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Potential importance of Socotra dragon’s blood tree cloud forests and woodlands for capturing horizontal precipitation
Abstract
The importance of populations of the Socotra dragon’s blood trees (Dracaena cinnabari Balf.f., 1882) for horizontal precipitation capture was estimated for the first time. Dragon’s blood trees (Asparagaceae) inhabit semiarid cloud forests with low levels of rainfall that strongly depend on additional moisture from fog and clouds. Our estimation was based on a detailed description of the aboveground biomass structure of stands of the dragon’s blood trees on Socotra Island. The aboveground biomass was described using non-destructive methods. An example of a well-preserved forest was measured in terms of the basic biometric characteristics of each tree, and the trees were divided into three classes based on crown projections. For each class, we took detailed measurements of one representative tree. All measured and counted growth characteristics were converted to the stand level. The tree population at the whole island level was investigated using remotely sensed data. The estimation of horizontal precipitation was performed using detailed and precise evaluation of the available climate data in half-hour intervals over the period of June 2009 and June 2010 and the ambulatory direct measurements (12.6.2009–26.6.2009). The mean annual horizontal precipitation below the crown of the dragon’s blood tree was estimated to be 792 mm in the highest (951–1545 m a.s.l.), 373 mm in the middle (601–950 m a.s.l.) and 46 mm in the lowest (180–600 m a.s.l.) altitudinal zones. Our model showed that the horizontal precipitation exceeded 40% of the total annual precipitation. The decline in the dragon’s blood tree forest could therefore cause the loss of additional water from the island’s hydrological cycle.
... The East African-Indian monsoon system strongly influences the climate of Socotra, with a biannual migrating intertropical convergence zone between the northern hemisphere winter position and the southern Indian Ocean summer position (Scholte and De Geest 2010). The summer monsoon accurs from May to September, and the winter monsoon lasts from October to January (Scholte and De Geest 2010;Kalivodová et al. 2020). ...
... This is also consistent with the finding that goats are let in quite often in October and December. The female becomes pregnant during the rainy season, which runs from May to September (Kalivodová et al. 2020) and from October to January (Scholte and De Geest 2010), meaning that there is enough food to cover the energy needs for fetal development. The same reproductive strategy is used, for example, in Mexico (Mellado et al. 1996). ...
... Notably, as depicted in Fig. 7, goats produce the highest milk yields during the rainy season. Favorable weather and better mountain greenery conditions have been confirmed by Kalivodová et al. (2020), who noted that horizontal precipitation could account for up to two-thirds of the total moisture at higher altitudes. However, other factors can also influence goats' dairy yields, such as breed, age, nutrition, environmental conditions (Erduran and Dag 2021), parity, season of kidding, and stage of lactation (Ciappesoni et al. 2004). ...
We examined the socioeconomic importance of goat farming on the island of Socotra. The study included 154 participants from various areas. These data were collected via a questionnaire and statistically analyzed using the Bayesian approach and Kruskal–Wallis test to offer insights into the subject matter. The collected data included important quantitative parameters, such as feeding, watering, herd composition, milk production, and mortality, as well as subjective parameters, including the breeders’ reasons for keeping goats. Our study revealed that the main reason for keeping goats on Socotra Island is livelihood purposes (60%), followed by cultural reasons (22%), whereas 18% of respondents keep goats as a companions. In terms of herd composition, generally a Socotri family keeps an average of 107 individuals per herd, of which 59% are adult females, 32% are young under six months, and 9% are adult males. Reproduction patterns indicate that the goats breed twice a year, primarily in May and October. For milk production, goats on Socotra produce an average of 368 ml/day on an annual basis, and the highest production is observed in the mountains. The study also revealed that goats are primarily slaughtered for social reasons, such as family attendance and weddings (55%). According to the respondents, the main cause of mortality in goats was disease (40%). The results of this study have implications for understanding the management of goat farming on the island and conserving the island’s biodiversity.
... Rejžek, et al. [17] considered D. cinnabari as a nurse tree with high ecological importance for biodiversity maintenance; every fallen tree can lead to decreases in the populations of other endemic plant species. Due to its ability to capture horizontal precipitation, the decline of the D. cinnabari population may increase aridification of the land which, in addition to overgrazing, makes natural regeneration even more difficult even though this species is well adapted to droughts [12,18,19]. Furthermore, D. cinnabari plays a crucial cultural role for the indigenous communities of Socotra, providing valuable resin and other non-timber plant products that have a wide range of medicinal and other ethnobotanical uses [5]. ...
... Moreover, these trees play an important ecological role for the entire island. This tree species helps to maintain biodiversity, has broad ethnobotanical uses and, as a part of cloud forests brings huge input of water for the hydrogeological cycle of Socotra [5,18,57]. The unique umbrella-shape of the crown constitutes a fundamental natural system that traps humidity brought by the ocean breeze and helps recharge the shallow aquifers of the island [18]. ...
... This tree species helps to maintain biodiversity, has broad ethnobotanical uses and, as a part of cloud forests brings huge input of water for the hydrogeological cycle of Socotra [5,18,57]. The unique umbrella-shape of the crown constitutes a fundamental natural system that traps humidity brought by the ocean breeze and helps recharge the shallow aquifers of the island [18]. Therefore, the disappearance of these dragon's blood trees would have a significant impact on the freshwater resources [18], biodiversity [58], and touristic attractiveness of Socotra [30], in addition to the potential loss of key human-nature linkages that the island is known for. ...
We examine the distribution of Dracaena cinnabari, the Socotran Dragon’s Blood Tree, an endangered species endemic to the island of Socotra (Yemen)—and we propose an accessibility approach to its conservation, taking the proximity of local communities and land users into account. Using the present occurrence of D. cinnabari, we applied a machine learning algorithm (random forest classifier) to estimate the potential distribution of the species across the island (overall validation accuracy of 0.91) based on available climatic and physiographic parameters. In parallel, we used an accessibility methodology to generate a map of the energy cost of accessing potential areas from the villages. This community-focused accessibility map, combined with the potential distribution map of Dracaena cinnabari, could contribute to decision-making processes related to long-term ecological restoration and reforestation activities. With our case study, we wish to emphasize that user-focused efforts and the implementation of sustainable land practices should play key roles in conserving endangered tree species.
... Socotra's climate is heavily influenced by the East African-Indian monsoon system, characterized by a biannual migrating intertropical convergence zone that shifts between its northern hemisphere winter position and southern Indian Ocean summer position [17]. The monsoon seasons are divided into two periods: the summer monsoon from May to September, and the winter monsoon from October to January [17,18]. The mean annual rainfall and temperature, measured in a network of meteorological stations from 2002 to 2006, were 216 mm and 28.9°C at high altitudes, amounting to 800 mm [17]. ...
... The island of Socotra remains poorly studied, and greater attention should be directed toward identifying these intermediate-host snails. Larvae were detected in droppings in November, with the rainy season beginning in October [17,18]. As the prepatent period for these species lasts 6-10 weeks [10], goats were probably infected at the beginning of this period. ...
Parasites play a significant role in biodiversity, yet research on these organisms remains limited, particularly in tropical and subtropical regions. Parasites are also an essential aspect of domestic animal husbandry, and their prevalence depends on various factors, such as husbandry conditions and the environment. However, no studies have been conducted on parasites affecting domestic animals on Socotra Island. This study aimed to investigate parasites in selected goat populations on the island using intravital fecal diagnosis. A total of 406 samples from adult goats across different locations (lowlands and highlands) and seasons (dry and rainy) were collected, fixed in 10% formalin, and transported to the Czech Republic for coprological examination using flotation and ether sedimentation methods. Statistical analyses, including partial canonical correspondence analysis (pCCA), the Monte Carlo permutation test, and the chi-squared test, revealed a high prevalence of gastrointestinal parasite infections, with 89% of goats infected. Eimeria spp. had the highest prevalence (76%). Co-infection was common, with 55.9% of goats infected with multiple parasites. Seasonality influenced parasitism, with other Protostrongylidae, Muellerius spp., and Trichuris spp. predominating during the rainy season, and Eimeria spp. and gastrointestinal strongylids predominating during the dry season. This first study on Socotra Island, Yemen, provides crucial insights into effective intervention strategies for controlling goat parasite infections.
... The climate of Socotra is mainly controlled by two monsoon seasons (Scholte, De Geest 2010). The summer monsoon lasts from May to September and is accompanied by strong winds (Scholte, De Geest 2010;Beresford et al. 2013); it affects the southern part of the island and mainly brings horizontal precipitation from clouds and fogs (Kalivodová et al. 2020). The winter monsoon mainly affects the northern part of the island, bringing rain (Scholte, De Geest 2010). ...
... obs.). Nurse shrubs may 'catch' the seeds that are carried by the wind from the mother tree and protect the seedling not only from grazing but also generate an improvement in the local environment by capturing humid air (Kalivodová et al. 2020), providing shade and promoting the humus layer. ...
... Fog is seen as a source of water in a local ecosystem, where the precipitation levels are incapable of fulfilling water requirements for both flora (Emery 2016;Jacobson et al. 2015) and fauna (Nørgaard and Dacke 2010;Parker and Lawrence 2001). The desert ecosystem is one such example where the vegetation is majorly dependent on fog for its moisture (Kalivodová et al. 2020;Lvončík et al. 2020;Riccardi et al. 2020;Lehnert et al. 2018) and nutrient (González et al. 2011) requirements. Hamilton and performed the most remarkable research that paved the way for studying the dependency of desert species on fog water; Seely and Hamilton (1976), reporting the fog basking physiology of tenebrionid beetle (Onymacris unguicularis, Lepidochora discoidalis, L. porti, and L. kahani). ...
... The presence of patches of rainforest found in the semi-arid climate of Chile is supported by the marine fog prevalent in the region; the windward side of the forest had maximum regeneration, whereas the leeward side had maximum mortality proving the significance of fog water in the region (del Val et al. 2006). There are many regions around the world, especially the tropical and subtropical regions where the presence of fog is a characteristic feature of the cloud forest, water loss due to transpiration in such forest type is primarily kept in check because of the wet and cold environment provided by fog (Regalado and Ritter 2021;Kalivodová et al. 2020;Goldsmith et al. 2013;Ritter et al. 2009) as well acting as a subsidiary water source (Berry et al. 2014). Mexican weeping pine species (Alvarado-Barrientos et al. 2014) of the montane forest also showed similar observations (Gotsch et al. 2014). ...
With the changing climate and environment, the nature of fog has also changed and because of its impact on humans and other systems, study of fog becomes essential. Hence, the study of its controlling factors such as the characteristics of condensation nuclei, microphysics, air–surface interaction, moisture, heat fluxes and synoptic conditions also become crucial, along with research in the field of prediction and detection. The current review expands for the period between 1976 to 2021, however, especially focused on the research articles published in the last two decades. It considers 250 research papers/research letters, 24 review papers, four book chapters/manuals, five news articles, 15 reports, six conference papers and five other online readings. This review is a compilation of the pros and cons of the techniques used to determine the factors influencing fog formation, its classification, tools and techniques available for its detection and forecast. Some recent advanced are also discussed in this review: role of soil properties on fogs, application of microwave communication links in the detection of fog, new class of smog, and how the cognitive abilities of humans are affected by fog. Recently India and China are facing an emergence and repetitions of fog haze/smog and thus their policies initiatives are also briefly discussed. It is concluded that the complexity in fog forecasting is high due to multiple factors playing a role at multiple levels. Most of the researchers have worked upon the role of humidity, temperature, wind, and boundary layer to predict fogs. However, the role of global wind circulations, soil properties, and anthropogenic heat requires further investigations. Literature shows that fog is being harnessed to address water insecurity in various countries, however, coastal areas of Angola, Namibia and South Africa, Kenya, Eastern Yemen, Oman, China, India, Sri Lanka, Mexico, along with the mountainous regions of Peru, Chile, and Ecuador, are some of the potential sites that can benefit from the installation of fog water harvesting systems.
