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Frankincense: Understanding the Plant’s Diversity Is Key to Its Future

By Sue Canney Davison, PhD, Frans Bongers, PhD, and Denzil Phillips, MSc

Frankincense and myrrh are the resinous exudates from two genera, Boswellia and Commiphora, respectively, of the Burseraceae family. The trees produce resin as an immune response to heal and close their bark after natural or human-caused wounding. Frankincense and myrrh are two of the most ancient phytomedicinal resins and have woven their way through human history for millennia. Incense is mentioned in the earliest papyri of the 27th-century-BCE Egyptian polymath and vizier Imhotep, and pharaohs sent ships to bring back frankincense and myrrh resin and live trees from the Land of Punt, which is assumed to be part of modern-day Somalia/Somaliland.1,2

Rendille/Samburu women harvesting B. neglecta in Kenya Photo ©2021 Sue Canney Davison

Rendille/Samburu women harvesting B. neglecta in Kenya
Photo ©2021 Sue Canney Davison

The Bible repeatedly mentions frankincense and myrrh, which the three wise men, or Magi, gifted to Jesus at his birth. Other sources reference resins being used for trade, sought as loot, and used as ransom payments, and over time, they became integral commodities in the first global trading routes.1 Traces of these resins have been found in archaeological and burial sites across the Arabian Peninsula, the Mediterranean, and northern Europe.3 Their medicinal uses have been recorded in traditional Indian and Chinese medicine for centuries. For millennia, their smoke has infused sacred rituals and churches,4 and resinous oils have been used to embalm the dead.5 These resins are fundamentally intertwined with the communities who live with, manage, and harvest them, and the local and international traders and processors who buy and trade them.*

Boswellia neglecta growing with Commiphora species in Meru National Park, Kenya Photo ©2021 Sue Canney Davison

Boswellia neglecta growing with Commiphora species in Meru National Park, Kenya
Photo ©2021 Sue Canney Davison

The Boswellia genus currently includes 24 recognized species,6 11 of which are found on the Yemeni island of Soqotra, also spelled “Socotra.” Though the trees and resins from these species have different local names, internationally, the generic name “frankincense” encompasses all their resins and resin products. With approximately 190 identified species in the genus Commiphora, debates are ongoing about which species constitute the myrrh referred to in ancient texts. Some Commiphora essential oils are more similar in composition to specific Boswellia essential oils, while others are more similar to Commiphora myrrha.7 It is still debated whether “myrrh” is a trade name for only Commiphora myrrha or some other Commiphora species.

In many regions, frankincense and myrrh trees grow in the same arid and semiarid ecosystems or Acacia-Commiphora woodlands and are equally vulnerable to drought, climate change, grazing livestock, fire, land-use changes, unsustainable harvesting practices, and felling for household uses.

The issue of whether existing populations of Boswellia trees can sustainably meet global demand raises complex questions about the trees and their products. The purpose of this article is to articulate some of the key issues surrounding the management of frankincense trees, the communities who manage and harvest the trees, the value chains, trade, and increasing uses of frankincense, and to highlight some of the gaps in current knowledge. This article will focus exclusively on frankincense, with the understanding that some Commiphora species face similar challenges as frankincense trees. The need to understand the current situation and identify workable, regenerative solutions has brought together scientists, exporters, distributors, trade associations, non-governmental organizations (NGOs), and representatives of national and governmental organizations in a number of recent international meetings.

These meetings include the International Federation of Essential Oils and Aroma Trades (IFEAT) in Athens, Greece (2017), which provided an initial platform to debate the current situation, and the First International Conference on Frankincense and Medicinal Plants (ICFMP) in Muscat, Oman (2018), where more than 300 scientists, company representatives, and NGOs presented and dicussed the problems and prospects for frankincense across a wide range of topics. These two important meetings were followed by a smaller special session on frankincense and myrrh at the World Congress of Medicinal and Aromatic Plants (WOCMAP) in Northern Cyprus (2019), which also saw the emergence of the Global Frankincense Alliance (GFA), which is described in this article.8

Also in 2019, parties of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) initatied an informal working group to gather information on the current status of frankincense trees to assess the need to mitigate any threat to their long-term future.

Differentiating the Species, Resins, and Resin Products

Boswellia trees range from India, across the Arabian Peninsula, the Greater Horn of Africa, and across the Sahel (the transition zone of semiarid short grasslands and savannas, just south of the Sahara desert) to West Africa. While “frankincense” is the generic trade name for the resin as well as the trees of all Boswellia species, the conservation, sustainability, and socioeconomic issues that affect the different species and the aromatic, medicinal, and other uses of the resins differ significantly among each species and their habitats.9 One of the key messages from the international meetings has been that recognizing this diversity is important to the future sustainable use of frankincense.

 

Table 1. Currently Identified Boswellia Species and Main Recorded Range States6a

Species

Range States

Species

Range States

Species

Range States

B. ameero

Socotra (Yemen)

B. aspleniifolia

Socotra

B. bullata

Socotra

B. dioscoridis

Socotra

B. elongata

Socotra

B. hesperiab

Socotra

B. nana

Socotra

B. popoviana

Socotra

B. samhaensis

Socotra

B. scopulorum

Socotra

B. socotrana

Socotra

B. globosa

Somaliland

B. sacra
(syn B. carteri)

Oman, Yemen, Puntland (Somalia), Somaliland

B. frereana

Puntland (Somalia), Somaliland

B. occulta

Somaliland

B. microphylla

Somalia, Somaliland, Kenya, Ethiopia

B. neglecta

Ethiopia, Somalia, Somaliland, Kenya, Uganda, Tanzania

B. pirottae

Ethiopia,

Sudan

B. ogadensis

Ethiopia

B. papyrifera

Sudan, South Sudan, Eritrea, Ethiopia, Uganda, Chad, and other locationsc

 

