
.
1.1
.
.
.
.
+.1
.
+.1
.
.
.
.
1.1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
2a.3
.
.
.
+.1
.
+.1
.
.
.
.
.
1.3
+.1
2a.3
+.1
+.1
.
.
.
.
.
.
.
+.1
.
.
+.1
.
.
+.1
.
.
.
.
.
+.1
.
.
.
.
.
.
.
.
.
+.1
.
.
.
.
.
.
.
.
.
.
.
+.1
.
.
.
.
.
.
.
.
.
+.1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1.1
.
1.1
+.1
1.1
.
.
.
.
.
+.1
.
+.1
.
+.1
.
.
.
.
.
.
.
.
.
.
Character species Boscio-Commiphoretalia and Boscio-Commiphoretea abyssinicae
Commiphora gileadensis (L.) C.Christ.
.
.
+.1
.
+.1
+.1
Cyphostemma ternatum (Forssk.) Desc.
.
.
.
.
+.1
+.1
Teramnus repens (Taub.) Baker f. subsp.
1.1
.
1.1
1.1
.
.
gracilis (Chiov.) Verd.
Flueggea virosa (Roxb. ex Willd.) Royle
.
.
+.1
.
.
.
Commiphora kua (J.F.Royle) Vollesen
.
.
+.1
.
.
.
Rhynchosia minima (L.) DC. var. minima
.
.
.
Character species Oleo-Juniperetalia procerae (Juniperetea procerae)
Jasminum grandiflorum subsp. floribundum
.
.
.
(Fresen.) P.S.Green
Olea europaea subsp. cuspidata
.
.
.
(Wall. ex G.Don) Cif.
Rhamnus staddo A.Rich.
.
.
.
.
2m.3
.
.
.
.
2a.3
2m.3
.
+.1
.
.
+.1
.
+.1
+.1
.
.
+.1
+.1
.
1.1
+.1
.
1.1
+.1
.
.
.
.
.
.
.
.
.
.
.
+.1
.
. Indo-Malay.
1.3 Somalia-Masai/
Indo-Malay.
+.1 Near-Endemic
. Somalia-Masai/
Sudano-Zamb.
. Pantrop.
Near-Endemic
Indo-Malay.
Somalia-Masai
Somalia-Masai
Near-Endemic
Near-Endemic
.
.
.
.
.
.
.
.
.
.
+.1
Somalia-Masai
Somalia-Masai
Somalia-Masai/
Sudano-Zamb.
. Palaeotrop.
+.1 Somalia-Masai/
Sudano-Zamb.
1.1 Pantrop.
.
.
.
.
.
.
.
1.3
1.1
+.1
1.1
+.1 Somalia-Masai
.
.
.
.
.
.
.
1.2
+.1
+.1
.
.
.
.
.
.
.
.
1.1
.
.
1.1
+.1 Pluriregional
.
Somalia-Masai
A. PATZELT
Impatiens balsamina L.
Wahlenbergia flexuosa (Hook.f. &
Thoms.) Thulin
Maytenus dhofarensis Sebsebe
Allophylus rubifolius (A.Rich.)
Engl. var. rubifolius
Mitreola petiolata (J.F.Gmel.)
Torr. & A.Gray
Anogeissus dhofarica A.J.Scott
Rungia pectinata Nees
Ruttya fruticosa Lindau
Launaea crassifolia (Balf.f.) C.Jeffrey
Blepharispermum hirtum Oliver
Exacum arabicum Thulin
T A B L E 1 . (Cont’d )
.
.
.
.
.
.
.
.
.
.
Euclea schimperi (A.DC.) Dandy
.
.
.
.
.
.
.
.
.
.
+.1
1.1
.
.
Pavetta longiflora Vahl
.
.
.
.
.
.
.
.
.
.
.
+.1
.
.
2a.3
2a.3
1.1 2m.3
2a.2
1.1
1.2
+.1
1.1
+.1
2a.3
2a.3
1.1
1.1
2b.3 Pantrop.
2a.3
2b.3
1.3
.
.
