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DISTRIBUTION, DIVERSITY AND CONSERVATION OF THE GENUS
ALOE IN KENYA
Author(s): Emily Wabuyele, Charlotte Sletten Bjorå, Inger Nordal, and Leonard E. Newton
Source: Journal of East African Natural History, 95(2):213-225. 2006.
Published By: Nature Kenya/East African Natural History Society
DOI: http://dx.doi.org/10.2982/0012-8317(2006)95[213:DDACOT]2.0.CO;2
URL: http://www.bioone.org/doi/full/10.2982/0012-8317%282006%2995%5B213%3ADDACOT
%5D2.0.CO%3B2
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Journal of East African Natural History 95(2):213–225 (2006)
DISTRIBUTION, DIVERSITY AND CONSERVATION
OF THE GENUS ALOE IN KENYA
Emily Wabuyele
East African Herbarium, P.O. Box 45166, Nairobi 00100, Kenya
and
Department of Biology, University of Oslo, P.O. Box 1045, 0316 Oslo, Norway
ewabuyeley@yahoo.com
Charlotte Sletten Bjorå,
Botanical Garden & Museum, University of Oslo, P.O. Box 1172
0318 Oslo, Norway
charlotte.bjora@nhm.uio.no
Inger Nordal
Department of Biology, University of Oslo, P.O. Box 1045, 0316, Oslo, Norway
inger.nordal@bio.uio.no
Leonard E. Newton
Department of Plant & Microbial Sciences, Kenyatta University
P.O. Box 43844,Nairobi, 00100, Kenya
ellyen@yahoo.com
ABSTRACT
The genus Aloe is common in Kenya, with about 60 taxa recognised. Observations
from this study indicate that most of the taxa have a restricted distribution, with only
Aloe secundiflora var. secundiflora being widespread in the country. The diversity
patterns indicate a high concentration of taxa in three areas that are identified as Aloe
hot spots and thus of high priority for conservation of the genus: The Kulal–Nyiro–
Ndotos–Marsabit area in the north, the Taita–Shimba Hills zone to the southeast and
the Naivasha–Baringo area in the Rift Valley. Most of the microendemic taxa are
concentrated in the Kulal complex, a few in the Taita complex while the Naivasha
complex includes mainly the widespread ones. Based on the computed Extent of
Occurrence (EOO) and the threats to individual populations of endemic taxa about
36% were assessed as being Critically endangered, 32% as Endangered, 12 % as
Vulnerable, 12% as being Near Threatened and 8% of Least Concern, according to
IUCN Red Listing Criteria.
Key words: mapping, endemic, extent of occurrence, species richness, terrain
diversity
214 E. Wabuyele, C. Sletten Bjorå, I. Nordal & L.E. Newton
INTRODUCTION
The genus Aloe L. is distributed on the African mainland south of the Sahara, on
Madagascar, the Arabian Peninsula and on several islands in the Indian Ocean, including
Socotra. The main centre of diversity for the genus is South Africa, with about 120 taxa.
Other important centres of diversity are eastern Africa and the Island of Madagascar. A
complete survey of taxonomic diversity for the genus Aloe over its geographical range is
given by Newton (2004a).
Aloes are known to occur in a wide range of habitats at altitudes that vary from sea level
to 3300 m. The physiological adaptations in aloes, like sunken stomata and a heavy wax
cover on the leaf cuticle, make the plants particularly fitted for xeric habitats. The plants also
possess traits that make them tolerant to disturbance, particularly the spiny leaves and bitter
taste, which are deterrent to browsing. According to Newton (2004a), aloes are rarely
dominant in the ecological sense, except in places where vegetation is sparse, with aloes
being the only large plants.
Kenya covers a total land area of 582 646 km2between latitudes 5oN-5oS and longitudes
34o-41oE, in northeastern Africa. Altitude varies from sea level (the Indian Ocean) to 5194 m
on Mount Kenya. The country is bisected by the eastern Great Rift Valley of tertiary volcanic
origin. The country’s climate is variable and mainly influenced by altitude, and the distance
from the Indian Ocean in the east or from Lake Victoria in the west (Lucas, 1968). Rainfall
is scanty and unreliable in most areas, with only 20% of the country receiving 500 mm or
higher per year.