 

B. rivae

Ethiopia, Kenya, Somalia, Somaliland

B. dalzielii

Mali, Burkina Faso, Nigeria, Cameroon, Niger, Benin, and other locationsc

 

 

B. serrata

India, Sri Lanka

B. ovalifoliolata

India

 

 

a The species most commonly traded internationally are in green.
b Species provisionally described, only from photographs
c From historical and/or herbarium records that need to be verified

 

While, in general, Boswellia species grow in harsh arid and semiarid environments and have adapted to be drought-tolerant and resilient, the growth patterns, adaptations, environmental conditions, management, and harvesting practices among, and even within, each species can be substantially different.10 New species continue to be identified. The difficulties of going to the source to collect botanical samples and identify different species, hybrids, and/or varieties have been highlighted in the emergence of B. occulta as a new species in Somaliland. For some time, despite the unique chemical profile and aroma of its essential oil, it was considered a chemotype (chemical type) of B. sacra until its leaves and fruits were further examined.11 At the same time, essential oil buyers may see both B. sacra and B. carteri on essential oil bottles. While they come from different geographical regions and have some significant differences that have created some debate,12 they currently are recognized as the same species.6 Further niche species likely will be identified, and future comparative genetic analyses of the 24 Boswellia species that are currently recognized will assist in the search for markers to distinguish different species and their resins for scientific, conservation, regulatory, and quality purposes.

Increased Demand for Some Frankincense Resin and Essential Oils

Boswellia species have been used for millenia in traditional Chinese and Indian medical traditions, and the last decade has witnessed increased scientific research and knowledge on the potential medicinal and therapeutic properties of some of these species13,14 both as internal, applied, and aromatic products. The growing understanding of the medicinal properties of the boswellic acids, found in commercially significant amounts in the resin of at least four species (Table 2), as well as the popularity of frankincense essential oil in aromatherapy have led to increased demand for certain frankincense resins and essential oils. Some market reports project a doubling in the frankincense essential oil market between 2018 to 202815 with a 7.7% cumulative annual growth rate, which is currently predominantly sourced from B. sacra in Somaliland, Puntland (Somalia), and Oman; B. serrata in India; and to lesser extents from B. papyrifera, B. neglecta, B. rivae, B. dalzielii and B. frereana.9 Given their diversity, the effect of an increased demand for certain frankincense resins for essential oils and medicinal uses is likely to affect each species differently across their different geographic ranges.

 

Table 2. Components of the Most Commonly Internationally Traded Boswellia Resins

Species

Current Main Commercial Area

Boswellic Acids and Other Pentacyclic Triterpenic Acids (PTAs)*14,52

Dominant Constituents of Essential Oil55

Suggested Chemotypes56

B. serrata

Madhya and Andhra Pradesh, India

Yes (most consistently)

a-thujene, estragole, a-pinene, sabinene, myrcene, 3-δ-carene,

Myrcene (forest collection Shivpuri)57

B. sacra

Dhofar Oman

Yes

 

a-pinene, limonene, myrcene, incensole

 

B. sacra (syn B. carteri)

 

Cal Madow, Somalia/ Somaliland

Yes

a-pinene, a-thujene, limonene, myrcene, sabinene, β-caryophyllene,

(Ia) α-pinene/myrcene/ sabinene/limonene,
(Ib) α-pinene/limonene,
(Ic) Limonene/α-pinene,
(II) α-thujene 58

B. papyrifera

Northwest Ethiopia, Sudan

Yes

Octyl acetate, octanol, incensole acetate

 

B. dalzielii

Burkina Faso, Northern Nigeria

Yes

a-pinene, myrcene, limonene, sabinene, a-thujene

(I) a-pinene

(II) myrcene 59

B. neglecta

Southern Ethiopia, Northern Kenya

Yes (Somali origin)

No (Kenya origin)

a-pinene, a-thujene, β-pinene, terpinen-4-ol, r-cymene

 

B. frereana

Cal Madow, Somalia/ Somaliland

No boswellic acids

a-thujene, a-pinene, sabinene, r-cymene, dimers of phellandrene,

 

B. rivae

Somali region of Ethiopia, Northern Kenya

Unknown

a-pinene, limonene β-pinene, r-cymene, d-3-carene

 

* Above trace amounts. The main PTAs being researched for their different biosynthetic and therapeutic pathways and applications are α-boswellic acid (α-BA), acetyl-α-boswellic acid (α-ABA), β -boswellic acid (β -BA), acetyl-β-boswellic acid (β-ABA), 11-keto-β-boswellic acid (KBA), acetyl-11-keto- β -boswellic acid (AKBA), lupeolic acid (LA), and acetyl-lupeolic acid (ALA), with different Boswellia species showing different compositions.14,52

 

Sustaining the Trees and the Communities that Harvest Them

To supply an increased demand, more frankincense needs to be harvested and traded, but the actual sustainable production capacity of each species that will also allow the trees to regenerate is unknown. As current production is based on sourcing resin from a limited number of wild trees of these species, the immediate future of the resource depends on proper management, harvesting, and regeneration of the current tree populations, but the available data on each of the different species vary.

Discussing harvesting techniques of accessible B. sacra trees in Somaliland Photo ©2021 Dayaxa Frankincense Export Company

Discussing harvesting techniques of accessible B. sacra trees in Somaliland
Photo ©2021 Dayaxa Frankincense Export Company

Of the 24 recognized species, overharvesting for trade purposes is estimated to affect four species: B. sacra (syn B. carteri), B. papyrifera, B. serrata, and B. frereana. Research shows that some of these key harvested populations are under severe pressure. This is notably the case for B. papyrifera in northern Ethiopia and Eritrea,16 some areas of B. sacra in Somaliland, and reportedly for some populations of B. serrata in India.17,18 Research data on harvested and traded species is often sourced from accessible areas, which may also be subject to greater harvesting pressure, while remote and inaccessible areas may be less likely to have experienced pressure from human activities.19

For some other species and locations, regeneration currently does not seem to be an issue,20 but for several geographical areas and species there is insufficient data, and confirmed data are scarce.