2a.3 2m.3 2m.3
2a.2
.
1.1
2a.3
.
2a.3
+.1 2a.3
+.1
2a.3 2m.3 2m.3
2a.3
.
1.3
.
1.1
2a.3
1.1
.
1.1 Pantrop.
2a.3 Somalia-Masai/
Indo-Malay.
+.1 Somalia-Masai/
Saharo-Sindian
. Palaeotrop.
Grazing indicators
Senna obtusifolia (L.) H.S.Irwin &
Barneby
Crotalaria retusa L.
Triumfetta pentandra A.Rich.
Solanum incanum L.
.
.
.
.
+.1
.
.
+.1
.
.
+.1
+.1
+.1
+.1
Bidens biternata (Lour.) Merr. & Sherff
.
.
+.1
.
.
.
.
.
.
.
.
.
.
+.1
2b.3
2a.3
2a.3
2b.3
2a.3
1.1
Companions
Arthraxon micans (Nees) Hochst.
Orthosiphon pallidus Royle ex Benth.
Vigna radiata (L.) Wilczek
Alysicarpus vaginalis (L.) DC.
Pimpinella schweinfurthii Asch.
Anagallis arvensis L.
Oldenlandia corymbosa L.
Buchnera hispida Buch.-Ham. ex D.Don
Euphorbia indica Lam.
Viola cinerea Boiss. var. stocksii
(Boiss.) Becker
Canscora concanensis C.B.Clarke
Cucumis sativus L.
1.1 2m.3
+.1
1.3
1.1
.
.
1.1
2m.3
1.1
.
+.1
1.2
1.1
2m.3 2m.3
1.1 2m.3 2m.3 2m.3
1.1
. 2m.3
.
.
.
+.1
.
.
+.1
.
+.1
2m.3
. 2m.3 2m.3 2m.3 2m.3
.
1.1
.
1.1
+.1
.
2m.3 2m.3
. 2m.3 2m.3
.
1.3
. 2m.3
+.1
1.3
1.3
.
.
.
+.1
.
.
.
.
1.1
+.1
.
.
2a.3 2m.3 2m.3
1.1
+.1
.
+.1
1.1
1.1
+.1
1.1
1.1
.
.
1.1
1.1
+.1
.
.
1.3
1.3
1.3
1.3
1.1
1.1
+.1
+.1
.
. 2m.3 2m.3
. 2m.3
.
+.1
+.1
+.1
.
.
. 2m.3 2m.3
.
1.3
.
.
1.3
.
1.1
.
1.1
.
1.1
+.1
1.1
.
.
.
2m.3
2b.3
.
+.1
.
.
. 2m.3
2m.3 2m.3
.
.
.
.
.
+.1
.
.
.
.
. 2m.3
+.1
+.1
2b.3 Pantrop.Pansubtrop.
. Somalia-Masai/
Sudano-Zamb.
. Regional-Endemic
2b.3 2m.3 Somalia-Masai/
Indo-Malay.
1.3
1.1 Palaeotrop.
1.1
1.1 Pantrop.
.
. Palaeotrop.
1.1
1.1 Saharo-Sindian
+.1
. Cosmopol.
.
. Pantrop.
1.1
. Somalia-Masai
.
1.2 Indo-Malay.
.
. Somalia-Masai/
Saharo-Sindian
1.1
. Indo-Malay.
+.1
. Pantrop.Pansubtrop.
THEMEDA QUADRIVALVIS SAVANNAH IN OMAN
Character species Pistachio-Eucleetalia schimperi (Hyperico-Rhamnetea)
Dodonaea viscosa (L.) Jacq.
.
1.3
1.1
.
307
308
T A B L E 1 . (Cont’d )
Digitaria stricta Roth ex Roem. & Schult.
Dichanthium annulatum (Forssk.) Stapf
Convolvulus prostratus Forssk.
. 2m.3
1.1 2m.3
+.1
.
.
.
.
1.1
2a.3
+.1
.
.
.
2m.3 2m.3
1.1
1.1
+.1
.
.
.
.