... Different areas are subjected to local climates within the main island due to the presence of elevated areas such as the Haggeher Mountains. In the higher eastern and some southern lower parts of Socotra, fog drip water captured by vegetation from clouds covering the highlands and mountains may precipitate (Mies and Beyhl, 1998;Kalivodová et al., 2020). A smaller northern part of Socotra Island lies in a rain shadow during the summer monsoon (Culek et al., 2006). ...
... In the higher plateaus around the average of 700 m a.s.l., the mean annual rainfall is 543 mm and the mean annual temperature is 22 C (Mad era et al., 2018). The highest elevations of the island that capture clouds are called wet centers or wet refugia (Miller and Morris, 2004), where the horizontal precipitation may exceed the rainfall (Kalivodová et al., 2020) and which play an important role in plant diversity. ...
The Socotra Archipelago contains islands of high conservation importance. Since 2003, the Socotra Archipelago is a UNESCO Man and Biosphere Reserve and since 2008 it was officially listed as a UNESCO Natural World Heritage Site. In addition, the Socotra Archipelago contains currently the only Ramsar Site of Yemen (Detwah Lagoon), and it has been declared as one of 200 WWF Global Ecoregions for its unique terrestrial ecosystems (xeric shrublands), the status indicated as critical/endangered by WWF. Even the freshwater ecosystems that harbor several endemics have been given a special status, as Socotra is recognized as one of the globally outstanding Freshwater Ecoregions of the World. Socotra is also part of the Horn of Africa Biodiversity Hotspot as recognized by Conservation International, and listed as a Centre of Plant Diversity by Plantlife International, ranked among the richest yet most threatened biodiversity areas on the Planet. The Archipelago was declared as its own Ecologically or Biologically Significant Marine Area (EBSA) at the Convention of Biological Diversity (CBD) meeting in 2016, and the same year as an Endemic Bird Area by BirdLife International, which listed several Important Bird Areas (IBAs) for the Archipelago. A number of endemic plants and vertebrates from Socotra have been included in the IUCN Red List, but updates are needed and very few of the many endemic invertebrates have been listed. However, the biodiversity of Socotra is increasingly affected by impacts that affect ecosystems globally, such as unsustainable resource use and global warming which are now visible in the islands. We discuss the main threats and list some general conservation needs in the Socotra Archipelago.
... Image from Google Earth, modified by Kay Van Damme extinction of a single individual or a small population, whether it belongs to a species of plants or animals, matters. 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 sheltered 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 (Kalivodová 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 warming and other, more direct, human interventions. ...
... The vegetation does not only play a key role in creating niches for other plant and animal species, but also may provide another important ecosystem 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. ...
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.
... The NE monsoon from November to March brings most of the rainfall, while the SW monsoon is drier and stormier (Scholte and De Geest 2010). The island has an average temperature of 28.9°C, and rainfall varies, with coastal areas receiving as little as 125 mm annually, while mountainous areas can receive up to 1000 mm, largely from fog (Scholte and De Geest 2010) and horizontal precipitation, which is critical for vegetation (Kalivodová et al. 2020). ...
Question
Plant–plant facilitation is a critical ecological mechanism in arid environments, influencing biodiversity and ecosystem resilience globally. Shrubs often serve as nurse species, enhancing tree regeneration and sheltering plant communities, particularly in overgrazed or degraded habitats. In this study, we examine the role of shrubs as nurse species in the Socotra Archipelago (Yemen), a biodiversity hotspot in which several endemic tree species, including the iconic frankincense ( Boswellia spp.), myrrh ( Commiphora spp.), and Socotran dragon's blood ( Dracaena cinnabari ) trees, are threatened. This is largely due to a lack of natural regeneration caused by the combined effects of overgrazing by goats, sheep, and climatic events such as extreme droughts and cyclones. To aid conservation of threatened trees in arid regions, nature‐based solutions are urgently needed to help tree regeneration. Effective nurse plants have this potential, particularly in arid environments. We therefore examined the role of thorny, poisonous, and/or unpalatable shrubs as nurse plants in sheltering threatened plant communities, with a focus on woody species in an arid insular context.
Study Area
The Socotra Archipelago (Yemen) situated in the western Indian Ocean, east of the Horn of Africa. It is a biodiversity sanctuary and a UNESCO Natural World Heritage Site.
Methods
Vegetation surveys were conducted in 144 paired plots under six common shrub species and adjacent open areas. Community data, environmental variables, and functional traits were analysed using RLQ and fourth‐corner analyses, while Linear Mixed Models (LMMs) evaluated the effects of environmental variables and nurse species on key functional traits based on Community Weighted Means (CWMs). Facilitation effects were quantified using the Relative Interaction Index (RII).
Results
Our analysis revealed significant variations in species composition and functional traits between under‐canopy and open‐area plots. Certain shrubs, such as Cebatha balfourii , facilitated significantly higher species richness under its canopy compared to open areas. Elevation and grazing pressure influenced these interactions, with notable effects on functional traits like the occurrence of legumes and tree growth forms. Buxus hildebrandtii was less effective in supporting species richness, while C. balfourii, Lycium sokotranum , and two Cissus species exhibited significant positive facilitation. The LMMs confirmed the importance of environmental variables and nurse shrub characteristics in shaping plant community dynamics.
Conclusions
The results highlight differences in the facilitative potential of the studied species, with some showing a stronger ability to act as nurse shelters through microhabitat amelioration and protection from herbivory. The presence of tree species under shrubs is confirmed, and the role of these nurse species in supporting diverse plant communities provides critical insights for conservation strategies, supporting biodiversity resilience and sustainable management in degraded landscapes like Socotra Island and other arid environments. Future efforts should focus on leveraging nurse shrubs to mitigate environmental pressures and enhance ecological restoration, in particular to help conserve range‐restricted and threatened plant species.
... A (sub)tropical arid climate governs the Archipelago (Scholte & De Geest, 2010); horizontal precipitation is of high importance for water availability and local vegetation (Brown & Mies, 2012;Kalivodová et al., 2020). ...
Societal Impact Statement
Conserving frankincense trees (Boswellia) is crucial for both ecological and socio‐economic reasons. Surveying these trees in the field and using remote sensing unmanned aerial vehicles in the Socotra Archipelago, we found that Socotran frankincense trees are threatened by forest fragmentation, overgrazing, and increasingly frequent extreme climate events. A better understanding of the distribution and the threats of these important insular species will improve the conservation policy of the local authorities and benefit local communities in the Socotra Archipelago. At the same time, this work serves as a good practice example to guide conservation efforts for other culturally important threatened tree species around the world, therefore helping to sustain local livelihoods, fostering ecological resilience, and supporting socio‐economic stability.
Summary
Globally, frankincense trees (Burseraceae: Boswellia) are increasingly under threat because of habitat deterioration, climate impacts, and the olibanum trade. Despite harboring nearly half of the species in the genus, up‐to‐date insights are lacking for the insular endemic frankincense trees of the Socotra Archipelago UNESCO (United Nations Educational, Scientific and Cultural Organization) World Heritage Site (Yemen).
We combined georeferencing of individual trees in the field with remote sensing applying unmanned aerial vehicles (UAVs) to evaluate Boswellia distribution and (sub)population sizes in the entire Socotra Archipelago.
We counted 17,253 trees across all 11 taxa and we surveyed almost 55% directly in the field, collecting individual information on threats and health indicators. We estimate that the current total population sizes of the relatively common Socotran Boswellia taxa (Boswellia elongata, Boswellia popoviana, and Boswellia ameero) consist of a few thousand mature individuals with fragmented distribution of which a large proportion occurs in highly disjunct relictual stands, while the more range‐restricted species survive only through a few hundred (Boswellia nana and Boswellia samhaensis) to fewer than a hundred trees (Boswellia scopulorum). Our field data show that the Socotran frankincense trees are threatened by fragmentation and overgrazing resulting in a lack of natural regeneration, in combination with effects of extreme climate events (e.g., higher frequency and intensity of cyclones and prolonged drought) and potential future infrastructure developments; the species are less impacted by resin collection.
We provide recommendations to strategize urgent protection of the declining Socotran frankincense trees, and we update their conservation status, resulting in an endangered status for seven and a critically endangered status for four taxa.
... Dragon trees comprise 10 arborescent species (Wilkin et al. 2012), all growing in seasonally arid climates with an annual rainfall of 200-500 mm and mean temperature between 18 and 20 °C (Marrero et al. 1998;Adolt and Pavlis 2004). Dragon trees are well adapted to capture horizontal precipitation (Nadezhdina et al. 2018) and their distribution is sometimes associated with seasonal cloud forests (De Sanctis et al. 2013;Kalivodová et al. 2020). Dragon trees are threatened by overexploitation, overgrazing and habitat degradation despite their economic and ecological values in dryland areas (Ghazali et al. 2008;Al-Okaishi 2020;Madera et al. 2020). ...
Dracaena ombet, a flagship tree species in arid ecosystems, holds a significant ecological, economic, and socio-cultural value. However, its persistence is currently under threat from both anthropogenic and natural factors. Consequently, the species has been listed as an endangered tree species on the IUCN Red List, requiring urgent conservation actions for its continued existence. To develop effective conservation actions, it is necessary to have information on the population dynamics of the species. A study was conducted in the lowland and midland agroecological zones (sites) within the Desa'a dry Afromontane forest, northern Ethiopia to analyze the population status of D. ombet and identify its site-specific threats. At each site, abundance, health status, diameter, height and threats of the species were collected using 60 sample plots (20 m × 20 m) distributed over six transects (500 m × 20 m) spaced one km apart. The study showed that the D. ombet population was characterized by low abundance and unstable structure. It was further characterized by a substantial number of unhealthy damaged and dead trees. The low abundance of the species with unstable age structure in the dry Afromontane forests can be attributed to various factors such as stem cutting and debarking, leaf defoliation, overgrazing, soil erosion, and competition from expansive shrubs. Alternative livelihood options for the local inhabitants should be introduced to minimize the overexploitation of D. ombet for subsistence use in the dry Afromontane forests. The impacts of overgrazing and soil erosion on D. ombet and its Desa'a habitats should also be addressed through the introduction of community-based exclosures and in-situ soil and water conservation practices, respectively.
... Increasing aridity due to ongoing climatic change is also negatively affecting the potential habitat of the Dragon's blood tree. The loss of Dragon's blood trees is also affecting the hydrological cycle as these plants capture horizontal precipitation [47]. ...
