Saudi
Arabia is generally an arid country with a few exceptional sub-humid
regions on the south-western escarpments and is divided into three
chorological units: the Saharo-Sindian, Somali-Masur, and Afro-Montane.
Approximately
24 different ecosystems comprise the functional elements of the
major floristic units. Most of these ecosystems cover large areas
and are widespread in the Kingdom. Ecosystems range from those
of the saline areas along the Gulf Coast and in the inland drainage
basins through the systems of the dune seas of the Nafud and Rub
al Khali to the complex and species-rich woodlands of the western
highlands. Most of the ecosystems are comparatively simple in
structure and species diversity, reflecting the aridity and high
summer temperatures experienced by most of the physiographic regions.
The
vegetation of most ecosystems of the Saharo-Sindian region is
generally sparse and about 60% of the vegetation, mainly in the
low lying areas, is represented by annuals. Population density
of these annual species varies from year to year, depending on
the amount of rainfall and the amount of seed remaining from previous
years. The western region is rich in vegetation when compared
to the central and eastern region. The north-western mountains
are rugged and floristically poorer than the south-western mountains,
with affinities to the Mediterranean and North African floristic
regions. The south-western region is the richest in terms of species
diversity, with elements of all chorological units being found.
The African element is especially noticeable, adding many species.
The south-western area also contains the highest concentration
of endemics, despite the fact that these high altitude areas are
heavily populated with human settlements dating to ancient times.
The
flora of Saudi Arabia is moderately well known at the taxonomic
level and species richness of the 15 Protected Areas administered
by the National Commission for Wildlife Conservation and Development,
as well as many of the areas under the administration of the Ministry
of Agriculture is well documented. Hence the relationships of
the flora to surrounding areas, as well as the numbers of endemic
taxa are well established. The 2,250 species of flowering plants
in Saudi Arabia belong to 132 families and 837 genera. About 105
species inhabit sand dunes, 90 are halophytes, 75 are trees and
12 are aquatic plants. No families or genera of flowering plants
are endemic, but there are some 246 species that are considered
regionally endemic. The influence of the floras of neighboring
countries, particularly Yemen and Oman, is high on the flora of
Saudi Arabia.
About 450 species (18%) of flowering plants have direct benefit
to man and 45 species (1.8%) are poisonous. Some 334 species (13.4%)
are used in folk medicine or are known to have medicinal value.
Thirty-eight species are important palatable fodder plants, 6
are important as fuel-wood, 25 species are human food plants and
47 species are used as ornamentals or for other purposes.
Related to the modest numbers of species and levels of endemism,
most families of flowering plants have only a very small proportion
of their worldwide total numbers of species found in Saudi Arabia.
Exceptions are two small families, the Ceratophyllaceae and Barbeyaceae,
in which all known species occur in the Kingdom.
In
contrast with the flowering plants, gymnosperms, pteridophytes,
bryophytes, and algae are not as well known. However, as the bibliography
and annexes show, some ground-breaking work has been done on some
groups.
Although
the species richness is quite well known, other measures of plant
diversity have not been widely determined for the Kingdom. Consequently,
the Red List status of plant species is very poorly known at this
stage. For example, the 2000 IUCN Red List of Threatened Species
did not include a single record for Saudi Arabia. Even with increased
the emphasis that is being placed on improving the state of knowledge
of biodiversity in the Kingdom, the 2003 Red List only contains
the five species listed in the table below. Non- Red List literature
sources however list 14 flowering plants as endangered, 11 vulnerable,
23 critically endangered, 1 rare and 14 extinct. Unfortunately,
since these figures are often based on single collection reports
and do not include any quantitative assessments of population
sizes and total distribution, it is difficult to determine their
significance and therefore to assess status adequately. However,
it has been estimated that about 20% of the flora, including the
rare and endemic species, are present in small populations in
their respective niches. Given the extent of over utilization
of rangelands in the Kingdom and the rapid growth of human population
in the most botanically diverse regions, it is most likely that
the real numbers of threatened plant species is considerably higher
than the currently available figures suggest.
Threatened
Plant Species Listed in the 2003 IUCN Red List of Threatened Species.
Species |
IUCN
Category |
| Acacia
pachyceras var najdensis |
LR/nt |
| Dracaena
ombet |
EN A1cd |
| Dracaena
serrulata |
EN A1abcd |
| Euphorbia
ammak |
VU A1c |
| uniperus
procera |
LR/nt |
Source: IUCN
2003 : IUCN Red List of Threatened Species