Boswellia sacra trees in a remote valley in Somaliland

Boswellia sacra trees in a remote valley in Somaliland
Photo ©2021 Dayaxa Frankincense Export Company

At this time of projected increased demand, these studies on harvesting pressure and regeneration have raised awareness and initiated the current push for greater collective action between landowners, communities, and harvesters who manage and know the status of the trees, as well as traders, exporters, international retail companies, and environmental and governance bodies. On the other hand, concerning findings in certain heavily harvested areas have led to some generalized sensationalized headlines about the status of frankincense in the popular press.21 Such headlines do not reflect the situation of all locations and certainly not of all Boswellia species.

In 2020, the secretariat of CITES collated the results of a questionnaire sent out to relevant frankincense stakeholders that asked for information on the biological data and population status of each species, harvesting and supply chains, threats and intentional propagation, and current regulations and ownership structures.22 Given the gap between increasing demand, increasing concern for some traded species, and the lack of current knowledge on the status of the trees, collective efforts to identify and fill these knowledge gaps and support the development of sustainable management systems are pivotal.

Accurate Data Are Needed

Accurate data on the exact geographical range of each species, the population densities, and the status of the trees has yet to be gathered, perhaps because supply was assumed to sustainably meet the demand and the trees were regenerating naturally in relatively inaccessible areas. By looking at historical data, mapping current knowledge, and layering climatic and environmental conditions likely to favor the different species, a recently updated map of the likely range of each species has been published in Nature Sustainability.16 Increased expertise in calibrating complex satellite mapping of changes in dryland trees and woodlands can generate maps based on recorded observations and the likelihood of suitable and changing environmental conditions. This is especially helpful in some areas such as in Dhofar in Oman where frankincense trees are the predominant tree species on otherwise vegetation-sparse landscapes. However, in other areas where frankincense trees do not represent the majority of vegetation, calibration of satellite data and verification on the ground (“ground truthing”) with sufficient numbers of survey plots is needed.23 These are costly, however, and installation and monitoring are a challenge in often remote and insecure areas.

Boswellia sacra in Dhofar, Oman

Boswellia sacra in Dhofar, Oman
Photo ©2021 Sue Canney Davison

Being a niche commodity and traditionally a secondary source of income, large-scale development-partner funding for reliably assessing the range, status, and health of the frankincense trees can be difficult to access. Given the current push for integrated large-scale drylands projects,24 gathering this information as part of integrated project activities will support the development of focused conservation practices which can incentivize and support harvesting communities to maintain healthy trees as well as inform local, national, and international regulatory decision-making.

Boswellia neglecta trees in Acacia-Commiphora woodlands in Kenya

Boswellia neglecta trees in Acacia-Commiphora woodlands in Kenya
Photo ©2021 Sue Canney Davison

The Harvesting and Management Practices of Different Communities and Stakeholders

Boswellia papyrifera, found in northern Ethiopia, is listed as “overutilized” and B. neglecta, B. rivae, and B. microphylla, found in southern Ethiopia, as “underutillized.”25 Do some of the biological and morphological characteristics of each species determine how they are harvested and utilized? The quality and properties of individual species’ resins aside, the resin structures in the inner bark of B. papyrifera have been thoroughly researched in order to ascertain the most effective and sustainable tapping methods and healing cycles.26 However, B. neglecta and B. rivae grow in arid and semi-arid migratory pastoralist systems of the Somali region of Ethiopia and northern Kenya on mostly communally owned land and are “almost exclusively collected from the natural exudates without tapping.”27 Further research is needed to confirm if this is because the resin canals in the inner bark are structurally unsuited to the tapping techniques used and recommended in B. sacra, B. papyrifera, and B. frereana, or there is some other underlying reason. In B. papyrifera, increased tapping has been shown to allow greater longhorn beetle infestation and susceptibility28, as well as reduced carbohydrate storage29 and seed reproductive capabilities.30 Boswellia neglecta in Kenya seems to depend on an interaction with the longhorn beetle larvae to produce its characteristic black resin, as its natural immediate exudate is very limited amounts of small white drops (H. Sommerlatte oral communication).

Boswellia rivae oozing naturally in southeast Ethiopia

Boswellia rivae oozing naturally in southeast Ethiopia
Photo ©2021 Abdnasir Abdikadir

 The landscapes in which each species grows can also determine who harvests them. In Somaliland, where the B. sacra trees can grow up to 8 meters, some on dangerous cliff faces and dry rocks, men harvest and dry the resin, then take it to collection centers where women sort some of it into grades, often sitting in the dust on the floor for long hours. In the Samburu region of Kenya, groups of women walk together to scrape B. neglecta off much shorter trees growing on hills close to savannahs, which provides them with limited but direct income.