Phytogeographically the zone between the Rift Valley and the coastal belt belongs to the
Somalia Masai Regional Centre of Endemism (RCE) according to White (1983). This is an
extensive region that is only occasionally broken by the Afromontane archipelago-like RCE
to which the highlands on both sides of the Rift Valley belong. The Western part of the
country belongs to the Lake Victoria Regional Mosaic (RM) and the coastal strip to the
Zanzibar-Inhambane RM. The coastal forests and some of the isolated mountains in
southeastern Kenya are part of the Eastern Arc and Coastal Forests Hotspot (Myers et al.,
2000). A recent reappraisal of the global hotspots by Conservation International recognised
second biodiversity hotspots in this zone, namely the Eastern Afromontane Hotspot
(Mittermeier et al. 2005).
The vegetation of Kenya is highly influenced by the wide range of altitudes and variation
in climate. Like in many other countries in sub-Saharan Africa, the natural vegetation is
degrading fast and conversion of land for agriculture reduces pristine habitats. The central
highlands of Kenya are characterised by high population density, with much of the land
under cultivation. The north and east are covered mainly by dry bushland and grassy plains.
The west is mostly cultivated with a few forest remnants and some swamps along Lake
Victoria while the coastal belt is dominated by mangroves in inter-tidal zones and estuaries
and along creeks, and some dry forest patches (Marshall, 1998).
According to recent estimates, Kenya is home to a total of 6500–6700 vascular plant
species, about 5% of which are endemic to the country (Marshall, 1998; Beentje & Smith,
2001; Simon Kang’ethe, pers. comm.). Since the publication by Reynolds (1966), in which
about 30 Kenyan Aloe taxa were listed, there have been considerable gains in the
documentation and knowledge of the genus in the country. The distribution and taxonomy of
Kenyan aloes are well studied at alpha-taxonomic level (Carter, 1994; Newton, 2001) and
chemical profiles of some taxa (Viljoen et al., 1998, 1999, 2001; Reynolds, 1985, 1986,
Distribution, diversity and conservation of Aloe in Kenya 215
2004). Newton (1996, 2004b) has exemplified the multi-use value of some aloes to local
African communities.
Of the more than 80 taxa (species, subspecies and varieties) of the genus Aloe recognized
in the East African Flora, at least 59 occur in Kenya. This number is considerably higher
than other country estimates in the region. For instance, the number of taxa known so far in
Eritrea and Ethiopia is 43, in Somalia 33, in Tanzania 40, and in Uganda 16 (Carter, 1994;
Lavranos, 1995; Newton, 2001; Sebsebe et al., 2001). The Kenyan richness in Aloe taxa is
emphasized further when translated into species densities per million km2, which amounts to
101 taxa for Kenya, 68 for Uganda, 52 for Somalia, 42 for Tanzania and 35 taxa for Eritrea
and Ethiopia.
In traditional local communities, the medicinal use of aloes was at a sustainable level.
During the last century, however, population pressure (both human and livestock) has led to
the increased destruction of plants in the wild. The problem is exacerbated by international
demand for and trade in aloe products, requiring the harvesting of tons of plants in the wild
in order to gather the leaf exudates that are processed into the commodity known as ‘aloe
bitters’ (Kihara et al., 2003). The taxa that are reported to be harvested in Kenya include
Aloe secundiflora,Aloe turkanensis and Aloe scabrifolia (Oketch, 1991).
Following a 1986 presidential decree against exploitation of wild-growing aloes
(Nyamora, 1986), the Kenya Wildlife Service, which is the national body that is charged
with the protection and conservation of the country's biodiversity, has maintained a ban on
the commercial exploitation of wild-growing aloes. Additional restrictions on international
trade in species of Aloe are imposed by the Convention on International Trade in Endangered
Species (CITES), to which Kenya is signatory (CITES, 2006). To a large extent, deficiencies
in the national wildlife conservation policy have been cited as an impediment to Aloe
conservation in Kenya (KAWG, 2004). The problem is further compounded by inadequate
substantiation on the data available on the genus.