The Dragon’s blood tree (Dracaena cinnabari) woodland is one of the oldest surviving endangered forest communities on Earth. This unique endemic species of Dragon’s blood tree is famous since antiquity for its bright red resin “Dragon’s blood” and umbrella-shaped canopy. They are almost extinct everywhere except present as small habitats in Socotra Archipelago (Yemen), a UNESCO World Heritage Site. In the last two decades, there has been a significant decline in Dragon’s blood tree population in the archipelago, posing a threat to its existence. We attempt to review the status of Dragon’s blood tree population in Socotra Archipelago, factors affecting its survival, and the status of conservation efforts propose recommendations to preserve this flagship species.
... We found the better developed seedlings often surrounded by stones. Such semiarid seasonal cloud forests have been shown to be important for the hydrological cycle (Hildebrandt et al. 2007;Eltahir 2011;Marzol et al. 2011;Kalivodová et al. 2020;Riccardi et al. 2020). Decline of these forests, therefore, may lead to local desertification and decreasing ability of tree regeneration Eltahir 2006, 2008). ...
... The highest crown age was estimated to be 198 years in trees with 30 branch orders, according to the fit model [21]. Therefore, our results are valid only for D. cinnabari on the Firmihin Plateau, as at the higher altitudes of Skant, fog is more likely to act as an important source of horizontal precipitation [47], leading to more suitable conditions for growth. ...
Background: Dracaena cinnabari is a monocot species that does not form annual tree rings; thus, its age can only be estimated. This species is threatened by low natural regeneration, with an evident absence of younger individuals most likely caused by overgrazing; therefore, knowing trees’ ages is important for possible conservation strategies; Methods: Data collection was conducted on the Firmihin Plateau on Socotra Island (Yemen) in 2021, and the diameter at breast height (DBH) of 1077 individuals was measured, the same as those established on monitoring plots 10 years before the current measurement. The 10-year radial stem increment and DBH obtained in 2011 served as a basis for the linear model from which the equations for the age calculation were derived. Results and Conclusions: A direct model of age estimation for D. cinnabari was developed. According to the fit model, the age in the first (10.1–15 cm) DBH class was estimated to be 111 years, while that in the last DBH class (90.1–95 cm) was estimated to be 672 years. The results revealed that the previously used indirect methods for D. cinnabari age estimation were accurate.
... On Socotra Island, which has a high ratio of endemic species [38], every tree counts because entire trophic chains depend on the Dragon's Blood Trees as primary producers, including other endemic organisms [39][40][41][42]. With every dead tree, we risk losing not only the endangered tree species itself but also all its ecosystem services (e.g., tourism, local medicinal uses, capturing horizontal precipitation, etc.), among which is their provision of a crucial link to the cultural identity of the Socotri and the importance of the tree as a vital habitat for sympatric endemic biodiversity. ...
The last remaining Dragon Tree Forest on Earth survives on a small plateau (Roqeb di Firmihin) in Socotra Island (Yemen). The Socotran Dragon’s Blood Tree (Dracaena cinnabari Balf. f.) is endemic to the Socotra Archipelago UNESCO World Heritage Site. Being a culturally important and endangered tree species, its conservation is a priority. Despite this, a complete inventory of the Firmihin Dracaena forest (14.9 km²) has never been attempted before. We applied the use of unmanned aerial vehicles (UAVs) for the first time in conserving the Socotran Dragon’s Blood Tree. A pair of UAVs (small drones) were used during field surveys in 2021 to spatially describe individual tree positions, tree density, mortality, and the forest age structure. Aerial images were processed into a single orthophoto image of high spatial resolution (8 cm/pixel) used for detailed analysis. We applied image-enhancement techniques, used object-based classification, and corrected every entry manually during the inventory process. In total 35,542 individual living trees and 2123 uprooted trees were inventoried. The mean age of the forest, based on crown age (derived from crown size) was estimated at an average of ca. 300 years (291.5 years) with some individuals older than 500 years. Our analysis reveals that the trajectory of recent cyclones and the average direction of fallen trees in Firmihin are correlated, suggesting that intensified winds (as a result of global warming) catalyze the decline of the overmature forest. Our study illustrates the use of UAVs in collecting crucial data for the conservation and threat assessment of endangered tree species in Socotra, and regular drone inventories could be applied (e.g., after future cyclone events or landslides) to better evaluate the status of these vulnerable island ecosystems.
... The first natural seedlings appear in September with last summer monsoon rainfalls and their growth is supported by showers within the winter monsoon from October to December [9]. Additionally, high air humidity and horizontal precipitation in July and August [29] can substantially contribute to the survival of young seedlings. Similarly, B. ovalifoliata seed germination is connected with the first rainfalls [25]. ...
The endemic Boswellia species (Burseraceae) on Socotra Island (Yemen) are of great local significance due to their various local ethnobotanical uses. However, despite the fact that these trees are endangered, little is known about their biology. We tested seed germination rates in controlled experiments (trials of 21 days) for two subsequent years and for nine endemic taxa of Boswellia occurring on Socotra Island. For this, seeds were collected island-wide from a wide range of localities and for several populations per species. We observed differences in germination among Boswellia species, among species and localities and among both years, which indicates that the development of seeds is strongly affected by external ecological factors. Although we noted a large variation in seed germination (relatively high in Boswellia socotrana), and half of the species showed relatively low mean daily germination, our study indicated that all endangered endemic Frankincense Tree taxa of Socotra harbor the potential for in situ conservation through recruitment, given that known impacts can be reduced in local replantation areas (e.g., grazing).
... Subsequently, the air descends, losing its watery content on the opposite slope. This causes a constant humidity in Anaga, which leads to the capture of horizontal precipitation that (Troll and Carracedo 2016) produces the Foëhn phenomenon (Kalivodová et al. 2020). Therefore, the geographical situation of Anaga, located in the northeast of Tenerife, its altitude and the constant humidity on the slopes, make this area of Tenerife one of the areas with the highest rainfall compared to the rest of the island (Diez-Sierra and del Jesus 2020). ...
Rockfalls are frequent and damaging phenomena that occur on steep or vertical slopes, in coastal areas, mountains and along coastal cliff. Water, in different forms, is the most common triggered factor of rockfalls. Consequently, we can consider that precipitation is the most influential factor for slope instabilities and it influences almost all other water parameters. Besides, the specific geology of the Anaga nature reserve in the volcanic island of Tenerife, together with its steep landscape, contributes to the instability of the slopes and frequent rockfalls. Recently, due to climate change and global warming, the annual precipitation/rainfall has declined but the number of heavy storms, associated with intense rainfall and strong winds, events that exceed precipitation thresholds in a brief period has increased which triggers slope movements. This paper describes the analysis of information on rainfall-induced rockfalls in Anaga, Tenerife (Canary Islands), to forecast rock failures of social significance and to improve the capability to respond and emergency decision making. To define reliable thresholds for a certain area, we analized information during the period 2010–2016, reconstructed the rockfall events, and statistically analyzed the historical rainfall conditions that led to landslides. The summary graph correlating precipitation to the probability of occurrence of an event was plotted. Statistical and probability graphs were made with the direct relationship between the number of rockfall events and total rainfall in that period by examining the maximum daily precipitation, not only on the day of the event but up to 3 days before. Hence, the results of this study would serve as a guide for the possible forecasting of rainfall-induced rockfalls, especially for road maintenance services, so that they can be on alert or mobilize the necessary resources in advance depending on the intensity of the expected rainfall.
... Often young trees are missing because natural regeneration is reduced by the overgrazing of livestock [3,5,[10][11][12][13][14][15][16][17][18]. Dragon trees can be found in areas characterized by a predominantly arid tropical climate with a monsoon seasonality bringing wet air in the form of clouds and fog [19,20]. They are well adapted morphologically and physiologically to capture water in such conditions [21][22][23]. ...
Few of the about 190 species currently described in the plant genus Dracaena [...]
... The loss of each tree leads to the decrease in biodiversity, dragon´s blood trees are important nurse trees [ 46 ] and habitats for the animals [ 107,108 ] also. The loss of dragon´s blood trees may also affect the hydrological cycle as these plants capture horizontal precipitation [ 109 ]. ...
Background
In this study, we present and analyze toponyms referring to Socotra Island’s endemic dragon’s blood tree (Dracaena cinnabari) in four areas of the Socotra Archipelago UNESCO World Heritage site (Republic of Yemen). The motivation is understanding of the past distribution of D. cinnabari trees which is an important part of conservation efforts by using ethnobotanical data. We assumed that dragon’s blood trees had a wider distribution on Socotra Island in the past.
Methods
This research was based on field surveys and interviews with the indigenous people. The place names (toponyms) were recorded in both, Arabic and indigenous Socotri language. We grouped all toponyms into five different categories according to the main descriptor: Terrain, Human, Plant, Water and NA (unknown). In addition, this study identified current and historical Arabic names of dragon’s blood trees of the genus Dracaena, through literature review.
Results
A total of 301 toponyms were recorded from the four study areas in Socotra Island. Among names related to plants, we could attribute toponyms to nine different plant species, of which six names referred to the D. cinnabari tree, representing 14.63% of total phytotoponyms in the category. Three historical naming periods prior to 2000 could be identified. The most commonly used Arabic name for dragon’s blood trees (D. cinnabari, D. serrulata. D. ombet) appears to be “ahrieb” "إعريهب", its resin “dum al-akhawin” “دم الأخوين”, while derived (mixed-cooked) products are called “edah” “إيدع”; while regionally different names can be found.
Conclusion
The place names that refer to D. cinnabari are herein suggested to represent remnant areas of once large populations. The toponyms may therefore support known hypotheses based on climate models that D. cinnabari had a wider distribution on Socotra Island in the past. This study also confirmed the historical importance of dragon’s blood
... We found the better developed seedlings often surrounded by stones. Such semiarid seasonal cloud forests have been shown to be important for the hydrological cycle (Hildebrandt et al. 2007;Eltahir 2011;Marzol et al. 2011;Kalivodová et al. 2020;Riccardi et al. 2020). Decline of these forests, therefore, may lead to local desertification and decreasing ability of tree regeneration Eltahir 2006, 2008). ...
We assessed seven decades of change in the largest known population of the endangered endemic Boswellia elongata Balf. F. (Burseraceae) on Socotra Island (Yemen). To quantify the population change we evaluated tree number and locations on digitized images from various sources in the period 1956–2017 and combined this with direct field measurements of the population between 2011 and 2017. Our study reveals that the Homhil Nature Sanctuary B. elongata population shows a continuous decline since 1956. The steady but slow natural decline was strongly accelerated by two catastrophic cyclones in November 2015, when 38% of the trees were directly destroyed by strong winds. During the following 2 years 29% of the remaining trees died additionally. The remaining population has a bell-shaped size distribution; most trees are around 40 cm in diameter (range 18 to 70 cm). Tree ring analysis of 11 dead trees with a diameter of 29 to 44 cm without bark, resulted in estimated tree ages between 80 and 101 years. We estimate that similar-sized trees showing strong signs of senescence have a maximum age of a little over 100 years. The age structure of the Homhil population is, therefore, unbalanced with large sized trees prevailing. Natural regeneration is absent for decades. Viable seeds are available and have been shown to germinate, but the development of seedlings into saplings is a bottleneck. If the decline continues at the current rate, only 30 trees will remain there in 2036. Protection, planting and awareness activities are needed to keep this unique frankincense tree in Homhil Nature Sanctuary.