White B. neglecta resin from a natural abrasion

White B. neglecta resin from a natural abrasion
Photo ©2021 Sue Canney Davison

In Oman, Omani women and men previously harvested the trees,31 but now it tends to be expatriate men. In Somaliland, as some landowners and their families move into urban areas, they may rent out their trees to harvesting groups and traders.32

In the Blue Nile state of Sudan, communities reportedly gain no benefits from the trees.33,34 However, receiving direct benefits from the trees is key to engaging communities in comprehensive long-term sustainable practices. The arid and semi-arid areas where frankincense trees grow are generally resource-poor regions where the maps of the likelihood of gums and resins trees overlap poverty maps. As alternative livelihood options to livestock or subsistence farming are few, harvesting frankincense in the dry seasons can contribute a significant portion to already low or minimal incomes.35,36,37 There is an increasing awareness that “the traditional supply chains of most resins can involve significant exploitation of the harvesters”9 and investing in the harvesting communities to support their development and incentivize sustainable tree management is a top priority to ensure the future of the trees and communites who harvest them.38 Also, these people often see very little profit margins compared to the powerful middlemen and end product producers and this can directly lead to unsustainable practices.39 When harvesters are living so marginally, it can be difficult for them to make long-term, sustainably based management decisions,” noted the authors of a 2020 paper in the International Journal of Professional Holistic Aromatherapy.9

Boswellia papryrifera in Tigray, Ethiopia

Boswellia papryrifera in Tigray, Ethiopia
Photo ©2021 Peter Groenendijk

To ensure the future of frankincense trees, communities need to be engaged in many aspects of sustainable management. Where harvesters are assessed as threatening adult tree health by making too many cuts in the tree too often and too deeply, conservation strategies that emphasize not harvesting adult trees may only be a partial solution, as the untapped live trees may then be vulnerable to being debarked or felled for medicinal uses, timber, firewood, fodder, or land clearance. In pastoralist dryland areas, where livestock are the main source of primary income, camels, cattle, and goats grazing on young saplings or shorter trees can be a major threat to woodland regeneration. In other areas, dry grass in open canopy woodlands, where free-ranging cattle graze, can be intentionally or unintentionally burnt, destroying both seedlings and saplings. In these areas, community-based livestock and fire management are an integral part of the long-term future of frankincense trees. Land tenure systems, ownership, harvesting rights, and the prices harvesters and communities receive also become critical factors, which need to account for the broader but localized shifting social and environmental dynamics as well as the changing climate. In short, harvesters and harvesting communities have perhaps remained the least visible actors in the value chain, whose knowledge, needs, and challenges must be heard and understood.

Boswellia papryrifera burning in Ethiopia

Boswellia papryrifera burning in Ethiopia
Photo ©2021 Yeshimebet Ayele Tegenie

Investing in Propagation and Intentional Planting

Perhaps because wild trees have traditionally supplied the niche market for frankincense products, there has been limited cultivation of Boswellia trees, which can take 10 to 20 years to develop girths that can sustain commercial harvesting. Different species have different seed germination rates, and seed viability can also depend on the health of the tree.29 Some with very low seed germination rates, like B. serrata, propagate more easily from root suckers. With increased knowledge and techniques, intentional planting likely will become a crucial part of longer-term conservation strategies. There are reports of previous plantations in Somaliland before 1991.40,41 Forest department records in India show that B. serrata was experimentally planted for paper purposes without much success.42 Consistent work with B. papyrifera root cuttings yielded stronger results.43 Others, such as B. frereana and B. sacra, have adapted to quite specific environments, with the ability to absorb the sea mists in otherwise hot and dry climates and grow on limestone with very high pH soils. It can take time to understand how to replicate the necessary conditions for resin production, particularly in other regions.

Jason Eslamieh in California, the Oman Ministry of Agriculture in Oman, and Guy Erlich in Israel are pioneers in propagating, hybridizing, and intentionally planting trees of the genus Boswellia. Eslamieh has focused more on research and experimentation and published his decades of knowledge and findings of working with these plants in the United States.44 The Oman Ministry of Agriculture has been planting and propagating B. sacra trees for more than 30 years and plantations have expanded to a larger scale. Those working with them have begun sharing their in-depth knowledge of the planting, watering, care, and environmental conditions needed to allow the trees to mature.45 In Israel, Erlich has focused on the Balm of Gilead (Commiphora gileadensis) and B. sacra and has demonstrated that irrigated plantations can be established outside of current range states.46 The overall quality and quantity of resin from intentionally planted trees compared with wild populations is still unknown.

Frankincense trees can be intentionally propagated in privately-owned plantations that prioritize frankincense resin production or as part of the restoration and enrichment of existing trees and woodlands. Understanding the activities, outcomes, and consequences of the two different approaches is important, as each one is likely to have different outcomes for existing tree regions and the communities who currently use and depend on the trees and surrounding biodiversity.

Boswellia neglecta seedlings propagated from seed

Boswellia neglecta seedlings propagated from seed
Photo ©2021 Sue Canney Davison

Regeneration and new growth (whether natural or planted) depends on the integrity of the forest and engaged sustainable management. One supportive mechanism that focuses of the health of current forests and communities is voluntary third-party certification. Some voluntary third-party certification schemes focus on the health of the trees, fair payment, and conditions for harvesters and can support greater confidence for those consumers concerned with buying sustainably harvested products. Further, wild-harvested Boswellia resin is intrinsically organic unless hormones are used to stimulate further resin production.47 Organic certification can add value,48 yet this increased value in and of itself does not ensure single-species harvesting or long-term regeneration.