1.1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1.1
1.1
.
+.1 Indo-Malay.
. Palaeotrop.
1.2 Somalia-Masai/
Saharo-Sindian
1.3 Pantrop.Pansubtrop.
. Pluriregional
. Palaeotrop.
.
+.1
.
.
.
+.1
.
.
.
.
1.2
.
Brachiaria eruciformis (Sm.) Griseb.
Fimbristylis bisumbellata
(Forssk.) Bubani
Adenium obesum (Forssk.)
Roem. & Schult.
Cyperus squarrosus L.
Woodfordia uniflora (A.Rich.) Koehne
Brachiaria lata (Schumach.) C.E.Hubb.
.
.
.
+.1
.
1.1
.
.
.
.
.
.
1.1
.
1.1
.
1.1
.
.
.
+.1
.
.
.
.
+.1
.
.
.
.
.
.
+.1
.
1.1
+.1
.
.
.
.
.
.
.
1.1 2m.3
.
.
.
.
.
.
.
.
1.1
1.3
.
.
.
.
.
1.2
.
.
.
+.1
.
.
.
.
.
+.1
.
.
+.1
.
1.1
.
.
1.1
1.1
.
.
.
.
Centaurea dhofarica Baker
Brachiaria ramosa (L.) Stapf
1.1
1.1
.
.
+.1
.
1.1
.
.
.
.
1.1
.
.
.
.
.
.
.
.
.
.
.
.
.
1.1
.
.
.
.
Plectranthus barbatus Andrews
Commelina cf. albescens Hassk.
.
.
.
.
1.1
.
.
.
.
1.3
.
1.2
.
.
.
.
.
.
.
.
1.1
.
.
.
.
.
+.1
1.1
.
.
Adiantum lunulatum Burm.f.
.
.
.
.
1.3
.
+.2
.
.
.
.
.
.
+.1
.
Lobelia heyniana Roem. & Schult.
Remusatia vivipara (Roxb.) Schott
Setaria intermedia Roem. & Schult.
.
.
+.1
.
.
.
.
.
.
.
.
.
.
.
.
1.1
.
.
.
.
.
.
.
.
1.1
.
.
.
.
.
.
1.3
.
.
.
.
.
.
.
Convolvulus arvensis L.
Tephrosia humilis Guill. & Perr.
+.1
.
.
+.1
1.1
1.1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
+.1
1.1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Hackelochloa granularis (L.) Kuntze
Hermannia paniculata Franch.
2m.1
+.1
.
1.1
2m.3 2m.3
.
1.1
1.3
1.1
. 2m.3
Somalia-Masai/
Sudano-Zamb.
Pantrop.
Somalia-Masai
Somalia-Masai/
Sudano-Zamb.
Near-Endemic
Somalia-Masai/
Indo-Malay.
Palaeotrop.
Somalia-Masai/
Sudano-Zamb.
Pantrop.Pansubtrop.
Indo-Malay.
Palaeotrop.
Somalia-Masai/
Indo-Malay.
Cosmopol.
Somalia-Masai/
Indo-Malay.
Pantrop.
Somalia-Masai
A. PATZELT
Blumea mollis (D.Don) Merr.
T A B L E 1 . (Cont’d )
.
.
.
.
.
.
.
.
.
.
.
.
.
.
+.1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1.1
1.3
1.3
.
.
.
.
.
.
.
+.1
+.1
.
.
+.1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1.3
.
. 2m.3
1.1
.
+.1
.
.
1.1
+.1
.
.
.
.
.
+.1
.
.
.
.
.
.
.
.
.
.
1.3
.
.
.
.
.
.
.
.
.
.
.
2m.3
.
Rhus somalensis Engl.
Ficus sycomorus L.
Anagallis pumila Sw.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
+.1
.
.
.
1.1
.
Cyperus alulatus J.Kern
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
2m.3
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1.1
.
.
+.1
.
1.1 2m.3
1.1
1.1
Regional-Endemic
Endemic
Indo-Malay.
Somalia-Masai
Somalia-Masai
Endemic
Pluriregional
Somalia-Masai/
Indo-Malay.