Citation: Maděra P., Attorre F., Van Damme K. (2025): New knowledge in dragon tree research. J. For. Sci. Abstract: Dragon trees, arborescent members of the genus Dracaena (Asparagaceae), provide a wide range of ecosystem services and have been ethnobotanically important plants since ancient times. Currently, their relictual distribution is fragmented, populations are isolated and often under threat. We provide a brief overview of scientific studies and the state of knowledge on dragon trees published since 2020, when the last review was published. More than 120 papers dealing with dragon trees have appeared, indicating a significant interest in their research, cultural uses and conservation. The most intensively investigated species are Dracaena cochinchinensis, D. cinnabari, D. draco and D. cambodiana. Almost half of the papers deal with the chemical composition of resin and its bioactivity, in addition to studies on ecology , conservation and genetics. Only a few studies are devoted to taxonomy and ethnobotany.
Macaronesian oceanic islands harbour the emblematic relict Canary Islands dragon tree (D. draco (L.) L. subsp. draco, Asparagaceae). Historical records suggest that its populations, nowadays restricted to Tenerife and Gran Canaria islands (Canaries) and Madeira Island, had a much wider geographic range in the past. In this study, we aimed at (i) testing whether current D. draco subsp. draco populations are relicts of a former wider distribution because of human impact, (ii) whether those populations are at risk with future climate change and (iii) targeting priority zones for in situ conservation face to global changes. We based our approach on the comparison between actual distribution, land use data and suitable area modelled via Environmental Niche Models (ENM) and projected under future climate change scenarios. ENM were calibrated at two different phylogenetic levels to account for taxonomic uncertainties. We found that: (i) The Canary Islands dragon tree populations occupy only 3–4% of their suitable area, reflecting their relict status due to past habitat alteration and overexploitation; (ii) Their response to future climate change varies depending on ENMs and climate change scenarios, but some projections suggest that climate may become unsuitable within their actual distribution range; (iii) Finally, we provide a map of zones to prioritize, specifically semi-natural areas predicted to remain suitable in the future, for in situ recovery operations.
The endangered and endemic Nubian dragon blood tree, Dracaena ombet, has been feared extirpated from core distribution areas in the Red Sea Hills, Sudan, after reported mass death events in the 20th century. Populations of dragon tree species are generally reported to be in decline, with a noticeable lack of recruitment and possible poor resilience. Rare recruitment events are, however, normal for species with remnant population dynamics, and when eventually occurring, such events can restore seemingly degraded populations. In response to recently reported observations of dracaena saplings in a historically core distribution area of the Red Sea Hills, we assess the status of this long-lived arboreal species. We describe a current realized niche, investigate a potential range shift by comparing the spatial distribution of saplings and older individuals, and assess population recovery based on pre-disturbance system identity derived from qualitative, historical observations. We document a beginning recovery of the dracaena population in the study area. Around half of the mapped population are individuals in the sapling stage, and they are in good health. Its current realized niche is described by higher altitudes, steeper slopes, more concave landscape forms and east-facing aspects compared to areas where dracaena individuals are absent. However, for the new generation of dracaena saplings we find signs of a leaning range shift where saplings are shifted towards higher altitudes near the mist-influenced escarpment. A full collapse and eventual extirpation of the endangered Dracaena ombet population may at best be averted, or at least delayed in the study area. Our resilience analysis indicates that a full recovery will be a slow process due to the inherent natural climate variability of arid lands, only allowing sporadic regeneration. Considering this species’ information legacy, saplings seem to be well equipped to survive such variability, but perhaps within a restricted safe operating space. Conservation measures should therefore be taken to secure the survival of the new generation along with broader spatial scale studies to confirm whether our findings reflect a regional phenomenon.
Background
In this study, we present and analyze toponyms referring to Socotra Island’s endemic dragon’s blood tree ( Dracaena cinnabari ) in four areas on the Socotra Archipelago UNESCO World Heritage site (Republic of Yemen). The motivation is the understanding of the past distribution of D. cinnabari trees which is an important part of conservation efforts by using ethnobotanical data. We assumed that dragon’s blood trees had a wider distribution on Socotra Island in the past.
Methods
This research was based on field surveys and interviews with the indigenous people. The place names (toponyms) were recorded in both Arabic and the indigenous Socotri language. We grouped all toponyms into five different categories according to the main descriptor: terrain, human, plant, water, and NA (unknown). Also, this study identified current and historical Arabic names of dragon’s blood trees of the genus Dracaena through literature review.
Results
A total of 301 toponyms were recorded from the four study areas in Socotra Island. Among names related to plants, we could attribute toponyms to nine different plants species, of which six toponyms referred to the D. cinnabari tree, representing 14.63% of the total phytotoponyms in the category. Three historical naming periods prior to 2000 could be identified. The most commonly used name for dragon’s blood trees ( D. cinnabari , D. serrulata , D. ombet ) appears to be “ ahrieb ” “إعريهب” and its resin “ dum al-akhawin ” “دم الأخوين,” while derived (mixed-cooked) products are called “ eda’a ” “إيدع,” while regionally different names can be found.
Conclusion
The place names that refer to D. cinnabari are herein suggested to represent remnant areas of once large populations. Therefore, the toponyms may support known hypotheses based on climate models that D. cinnabari had a wider distribution on Socotra Island in the past. This study also confirmed the historical importance of dragon’s blood.
Umbrella species are defined as species that can be rare and sensitive to human disturbance, whose protection may confer the protection of other co-occurring species. The dragon’s blood tree Dracaena cinnabari Balf.f. was already considered an umbrella species on Socotra Island (Indic Ocean, Yemen) due to its ecological importance for some native biota. We studied the reptile community living on D. cinnabari from Socotra Island. We sampled reptiles on trees across most D. cinnabari populations and applied co-occurrence and network partition analyses to check if the presence of reptiles on D. cinnabari populations was random or structured. Regardless of its patched and scarce actual distribution, we report the use of this tree as a habitat by more than half of the reptile community (12 endemic reptiles). Co-occurrence and network partition analyses demonstrate that this community is structured across the distribution of dragon’s blood trees, reflecting complex allopatric, vicariant, and biotic interaction processes. Hence, these trees act as micro-hotspots for reptiles, that is, as areas where endemic and rare species that are under threat at the landscape scale co-occur. This Socotra endemic tree is currently threatened by overgrazing, overmaturity, and climate change. Its protection and declaration as an umbrella species are expected to benefit the reptile community and to protect evolutionary processes that are partially driven by the ecological links between reptiles and this tree. To our knowledge, no tree species has been proposed as an umbrella species for island vertebrate endemics so far, highlighting the ecological uniqueness of Socotra Island.
Populations of Dracaena serrulata are disappearing at an alarming rate in the Arabian Peninsula. They are being destroyed by herders who use the leaves as fodder for camels, goats, and sheep during the dry season. Up until now, precise information about the current distribution and population status of D. serrulata in Oman have not been published. To fill this gap, the main aim of this work was to map the species distribution in the Dhofar Mountains (Oman) and to define the conservation and health status of the populations. Three isolated sub-populations of the study species were defined and mapped: the Jabal Samhan, Jabal al Qara, and Jabal al Qamar sub-populations. Dracaena serrulata occupies an area of 227 km² in the Dhofar Mountains. More than 43,000 trees were counted, and 2387 trees were inventoried in total. The Jabal Samhan sub-population is an example of an extensively damaged population with 59% of the trees recorded as dead and only 21% healthy trees. Populationsin the western portions of the Dhofar Mountains., Jabal al Qamar, and Jabal al Qara are comparatively abundant stands of healthy trees with a higher proportion of seedlings. The health of trees is strongly influenced by accessibility and precipitation provided by the southwest summer monsoon: the healthy individuals predominate on the steep terrain along the seaward facing cliffs.
Research Highlights: The first model for crown age estimation was developed for Dracaena ombet Heuglin ex Kotschy and Peyr. and D. draco subsp. caboverdeana Marrero Rodr. and R. Almeida. Background and Objectives: Dracaena species are monocotyledon trees without annual tree rings. Most arborescent dragon tree species are endangered; thus, it is important to determine the age structures of these populations for proper conservation management strategies, and for modelling of population trends. For these reasons, it is necessary to develop a methodology of crown age estimation. Materials and Methods: Field data were collected in the Desa’a Forest (Ethiopia) and in Santo Antão (Cape Verde Islands). Trees within each age class, as expressed by the number of branch orders, were measured. The diameter at breast height, tree height, stem height, number of branch orders, number of all leaf rosettes and number of flowering leaf rosettes within the crown were recorded for each sampled tree. The flowering probabilities were counted as input data for the model used. Results: The duration of the interval between flowering events was 5.23 years for D. ombet and 4.94 years for D. draco subsp. caboverdeana. The crown of the oldest tree of D. ombet with 18 branch orders was estimated to be 94.2 years old, and the crown of the oldest tree of D. draco subsp. caboverdeana with 22 branch orders was estimated to be 108.6 years old.
Detailed, three-dimensional modeling of trees is a new approach in botanical taxonomy. Representations of individual trees are a prerequisite for accurate assessments of tree growth and morphological metronomy. This study tests the abilities of 3D modeling of trees to determine the various metrics of growth habit and compare morphological differences. The study included four species of the genus Dracaena: D. draco, D. cinnabari, D. ombet, and D. serrulata. Forty-nine 3D tree point clouds were created, and their morphological metrics were derived and compared. Our results indicate the possible application of 3D tree point clouds to dendrological taxonomy. Basic metrics of growth habit and coefficients derived from the 3D point clouds developed in the present study enable the statistical evaluation of differences among dragon tree species.
This article is a broad review focused on dragon trees—one of the most famous groups of trees in the world, well known from ancient times. These tertiary relicts are severely endangered in most of the area where they grow. The characteristic features of the dragon tree group are described and the species belonging to this group are listed. This review gathers together current knowledge regarding the taxonomy, evolution, anatomy and morphology, physiology, and ontogeny of arborescent dragon tree species. Attention is also paid to the composition, harvesting, medicinal, and ethnobotanical use of the resin (dragons’ blood). An evaluation of population structure, distribution, ecology, threats, and nature conservation forms the final part of the review. In the conclusions we recommend further avenues of research that will be needed to effectively protect all dragon tree species.
Unsustainable overgrazing is one of the most important threats to the endemic and endangered population of dragon’s blood tree (Dracaena cinnabari) on Socotra Island (Republic of Yemen). However, there is a lack of information about the exact population size and its conservation status. We estimated the population size of D. cinnabari using remote sensing data. The age structure was inferred using a relationship between crown projection area and the number of branch sections. The conservation importance of each sub-population was assessed using a specially developed index. Finally, the future population development (extinction time) was predicted using population matrices. The total population size estimated consists of 80,134 individuals with sub-populations varying from 14 to 32,196 individuals, with an extinction time ranging from 31 to 564 years. Community forestry controlled by a local certification system is suggested as a sustainable land management approach providing traditional and new benefits and enabling the reforestation of endemic tree species on Socotra Island.