Conservation concerns raised in the international gatherings include the impacts of increased demand, armed conflict, war, famine, increased human population densities, increased livestock numbers, better road access, and changes in land use and agricultural practices on traditional patterns of tree management, harvesting, and trade in some of the main sourcing areas of frankincense. As outlined above, to ensure sustainable management and regeneration of the trees and to address some of these concerns, a broader landscape approach and full community engagement is important. A summary of solutions which now need collective action and investment was presented at the WOCMAP meeting in 2019 (Table 3).49

 

Table 3. Actions Needed to Ensure the Future of Frankincense Trees

Issue

Challenges

Possible Solutions

Land conversion

Agriculture (sesame [Sesamum indicum, Pedaliaceae], cotton [Gossypium spp., Malvaceae], cattle), mining (gravel), logging

Create reserves and parks to protect areas of high genetic variability and mature trees; propagate and enrich current areas and create frankincense plantations; provide alternative domestic cooking and other energy sources
 

Grazing and fire

Increase in livestock; fire as a by-product of agriculture; uncontrolled fire

Install effective fencing, reduce herd size, control free grazing with set-aside areas; apply fire breaks; protect trees until they are above livestock heights; provide education and on-site training

Tapping

Too many deep and rough cuts; too many within-season cycles; too many year cycles without adequate rest and healing periods

Reduce numbers of tapping cuts and within-season cycles; develop and promote lower impact tapping techniques, practices, and systems; install rest years every third or fourth year with 5-10 years of rest every 20 years

Whole supply chain

Little assessment and management of trees and forests in some key areas; resin quality and (up) grading; unclear and confusing ownership (land tenure, use rights); lack of clear trade standards and regulations; insufficient national and international regulations for management and sustainable use of resources and weak implementation

Shift focus towards long-lasting health of trees and forests; stimulate collection incentives towards quality rather than quantity; follow the resin and who earns the money (equity and gender); upgrade and add value in production country (e.g., distilling essential oils, making end products); install trade control and “just” rules and regulations; adapt land tenure and modernize use rights (e.g., community-owned long-term use rights); increase transparency, improve trade regulation, and introduce third-party certification; create regulations adhering to international standards of sustainable use and management; increase awareness (and support pressure) by consumers

Note: This is a revised version of a table Frans Bongers introduced during a presentation at WOCMAP (2019).49 Reproduced with permission from the author.

 

The natural colors of B. carteri from Somaliland

The natural colors of B. carteri from Somaliland
Photo ©2021 Sue Canney Davison

Using the Resins and Essential Oils

It can be surprising and informative to learn of the many different species, phenotypes, qualities, colors, and aromatic profiles of the resins and essential oils of frankincense. Especially in Ethiopia and Oman, much frankincense resin is used in traditional and cultural practices without being exported. It is chewed for its health benefits and gum properties and burnt to produce smoke as part of cultural, sacred, or personal hygiene rituals and practices.27,50

A traditional incense burner in the Museum of Frankincense in Oman

A traditional incense burner in the Museum of Frankincense in Oman
Photo ©2021 Sue Canney Davison

One of the most expensive frankincense resins is “Mushaad” — the first-grade slabs of B. frereana found on steep slopes in the highlands of Somaliland and Puntland (Somalia). Large fresh pieces have traditionally been sold in Saudi Arabia and Yemen as chewing gum and after-meal mouth fresheners. Significant quantities of B. papyrifera and other resins have also been exported, often through Europe, as ritual incense for church services.50

“Mushaad” frankincense resin

“Mushaad” frankincense resin
Photo ©2021 Sue Canney Davison

The resin production processes of the different species are not well studied. Whether or not resin, which is produced in the inner bark, is constitutional (already available in the bark) or quickly produced upon natural or intended wounding, or both, is not well known. For B. papyrifera, constitutional resin is available in the resin canals and is drained upon wounding.26,51

Frankincense resin contains three main components: resins, gums, and essential oils. The water-soluble gums often accounts for 6-30% of the raw frankincense. The alcohol-soluble resin can account for 60-85% and contains boswellic and lupeolic acids, which are being researched for their therapeutic properties. Essential oils often account for 1-10% and are a mixture of predominantly monoterpenes with diterpenes and sesquiterpenes.52 The percentages and ratios of these components can vary significantly between different Boswellia species, and the quantity and quality of the resin harvested from one species is dependent on the age and stem diameter of the tree, the number of current and previous harvests, and environmental conditions, including altitude, rainfall, sea mist, solar irradiation patterns, nutrients, and insect and animal challenges.53 The realities of the natural variation between individual trees and populations of Boswellia species lies at the heart of current debates about trade standards, purity, quality, and regulation. Nevertheless, current understanding of the exact sources of and reasons for these similarities and differences is still limited.

More than 300 volatile compounds have been identified among the Boswellia species. Two of the major weaknesses in our current knowledge of the constituents and composition of frankincense essential oils are:

  • Researchers are yet to understand the extent to which variance and different chemotypes between individual trees and populations of the same species is genetic (most likely) or due other factors listed above.
  • Many samples in published papers are taken from markets where the exact source is not always known. Some vouchered samples (resin samples that are connected to individual trees and where the tree is identified with an herbarium collection voucher attached to it), can produce outlying results, creating the need to look deeper. Differences could be genetic yet may also be a result of different storage conditions, distillation methods, analysis techniques and libraries, and possible equipment contamination.

Variation across and within Species

Frankincense essential oils are now a common retail product. Understanding the normal composition of the oil of each species can be important for quality and regulatory purposes. Nevertheless, overlap between species, as well as natural variation within species, is making it difficult to be certain that a particular oil comes from a particular species. As shown in Table 2, a-pinene, a-thujene, limonene, sabinene, and myrcene predominate in quite a few Boswellia species. While general patterns for each species can emerge, such as B. sacra from Oman usually having the highest a-pinene between 60% and 80%,9 sometimes an individual Omani specimen can be lower.54 A few compounds may be unique to one species. For instance, high levels of octyl acetate in B. papyrifera essential oil and methoxydecane in B.occulta essential oil are not found in other species 9 . They can act as reliable identifying markers for those two species. Because of this, researchers also look for much lower amounts of a unique terpene that could be specific to a particular species. However, it is hard to prove that they will never be found in others. More in-depth work using only vouchered specimens is urgently needed before Boswellia essential oil composition can adequately define most original species.

Beyond issues of freshness, oxidation, and quality, causes of adulteration of frankincense essential oils can include species mixing, as well as intentional addition of key constituents from other species and sources.