. Somalia-Masai/
Sudano-Zamb.
+.1 Somalia-Masai
. Pluriregional
. Somalia-Masai/
Saharo-Sindian
. Somalia-Masai/
Sudano-Zamb.
Additional species:
A 2: Senra incana Cav. +.1; Tripogon leptophyllus (A.Rich.) Cufod. 1.3. A 8: Gramineae indet +.1. A 22: Abelmoschus manihot (L.) Medik. 1.1. A 24: Orobanche
dhofarensis M.J.Y.Foley 1.3. A 25: Andrachne aspera Spreng. 1.2; Carissa spinarum L. +.1; Corchorus trilocularis L. +.1; Cordia crenata Delile subsp. crenata +.1.
A 51: Heliotropium longiflorum (Hochst. ex A.DC.) Jaub. & Spach +.1; Nicandra physalodes Gaertn. +.1. A 52: Schizachyrium brevifolium (Sw.) Nees ex Büse 1.1.
A 54: Eclipta prostrata (L.) L. r.1; Eragrostis viscosa (Retz.) Trin. 2m.3; Cyperus longus L. +.1; Ficus vasta Forssk. +.1; Indigofera tinctoria L. +.1. A 55: Achyranthes
aspera L. +.1; Ceropegia bulbosa Roxb. +.1; Aloe praetermissa McCoy & Lavranos +.1; Scrophularia arguta Aiton 2m.3. A 73: Cleistachne sorghoides Benth. +.1;
Digitaria ciliaris (Retz.) Koeler 1.1; Vernonia cinerea (L.) Lees 1.1. A 74: Enicostemma axillare (Lam.) A.Raynal 1.1; Sida ovata Forssk. +.1.
THEMEDA QUADRIVALVIS SAVANNAH IN OMAN
Polygala tinctoria Vahl
Chrysopogon macleishii Cope
Dimeria ornithopoda Trin.
Dorstenia foetida (Forssk.) Schweinf.
Gladiolus candidus (Rendle) Goldblatt
Dyschoriste dalyi A.G.Mill.
Gomphocarpus fruticosus subsp.
setosa (Forssk.)
Goyder & Nicholas
Arundinella pumila (Hochst.
ex A.Rich.) Steud.
Negripteris sciona (Chiov.) Pic.-Serm.
309
310
A. PATZELT
analysis. Soil texture was determined according to Benzler et al. (1982). Soil-water
extracts (1:5) were prepared for measurement of pH. To test carbonate content,
hydrochloric acid was added to 5 g of sieved soil (air-dried soil fraction , 2 mm) on
a watch glass. The carbonate content was measured on the basis of the intensity and
time of effervescence (Benzler et al., 1982).
Results
Soil, vegetation structure and species composition of the Arabian Themeda grassland
The Themeda grassland (Fig. 2) forms a belt on the gentle seaward slopes with
a width of about 3–5 km and is restricted to a narrow altitudinal range of 500–800 m.
The grassland is found almost exclusively on south-facing slopes with an inclination
of 4–20°. The soil texture is silty clay with a pH between 6.4 and 6.7; carbonate
content is low. The soil type is a vertisol. During the dry season the soil becomes
extraordinarily hard and is divided into rough polygons and prisms; wide cracks
develop to a depth of 50 cm or more. The cracks close during the monsoon when the
clay minerals swell. Skeletal rock comprises up to 10% of the surface of the relevés.
F I G . 2. Typical aspect of the Themeda quadrivalvis grassland in southern Oman.
THEMEDA QUADRIVALVIS SAVANNAH IN OMAN
311
The Themeda grassland is rich in species (112 taxa, mean species number/relevé 5
32; Table 1). Twelve species (11%) found in the grassland are endemic, near-endemic
or regionally endemic (Table 3). Both structurally and floristically, the grassland
community is characterised by the dominance of the annual grass Themeda
quadrivalvis, which can reach 2.5 m in height and often occupies more than 70%
of the total cover.
