Twenty years of biodiversity research and nature conservation in the Socotra Archipelago (Yemen)

Abstract

The topical collection ‘Twenty years of biodiversity research and nature conservation in the Socotra Archipelago’, in short ‘Socotra biodiversity research and nature conservation’ was conceived at the 18th Friends of Socotra annual meeting and Socotra conference which took place at the Orto Botanico di Palermo, Palermo, Italy, 26–29 September, 2019. In total, 13 research papers are included in the collection, which covers a selection of the latest scientific progress on the fauna and flora of the terrestrial and aquatic environments of the Socotra Archipelago UNESCO World Heritage Site (Yemen). Topics include conservation, taxonomy, ecology, biology and biogeography. The focus is mainly on biodiversity conservation and aimed at identifying current challenges, trends and processes that may impact on local ecosystems and livelihoods, based on analysis of data collected over the last decades. With this collection, we wish to emphasise the importance of taking into account science-based conservation approaches in future strategic steps towards safeguarding the ecosystems of Socotra.

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Rendiconti Lincei. Scienze Fisiche e Naturali
https://doi.org/10.1007/s12210-020-00941-7
SOCOTRA BIODIVERSITY RESEARCH ANDNATURE CONSERVATION
Twenty years ofbiodiversity research andnature conservation
intheSocotra Archipelago (Yemen)
FabioAttorre1 · KayVanDamme2
© Accademia Nazionale dei Lincei 2020
The topical collection ‘Twenty years of biodiversity research
and nature conservation in the Socotra Archipelago’, in
short ‘Socotra biodiversity research and nature conserva-
tion’ was conceived at the 18th Friends of Socotra annual
meeting and Socotra conference which took place at the
Orto Botanico di Palermo, Palermo, Italy, 26–29 Septem-
ber, 2019. In total, 13 research papers are included in the
collection, which covers a selection of the latest scientific
progress on the fauna and flora of the terrestrial and aquatic
environments of the Socotra Archipelago UNESCO World
Heritage Site (Yemen). Topics include conservation, tax-
onomy, ecology, biology and biogeography. The focus is
mainly on biodiversity conservation and aimed at identifying
current challenges, trends and processes that may impact
on local ecosystems and livelihoods, based on analysis of
data collected over the last decades. With this collection,
we wish to emphasise the importance of taking into account
science-based conservation approaches in future strategic
steps towards safeguarding the ecosystems of Socotra.
1 Background
For centuries, islands and their biotas have appealed to biol-
ogists. Covering only 5% of the Earth’s land surface, these
‘living laboratories of evolution’ account for a high propor-
tion of endemics—about 20% of all known vascular plants
and 15% of all amphibians, mammals and birds are found
exclusively on islands (Da Fonseca etal. 2006). However,
due to several factors that are typical to insular ecosystems
such as isolation and small sizes of local populations, over-
whelming evidence has shown that species on islands are
easily driven to extinction. General factors are well known
and include the effects of exotic species, habitat degradation
and deliberate destruction (Sax and Gaines 2008; Caujapé-
Castells etal. 2010; Wood etal. 2017). Therefore, in con-
servation efforts, approaches for islands must be very dif-
ferent to those in the continent (Whittaker 1998). The rich
biodiversity of the Socotra archipelago forms no exception
to the brutal mathematical reality of how rapidly extinction
occurs on islands.
The Socotra Archipelago is situated in the western
Indian Ocean near the Horn of Africa and belongs to
Yemen. It consists of a few islands of which Socotra is
the largest (Fig.1), the latter covering a land area of about
3600 km2. Ever since the first scientific expeditions to
Socotra towards the end of the nineteenth century, biolo-
gists have been fascinated by this place with its strange
umbrella- and bottle-shaped trees. Most likely, Charles
Darwin would have loved visiting the ‘Galápagos of the
Indian Ocean’ instead of the Ecuadorian islands; how-
ever, strong monsoons used to cut Socotra off from the
world for about half a year and therefore opportunities for
research were few. Only in the last 50years has Socotra
been more accessible to researchers, in particular since the
establishment of an airstrip and an increase in traffic and
immigration over the last two decades (Van Damme and
Banfield 2011). The turn of the last millennium is also the
period when major conservation programmes started on
This paper belongs to a Topical Collection “Twenty years of
biodiversity research and nature conservation in the Socotra
Archipelago” edited by Fabio Attorre and Kay Van Damme,
conceived at the 18th Friends of Socotra Conference, 26–29
September, 2019, Orto Botanico di Palermo, Palermo, Italy.