This paper aims to enhance the conservation of aloes in Kenya by presenting information
in a direct and illustrative way. Geographical Information System (GIS) technology was used
to display the spatial patterns of aloe distribution and diversity based on point (locality) data.
On the basis of distribution and diversity patterns, Aloe ‘hot spots’ were identified.
Furthermore, a preliminary red data listing for individual taxa was done and appropriate
conservation priorities are proposed. It is hoped that these will nurture the sustainable
utilization of the genus by promoting monitoring initiatives for wild-growing populations of
aloes.
MATERIALS AND METHODS
Benchmark publications on the genus (Reynolds, 1966; Carter, 1994; Newton, 2001, 2004a)
were consulted to identify all Aloe taxa with a Kenyan distribution, their habit, habitats and
altitudinal ranges at sites of occurrence. Using the BRAHMS software (Botanical Research
and Herbarium Management Systems, The BRAHMS Project, Department of Plant Sciences,
University of Oxford), details of about 850 specimens of Kenyan aloes were captured from
the East African Herbarium (EA) and the Herbarium at the Royal Botanic Gardens, Kew (K).
In cases where specimen localities were not geo-referenced, the gazetteer of collecting
localities by Polhill (1988) was consulted. It was inevitable that in many cases, several
specimens were linked to a single reference point. Extensive field surveys were carried out in
216 E. Wabuyele, C. Sletten Bjorå, I. Nordal & L.E. Newton
most parts of the country to verify known populations and hunt for unknown ones. It must be
emphasized that some of the recorded localities may have been destroyed or reduced, as is
the case of the population at the type locality of A. ballyi in Taita Taveta District (Newton, in
press).
Digital maps of Kenya were obtained from the Norwegian Institute for Nature Research
(NINA) and the National Museums of Kenya (NMK). Using Arc View software version 3.3,
latitude/ longitude values from the specimen database were plotted onto a country map that
was subdivided into quarter (30ƍ × 30ƍ) degree square grids. Species richness (diversity) was
inferred from simple grid diversity counts.
Based on distribution records for the taxa, endemic taxa were filtered out and plotted on a
separate map. Species rarity was deduced from total specimen and locality records for each
species. Using the X-tools option for calculating polygon areas in Arc View, the Extent of
Occurrence (EOO), was computed for taxa known from three or more data points. The EOO
as defined by IUCN (2001) is the area contained within the shortest continuous imaginary
boundary that can be drawn to encompass all the known, or inferred or projected sites of
present occurrence of a taxon.
In order to make red data assessments for the endemic taxa, we used our personal field
knowledge of Kenyan aloes as a well as a status report by Newton (1995) to evaluate the
levels of fragmentation of the species, their population sizes and trends and threats to their
survival. In addition, botanists with first hand knowledge of the plants and their locations in
the field, such as Stella Simiyu (SCBD / BGCI) and Quentin Luke (National Museums of
Kenya) were consulted before reaching a status assessment.
RESULTS
Distribution and species richness
About 66% of the taxa occur in deciduous bushland/woodland vegetation, 14% in grasslands,
while the remaining 20% inhabit edges of thickets, riverine woodlands, scrubland or rock
outcrops. A wide range of altitudes is encountered, from sea level for Aloe massawana to as
high as 2300 m for Aloe juvenna. Approximately 10% of the taxa are found at altitudes of
between 0-500 m, 24% between 500-1000 m, 32% between 1000-1500 m, 24% between
1500-2000 m and 10% between 2000-2500 m.
The entire distribution of the genus in Kenya was represented by 385 data points, collated
from herbarium records in EA and K, published literature and field observations. The Aloe
data points emerged in about 50% of the quarter degree squares (108 of the 219). Generally,
there is positive correlation between the number of collections, taxonomic diversity and
levels of endemicity per grid. With reference to the Equator, running approximately through
the middle of the country, the southern half of the country contains more aloes than the
northern half. Aloe secundiflora var. secundiflora is the most widespread taxon, represented
by at least 57 data points (EOO = 136 287 km2). Most of the other taxa had restricted ranges
or occurred in relatively small disjunct patches over their ranges. The ten most
common/widespread Kenyan Aloe taxa are presented in table 1.