In Arabia Themeda quadrivalvis is restricted to southern Oman and southeastern
Yemen, whereas Themeda triandra Forssk. is found along the western mountain
chain in Yemen and also in Soqotra (Cope, 2007). Themeda quadrivalvis was also
recorded from Soqotra in the 19th century but has not been seen since (Miller &
Morris, 2004). Globally the annual Themeda quadrivalvis has a much more restricted
distribution, whereas the perennial T. triandra is distributed throughout the tropical
and subtropical Old World and, in many places, is regarded as a problematic species.
In Oman Themeda quadrivalvis and other grasses are associated with groups of
trees and shrubs mainly composed of the endemics Anogeissus dhofarica and
Maytenus dhofarensis Sebsebe, and the evergreen Olea europaea subsp. cuspidata
(Wall. ex G.Don) Cif. The herb and shrub layer is characterised by three distinct
strata. The upper stratum is dominated by the tall annual Themeda quadrivalvis.
Shorter grasses (e.g. Apluda mutica L., Setaria pumila (Poir.) Roem. & Schult.) form
an intermediate stratum up to 80 cm tall. The lowest stratum consists mainly of small
annual grasses and therophytes up to 15 cm tall. Therophytes clearly dominate the
grassland (50%), but shrubby chamaephytes (19%), hemicryptophytes (11%) and
phanerophytes (16%) are common as well. Geophytes play a minor role (3%). Rocks
provide a more sheltered habitat and thus enable some perennials to grow, such as
the stem succulent Dorstenia foetida (Forssk.) Schweinf.
T A B L E 2. Percentage of different chorotypes in the Themeda quadrivalvis grassland in
different strata, reflecting the phytogeographical affinities
Endemic/Near-Endemic/
Regional-Endemic
Somalia-Masai
Indo-Malayan
Biregionals: Somalia-Masai/
Sudano-Zambesian
Biregionals: Somalia-Masai/
Indo-Malayan
Biregionals: Somali-Masai/
Saharo-Sindian
Palaeotropical
Pantropical
Pluriregional
Tree layer
Shrub layer
Herb and dwarf
shrub layer
(n 5 87)
(n 5 7)
(n 5 18)
28.5
17
7
28.5
–
14.5
33
–
17
8
16
9
13
12.5
11
17
14
–
5.5
–
5.5
4.5
5.5
5.5
11
11.5
21
6
–
–
28.5
All layers
(n 5 112)
10
4.5
10
17
8
312
A. PATZELT
T A B L E 3. Range-restricted species in the Themeda quadrivalvis grassland
Species
Family
Chorotype
Dyschoriste dalyi A.G.Mill.
Aloe praetermissa McCoy & Lavranos
Blepharispermum hirtum Oliver
Centaurea dhofarica Baker
Maytenus dhofarensis Sebsebe
Anogeissus dhofarica A.J.Scott
Exacum arabicum Thulin
Arthraxon pusillus Bor
Chrysopogon macleishii Cope
Polygala tinctoria Vahl
Pavetta longiflora Vahl
Orobanche dhofarensis M.J.Y.Foley
Acanthaceae
Asphodelaceae
Asteraceae
Asteraceae
Celastraceae
Combretaceae
Gentianaceae
Poaceae
Poaceae
Polygalaceae
Rubiaceae
Scrophulariaceae
Endemic
Endemic
Near-Endemic
Near-Endemic
Near-Endemic
Near-Endemic
Near-Endemic
Endemic
Endemic
Regional-Endemic
Regional-Endemic
Endemic
The yearly cycle of plant activity is strongly correlated with the monsoon precipitation and corresponding changes in available moisture. As soon as the first fog
arrives at the end of June, the annual species germinate and deciduous perennials sprout
their first leaves. Most of the annuals set seed at the end of the humid season in October/
November. The grassland is used for grazing of livestock, mainly after the monsoon
fogs have lifted. Grazing indicators are common and conspicuous non-palatable
palaeotropical and pantropical weeds can reach high cover values. The chorotype
analysis indicates a community with strong affinities to xerotropical and subtropical
grasslands of Yemen and East Africa as well as subtropical Southeast Asia (Table 2).