Dracaena cinnabari is a relict of the remote Socotra Island (Yemen) where it grows at higher altitudes with the frequent occurrence of fogs. D. cinnabari as the only representative of the dragon tree group creates woodlands and forests on the Socotra Island. It is not clear what mechanisms allow this relict arborescent monocot to survive harsh climate and poor soil of karst rocks there. In this work, we conducted long-term sap flow monitoring in the stem and roots of the mature D. cinnabari plant during the driest period of year between two regular monsoons. We aimed to reveal plant responses to a range of environmental conditions and to understand mechanisms of drought survival by this woody monocot. Several following features of sap flow performance were found: high flow sectoriality in the stem and in roots corresponding to the intensity of insolation, free lateral flow, higher stem integrity compared to roots, internal storage replenishment from the fog followed by increased transpiration presumably from the refilled stem storage. Results indicate that in studying the sap flow dynamics in the mature D. cinnabari tree, plant water storage should be included in the analyses in addition to soil water availability and intensity of evaporating demands. The ability to replenish succulent woody organs from atmospheric water and to survive long periods of drought from the internal supply distinguishes the behavior of this short-rooted arborescent monocot from the known strategies of deep-rooted trees in arid areas.
Dragon’s blood tree, a flagship endemic species of Socotra, is threatened with extinction due to lack of natural regeneration, likely because of goat herbivory and/or climatic factors. Loss of dragon’s blood tree would result in loss of other native flora, heightening the importance of formulating a conservation strategy for it. Although artificial afforestation might be used to offset the lack of natural regeneration, it would have to overcome the same threats faced by naturally occurring seedlings. Moreover, there is no published information on the growth dynamics of seedlings in plantations in situ on Socotra. To fill this information gap, we compared seedling growth (total plant height, leaves number, stem height, stem diameter) over an 8-year period after planting at three sites that differed in the degree to which goats were excluded and in whether they were watered regularly over the period. In addition to developing a new classification of the growth stages, which will enable better tracking of population dynamics, we found that continuous goat exclusion was necessary to prevent seedling mortality. Also, although seedling growth overall was slow, growth parameters of regularly irrigated seedlings ranged from 156% to 446% of those not regularly watered, suggesting that this treatment can speed seedlings’ escape from goat browsing. For the dragon’s blood tree and likely for other taxa within this group, extremely slow growth and long generation times suggest that conservation and restoration efforts will require a commitment to active management that will last decades, rather than a short-term approach.
Micromorphological features of the leaf epidermis and the inner structure of leaf tissues of eight arborescent taxa of the genus Dracaena were analysed using light and scanning electron microscopy. The plants are xeromorphic or mesomorphic. Their leaves are isobilateral and amphistomatic, and the stomata are anomocytic and tetracytic. The mesophyll in all the species is divided into an outer chlorenchyma and a central region with colourless water-storage cells, chlorophyll cells and vascular bundles. Water-storage cells have wall bands and reticulate thickenings on the walls. The article describes and illustrates several new quantitative and qualitative leaf characters of the dragon tree group. Our findings can be used to identify the dragon tree group leaves, while the shape of epidermal cells and stomata types may be useful in the identification and classification of fragments of fossil leaves. We conclude that D. ombet and D. schizantha are not two distinct species, but should be treated as subspecies of D. ombet. Leaf characters, especially stomata depth on adaxial epidermis, height of adaxial epidermal cells and the presence and thickness of hypodermal fibre bundles markedly differ between geographical groups: Macaronesian species (D. draco and D. tamaranae), the species found in East Africa and Arabian Peninsula (D. ombet subsp. ombet, D. ombet subsp. schizantha, D. serrulata and D. cinnabari) and Southeast Asian species (D. kaweesakii and D. jayniana).
This review aims to focus on the Nubian dragon tree, which is a distinctive mark of the Gabal Elba area and is native to that part of Egypt. The dragon trees grow slowly, long-lived, umbrella-shaped, with sword-shaped leaves and found in the semi-desert area, where they grow on inaccessible slopes. The average precipitation on the Gabal Elba area, where the Nubian dragon trees are found is not more than 50 millimeters per year, but the unique location of the mountain in front of the Red Sea and its height about 1435 m, captures water vapour and thus increase the precipitation rate to 400 millimeters per year. The Nubian dragon trees are threatened due to the change of their habitat, over-grazing, the diseases and harmful insects; however, the main factor influencing the Nubian dragon tree is the extreme drought. From total 1450 trees recorded only 870 trees have survived while 580 trees were dead, which represents about 60% survival and mortality about 40%. The Nubian dragon trees have aesthetic, medicinal, as well as commercial values. One trail succeeded in propagating of Dracaena ombet. The target species was recorded to be endangered and consequently, a plan of conservation should be prepared, fortunately, all the individuals of the population are located inside the Gabel Elba as a protected area, which helps managing the population. Moreover, plant propagation trials should be considered as well as establishing gene bank, conserving its genetic resources. Eventually Dracaena ombet is a unique medicinal plant that needs to be preserved in these natural habitats.
For the first time, in situ field measurements of sap flow were conducted in adult Dracaena cinnabari plant native to the arid tropical climate of Socotra Island. The heat field deformation (HFD) method was applied using both single and multi-point sensors to study azimuthal and radial sap flow variability in stem, roots and first-order branches over two weeks during a winter monsoon. The main aim of this work was to monitor sap flow in adult D. cinnabari in-situ to better understand its physiological adaptation to extreme arid environments. The second aim was to compare our results with earlier sap flow measurements in adult D. draco uing the same HFD method. The last question we wanted to answer was comparison of sap flow measurements in both, young and adult Dracaena species. We found that sap flow magnitude is low and of a similar range in all observed D. species. High sap flow variability was recorded in different parts of adult D. cinnabari plant which changed throughout the day responding to interplay between intrinsic and extrinsic water potential gradients induced by sunlight. Maximum sap flow levels had variable pattern around stem in response to sun exposure, similarly as it was observed in adult D. draco plant. Sensors installed tangentially in stem xylem showed that water transport in adult D. cinnabari may move in lateral direction. This work also presents several methodological aspects detected from earlier observations of dicots which proved to be more pronounced in adult D. species. These methodologies relate to interpreting negative sap flow rates in conjunction with established axial flow reversal during hydraulic redistribution usually occurring under low evaporative demands and dry soil. Conversely, flow reversal during the day under high evaporative demands and wet soil may designate lateral water movement induced by internal water redistribution.
The Kingdom of Saudi Arabia (KSA) is an arid dessert with less than 100 mm yearly rainfall in addition to a high-water consumption per capita. The collection of fog water is a simple and sustainable technology and may offer a supplementary water supply. Data were collected for a whole year from the Rayda reserve weather station, and two standard fog collectors (SFCs) were installed near the weather station. The results indicated that the average water collected by the local mesh was 6.7 L/m2/day, compared with 5.5 L/m2/day collected by the imported mesh. The highest quantity of water was collected in March by the local mesh, at 22 L/m2/day. The effectiveness of the fog collection was calculated and compared with the international standards. The obtained results indicate that fog can be utilized as a supplementary water source for the agriculture sector in the southwest KSA.
Socotra Island (Republic of Yemen) is inhabited by descendents of a primeval south-Semitic language group for some 3000 years. The main way of living is traditional pasturage husbandry and in the lesser extent also fishery. Pasturage is practised in a similar extensive way as on continental Yemen. Increasing anthropogenic pressure on the natural resources is thus above all driven by livestock grazing and by excessive wood depletion used for construction and fuelwood. As a matter of fact, grazing practice influenced plant communities and notably contributed to the contemporary distribution and structure of tree populations around the island, including endemic Commiphoras, Boswellias, Dendrosicyos socotrana and Dracnena cinnabari. Consequently, the most extensive vegetation type is low grazed forest dominated by some Euphorbiaceae representatives as Croton sp. or Jatropha unicostata, species unpalatable to the livestock. Preservation of the biological richness of Socotra Island will not be, therefore, possible without restrictions aimed at pasturage husbandry, at least in the key structural segments of the ecological network. Precise geobiocoenological differentiation is needed for recognizing the detailed state of natural conditions of the island.
Woody vegetation dynamics and Dracaena cinnabari regeneration have been studied for five years in the conditions of Socotra Island. Woody plants were measured regularly inside and outside the exclosure area, and the growth and survival of D. cinnabari seedlings were observed. In the exclosure of about 1000m2 a total of 49 species were identified, including 23 endemics, growing in the average density of 3.82 specimens per m2. The fenced area was overgrown relatively rapidly by dense grass cover – reaching approx. 2.7t/ha. Species growth dynamics inside and outside the exclosure shows that grazing had a marked impact, leading to the elimination of trees and shrubs. All grazed species grew noticeably in the exclosure, in the average of 50cm in 5years. D. cinnabari as the dominant flagship species of Socotra has been studied with regards to regeneration dynamics. Observations indicate that probability of its seedlings survival increases with their age. No seedlings germinated from the seeds sown in the experiment, however, outplanted seedlings performed relatively well. Field observations show that D. cinnabari seed germination is triggered when the seed reaches a protected micro-habitat with a developed humus layer and high relative humidity in the soil lasts for at least two days.
Water relations for two remote populations of Dracaena tree species from the dragon tree group, Dracaena cinnabari Balfour f. and Dracaena draco (L.) L., were studied to test our hypothesis that morphological and anatomical differences in leaf structure may lead to varied functional responses to changing environmental conditions. Sap flow measurements were performed using the heat field deformation method for four Dracaena seedlings grown in one glasshouse and two greenhouses, and leaf traits related to plant–water relationships were characterised. All traits studied confirmed that D. cinnabari leaves are more xeric in their morpho-anatomical structure compared with D. draco leaves. No radial sap flow variability was detected in D. draco plant stems, whereas sap flow was found to be higher in the inner part of D. cinnabari stems. The regular occurrence of reverse sap flow at night in both Dracaena species was consistent with a staining experiment. Vapour pressure deficit (VPD) was found to be the main driver for transpiration for both Dracaena species. However, the relationship between VPD and sap flow appeared to be different for each species, with a clockwise or no hysteresis loop for D. draco and a counter-clockwise hysteresis loop for D. cinnabari. This resulted in a shorter transpiration cycle in D. cinnabari. The observed superior water-saving strategy of D. cinnabari corresponds to its more xeric morpho-anatomical leaf structure compared with D. draco.
Dracaena cinnabari Balf. fil. is an endangered endemic species growing on the Yemeni island of Soqotra. Dracaena woodlands are considered one of the oldest forest communities on the Earth. Uncontrolled grazing unfortunately caused a lack of naturally occurring regeneration. Our two-year research was focused on the growth dynamics of Dracaena seedlings from two separate populations. One hundred of germinated seeds from two different altitudes from the island were sown and planted under the same conditions. Average increment and difference between the growth dynamics of plants from the two localities were investigated. The observed data on this plant species revealed very interesting, hitherto unknown results. (1) The seedlings germinated within a time period from four to ten weeks. Germination rate was 90% on the Firmihin highland plateau and 78% on the Scand Mountain. (2) Average plant length from both localities was almost the same (24.9 cm) at the end of measurement. Differences in values between the two populations proved as non-significant. (3) A significant difference was found in the number of leaves and in the sum of lengths of all leaves on one plant.While the seedlings from Firmihin featured a wide spreading above-ground part with a large number of leaves, the plants from Scand invested more energy into faster leaves elongation rate. (4) Growth dynamics reflected seasonal changes. Increments were slower or ceased during the period of vegetative rest from autumn to spring. (5) Average mortality rate was 13%. Most of the plants died during the period of vegetative rest. Further study on germination and regeneration under artificial conditions seems like the only way to prevent species extinction.