Grid square diversity ranged between zero and nine taxa per square (figure 1). The
highest grid diversity was registered in squares around the Taita–Taveta area (Somalia-Masai
RCE). Grid square diversity of up to eight was recorded around the valleys and ridges within
one degree north/south of the Equator and immediately flanking the Rift Valley. Within the
Lake Victoria and western Kenya areas (Lake Victoria RM), grid diversity ranged between
Distribution, diversity and conservation of Aloe in Kenya 217
zero and six. The expansive North Eastern Province (Somalia Masai RCE) had the highest
number of blank grid squares with occasional grid square diversity records of two to four,
while the lowest levels of zero to two taxa were recorded in the West Pokot-Turkana areas.
Table .1 Occurrence of the 10 most common aloes of Kenya based on computed values of
EOO. Distribution (K1–K7) according to Polhill (1988).
Taxon Data
points
Total grid
squares
EOO (km2) Kenyan Distribution
Aloe secundiflora Engl. var.
secundiflora
57 36 136 287 K1, 3-7; not endemic
Aloe myriacantha (Haw.)
Schult. & Schult.f.
9 7 37 869 K3, 4,6,7; not endemic
Aloe deserti A.Berger 18 14 26 130 K4, 6, 7; not endemic
Aloe volkensii Engl. 9 9 23 518 K6, 7; not endemic
Aloe lateritia Engl. var.
lateritia
13 10 20 833 K4,6 7; not endemic
Aloe scabrifolia L.E.Newton 9 6 16 575 K1,4; endemic
Aloe dawei A.Berger 7 7 13 727 K5; not endemic
Aloe kedongensis Reynolds 17 12 12 670 K3-6; endemic
Aloe ellenbeckii A.Berger 3 3 12 598 K1, 4; not endemic
Aloe lateritia Engl. var.
graminicola (Reynolds)
S.Carter
19 11 11 460 K1, 3, 4-6; endemic
Figure 1. Patterns of taxonomic diversity of the genus Aloe in Kenya. The numbers 0-9 refer to
the total number of taxa recorded in each square.
218 E. Wabuyele, C. Sletten Bjorå, I. Nordal & L.E. Newton
Patterns of endemicity
The 25 Kenyan endemic taxa were represented by 35% of the total data points registered for
the entire generic range, one third of which represented only two of the most common taxa.
Most of the endemic taxa have restricted distributions, and are frequently known from only
one data point (seven taxa, which accordingly may be denoted micro-endemics) or two data
points (three taxa). It was therefore not feasible to compute EOO values for these (table 2,
marked with * under EOO) as was done for taxa known from three or more data points. The
computed EOO values for the endemics category shows Aloe scabrifolia to be the most
widespread species. However, it is should be noted that A. scabrifolia (EOO = 16 575 km2)
is a rare species and is far less abundant than for instance A. kedongensis (EOO =12 670
km2) and A. lateritia var. graminicola (EOO = 11 460 km2), respectively.
The largest diversity of narrow endemic taxa was found in the northern half of the
country (figure 2). Examples of such taxa include A. archeri, A. pustuligemma and A.
kulalensis. Although peaking on the cells around Mount Kulal, it is apparent that several of
the isolated volcanic formations neighboring the Chalbi Desert in this zone are part of this
unique biodiversity-rich complex in the arid north. These include Mount Nyiru (2743 m), the
Ndotos (2688 m) and Mount Marsabit (1828 m).
Figure 2. Patterns of endemicity of the genus Aloe in Kenya. The numbers 0-4 refer to the
number of endemic taxa recorded in each square.
The South Eastern corner of the country (Taita–Shimba hills complex) exhibited moderate
levels of endemicity, which also include some narrow endemic taxa such as A. penduliflora
Distribution, diversity and conservation of Aloe in Kenya 219
Table 2 Extent of Occurrence for Kenyan endemic Aloe taxa and proposed IUCN (2001) Red list categories.