In some source regions, one frankincense species usually predominates, making it easy to harvest species-specific resin. Examples are India (B. serrata), Oman (B. sacra), and northern Ethiopia, Eritrea, and Sudan (B. papyrifera), and West Africa (B. dalzielii). By contrast, in the Somali region of Ethiopia, northern Kenya, and parts of Somalia, where B. neglecta and B. rivae grow close to Commiphora species, harvesters can be aware of the different species, but apply the same vernacular names to more than one species. For instance, “Midhafur” can be applied to B. neglecta, B. rivae, Commiphora boransis, and C. ogadensis in the Somali region of Ethiopia (email from Abdinasir Abdikadir, June 2019). There needs to be an informed awareness and value-added incentive among harvesters to keep the resins from different scientific species separate in order to gain the higher market prices. As the B. occulta story in Somaliland showed,60 an unidentified species can unwittingly be harvested as a known species.

As the resins and oils of different frankincense species have been shown to have different antimicrobial, antibacterial, and antifungal properties, species purity becomes critical to building consumer trust.14,61 The issues of intentional adulteration of frankincense oil also need to be watched carefully as demand increases. From a different point of view anecdotally, some wonder if a frankincense-like oil that gives the same medicinal and aromatic properties as wild harvested oil can be developed to take the pressure of wild trees. Would it be frankincense?

Medicinal Uses

The range of medicinal uses being researched continues to grow. In traditional Chinese medicine, frankincense (ru xiang) and myrrh (mo yao) belong to the herbs that invigorate blood. Being regarded as bitter and pungent, frankincense is seen to have a cleansing action on the body, moving qi, opening channels, clearing damp, and relieving pain.62 Shallaki, as B. serrata is known in the Ayurvedic medical tradition in India, has mostly been used to lower inflammation and ease joint pain. Traditional herbal medicine often depends on synergistic actions among different herbs and resins, and frankincense and myrrh are often prescribed together.

Boswellia sacra resin and oil

Boswellia sacra resin and oil
Photo ©2021 Sue Canney Davison

The genetic pathways for the biosynthesis of boswellic acids are still to be identified, yet many of the known in vitro and in vivo pathways and cytotoxic and anti-inflammatory mechanisms of boswellic acids have been analysed and published, along with the different antibacterial, antifungal, anti-inflammatory, and other medicinal properties of different frankincense resins. Human clinical trials are still limited.13,14,53,63 Incensole acetate, found in the highest concentrations in B. papyrifera, has been shown to have a robust neuroprotective effect after brain trauma and antidepressant and anxiolytic effects in mice.64 Inhaling smoke65 and diffusing essential oil may have medicinal and mood benefits as well, in particular decreasing anxiety.14

Exactly how many boswellic acids remain after supercritical fluid (CO2) extraction of vouchered specimens of relevant species is yet to be published. When distilling the resin using steam or hydro-distillation, there is no evidence that these heavier lipophilic boswellic acids are taken up into the essential oil. They largely remain in the boiling water/raw resin mixture. Nevertheless, the preliminary experimental cytotoxic effects of boswellic acids have led to some unsupported claims that steam or hydro-distilled frankincense essential oil can “cure cancer.”66 To quote Abdul Latif Khan, PhD, of the University of Nizwa: “We do not want to get to the point where pseudo-science and misinformation is used to sell the product.”32 Nevertheless, increased access to information of traditional medicinal uses, in vitro and animal results, and proposed research into B. sacra and B. serrata for different cancers and COVID-19 remediation67 could lead to increased popular demand.

Compared with traditional medicinal uses of the whole resin or infusions, the growing therapeutic use of distilled essential oils is relatively recent. Even so, there is an increasing body of in vitro and in vivo experimental results on the bioactivity of frankincense essential oils, in particular focusing on antibacterial, anticancer, antifungal, anti-inflammatory, antioxidant, insecticidal, and larvicidal properties.68-70 Clinical evidence from human trials is lacking. Frankincense oil is regarded as relatively “safe” in terms of topical allergenic and phototoxic properties.71 More systematic research is needed to understand and support the current medicinal and therapeutic claims of the benefits of the vouchered essential oils of each frankincense species.

Perfumery

Frankincense plays a large role as a natural perfumery ingredient. Some of the signal aromatics, such as the musty “old church smell,” may arise from very small percentages of heavy sesqui- and di-terpenes such as olibanic acids. Nicolas Baldovini, PhD, summarized some of his main olfactory findings at the special session at WOCMAP (Table 4).

 

Table 4. Aromatic Profiles of Some Boswellia Species

Boswellia Species

Average Oil Yield[1]

Aromatic Description

B. sacra (syn B. carteri)

4-8%

Balsamic, resinous, spicy, “old church” base note

B. papyrifera

1-2%

Very dusty, aldehydic, green (coriander-like), soapy, fruity (pear), rough

B. neglecta

5-6%

Dry woody, pine needles, dusty, warm, floor wax, slightly camphoraceous

B. occulta (methoxydecane type)

1-6%

Fatty, soap, citrusy

B. socotrana

7.6%

Almond, plastic, woody, warm, humid, soapy

B. elongata

7.6%

Smoky woody, very waxy, plastic, zest/bitter, old church-like base note

Note: This is a revised version of the table Nicolas Baldovini introduced at WOCMAP (2019).8 Reproduced with permission from the author.

[1] The essential oil yield depends on many factors including population genetics, harvesting practices and timing, and lab scale distillation under optimal conditions versus larger scale commercial distillation. There is no collated published data on the exact ranges for each species so these figures are based on the authors’ experience and what Nicolas Baldovini presented at WOCMAP.