The phytosociological analysis of the community has led to the description of
a new plant community, the Desmodio gangetico-Themedetum quadrivalvis (see
Table 1). Characteristic species are the grasses Themeda quadrivalvis, Setaria pumila
and Apluda mutica, and the herbs Desmodium gangeticum (L.) DC., Abelmoschus
esculentus (L.) Moench and Alysicarpus glumaceus (Vahl) DC. The DesmodioThemedetum is relatively uniformly developed but towards the escarpment rim trees
and shrubs become more dominant, indicated by species of the sclerophyllous
evergreen Anogeissus dhofarica woodlands (relevés nos. 11–15 in Table 1).
Discussion
Environmental determinants
A total of 112 taxa were found in the Themeda grassland on Jebel Qamar. As the
country’s total flora comprises c.1200 species (Miller & Cope, 1996), 9.5% of the
total flora is represented in the grassland, a high percentage.
The geographically closest tall-grass savannah dominated by Themeda sp. is
located in Yemen, including Soqotra, and Ethiopia (Pichi-Sermolli, 1957; White,
1983; Friis, 1992; Miller & Morris, 2004; Suttie et al., 2005; World Wildlife Fund,
THEMEDA QUADRIVALVIS SAVANNAH IN OMAN
313
2010). A comparison with phytosociological studies from East African data
extracted from Lebrun (1947), Knapp (1973), Schmidt (1975a, 1975b) and White
(1983) reveals a number of linking species: Eustachys paspaloides (Vahl) Lanza &
Mattei, Heteropogon contortus (L.) P.Beauv. ex Roem. & Schult. and Bothriochloa
insculpta (Hochst.) A.Camus.
Grassland dominated by Themeda quadrivalvis is also found on the outer
escarpment mountains of southeastern Yemen (A. G. Miller, pers. comm.). In
Yemen, Heteropogon contortus, Bothriochloa insculpta and Eustachys paspaloides are
found in similar grassland vegetation (A. G. Miller, pers. comm.). Further studies
are required to investigate the Themeda grasslands on the monsoon-affected
mountains of Soqotra and on the escarpment mountains of Yemen to elucidate
their relationship with the Themeda grassland of southern monsoon-affected Oman.
Compared with the Themeda triandra savannah in East Africa, however, species
diversity in southern Arabia is far lower. For example, Schmidt (1975b) reported at
least 260 taxa from Tanzania. Studies of the Themeda grasslands of Ethiopia (Suttie
et al., 2005) reveal that species diversity seems to be higher than in the Themeda
quadrivalvis grassland of Oman. The Themeda grassland of Oman is impoverished in
species compared with the African Themeda savannah.
Low shrub and tree cover in savannah vegetation on vertisol has been explained
by wetness of the soil and resulting low levels of oxygen during the monsoon with
correspondingly extreme shrinkage and hardness in the dry season (Schmidt, 1975b).
Therefore, the dominant life forms are therophytes, which can withstand these severe
environmental conditions (Huntley, 1982; Menault, 1983). Higher cover and
abundance of trees and shrubs on steeper slopes towards the escarpment rim can
be explained by better drainage conditions.
The use of the Anogeissus forest for browsing and the clearing of forest to provide
pastures have a long history in Dhofar. The grassland of Oman has supported
pastoral communities for thousands of years without excessive overgrazing except in
the last three decades (Miller & Morris, 1988). In recent years, high densities of
grazers, principally cattle and camels, and changes towards the communities
becoming more sedentary have had a severe effect, leading to high cover values of
unpalatable herbs, such as Crotalaria retusa L. and Nicandra physalodes (L.) Gaertn.