Taxon Data
points
Total grid
squares
EOO in
( Km2)
Distribution Proposed IUCN listing/criteria
Aloe amicorum L.E.Newton 1 1 * K1 Critically Endangered [B1ab, B2ab(iii)]
Aloe carolineae L.E.Newton 1 1 * K1 Critically Endangered [B1ab, B
Aloe classenii Reynolds 2 2 * K7 Critically Endangered [B1ab+ B
Aloe juvenna Brandham & S.Carter 2 1 * K6 Critically Endangered [B1ab(v)+
Aloe ketabrowniorum L.E.Newton 1 1 * K1 Critically Endangered [B1ab, B2
Aloe kulalensis L.E.Newton & Beentje 2 1 * K1 Critically Endangered [B1ab(iii
Aloe lensayuensis Lavranos & L.E.Newton 1 1 * K1 Critically Endangered [B1ab, B2
Aloe lolwensis L.ENewton 1 1 * K5 Critically Endangered [B1ab, B2
Aloe multicolor L.E.Newton 1 1 * K1 Critically Endangered [B1ab, B2
Aloe murina L.E.Newton 1 1 * K6 Least Concern
Aloe powysiorum L.E.Newton & Beentje 2 2 * K1 Endangered [B2ab(iii) ]
Aloe vituensis A.Baker. 2 2 * K4,7 Endangered [(B2ab(iii)]
Aloe francombei L.E.Newton 4 2 52 K3 Vulnerable (D2)
Aloe archeri Lavranos 4 2 552 K1, 3 Endangered [B1ab(iii) ]
Aloe penduliflora A.Baker 7 4 869 K7 Endangered [B1ab(v) ]
Aloe tugenensis L.E.Newton & Lavranos 7 2 1029 K1,3 Endangered [B1ab(iii) ]
Aloe chrystostachys Lavranos &
L.E.Newton
7 5 2522 K4 Vulnerable (D2)
Aloe nyeriensis Christian 13 7 2544 K1,3,4 Near Threatened
2ab(iii)]
2ab(iii)]
2ab(v)]
ab(iii))]
)+2ab(iii)]
ab(iii)]
ab(iii)]
ab(iii)]
Aloe aageodonta L.E.Newton 5 3 2625 K4 Least Concern
Aloe elgonica Bullock 6 3 3410 K3 Endangered [B1ab(iii)]
Aloe pustuligemma L.E.Newton 5 4 3687 K1 Near Threatened
Aloe ukambensis Reynolds 10 5 4709 K4,7 Endangered [B1ab(iii)]
Aloe lateritia Engl.var. graminicola
(Reynolds) S.Carter
19 12 11 460 K1,3,4-6 Vulnerable [B1ab(iii,,v)]
Aloe kedongensis Reynolds 17 9 12 670 K3-6 Near threatened
Aloe scabrifolia L.E.Newton & Lavranos 9 6 16 575 K1,4 Vulnerable [B1ab(v)]
220 E. Wabuyele, C. Sletten Bjorå, I. Nordal & L.E. Newton
and A. classenii. Around the central Kenya Rift Valley complex, another peak of endemism
is apparent, but mostly comprising the more widespread endemic elements such as
A. kedongensis. The western Kenya area has the lowest endemicity level of one taxon only.
Based on the distribution patterns, threats to populations and computed values of the
EOO, the endemic taxa were evaluated against the IUCN (2001) criteria to assess their risk
for extinction (table 2). Most of the taxa satisfied criteria for listing as Critically Endangered
(36%), Endangered (32%), Vulnerable (12%) or Near Threatened (12%) while only two of
them were assessed to be species of Least Concern (8%).
DISCUSSION
The compilation and mapping of distributions based on point data has been recognized as the
finest scale at which geographical ranges of taxa can be assessed (Peterson & Watson, 1998,
Baillie et al., 2004). For individual entities, the EOO based on a combination of known
records is an important predictor of levels of threat. This, however, has been shown to
greatly overestimate occupancy within range (Corsi et al., 2000). It has also been shown that
the use of a relatively small grid size enables detailed analysis of the topographical complex
areas within a study area (Linder, 2001).
Although uneven and incomplete sampling is a general limitation in the application of this
approach (Küper et al., 2006), our data are based on documentation accumulated and collated
over many years of research and specialist experience with the genus Aloe in East Africa in
general and in Kenya in particular. The problem of sampling bias could be most significant
for the remote North Eastern Province, where insecurity and a poor road network restrict
access to large areas, a phenomenon that is not limited to this group of plants (Hepper, 1979;
Beentje and Smith, 2001).