* Kay Van Damme
kay.vandamme@gmail.com
Fabio Attorre
fabio.attorre@uniroma1.it
1 Department ofEnvironmental Biology, Sapienza-University
ofRome, Piazzale Aldo Moro 5, 00185Rome, Italy
2 Senckenberg Research Institute andNatural History Museum
Frankfurt, Senckenberganlage 25, 60325FrankfurtamMain,
Germany

Rendiconti Lincei. Scienze Fisiche e Naturali
1 3
the islands, which in 2008 received recognition as UNE-
SCO World Heritage Site, based purely on the criterion
of harbouring globally important biodiversity and a high
proportion of endemics (Natural WH Site).
About two decades ago, when the most recent episode
of research in Socotra had just started, a charity by the
name Friends of Socotra (FoS) was established. The non-
governmental, non-profit organisation consists of predomi-
nantly researchers and provides a multidisciplinary and
politically neutral platform for discussion, interaction and
synergies related to the conservation of the unique bio-
diversity and culture of these Yemeni islands. Through
annual conferences, a newsletter and small awareness or
pilot activities on the ground together with other organisa-
tions and local NGOs, FoS (www.frien dsofs oqotr a.org) is
the only organisation of its kind that focuses on scientific
efforts related to the unique cultural and natural heritage
of the Socotra Archipelago. The organisation is unusual,
as few islands or island groups in the world have an inter-
national, multidisciplinary group of scientists investing
voluntary time in promoting awareness for local science
and conservation. The group is driven entirely by the enor-
mous efforts by former and current volunteers from all
over the world who have supported the organisation in the
past two decades, and who have a heart for Socotra.
2 The topical collection
The topical collection ‘Socotra Biodiversity Research and
Nature Conservation’ materialised as a result of the impor-
tant synergies that are generated at the Friends of Socotra
meetings. In the last two conferences, which took place
in the Kingdom of Bahrain and in the Botanic Garden of
Palermo in Sicily, respectively, we proposed a topical col-
lection which crystallised into the current output. Repre-
sentatives from Yemen were present, and several Socotran
conservationists scientifically contributed to the meet-
ings and to the papers in this collection. At the Palermo
meeting (Van Damme and Livadiotti 2020), an important
awareness activity focusing on Socotra biodiversity was
launched, the UNESCO-FoS campaign entitled Connect-
2Socotra which took place in different scientific institutes
around the world (https ://en.unesc o.org/conne ct2so cotra ).
The topical collection focuses on 20 years of biodiver-
sity research and conservation of the terrestrial environ-
ment of the Socotra Archipelago UNESCO World Heritage
Site. The reasoning behind this collection is to provide
the scientific data and approaches to conservation and to
evaluate what can be learned from assessing the environ-
mental information that was gathered through international
collaborations in recent years. The collection focuses on
trends through the analysis of decades of data and includes
completely new observations as well as introducing new
techniques that can locally be used for biodiversity moni-
toring. Several studies in this topical collection result from
years of continued data acquisition under difficult field
conditions in close coordination with local authorities
and conservationists, with full support by the Ministry
of Water and Environment and the Environmental Protec-
tion Agency (EPA) of Yemen and EPA Socotra Branch,
to whom we are very grateful. The interaction between
conservationists from different cultures working on a com-
mon goal over many years, continuing essential scientific
work for biodiversity during a time of hardship and war in
Yemen, has led to fruitful collaborations.