We present the results of fog water collection obtained with cylindrical fog gauges at three locations on the northern side of Tenerife island (Spain): La Esperanza (1093 m a.s.l.), Taborno (1015 m a.s.l.), and El Gaitero (1747 m a.s.l.). Concomitant meteorological variables were also measured. We show that fog precipitation was more frequent than rainfall. However, the volumes and frequency of daily fog water collection varied among the three studied sites, usually not exceeding 10–40 L d⁻¹/m² of collecting surface. In La Esperanza, fog water harvesting occurred frequently, but was considerably lower than in the other two locations. However, while in Taborno fog water collection episodes were distributed throughout the period, in El Gaitero these were mainly concentrated in two periods, during autumn and winter 2012–2013. The study of the relationships between daily fog water yields and the averages of meteorological variables did not show any clear trend, but it suggested that the greater volumes of collected fog water were logically associated with higher wind speeds and lower solar radiation conditions. Fog water collection in La Esperanza and in Taborno typically occurred within a similar temperature interval (7.5–12.5 °C), while in El Gaitero the phenomenon was associated with a lower temperature range (2.5–10 °C).
Some misunderstandings persist in the biological literature, concerning the geological evolution of the Socotra Archipelago. The aim of this paper is to interpret new information about the Gulf of Aden geology, from the view of possible methods of terrestrial biota species migration to the Socotra Islands. An overview of the Socotra Platform with the Socotra Archipelago topography is given. Present-day geological publications are mostly oriented towards tectonic structure of the Gulf and its tectonic evolution, and thus information concerning the elevation of the land surface and the sea level was necessary to deduce. The first biogeographically relevant emergence of a land mass in the area of present-day Socotra Archipelago commenced during the late Eocene Epoch (38-34 Ma BP). Some islands persisted after later transgressions of the sea, before the time of the opening of the Gulf of Aden rift (ca 20-17 Ma), accompanied by substantial uplift and large-scale uplift of the land. This was the last time when terrestrial biota could, relatively easily, reach the area of the Socotra Archipelago on land from the African mainland, and also with medium probability from present-day Arabia. The total evaporation of the Red Sea from 11-5 Ma BP enabled the migration of terrestrial species from and to Arabia via Somalia. Nevertheless, channels in Guardafui and Brothers basins made important, but perhaps nonfatal, barriers. The last and most important uplift of Haggier Mts. on Socotra occurred at the end of the Miocene Epoch (9-6 Ma BP). That was probably the time of the last Tertiary emergence of the Socotra Platform, potentially enabling some species to migrate across narrowed abovementioned channels. Great changes in sea level occurred during the Quaternary Period, periodically exposing the surface of the Socotra platform. Two channels persisted, preventing the invasion of modern species onto the Socotra Archipelago. Channels within the Brothers basin between Abd al-Kuri Isl. and other islands of the Archipelago formed some barriers to dispersal, and probably led to important biota differences in the scope of the Archipelago. Finally, a scenario of the “facilitation” provided by tsunami and sea currents for the immigration of biota onto the Archipelago is presented.
The Socotra archipelago is an ancient continental fragment situated in the Western Indian Ocean that has been isolated for at least 18 million years (Ma). Although often described as the ‘Galapagos of the Indian Ocean’, compared to the Galapagos and other island systems, this Arabian Sea archipelago is relatively poorly studied and often overlooked in works on island biology. Nevertheless, the Socotra archipelago is characterised by relatively high floristic diversity and endemism with local adaptations and radiations , making it a good example of a system suitable for the study of island biogeography . We discuss origins, affinities, disjunctions and adaptations in the flora and explore underlying environmental and evolutionary processes that may have helped the Socotra archipelago to its present uniqueness.
Key message
Large aerial roots grow out from the branches of injured
Dracaena draco
trees. They integrate with the trunk or cause the branches to break off the tree and deform it.
Abstract
Dracaena draco, the dragon tree, is an iconic monocot of the Canary Islands with a tree-like growth habit and some distinctive features that are unique in the plant kingdom. We report about the massive aerial roots in this tree. They appear on trees that are injured or under environmental stress and affect growth form and the whole life of the plant. We analysed the growth of these roots and tested our findings in experiments on plants. Clusters of these roots emerge from the bases of the lowest branches and growing down they may reach the soil. Descending along the trunk, they cling tightly to the trunk, integrate with it and contribute to its radial growth. This may explain (1) why the trunk of a mature D. draco tree looks fibrous, as if made of many individual strands, and (2) how some trees reach enormous radial dimensions. Alternately, a large, 2–5 m high, multi-segmented branch with aerial roots at its base, may break off the tree and grow on its own, as a mammoth off-cut, perhaps the largest known in the plant kingdom. This detachment would cause a significant reduction in the size of the crown and deform its original, highly organized pattern of branching. In the extreme condition this may result in the destruction of the mother plant.
This study evaluates the size frequency distribution of 11 trees and shrubs in the cloud forest in Wadi Garziz, southern Oman, in order to assess their current situation, which is affected by cutting, overgrazing and other constraints. A size class distribution and a vegetation structure analysis were applied in order to analyze the dynamics of this forest using census data from 51 plots selected across 5 transects covering the hill-slope and wadi-bed habitats. Some of the trees inhabiting the hill-slopes (e.g. Acacia senegal and Commiphora spp.) were found to exhibit an inverse J-shaped distribution with constant regeneration, whilst in the wadi bed these same trees exhibited a J-shaped distribution (i.e. of declining populations). On the other hand, Acacia etbaica inhabiting the hill-slopes exhibited a tendency towards a J-shaped distribution and an inverse J-shaped distribution in the wadi-bed. All the populations (i.e. inhabiting the hill-slopes and the beds) of Anogeissus dhofarica had a J-shaped distribution whereas all the populations of Blephari-spermum hirtum had a more or less inverse J-shaped distribution. The Ziziphus spina-christi and Acacia tortilis populations, meanwhile, exhibited the bi-modal shape of size distribution. The shrubs inhabiting the hill-slopes (e.g. Coroton confertus and Ormocarpum dhofarense) exhibited a tendency towards a J-shaped distribution; such distribution characterizes a declining population with a limited regenerational capacity. Overall, most of the examined populations, except those of Acacia etbaica in wadi-bed and Blepha-rispermum hirtum, seemed to be under stress from both environmental and human factors, particularly in the wadi bed. This type of study can provide a basis for the development of a management plan to support the conservation and sustainable use of forest vegetation in an arid region.
Between 2010 and 2011 a field survey dedicated to Dracaena cinnabari (DC) population was conducted in Firmihin, Socotra Island (Yemen). It’s main goal was to collect data that would make it possible to unbiasedly estimate main characteristics of the local DC population. Our motivation was to provide reliable information to support decision-making processes as well as other research activities. At the same time we were not aware of a survey which could provide this kind of statistical-sound estimates for the whole population covering an area of almost 700 ha.
This article describes how the survey has been planned and carried out in practice. In addition, we also provide a set of preliminary estimates of the main DC population figures - totals and per hectare densities of stems, overall and partitioned according to predicted crown age. Among estimated parameters there are also mean crown age and proportions of predefined age classes on the total number of living DC stems. These estimates provide an explicit information on age structure of the whole DC population in Firmihin.
Although we collected data on more than one hundred randomly located plots, the reported accuracy of our estimates is still rather limiting. We discuss several possibilities to obtain more accurate results or at least to approach the supposedly lower true variance that can’t be calculated by approximate techniques applied here.
The design and concept of our survey makes it possible to evaluate changes over time on stem by stem bases and to generalize these stem-level details to the whole population. Mortality, regeneration and even change of population’s mean crown age can be estimated from a future repeated survey, which would be extremely useful to draw firm conclusions about the dynamic of the whole DC population in Firmihin.
The flora of the archipelago of Socotra has been described so far although remaining incomplete, but the vegetation and ecology is mostly unknown. The altitudinal zonation of the vegetation is described here depending on specific species composition, and different ecological features are proven. The Socotran lowlands comprise arid alluvial plains, rocky slopes, and semi-arid inland hills and valleys until 400 to 500 m a.s.l. The humid cloud zone can be described by the potential occurence of the dragon tree (Dracaena cinnabari) from 400 to 1200 m a.s.l. The peaks of the Hagher (Hajhir, Ha Geher) Mountains which exceed 1200 m a.s.l. bear herbs and low-growing shrubs. Nocturnal dew plays the essential role in the continous water supply, especially in the mountain belt. The mountainous cloud zone provides ground water and running water for the whole island. A rough estimation of the water yield from dew is approximated to 135 Mio m³ per annum.
Drought, heat stress and salinity are the main factors which impair plant survival on the island. Some species hide in clefts or under the shady canopy of trees in order to diminish the stress caused by water loss. Species with xeromorphic adaptations or succulence prevail in the lowlands and hillsides. Basic ecomorpological and ecophysiological data are given. Annuals (C3 and even C4 plants), deciduous plants, and geophytes thrive only in the humid season and immediately after it. The green succulents (e.g. Aloe, Caralluma, Crassula, Echidnopsis, Euphorbia, and Kalanchoe spp.) exhibit Crassulacean acid metabolism (CAM) to avoid transpiration stress over day-time. Caudiciform succulents (Adenium socotranum, Dendrosicyos socotrana, Dorstenia gigas) store considerable amounts of water in stems and roots. Browsing and phytophagous animals are often deterred by secondary metabolites (phenolic compounds, steroids, alkaloids, e.g.).
The flora and the vegetation of the archipelago are merely naturally preserved and the indigenous population depends on an equilibrium with the natural ressources. Thus, the ecology of Socotra is still unique in a regional but also global view: Measures for the protection of the islands’ vegetation should take into account the ecological potential of the most endangered species. Agricultural and water exploitation, road and urban constructions, introduction of browsing animals and of crop plants should be done very carefully evaluating environment and natural ressources especially.
The Nubian dragon tree
Dracaena ombet
, which is categorized as Endangered on the IUCN Red List, is found on the highest slopes of Gebel Elba National Park in Egypt, with scattered populations in Sudan, Djibouti, Ethiopia and Somalia. The Gebel Elba population is threatened by drought. Surveys were conducted in the Park to assess the condition and document the distribution of the species to prepare a baseline for conservation efforts. Eight sites were surveyed during 2007–2009: trees were tagged and their locations were recorded using a global positioning system, and tree density, diameter at breast height and population status were estimated. Of 353 trees recorded only 46% (161 individuals) were alive and only 27% (96 individuals) were in a healthy condition. Only 1% (2 individuals) were young trees, indicating a low regeneration level. Field-based observations suggest that 80% of the
D. ombet
population in Gebel Elba may soon be extinct. A conservation action plan is needed for this flagship species in Egypt and throughout its range.