Diversity in Kenyan aloes
For a genus whose members possess leaf succulence and therefore tolerance to water stress,
its presence/dominance on the Kenyan landscape (with 80% dry lands) is not surprising. The
various Aloe life forms as outlined by Holland (1978) for mainland Africa and Madagascar
are well represented in Kenya: miniature aloes (3%), solitary rosettes (12%), suckering
rosettes (27%), pendulous plants (7%), sprawling plants (24%), erect shrubs (20%) and trees
(7%).
The distribution maps for the genus in Kenya show that taxa are spread more or less
across the whole country. What is evident, however, is the fact that even within the same
general geographical region some grid squares of exceptionally high species richness stand
out from squares of generally low taxonomic diversity, a fact that may be attributed to
uneven sampling or the existence of pockets of suitable habitats within generally unsuitable
regions.
Holland (1978) observed that aloes occur in all vegetation types, except in the equatorial
rain forest, and that they grow best in areas of about 200–800 mm of rainfall per annum. The
distribution of the Kenyan taxa corroborates these observations. Species diversity is highest
in the Taita Taveta area in the south eastern corner with moderate amounts of rainfall that
support woodland and bushlands. Low species diversity is observed in the Western Region,
which receives high amounts of rainfall that support lush vegetation approaching the ‘rain
forest’ type in some places.
Distribution, diversity and conservation of Aloe in Kenya 221
Evidently, extreme dryness/aridity as found in some localities in northern and north-
eastern Kenya is detrimental to Aloe diversity. As shown from the analysis here, species
richness peaks around the Taita Hills to the south-east and the valleys and escarpments to the
east and west of the Rift Valley around Naivasha-Nakuru-Baringo areas. These can be seen
as ‘islands’ of aloe diversity that have in common a high diversity of terrain and habitats that
jointly support varied life forms. This being the case, however, regions with ‘optimal’
ecological conditions for the genus include many widespread taxa as opposed to the
rare/endemic ones (Fox & Fox, 2000).
Extrapolated onto the phytochoria classification of White (1983), these data show the
highest diversity of aloes in the relatively wetter parts of the Somalia-Masai RCE, and parts
of the Zanzibar-Inhambane RM. The Lake Victoria RM has the lowest levels of Aloe
diversity.
Endemicity in Kenyan aloes
Although most of the grid squares in the northern part of the country had no records of Aloe
taxa, the majority of occupied squares registered one hundred percent endemicity, i.e. the
one and only taxon recorded for a grid square occurs nowhere else. The elevated degree of
endemicity in this part of the country climaxes in cells around Mount Kulal in which the
highest national level of four endemic taxa is recorded. The significance of the northern half
of Kenya as an area of Aloe endemicity is emphasized further by the predominance of micro-
endemic taxa.
Cox and Moore (2005) observed that the degree of endemicity is determined by two
major factors, namely isolation and stability. This confinement of species to areas where they
evolved may be due to physical barriers to dispersal (paleoendemics) or to the fact that they
have only recently evolved and therefore not had time to spread from their centres of origin
(neoendemics). It may also be due to the fact that the taxa have poor dispersal ability, or are
adapted to surviving in specific environmental conditions and cannot compete outside their
home range (Lovett & Friis, 1996).
In general terms, the ecological conditions of the north and north-eastern region of Kenya
are harsh. Rainfall is low to the extent that it only supports simple/impoverished vegetation
gradients. However, Mount Kulal occupies a unique ecological position in the northern
region. There is an abrupt topographical transition from the surrounding Lake Turkana (23
km away) at 370 m altitude to the highest peak of the mountain at 2116 m above sea level. In
sharp contrast to the extremely harsh ecology in the neighbourhood, a range of habitats exist
on Kulal that include desert, semi arid zone and a montane zone supporting rain forest
(Hepper, 1979). The ecological setting of Mount Kulal and findings of elevated endemism
are in line with observations on some Ethiopian geophyte taxa (Nordal et al., 2001).