 

Key Trade Issues

Discussions on trade and markets at international gatherings have also raised quite a few important issues, not least that data on trade volumes, the complexities within some of the value chains, and accurate import and export figures are hard to access and collate. The scientific information above can provide the background to discuss different approaches to some key concerns and trade issues. Two such issues are standardization and expanding the portfolio of frankincense retail products and uses.

Given the natural variations, could standardization expand or limit market access for genuine pure frankincense products? National or international trade regulations do not always concern the Boswellia trees themselves, but focus more on the resin and resin products. Frankincense resin is usually sold as species-specific. On the other hand, frankincense essential oil can refer to either a blend of essential oils from different Boswellia species, or the essential oil from one Boswellia species. As shown above, the essential oils of different Boswellia species can have similar dominant or distinct terpenes (Table 2), with distinct chemotypes within the same species.56,59 In order to accommodate genuine natural variation, the percentage of terpenoid components of the essential oil of any one Boswellia species is accurately expressed in ranges.9 Some traders have created their own desired constituent ranges of the most popular frankincense species essential oil, even if it means rejecting and maybe limiting access to some markets for some genuine vouchered oils. Other retailers are happy to integrate natural variance into their business models, treating each vouchered batch more like a vintage in the wine trade.

More work is needed to analyze the similarities and differences across a broader range of vouchered samples from different trees and locations of the same species and different species in order to compile comparable results. As so little is currently understood about the reasons for differences among individual trees and populations, setting essential oil standards on such natural variation is probably a less effective way to support regenerative tree populations and harvesting communities than advocating for transparent supply and value chains.

Adding Commercial Value to the Whole Resin and Byproducts

Over the last 10 to 15 years, the essential oils distilled from whole resin are receiving the most commercial focus. Given that essential oil only constitutes between 1% and 10% of the resin (Table 4), can the rest (“waste”) be used in or transformed into byproducts, making the resin even more valuable? With little research published so far, views differ on whether and how many useful boswellic acids remain in the post-distillation resin from key species.52 Some of the “old church smell” molecules are heavy and may also remain in the post-distillation resin, opening opportunities to use it as incense.

The hydrosol (distillate water) gathered from the distillation of different species can have a pleasant aroma and contain up to 700 mg/L of the hydrophilic volatiles, with verbenone and terpinene-4-ol often predominating.72 Using and selling the hydrosol commercially as perfumed water or mists could allow greater value to be extracted from the harvested resin. One important trade issue will be to extend the registration of different products from different Boswellia species for various cosmetic, consumable,73 and medicinal uses in different markets.

Transparent Supply and Value Chains

During the different international gatherings, it also became clear that the ethics of the supply chains of importing companies have a large role to play in the sustainable future of frankincense and are deeply dependent on the contextual realities and activities of the harvesters, middlemen, and traders. Traceability is made more complex as middlemen and traders often aggregate resin from different sources within a country into larger single lots, many of which are aimed for export. At the same time, shorter, more transparent value chains with fewer middlemen are expected to lead to communities or smaller-scale range state businesses getting more direct benefits. What is more, an increasing number of end-users are demanding equitable and sustainable supply chains.74

Harvesting B. sacra in Somaliland

Harvesting B. sacra in Somaliland
Photo ©2021 Dayaxa Frankincense Export Company

As mentioned above, third-party certification of the sourcing practices and supply chains can support sustainable practices, as has been shown for other commodities such as timber, coffee (Coffea spp., Rubiaceae), and chocolate (derived from Theobroma cacao, Malvaceae). With harvesters and harvesting communities often receiving relatively little income from their raw forest products, they can seldom afford the upfront and ongoing costs of voluntary or regulated certification. These realities can push the pricing and buying power in the value chain into the hands of larger brokers and commercial entities whose approach and commitment to sustainability becomes all-the-more critical to the survival of the trees and the future supply of resin.

In some harvesting areas, harvesters are being supported to form cooperatives to share best practices, act as centers of intentional propagation, stabilize prices, and gain more reliable access to markets. In the future as phone connectivity spreads to currently inaccessible areas, taking photographs of tapping practices, marking the GPS location of the harvested trees, and sending that information or capturing it in emerging technologies, such as blockchain, will provide a verifiable record.75 Digital payments based on the these records will allow for more direct remuneration of harvesters. This level of diligence may add additional upfront costs, especially for small scale businesses, but will add very little to retail prices at scale. The additional brand value created by confirming sustainability is likely to outweigh any reasonable additional retail cost and meet the needs of consumers wanting to ensure sustainable sourcing.

A cooperative in southeast Ethiopia

A cooperative in southeast Ethiopia
Photo ©2021 Abdinasir Abdikadir

The Creation of the Global Frankincense Alliance

The future of frankincense relies on the support of the wide range of stakeholders, who each play their part in ensuring sustainable trade. Given the uncertainties, complexities, and unknowns in this commodity market, at the meeting of WOCMAP in Cyprus in 2018, some delegates suggested creating a lean international platform as a focal point for the collection and dissemination of information on the taxonomy, scientific discoveries, conservation issues, industry activity, new legislation, and trade developments in this sector. In response to this request, the GFA (www.globalfrankincensealliance.com), a nonprofit organization and platform, was established by concerned scientists and other interested parties in 2020 (see sidebars 1 and 2).