Studies that examine actual changes in the Socotran
ecosystems over time are few (Van Damme and Banfield
2011; Madĕra etal. 2019). Nevertheless, such studies are
crucial to assess imminent extinction risks and to strate-
gise proposed solutions. The main threats to the terrestrial
environment are well known (Van Damme and Banfield
2011) and have been highlighted since years by the World
Heritage Committee for Socotra. The IUCN Conservation
Outlook (2017) has put the digit at an alarming ‘Signifi-
cant Concern’ for Socotra. This topical collection also
serves the purpose of a warning by the scientific com-
munity: as shown here, there are clearly processes on
Socotra that can lead to imminent extinctions. And the
Fig. 1 Socotra Island is part of a small yet significant Yemeni archi-
pelago, situated in the western Indian Ocean just off the Horn of
Africa. It is the largest island of Arabia. Since 2008, the Socotra
Archipelago has been listed as one of Yemen’s UNESCO World Her-
itage Sites, in particular for its rich biodiversity and high number of
endemic species. Image from Google Earth, modified by Kay Van
Damme

Rendiconti Lincei. Scienze Fisiche e Naturali
1 3
extinction of a single individual or a small population,
whether it belongs to a species of plants or animals, mat-
ters. For example, the loss of a single individual of the
iconic Socotra Dragon’s Blood Tree (Dracaena cinnabari)
would not only affect the entire vegetation that lives shel-
tered below the canopy and the animals associated with it
(Rejžek etal. 2016; Vasconcelos etal. 2020), but it may
also change the amount of water that is part of the island’s
hydrological cycle on which human life depends (Kalivo-
dová etal. 2020). Often, effects that we see today are the
results of trends that have been set in motion over the last
decades, and which are accelerated through global warm-
ing and other, more direct, human interventions.
This is the case for the frankincense tree Boswellia elon-
gata (Fig.3) which is one of the most important endemic
plant species in Socotra. Not only is the most typical Socotra
frankincense tree endangered, but it also plays a key role in
the island’s culture and has potential benefit for economy, as
perhaps it did in a distant past. A close study of individual
trees from aerial photographs now provides the first direct
visual evidence of this species’ decline and indicates the
imminent extinction of its largest subpopulation. Research-
ers witnessed a clear reduction in the largest subpopulation
of Boswellia elongata on Socotra Island between 1956 and
2017, a period of 61years, by about 78% (Lvončík etal.
2020). Through experimental designs and assessment
of the potential causes, the decline has been attributed to
both natural and human-mediated factors. Senescence of
the tree stands and decades of overgrazing by goats (now
roaming more freely because of a shift in culture, i.e. use
Fig. 2 Overmature stands of one of the archipelago’s unique and
endangered frankincense tree species (Boswellia elongata) in an
overgrazed Socotran landscape before (left) and after (right) damage
caused by climate change (cyclones in 2015). Photos from Homhil
Nature Sanctuary, eastern Socotra Island, by Kay Van Damme (May
2010) and Petr Madĕra (2016)
Fig. 3 The analysis of data that
has been collected over decades,
now provides an objective view
on how the immune system of
Socotra’s terrestrial environ-
ment, on which local people
depend, is compromised. Stra-
tegic efforts to increase local
resilience of plant and animal
populations are vital to ensure
that future generations can ben-
efit from the ecosystem services
of the iconic species that have
made the island so famous. The
Socotra Dragon’s Blood Tree,
for example, does not only har-
bour a wide range of endemic
species, it also plays a role in
the island’s hydrological cycle.
Photo by Kay Van Damme,
Socotra Island, 2014

Rendiconti Lincei. Scienze Fisiche e Naturali
1 3
of the rangeland), have made natural regeneration of most
ground-dwelling palatable plants in accessible areas nearly
impossible, in particular in times of drought when grazing
pressures intensify (Miller and Morris 2004; Lvončík etal.
2020). The process is catalysed by non-selective overarching
events such as climate change, which could potentially give
the final nudge for Socotran species that are on the edge at
the downward slope towards extinction (Van Damme and
Banfield 2011).
Global warming recently manifested itself in Socotra in
the form of extreme weather events (cyclones and torrential
rains) which have caused damage to the terrestrial environ-
ment. Physical destruction to the frankincense trees caused
by unusually strong winds could be clearly attributed to two
cyclones in 2015 and are accountable for more than a third
of the individual trees that have disappeared in one of the
island’s largest populations (Fig.2). Weakened by the com-
bination of overgrazing and damage by wind, the popula-
tion was attacked by a local species of bark beetles on top
of that. If the trend continues, the iconic subpopulation of
frankincense trees in a well-known protected area on the
island (Homhil Nature Sanctuary) will be gone in only a
few decades from now (Lvončík etal. 2020). The events are
not localised; we may expect that the majority of exposed
areas where this and other endemic ground-dwelling tree
species occur on the island are facing a similar situation.