Phytogeographical affinities of the Themeda quadrivalvis grassland
Phytogeographically the vegetation of the monsoon-affected mountains in Dhofar
marks the easternmost extent of the Somalia-Masai regional centre of endemism
(Léonard, 1988; White & Léonard, 1991; Ghazanfar, 1992; Kürschner, 1998). The
close floristic relationships between East Africa and southern Arabia are evident
from the 24% of species which belong to the Somalia-Masai and Sudano-Zambesian
chorotype (Table 2). These palaeotropical African floristic elements reach their
easternmost limit in Dhofar, whereas the Indo-Malayan species are at their
westernmost limit in southern Arabia.
314
A. PATZELT
Clayton & Cope (1980) indicated that the grasses in southern Arabia have strong
links to Asia. This is well supported by the present study. Only a few Saharo-Sindian
geoelements are found in the Themeda grassland, although the mountain chain is
bordered to the north by a desert dominated by Saharo-Sindian species. The absence
of these taxa is due to the humid site conditions during the monsoon season which
restricts Saharo-Sindian elements. The palaeotropical species clearly reflect the
former land connection of Arabia with Africa and Asia. The pantropical and
pluriregional species are mainly weedy and ruderal species, indicating recent human
influence.
The occurrence of endemic and near-endemic species in the Themeda grasslands
underlines the importance of the monsoon-influenced mountains of southern Arabia
as a refuge area, representing a regional centre of endemism (Table 3). The ‘Dhofar
Fog Oasis’ is a centre of species richness (Miller & Nyberg, 1991; Miller, 1994) and
these centres usually coincide with centres of endemism (Crisp et al., 2001). Recent
work highlights the concentration of range-restricted and rare and threatened species
in southern Oman where a total of 145 range-restricted species, representing 12.1%
of the total flora, are found (Patzelt, 2008). Endemic and near-endemic species occur
quite frequently in the grassland and are relatively widespread. These species are, per
definition, rare, and therefore potentially threatened on a global level (Myers et al.,
2000). The Themeda grassland is thus an important habitat for the survival of species
with restricted distribution and requires greater conservation effort.
Phytosociological classification reveals the position within the East African
Themedo-Hyparrhenietea
Classification at the community level has so far not been performed on Arabian
grasslands (Deil & Al Gifri, 1998) and only on small portions of the African
savannah (e.g. in East Africa by Lebrun, 1947; Troupin, 1966; Leippert, 1968;
Quezel, 1969; Schmidt, 1975b) and South Africa (reviewed in Cowling et al., 1997).
No detailed analysis at community level from the grasslands on the Indian
subcontinent has so far been undertaken (Misra, 1983).
On the basis of close floristic relationships, the Themeda grasslands in Oman are
interpreted as the easternmost outliers of the African Themeda tall-grass savannah.
Stand number 3 represents the typus stand of the Desmodio gangetico-Themedetum
quadrivalvis ass. nov.
Knapp (1965) combined all East and South African tall-grass savannah types into
the class Themedo-Hyparrhenietea Knapp 1965. The analysis of the herbaceous layer
of the Themeda quadrivalvis grasslands from Dhofar reveals its position in this class
(Knapp, 1965, 1968), with Heteropogon contortus as a characteristic species of the class
and Bothriochloa insculpta and Eustachys paspaloides as characteristic species of the
order Themedetalia triandrae sensu Lebrun 1947. Classification within an alliance still
remains unclear and the relationship of the grasslands dominated by Themeda
quadrivalvis to the grasslands dominated by T. triandra requires further study.
THEMEDA QUADRIVALVIS SAVANNAH IN OMAN
315
Besides taxa of the tall-grass savannah, species of other phytosociological classes
are important for the characterisation of the Dhofar grassland. Further species that
always occur are characteristic of the Hybantho durae-Anogeissetum dhofaricae
Kürschner et al. 2004, a drought-deciduous forest community of the BoscioCommiphoretea abyssinicae (5 Acacia–Commiphora drought-deciduous woodland –
Zohary, 1973). In East Africa these are often replaced by evergreen shrub communities
of the Pistachio-Eucleetalia schimperi (Gillett, 1941; Hemming, 1966). Montane
African-Arabian forest communities of the Oleo-Juniperetalia procerae (Pichi-Sermolli,
1957; Knapp, 1965, 1968, 1973; White, 1983; König, 1987) are restricted to forested
patches within the grassland.