Viewed against the general ecological setting and the specific conditions on Mount Kulal
and similar formations in northern Kenya, it seems logical to speculate that aridity, which is
the most prominent selection pressure in northern Kenya, is responsible for the elimination of
poorly adapted taxa of Aloe. This ensures low establishment rates, and the ensuing genetic
drift as a result of isolation (by distance/altitude) enhances divergence in populations and
taxa. This effectively leads to high prevalence of speciation events in northern Kenya as
compared to other areas. In addition to this, the predictability of aridity in this zone probably
confers environmental stability that offers larger opportunity for continuous terrestrial
evolution while at the same time imposing stringent conditions of survival due to punishing
arid conditions (Lovett & Friis, 1996; Hopper & Gioia, 2004).
222 E. Wabuyele, C. Sletten Bjorå, I. Nordal & L.E. Newton
Conservation
For the purpose of this analysis and conservation planning, we advance the following
categorization in order of increasing species diversity and endemicity levels: 1) ‘Aloe Cold
Spots’, centred on grid squares with diversity of zero to four taxa; 2) ‘Important Aloe Areas’,
centered on grid squares with diversity of five to nine taxa or any square containing an
endemic taxon; (3)‘Aloe Hot Spots’ (AHS), centred on grid squares with total diversity of
more than five taxa and including one or more endemic taxa. It remains to be investigated
whether the patterns of Aloe diversity can reliably be used to predict the distributions of
similarly adapted plant groups of the country and the East African region in general.
Based on the limited distribution and small values of the EOO, most Kenyan endemic taxa
qualify for listing under the IUCN (2001) guidelines as indicated in table 2. In assessing the
conservation status of the various taxa and their priority for conservation intervention
consideration has been given to the threats to the populations, level of fragmentation as well
as the level of use at the various locations. However, the categories accorded to the taxa here
should be considered tentative pending formal validation by the relevant Red Listing
Authorities.
CONCLUSIONS AND RECOMMENDATIONS
Although Kenya has a large Aloe flora, the distributions of most taxa are restricted to
sections of the country. Aloe secundiflora var. secundiflora was found to be both common
and widespread; ten endemic taxa are known from less than three localities, while seven of
them are micro-endemic. This study has identified criteria by which areas and taxa,
respectively, should be prioritised for conservation of the genus Aloe in Kenya. The Aloe
hotspots, which should be given the highest priority for the conservation of the genus in
Kenya, roughly coincide with following areas:
xTaita–Shimba Hills complex to the south-east
xNaivasha–Baringo complex in the central Rift Valley
xKulal–Nyiru–Ndotos–Marsabit complex in the north.
Of these areas, part of the Shimba hills is a nature reserve with a considerably high level
of stability and protection. Although gazetted as a biosphere reserve the ecosystem health of
Mount Kulal is generally on the decline with increasing loss of habitats (Quentin Luke, pers.
com.). Similarly, most sections of the Taita Hills area and the Naivasha-Baringo hot spot
occur on private land. In the absence of guaranteed regulation of land use, habitats in this
area may be altered or destroyed without warning or consultation, thus putting Aloe
populations at a risk of depletion.
Although a considerable number of endemic taxa occur in remote areas (e.g. Mount
Kulal) where anthropogenic threats to their survival are not immediate (Newton, 1995),
general deterioration in the habitat is on the increase and hence the need for ecological
monitoring and conservation intervention. With the various hot spots and important areas
identified in this study, it seems feasible to adopt an ecosystem approach to the conservation
of aloes in Kenya and the region as a whole.
Distribution, diversity and conservation of Aloe in Kenya 223
ACKNOWLEDGMENTS
We would like to thank the East African Herbarium and herbarium at the Royal Botanic
Gardens, Kew, for permission to study their Aloe collections; Salome Wabuyele for initial
instruction in mapping and GIS software; Vegar Bakkestuen of NINA for providing base
maps on Kenya and tutorials on the use of Arc View software; Dennis Malewa and Pius
Namachanja of the NMK for providing digital maps of the flora area; Mathias Mbale for
technical support in the field and herbarium in Kenya and Craig Hilton-Taylor (Cambridge)
for help with the Red Listing process. This work was supported by grants from the Kenya
Museum Society and the Norwegian Council of Universities’ Committee for Development
and Education.
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