The rate of extinction is specific to biological attributes of
the species, however, studies show similar trends for other
endemics, like Dracaena cinnabari, albeit over centuries
rather than decades (Madĕra etal. 2019). First estimates of
age indicate that many trees of the latter species can easily
be several centuries old (Madĕra etal. 2020). In some spe-
cies, relatively less palatable to goats, regeneration is good,
such as in the endemic Dendrosicyos socotranus, Socotra’s
famous cucumber tree. Habrová etal. (2020) found regenera-
tion for this species in 77% of the locations studied. How-
ever, to avoid an entirely skewed landscape that is mainly
dominated by grazing-tolerant species, efforts are needed
because ground-rooting species are truly at risk. The grazing
impacts on vegetation is stronger during dry periods when
there is less choice for alternatives, as exclosure experiments
show (Lvoncik etal. 2020).
Ecosystems dominated by trees in the Socotran land-
scape are not as widespread as it would appear to the out-
side. Satellite image analysis using available state-of-the-art
approaches combined with ground-trouthing indicates that
the Socotra highlands and mountains harbour the majority
of the trees (Riccardi etal. 2020). Statistical analysis sug-
gests that the overall distribution of trees on the island is still
largely governed by natural factors such as soil availability
and local climate, less so by direct human impacts. For now.
As the population grows, these impacts may increase further
as well. Such impacts can be monitored also using remote
sensing technologies. Vegetation productivity in Socotra was
assessed over ca. 20years using NVDI (normalised differ-
ence vegetation index) (Rezende etal. 2020). The results
show that overall the island seems very dynamic in terms
of vegetation productivity, however the mountain areas and
wadi slopes show a clear decrease over the past decades and
in particular over the last few years (Rezende etal. 2020).
The decrease could be attributed to the long-term effects
of grazing combined with the effects of extreme weather
events, leading the loss of vegetation, as in the Boswellia
case study, and the loss of soil linked to erosion.
Plants are also important for many endemic vertebrate
species on the island, such as birds and reptiles that are
strongly dependent to the availability of healthy stands of
woody vegetation. About 90% of the terrestrial reptiles are
endemic to the archipelago, and several of those rely on the
availability of the trunks and branches of trees or bushes
(Fasola etal. 2020). The endemic gecko Hemidactylus dra-
caenacolus, assessed as critically endangered in the IUCN
Red List, is even found exclusively on tree trunks of the
endemic Dragon’s Blood Tree (Vasconcelos etal. 2020).
Therefore, the declines or the disappearance of vegetation
through a combination of factors, may accelerate the direct
extinction of associated species in the absence of vegetation
cover. Considering the rapid changes in vegetation over the
last decades (Lvoncik etal. 2020; Rezende etal. 2020), the
fact that some endemic reptiles have a total area of occupa-
tion of less than 10 km2 (Fasola etal. 2020) and the pres-
ence of invasives such as rats and cats, extinction scenarios
for these island endemics are realistic if there is no direct
intervention.
On an island, everything is closely connected, and so are
people to their environment. The vegetation does not only
play a key role in creating niches for other plant and animal
species, but also may provide another important ecosys-
tem service as part of the hydrological cycle of the island.
Kalivodová etal. (2020) measured the amount of horizontal
precipitation caught by individual Dragon’s Blood Trees.
The authors estimated that at the highest altitudes (ca.
950–1550m a.s.l.), the mean annual horizontal precipitation
below the tree crown is about 790mm, exceeding 40% of the
total annual precipitation. Considering the relatively slow
growth of Dragon’s Blood Trees (Madĕra etal. 2020), con-
servation strategies to preserve these assets will need local
involvement for the duration of more than a human lifetime.
The freshwater environments also show a decline in
indicator species. A first analysis of 123years of drag-
onfly records in the archipelago suggests a decline in the
relative richness of these conspicuous insects in the area of
the coastal capital of Socotra, Hadiboh (Van Damme etal.
2020). Although species richness in this animal group is
not high, the pattern is clear and it affects several species.