The climate of Socotra, influenced by the Indian Ocean Monsoon, is poorly known, hampering understanding
of its paleoclimate and (endemic) biodiversity. Mean annual rainfall and temperature, measured
in a network of meteorological stations from 2002 to 06, were 216 mm and 28.9 �C. Combined with cloud
cover information from satellite images, this data provides clear ideas on inter- and intra-annual
variability. Precipitation derived from the northeast (NE) winter monsoon influences especially the NE
plateaus and windward side of the Haggeher Mountains because of orographic effects. The southwest
(SW) summer monsoon concentrates at the southern half of the island and generally produces less
rainfall. During the SW summer monsoon, clouds cover the highlands and plateaus south of the
Haggeher Mountains, creating fog. Preliminary measurements suggest that at higher altitudes, fogderived
moisture may constitute up to two-thirds of total moisture, amounting up to 800 mm. The
predominant SW aspect of the enigmatic dragonblood tree underlines the importance of fog. Long-term
weather observations by Socotri put these short-term meteorological observations into a longer
perspective. Socotri informants also described the drought years when livestock populations crashed,
after which windows of opportunities for the regeneration of dragonblood and other grazing-sensitive
trees may have occurred.
Unique woodlands of Dracaena cinnabari (DC) are at risk throughout most of their range (Socotra Island, Yemen) as a result of missing regeneration and overmaturity. Effective conservation measures depend on reliable predictions of future population dynamics, which depend on accurate data on current age structure. However, age determination of Dracaena sp. has long been a scientific challenge, because the common method of tree ring counts cannot be applied to this or to most other monocotyledonous trees. In the present study, the indirect method for crown age estimation proposed by Adolt and Pavlis (Trees 18:43–53, 2004) was further developed using a more appropriate statistical technique and an intuitive model formulation. This new technique is based on the relationship between the number of branching orders and the number of flowering events that result from a specific growth pattern. We used logistic regression to directly model annual flowering probability, the reciprocal value of which corresponds to the length of the interval between flowering events. Our methodology was applied to data sets collected at two ecologically distinct sites. In Firmihin, the time between flowering events decreases from 28 years between the first and second event to 10 years between the 25th and 26th event. The length of time between flower events in Skant, however, was estimated to be a constant value of 6.5 years. We propose the application of generalised mixed-effects models and methods of survey sampling to improve the accuracy of crown age estimation in DC. Our methodology may also be useful for age estimations of other tree species with similar growth patterns, such as Dracaena draco and Aloe dichotoma.
A water balance study of a small subtropical rainforest catchment (10 ha, 1000 m altitude) was conducted at Gambubal State Forest, near the headwaters of the Condamine River, 200 km south-west of Brisbane, south-eastern Queensland. Mean annual rainfall of the site is approximately 1125 mm, but is variable and often less than 900 mm. Tree transpiration rates are low and depletion of the large soil moisture reserves enables extraction for lengthy periods of time, permitting survival during extended dry seasons (May–November). Fog deposition to the forest provides the equivalent of an additional 40% of rainfall to the site as measured using a conventional rain gauge. A frequently wet canopy results in reduced transpiration rates and direct foliar absorption of moisture alleviates water deficits of the upper crown leaves and branches during the dry season. These features of this vegetation type may enable long-term survival at what could be considered to be a marginal rainforest site.
The Supply of sustainable freshwater has turned into a fundamental problem in numerous countries. The increment in population, the industrialization of the world, and variation in global warming temperatures lead to an increase in droughts, storms, and floods around the world. Therefore, the problems of water scarcity appear worldwide. Contrary to popular belief, the largest reserves of water are available in the air. Accordingly, several technologies have been developed for the production of drinking water from humid air in the research works. But, the critical problem is the high energy consumption in this equipment. Therefore, the issues of water-energy nexus are the particular subject in the design and the construction of this equipment. The use of renewable energy (solar and wind energy) proposed as the solution for the reduction of energy costs. For example, the development of new desiccants for water harvesting by the utilization of solar energy has been reported in the literature. This paper describes an overall summarized presentational view of the various technologies for water extraction from humid air with the focusing on the water-energy nexus.
The position of Egypt – at the cross-roads between the Middle East and Africa – has attracted the attention of naturalists and explorers for many centuries. Yet while there are many studies relating to the ecology and biology of Egyptian vegetation, the first issue of Zahran and Willis’ Vegetation of Egypt (1992) represented the first attempt to draw this diverse information together. In this second edition, this invaluable text is both updated and expanded to include additional topics such as the role of remote sensing in mapping Egypt’s vegetation, and the economic potential of major desert species.
Covering each of the four major eco-geographical regions of Egypt – the Western Desert, the Eastern Desert, the Sinai Peninsula, and the Nile Region – the book integrates a wealth of detail and represents an important landmark in the vegetation of arid and Mediterranean-type regions. As such, it will provide an essential reference to advanced students and researchers in plant science, ecology, biogeography, climatology, economic botany and remote sensing.
In arid and semi-arid environments, fog interception as a water acquisition mechanism has been long recognized as an important factor for plant survival. The “narrow-leaf syndrome” increases water absorption from horizontal precipitation and is typical of nebulophytes characterized by dense rosette type crowns, to which also Dracaena species belong. In this paper, we demonstrate that Dracaena nebulophytes are able to direct water intercepted from fog through the leaf axils into their succulent woody organs to be stored for later use. We conducted leaf axil watering (LAW) experiments in four young Dracaena plants (two Dracaena cinnabari and two Dracaena draco) while simultaneously measuring sap flow in plant stems using the heat field deformation method. It was assumed that inducing water potential within stems closed to zero would initiate simultaneous bidirectional water transport from the stem to the crown and roots, and that this moment would be reflected in corresponding sap flow. Three hypothetical scenarios of induced water transport imbalance were confirmed by analyzing measured temperature gradients around heated probes and calculating sap flow. Sap flow responses to LAW clearly appeared to be dependent on flow direction prior to water treatments, on the strength of forces driving upward and downward water movement and the quantity of water applied. Intrinsic sap flow changes depicted in the results confirm the hypothesis that the Dracaena species are able to direct atmospheric water through the axils of their leaves to stem tissues. This mechanism of bypassing soil water represents an alternative means of water uptake in plants and is especially important in foggy areas of arid and semi-arid climates.
Dracaena cinnabari, the dominant endemic tree of Socotra Island (Yemen), is in serious decline. The effect this will have on the island's plant diversity remains unknown. We aimed to identify plants associated with Dracaena understorey and assess the importance of Dracaena for maintaining plant diversity. A total of 272 relevés were sampled in Dracaena understorey and in open sites to record the number of individuals of vascular plants. Species richness and composition were compared between understorey and open sites, and species associated with each of these habitats were identified. Additionally, the effect of canopy closure on species richness and abundance was analysed. We also recorded woody species composition of Dracaena stands and investigated spatial relations between Dracaena and other mature woody plants. Understorey plant species composition differed from open site composition. The former habitat showed higher β-diversity and species richness. Among recorded plants, 15 species were classified as understorey specialists, 6 as open-site specialists, and 23 as generalists. Rare species, especially endemics, were more common in the understorey. Canopy closure had differential effect on species abundances among the species classes. Species richness and total abundance were found to be highest in the understorey, particularly in the case of low-to-intermediate canopy closure where understorey and open-site specialists may co-occur. For mature woody plant species, Dracaena was spatially independent from other woody species at most distances. Our results suggest that the decline of Dracaena may negatively affect plant diversity, reduce abundance of rare endemic plants and lead to homogenization of vegetation. As no other tree species exists in the study area which could replace the Dracaena, our findings underline the importance of conservation efforts to preserve Dracaena stands on Socotra.
This volume represents a uniquely comprehensive overview of our current knowledge on tropical montane cloud forests. 72 chapters cover a wide spectrum of topics including cloud forest distribution, climate, soils, biodiversity, hydrological processes, hydrochemistry and water quality, climate change impacts, and cloud forest conservation, management, and restoration. The final chapter presents a major synthesis by some of the world's leading cloud forest researchers, which summarizes our current knowledge and considers the sustainability of these forests in an ever-changing world. This book presents state-of-the-art knowledge concerning cloud forest occurrence and status, as well as the biological and hydrological value of these unique forests. The presentation is academic but with a firm practical emphasis. It will serve as a core reference for academic researchers and students of environmental science and ecology, as well as practitioners (natural resources management, forest conservation) and decision makers at local, national, and international levels.
This chapter uses a combination of remote sensing, computer modeling, and data assimilation to provide: (i) estimates of the global extent and distribution of “hydro-climatically” defined tropical montane cloud forests (TMCFs), and (ii) an initial assessment of the past and future impacts of climate change and land-use change upon them. The overall goal is to improve the understanding of cloud forests as an ecosystem and to assist in the geographic targeting of research, inventory, and conservation priorities. These hydro-climatically defined TMCFs might be better termed “significantly cloud-affected forests, ” since most – but not all – occur in areas of high elevation and high rainfall and show the structural characteristics typically associated with wetter TMCFs. The distribution of these forests was modeled on the basis of satellite-observed atmospheric cloud presence and/or modeled ground-level condensing conditions. Areas which experience these conditions >70% of the time gave the best fit with the UNEP–WCMC database of known cloud forest sites. Significantly cloud-affected forests have been estimated by this analysis as representing some 14.2% of all tropical forests and covering an area of 2.21 Mkm2 between 23.5° N and 35° S. This figure is much greater than previous estimates for the area covered by TMCF based primarily on altitudinal criteria but is likely to be reduced if the exercise were to be repeated with higher spatial resolution data than are currently available. […]
Mountain cloud forests (also known as nebelwald, forêt néphéliphile, bosque de ceja montaña, and several other names) are characterized by the presence of persistent or frequent wind-driven cloud. The net precipitation is significantly enhanced by direct canopy interception of cloud water. This, combined with low water use by the vegetation due to reduced solar radiation and vapor deficit, canopy wetting, and general suppression of evapotranspiration, results in net additions to the water yield of the watershed. If these forests are removed an important water supply function is lost. Cloud forests have great biological diversity value, especially because they contain a very high proportion of nationally or regionally endemic species. The most serious threats ranging from climate change to alien species introductions are described; strategies for achieving conservation and better management of cloud forests are discussed and, finally, from a symposium and workshop attended by cloud forest researchers and managers, a set of high priority research topics is presented. /// Les forêts néphéliphiles (mountain cloud forest, nebelwald, bosque de ceja montana, et bien d'autres désignations) sont caractérisées par la présence de nuages persistants ou fréquents, poussés par les vents. La hauteur nette des précipitations est sensiblement augmentée par l'interception directe de l'eau des nuages par la voûte des arbres. Ce phénomène, combiné avec la basse consommation d'eau par la végétation, causée par la radiation solaire réduite et le déficit de vapeur, le mouillage de la voûte des arbres, et une suppression générale de l'évapotranspiration, augmente nettement l'apport d'eau du bassin versant. Si ces forêts sont éliminées, une importante source d'approvisonnement en eau sera perdue. Les forêts néphéliphiles présentent une grande valeur du point de vue de la diversité biologique, en particulier du fait qu'elles contiennent un très grand pourcentage des espèces endémiques nationales ou régionales. Les dangers les plus sérieux, depuis les changements de climat à l'introduction d'espèces étrangères, sont décrits; des stratégies de préservation et de meilleure gestion des forêts néphéliphiles sont examinées. Finalement, une liste de sujets de recherche prioritaires, basée sur les activités d'un symposium et d'un atelier auxquels ont participé des chercheurs et des responsables de la gestion des forêts néphéliphiles, est présentée. /// Montane Nebelwälder (mountain cloud forest, foret néphéliphile, bosque de ceja montana, und viele weitere Bezeichnungen existieren dafür) sind dadurch charakterisiert, daß in ihnen Bedingungen herrschen, die Wälder permanent oder zumindest häufig wind-verursachten Wolken aussetzen. Die Nettobeträge der zur Verfügung stehenden Wassermengen werden beträchtlich durch die direkte Aufnahme von Wolkenfeuchtigkeit im oberen Dachstock des Waldes erhöht. Dieses Phänomen trägt in Verbindung mit einer geringen Wasseraufnahme der Vegetationsdecke infolge reduzierter Einstrahlung und Verdunstungsdefizite, Walddachbefeuchtung und einer allgemein verringerten Evapotranspiration zu einer höheren Netto-Wassermenge im Einzugsbereich bei. Falls diese Wälder vernichtet werden, wird eine wichtige Wasserversorgungsquelle aufgegeben. Nebelwälder weisen eine hohe Biodiversität auf, insbesondere aufgrund ihrer Eigenschaft als Träger national oder regional endemischer Arten. Dieser Beitrag beschreibt die wichtigsten Gefahrenpotentiale für den Erhalt der Nebelwälder in einem Spektrum von Klimawandel bis hin zum Einzug fremder Arten. Weiterhin werden Maßnahmen zur Erhaltung und verbesserten Verwaltung von Nebelwäldern diskutiert. Letztlich werden die Ergebnisse eines Arbeitstreffens von Nebelwaldforschern und Verantwortlichen präsentiert, die eine Prioritätenliste für zukünftige Forschungen einfordern.