In Dhofar, the Themeda grassland is in direct contact with two different forest
communities of the Boscio-Commiphoretea abyssinicae. On the south-facing seaexposed side the gentle slopes covered in grassland are suddenly replaced by
Anogeissus forest on steep, almost perpendicular, escarpments. On the north-facing
slopes, beyond the monsoon precipitation, the grassland is replaced quite abruptly
by drought-deciduous Acacia–Commiphora woodland. Many of the grassland
species occur as marginal intruders on edaphically shallow sites in the Anogeissus
forest but are absent from the dry woodland.
Thus, most grassland species are ‘borrowed’ from adjacent forests with similar
moisture conditions and were able to invade open habitats created after clearing of the
forests. This is in agreement with the suggested origin of most African savannah grass
species (White, 1978). It is therefore suggested that the Themeda grassland in Oman
results from anthropogenic activities. A similar explanation is suggested for the
grassland in open areas in Anogeissus forest in southeastern Yemen (Hauf), situated
within the same geographic region (Kürschner et al., 2004). An anthropogenic origin
has also been suggested for grassland-fragments in Yemen with Heteropogon contortus,
Bothriochloa insculpta and Themeda triandra (Deil & Müller-Hohenstein, 1985).
As all the mountains of southern Arabia are affected by the southwest and
northeast monsoons, it is highly likely that the newly described association will also
be found within Anogeissus forest on Ras Fartak west of Hauf in Yemen and may
also extend into Soqotra (A. G. Miller, pers. comm.).
Conservation status
Within the grasslands there are 12 taxa, representing 11% of the total within the
grasslands, which require a high conservation priority (Patzelt, 2008) in order to
maintain the current high plant diversity. Overgrazing has already led to a degeneration of the plant community and an invasion of many unpalatable weeds which now
dominate in severely overgrazed areas. In many areas in Dhofar the grasslands are so
heavily grazed that the grasses no longer reach reproductive maturity.
Although overgrazing is the major direct threat to this plant community it is clear
that without the involvement and cooperation of local people there can be little hope
for future conservation efforts. The inclusion of local people offers the best prospect
316
A. PATZELT
for the control of grazing pressure and for exploration of new practices and new uses
of rangelands. It is therefore essential that efforts be made to promote a policy of
sustainable development and conservation of the environment to ensure a good
standard of living for local people while conserving the native flora.
Principal Results
1 Isolation in space, time and climate has led to a unique and endemic plant
community, the Desmodio gangetico-Themedetum quadrivalvis ass. nov., which is
found exclusively in the monsoon-affected mountains of Dhofar and probably
also in adjacent Yemen.
2 This annual grassland is interpreted as the easternmost outlier of the East African
tall-grass savannah in the class Themedo-Hyparrhenietea Knapp 1965.
3 Taxa of xeric-African, mesic-African and mesic-tropical Asian origin indicate the
importance of southern Arabia as a migration link during the Tertiary.
4 The seasonal fog-oasis conditions in an otherwise arid environment offer a refuge
area for palaeotropical mesic elements.
5 The tall-grass savannah in Oman is an important habitat for endemic and nearendemic species and thus deserves further investigation and greater conservation
effort.
Acknowledgements
I am very grateful to Anthony G. Miller and Sabina G. Knees (Royal Botanic
Garden Edinburgh, UK) for valuable and stimulating discussions on the grassland
vegetation of Dhofar and Yemen and for helpful comments on the manuscript. I
would like to thank the National Herbarium, Ministry of National Heritage and
Culture, Oman, for allowing me to work on its plant voucher collection. I am also
grateful to Laila Al Harthi, Oman Botanic Garden (Oman), who helped to analyse
the soil samples, and to Mansoor Amerjeed, Directorate General of Municipalities
and Water Resources, Salalah (Oman), who provided meteorological data.
I am also very grateful to David Middleton (Royal Botanic Garden Edinburgh)
for very helpful comments on the manuscript.
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Received 23 July 2010; accepted for publication 29 March 2011