The latter is relevant to the protection of local wadis, but

Rendiconti Lincei. Scienze Fisiche e Naturali
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particularly shows the need to protect coastal lagoons, which
harbour a rich diversity of birds, fish and arthropods. A con-
spicuous dragonfly called the phantom flutterer (Rhyothemis
semihyalina), disappeared from Socotra’s coastal lagoons
in the east and the west. Even though the latter study is not
based on standardised surveys, it is the first long-term study
assessing changes over time in animal species richness on
Socotra. In this case the decline was attributed primarily
to habitat alteration through urban development. The study
shows also that there is a cultural dimension to these insects
locally—the people of Socotra recognise dragonflies as a
sign of good water and they have no less than six terms in
the unique language to describe them. Such positive inter-
action towards invertebrates can be a very valuable asset in
local conservation, for example to protect the iconic beauti-
ful Socotra bluet (Azuragrion granti), the archipelago’s only
endemic damselfly, Near Threatened in the IUCN Red List
(Van Damme etal. 2020).
The above, habitat degradation and climate change, are
all well-known factors that impact on biotas worldwide.
However, arguably the worst known drivers of extinctions
on islands are the invasive alien species. Exotic species
are a well-known threat to biodiversity on Socotra, but the
arrival of new and unwanted guests may strongly impact
on local economy and culture as well. Witt etal. (2020)
present the first records of detrimental plant pests, the red
palm weevil (Rhynchophorus ferrugineus) and the dubas bug
(Ommatissus lybicus) on Socotra, two invasive alien spe-
cies which are known to strongly reduce date palm yields
in the region. Another new invasive on Socotra is recorded
in Hula and Niedobová (2020), the Mediterranean recluse
spider, of which the bite can pose a risk to children. Based
on successful eradication programmes in other places in the
world, Witt etal. (2020) suggest that more measures are
urgently needed to protect the island and its biodiversity
and livelihoods, from exotics. Such measures would include
phytosanitary approaches, quarantine facilities at the port
and airport, and most importantly a good communication
between all stakeholders to mutually arrive to the best strate-
gies (Witt etal. 2020). Even though such suggestions have
been made repeatedly in recent years and despite efforts as
part of ongoing projects, and a priority issue as identified by
the World Heritage Committee, such measures were unfor-
tunately never achieved on the ground. However, the delays
in implementation increase the risk of more pest incursions
as evident in the presence of the red palm weevil and other
invasive alien species. Therefore, such exotics pose huge
risks, not only towards the unique biodiversity of Socotra,
but also for local livelihoods, the unique culture and human
health. More invasives may be present on the island yet
remain undetected.
Despite the challenges, Socotra is still at this moment,
a treasure trove of biodiversity. While freshwater
environments are largely well studied, the terrestrial envi-
ronments still harbour new species that rest in existing col-
lections. For example, new species are being described from
collections from the first large (among the recent biological)
expeditions, now 20 years ago. People who describe spe-
cies in animal and plant groups are part of an endangered
population themselves; however they keep carrying out this
important and tedious taxonomical work. In this topical col-
lection, malacologists Neubert and Bochud (2020) describe
two new endemic species of molluscs from the terrestrial
environments of Socotra. Also, in the flora of Socotra, still
a large amount of work remains to be done, in particular in
assessing the genetic diversity of plant populations that may
or may not harbour cryptic species, although much more
research is needed for single species (Giovino etal. 2020).
All these taxonomical works can help to understand patterns
of diversity, areas of higher richness, and help to even look
into biogeographical patterns of richness and evolution, as
Purchart etal. (2020) have started for butterflies, darkling
beetles and spiders in the archipelago. Comparing such pat-
terns in diversity and comparison to other islands can be key
to global research in biodiversity and biogeography.
3 Outlook
As the publications in this topical collection contribute to
our knowledge of the terrestrial and aquatic environments in
the Socotra archipelago, they thereby may help to identify
the challenges that other fragile insular ecosystems and arid
lands in the world face. These challenges are global and have
been identified on Socotra years ago, before the effects were
as visible as now. It is clear from the studies herein that if
the current trend continues, the Socotran ecosystems may
actually rapidly lose iconic endangered species and a per-
haps equally fragile endemic culture over the next decades
or centuries (Fig.3). This trend is realistic and should be met
with matching efforts in conservation.