The monocot tree Dracaena draco L. is famous for the production of a red resin referred to as dragon's blood. This resin has been used in traditional medicine since ancient times by many cultures. Dragon's blood chemistry is well desribed, however, the data concerning its secretion and distribution following injury is still fragmentary, although it can help in resin sourcing. The goal of the study was to characterize for the first time the anatomical status of the secretory tissue responsible for the red resin production and storage. The study was carried out with hand sections and thin sections of an Epon-embedded samples collected from the cut and wounded stem of a 5-year-old D. draco plants.
The arborescent taxa ofDracaenawhich form the dragon tree group comprise five species found in Macaronesia, Morocco (D. draco), East Africa (D. ombet,D. schizantha), Arabia (D. serrulata) and the island of Socotra (D. cinnabari). A new species of dragon tree,Dracaena tamaranaeA. Marrero, R.S. Almeida & M. González-Martı́n, is described from Gran Canaria, Canary Islands. This new species differs fromD. draco, the only otherDracaenaspecies currently known in Macaronesia, in having a growth form and inflorescence type and leaves more similar to the East African and Arabian species ofDracaena. In contrast,D. dracoappears to be related toD. cinnabari. In this paper, we also present a study of the taxonomy, habitat and ecology of all the species of the dragon tree group. These are found in thermo-sclerophyllous plant communities of tropical–subtropical regions which are rather xerophilous and have a rainfall range of 200–500 mm. Our study indicates two independent colonization events forDracaenain Macaronesia. In addition, we suggest that the dragon tree group provides an example of two major biogeographical disjunctions between East and West Africa. We postulate that this group has a Tethyan origin, a hypothesis supported by fossil and palaeoclimatic data, and thus parallels the distribution and dispersal pattern of other taxonomic groups.
Vegetation changes in Sahel have been partly explained by overgrazing. Some authors have queried the importance of herbivory as a cause of succession in arid areas, but this requires a differentiation between life-forms. In this study abundances of phanerophytes and chamaephytes were estimated on 30 hills on an arid mountain plateau in eastern Sahel, influenced by mist from the Red Sea. Their relative abundances were compared with a similar study in 1953 when the area was partly protected against browsing. Significant spatial and temporal trends were found by ordination techniques. Succession from an open woodland to a very open shrubland was revealed. Hardwood trees suitable for fuel and other plants of direct commercial value decreased. Plants with small, sclerophyllous leaves, and/or toxic chemicals increased. The changes are attributed to an increased human population and intensified browsing. These biotic factors interacted with drought periods. Species that also grow in the surrounding Sahelian transition zone were relatively more stable than those with a disjunct distribution in the region, which occur in the area of more moist regional climate found in the Ethiopian highland.
Dracaena cinnabari Balf. On The Soqotra Island is a spectacural relict of the Tethys tropical forest. This unique endemic plant, producing medicinally valuable sap, used to cover larger areas in the past. Natural regeneration of this species is restricted to inaccessible localities with steep slopes. All seedlings are threatened by goats grazing. Age structure of Dracaena populations indicates maturity and overmaturity depending on browsing. The objective of this work is to predict growing dynamics of Dragon's Blood Trees in permanent sample plot at Firmihin, where there is the largest existing stand of Dracaena species. The prediction and visualization of variation in abundance of trees over 100 years is based on direct field measurements supported by mathematical calculations. The study presents options in forest regeneration and identifies threats that might occur during the implementation.
Among the most prominent examples for the disjunct distribution of xeromorphic-sclerophyllous plants in Macaronesia and eastern Africa–Arabia, referred to as the Rand flora biogeographic pattern, is the “dragon tree group” within Dracaena (Asparagaceae). However, little is known about the evolutionary origin of this iconic group of semi-desertic trees. Here, we use exceptionally well-preserved fossils from western Anatolia to demonstrate range and ecological shifts of the lineage probably leading to some of the modern dragon trees. Compression fossils of apical leaf rosettes and detached leaves of Dracaena tayfunii spec. nov. were compared to modern Dracaena using the architecture of leaf-bearing branches, leaf morphology, and highly diagnostic leaf epidermal features observed with light and electron scanning microscopy. The palaeoecology of Dracaena was inferred using the depositional setting and associated plant taxa. The ca. 16 million-year-old (Ma) Dracaena from western Anatolia shows a character combination restricted today to the Macaronesian dragon tree, Dracaena draco: (1) Leaves are arranged in terminal rosettes; (2) leaves are ensiform, oblong, with a conspicuously dilated base (pseudo-sheath); and (3) leaf epidermis is strongly papillate with sunken stomata overarched by papillae of four neighbouring epidermal cells. Depositional setting, taphonomy, and the fossil plant association indicate that the Miocene Dracaena either grew in seasonally dry swamps within a complex fluvial–lacustrine environment or on adjacent slopes under a humid, warm climate. Hence, semi-desertic modern dragon trees allied to D. draco displaying distinct xeromorphism may have originated from a western Eurasian mesic lineage that had evolved xeromorphic characteristics by the Miocene. The morphology of this mesic ancestor later enabled the lineage to colonize and survive in the semi-desertic environments where it is found today. The new fossil species of Dracaena represents a classic example of pre-adaptation and niche shift.
Laurel forests in the Canary Islands (Spain) survive where humid conditions are guaranteed throughout the year. On peaks and ridges, laurel forest gives way to mixed evergreen tree-heath/beech forest of low stature (“fayal–brezal”) that has to cope with rapidly changing light, temperature and humidity conditions due to the occurrence of intermittent sunny and foggy periods during the mostly rainless summer. These conditions are poorly understood and there is a lack of information on the interrelations between tree physiological behavior and ambient climatic and soil water conditions in fayal–brezal. In this study sap velocities were measured for 2 years in two dominant tree species (Myrica faya and Erica arborea) in a ridge-top forest in the National Park of Garajonay on the island of La Gomera. The resulted average daily stand transpiration was 1.2 ± 0.12 mm (416 mm year−1). However, the narrow-leaved E. arborea exhibited higher sap velocities than the broad-leaved M. faya. Also, sap velocity increased with stem diameter in E. arborea but not in M. faya. Nocturnal flow activity was observed throughout the year and reflected ambient conditions on some occasions, and stem water storage recovery on others. Strong stomatal control in response to increases in vapor pressure deficit was seen in both species. Fog reduced sap velocity from 10% up to 90% but no consistent pattern was found. Soil water uptake during the dry summer (246 mm) was much larger than atmospheric water inputs (41 mm, rain and fog). The low moisture levels in the top 0.3 m of the soil had limited influence on transpiration rates indicating that vegetation must have had access to moisture in deeper layers.
Basement rocks crop out in three main uplift areas; elsewhere they are overlain by a veneer of Cretaceous and Tertiary plateau limestones. The oldest basement rocks are amphibolite facies meta-sediments and meta-igneous rocks which have been intruded by synkinematic granites and late-kinematic gabbros; younger weakly metamorphosed tufts and mudstones also occur. Post-kinematic igneous activity gave rise to a sequence of volcanic rocks, hornblende/ biotite and peralkaline granites, gabbros and minor intrusions which make up the bulk of the Haggler mountains. Of these the large occurrence of peralkaline granites is considered in detail. Following a long period of basement peneplanation, sediments were deposited which consist of Lower and Middle Cretaceous limestones, with some basal sandstones, followed without apparent break by cliff-forming shelf limestones of Palaeocene-Eocene age. Oligo-Miocene chalky deposits are only preserved in structural depressions. Vertical movements were predominantly responsible for the structure which is simple in the east but dissected by WNW-ESE block faulting in the west. Correlation with southern Arabia and Somalia suggests that the basement metamorphic association is Pre-Cambrian and the post-kinematic igneous rocks are early Palaeozoic; the sedimentary formations broadly correlate with those of southern Arabia and the Oligo-Miocene deposits in particular are most closely related to those of Dhufar.
Present study has produced first detailed land‐cover map of Socotra Island. A Landsat 7 ETM+ dataset was used as a main source of remotely sensed data. From numerous reference points (more than 250) coming from the ground data verification the set of training fields and the set of evaluation fields were digitised. As a classification method the supervised maximum likelihood classification without prior probabilities was used in combination with rule‐based post‐classification sorting, providing results of sufficient accuracy and subject resolution. Estimates of the area and degree of coverage of particular land‐cover classes within Socotra Island have brought excellent overview on state of island biotopes. Overall accuracy of the map achieved is more than 80%, 19 terrestrial land‐cover classes (including three types of Shrublands, three types of Woodlands, two types of Forests and Mangroves) have been distinguished. It consequently allows estimates of the current and potential occurrence of endemic plant populations, proposals of management and conservation plans and agro‐forestry planning.
Each summer between June and September, the Dhofar region in the Sultanate of Oman is subjected to a high incidence of fog. Generally, fog occurs on 20 to 25% of days during the year. This study was to investigate the fog water potential of the area. Field measurements began in July and continued into mid-September 2005 when the fog, although less frequent, was still present. Experiments were conducted using three fog collectors with different local materials: AC filter, green shade filter, and aluminium filter. The results indicated that the total fog water collected during the experimental period of 76 days by AC filter, green shade mesh, and aluminium shade mesh was 995.04, 879.93, and 752.58 L/m(2) respectively. The ion concentrations at the Dhofar site were studied and found to meet World Health Organization drinking water standards. Water from the three fog collectors was found to be of good quality. Since fog water collection rates are dependent upon meteorological variables, the impact of the various meteorological parameters on collection rates was also investigated in this paper. The results indicated a significant linear association between the collected fog water and the wind speed and rainfall. It was found that fog water collection rates increased with increasing wind speed and rainfall, but this relationship was not seen with temperature, relative humidity, or pressure. More studies are needed to address and clarify the question of bacterial concentrations and heavy metals in the collected fog water.