Socotra has changed. The changes in the terrestrial eco-
systems now have become tangible and seem to manifest
themselves clearly when examining processes over a few
decades. Such processes can only be observed through rig-
orous scientific approaches and targeted monitoring, cover-
ing years of data. Such research, which only started at the
turn of the millennium in Socotra, is vital to strategise con-
servation priorities, while practical activities are needed to
focus on applied science that assesses positive effects from
interventions. Primarily environmental factors, more than
human factors, seem to currently drive the dynamics of the
terrestrial ecosystems in Socotra, sometimes in pulses of
increased intensity, and these effects likely will continue to
catalyse changes on the islands and its inhabitants in the
years to come. Climate change impacts have also clearly

Rendiconti Lincei. Scienze Fisiche e Naturali
1 3
revealed the sensitivity of local endemic plant species, which
will need to retain a strong resilience and positive human
interventions to avoid extinction. However, the new studies
in this topical collection reveal that not only climate change,
but also cultural and socio-economic effects play a role in
affecting the landscapes, albeit through perhaps slower and
sometimes more localised processes. These include effects
of (i) overgrazing, leading for example to overmature tree
populations of palatable species, (ii) urbanisation, altering
coastal areas including lagoons and wadis, and (iii) new
invasive alien species which are more likely to arrive now
due to an increase of import and lack of control measures
at entry pathways, and which may have a devastating effect,
not only on biodiversity, but also on food security and local
livelihoods. The combined effect of overgrazing and climate
impacts, seem to also lead to loss of vegetation in the moun-
tains, Socotra’s local biodiversity hotspot. Even though we
have an image of the Socotran people as being stewards of
their environment for centuries (Van Damme and Banfield
2011), new challenges arise and cultural shifts have been
disrupting the bond between people and their environment
since decades, as is evident in the overgrazing effects. The
local capacity to cope can benefit from strategic and cost-
effective solutions, which can be helped by science.
The immune system of Socotra is now compromised. The
current status of the ecosystems is unravelled by impacts that
painstakingly reveal slower underlying mechanisms. Extinc-
tion is a relatively slow process; however as it is known to
be accelerated strongly in island biotas, we may soon be
running out of time to protect Socotra’s most iconic flagship
species and the biota associated with them. The causes and
pathways for extinction are well known, and if not countered
by immediate strategic conservation action involving local
communities, several typical species will clearly not survive
the coming centuries. If the trend continues, future genera-
tions might be able to visit a Socotran frankincense tree only
in a botanical garden, accompanied by a little plaque saying
‘extinct in the wild’.
We believe there is time to turn the tide. Human impacts
on nature can be reduced as shown in other places in the
world. It needs all crew aboard working together and some
positive currents to avoid a ship from crashing. In order
for the ecosystems to be resilient in the face of upcoming
challenges, it will require all hands on deck. Science-based
strategies, cooperation and community involvement are key
and have shown to be effective in other highly valuable bio-
diversity areas in the world.
As Socotra is recognised by UNESCO as a Natural World
Heritage Site, there is a large interest in supporting the local
environment, materialised in several ongoing conservation
projects. If such efforts are managed properly and in full
support of the local authorities and local communities to
help against the coming challenges, major challenges can
be faced. Improved biosecurity measures are an example of
cost-effective priority measures to avoid loss of future local
livelihoods and biodiversity, and to avoid more costly future
interventions to eradicate invasives. To keep promoting the
communication of scientific outputs towards a wider pub-
lic, providing science-based options to conservation, and to
keep spreading awareness about the island’s uniqueness, an
organisation like FoS and collaboration with local environ-
mentalists and authorities are key. The latter is illustrated by
the fact that no less than five papers in this topical collection
include indigenous co-authors from Socotra Island.
We hope that these scientific contributions related to
conservation science in Socotra, presented in this topical
collection, can help to strategise future activities and help
reverse some adverse impacts from climate change and other
processes that drive species to extinction.
Acknowledgements Several studies of the Topical Collection were
partially funded by the UNE-GEF Project #5347 which has been locally
executed by the Ministry of Environment (Yemen) and the Environ-
mental Protection Agency (Yemen): “Support to the Integrated Pro-
gram for the Conservation and Sustainable Development of the Socotra
Archipelago”. A special thanks is due to Friends of Socotra (FoS)
and its volunteers, for the enabling environment that stimulated this
collaborative effort. This topical issue could not have been realised
without the efforts of all contributors, including authors, reviewers
and colleagues helping in the field surveys. We also thank the Italian
Agency for Development Cooperation for the financial and institutional
support for the organization of the Friends of Socotra meeting that took
place at the Botanic Garden of Palermo, Italy, 26–29 September, 2019.
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