 

Sidebar 1. Meetings, Articles, and Events Informing the Formation and Activities of the GFA

May 2016+ Environment Society of Oman meeting (Salalah, Oman)
September 2016 IFEAT Fragrance and Flavors annual Conference (Dubai, UAE)
October 2018 1st International Congress on Frankincense and Medicinal Plants (Muscat, Oman)
May 2019 CITES Secretariat report on Boswellia trade (Geneva, Switzerland)
April-June 2019 Perfumer & Flavorist three-part article on frankincense76-78
July 2019 Bongers et al paper in Nature Sustainability16
October 2019 WOCMAP special session on frankincense and myrrh (Bafra, Cyprus)8
January 2020 GFA founded (London, England)
April 2021 GFA “Future of Frankincense” online workshop
June 2021 CITES Plants Committee online meeting

 

 

 

 

 

 

 

 

 

 

Sidebar 2. Objectives of the GFA

  • To advocate for and stimulate worldwide attention and education on the scientific, commercial, and cultural importance of frankincense and myrrh products and the challenges faced by the trees and harvesters.
  • To encourage national, regional and international collaboration between individuals, universities, companies, and organizations involved in all aspects of frankincense and myrrh.
  • To disseminate information on the status of the trees, populations, and forests in their range states and the economic and environmental threats and challenges they face.
  • To share best practices on sustainable propagation and regeneration of the trees, as well as traditional and novel techniques for traceable sustainable production, harvesting, and processing.
  • To encourage research and development into novel value-added products from frankincense and myrrh.
  • To collate and disseminate information on the status, patterns, and volumes of global trade in frankincense and myrrh.
  • To enable all players involved to be fully aware of current and future legislation, encouraging all concerned to proactively implement necessary changes, and ensure the sustainable long-term future of the trees.

 

In March 2021, the GFA organized an online workshop titled “The Future of Frankincense,” which had more than 300 registered delegates from 38 countries. Many filled out an initial questionnaire, and the purpose of the ensuing meeting was to collectively explore the following question: “What are the most important questions that need to be answered and actions that need to be taken to support the long-term future of frankincense trees and the communities that harvest them?” The workshop had four major themes: (1) Botany, identification, and current status of the trees; (2) Communities, regeneration, and forest management; (3) Biochemistry and medicinal applications; and (4) Supply chains, products, regulations, and trade. While networking and side conversations are limited online, the virtual gathering made it possible for farmers, traders, and harvesting community representatives in range states with sufficient internet connectivity to participate and report back directly on range state focal group meetings. The workshop reports and video can be found on the GFA website. The main results of this workshop will be reported in an upcoming article. The organizers hope that these documents can form the basis for a roadmap for the conservation and sustainable development of the species.

It is a huge challenge to gather and provide international regulatory bodies such as CITES with adequate, scientifically verified evidence on the status of the different species and information on the supply and value chains and international trade — all of which are needed for making informed and effective decisions. Much of the existing knowledge on the status of frankincense trees currently lies with those people and organizations managing and harvesting the trees and private sector stakeholders directly involved in the trade. Some of this is reflected in scientific reports or papers, but much is lacking public availability and accessibility. Multi-stakeholder forums and collaborative projects and working groups focused on frankincense, where researchers and public and private organizations share information, have become ever more important for identifying and promoting effective species-specific sustainable practices.

 

* For more information about this aspect of the frankincense trade, useful historical articles can be found here: https://globalfrankincensealliance.com/articles-and-reports-history-and-culture.

ICFMP abstracts are available on GFA’s website.

Sue Canney Davison, PhD, grew up in northern England and has lived in India and Kenya for the last 28 years. She has focused professionally on facilitating diverse collaborations and knowledge creation. Her passion for Burseraceae trees and harvesting communities started in Kenya in 2012. She has been involved with the Global Frankincense Alliance (GFA) since November 2019, and supported the design, facilitation, and reporting on the “Future of Frankincense” online gathering in March 2021. She is continuing to deepen her understanding of Burseraceae as a research associate in the Department of Botany and Plant Biotechnology at the University of Johannesburg.

Frans Bongers, PhD, is professor of tropical forest ecology at Wageningen University & Research (WUR) in the Netherlands and works on succession, biodiversity, forest regeneration and forest management in various tropical countries, both in Africa and Latin America. He is a world-leading expert in the study of sustainable use and management of Boswellia trees. He has worked for 20 years on Boswellia populations in Eritrea, Ethiopia, and Sudan and is author or co-author of more than 35 publications related to frankincense. As board member of the GFA he strives to improve sustainability of the frankincense production chain worldwide.

Denzil Phillips, MSc, has worked for more than 30 years in the field of conservation and sustainable sourcing of medicinal plants. He has undertaken consultancies in more than 35 countries in Europe, Asia, Africa, and the Caribbean, working with some of the world's leading development agencies and natural products manufacturing companies. Denzil has done pioneering work with endangered plants such as Taxus baccata, Aquilaria malaccensis, and more recently Boswellia sacra. He is a founding member of the Association of African Medicinal Plants Standards (AAMPS) and the GFA.

References

  1. Groom NSJ. Frankincense and Myrrh: A Study of the Arabian Incense Trade. London, UK, and New York, NY: Longman; 1981.
  2. Dickson DM. The transplantation of Punt incense trees in Egypt. Journal of Egyptian Archaeology. 1969;55:55-65.
  3. Brettell RC, Schotsmans EMJ, Walton Rogers P, Reifarth N, Redfern RC, Stern B, Heron CP. ‘Choicest unguents’: Molecular evidence for the use of resinous plant exudates in late Roman mortuary rites in Britain. Journal of Archaeological Science. 2015;53:639-648.
  4. Grbić ML, Unković N, Dimkić I, et al. Frankincense and myrrh essential oils and burn incense fumes against micro-inhabitants of sacral ambients. Wisdom of the ancients? Journal of Ethnopharmacology. 2018;219:1-14.
  5. Baumann BB. The botanical aspects of ancient Egyptian embalming and burial. Economic Botany. 1960;14(1): 84-104.
  6. Thulin M. The genus Boswellia (Burseraceae): The frankincense trees. Symbolae Botanicae Upsalienses. 2020;39.
  7. Asfaw N, Sommerlatte H, Demissew S. Uncommon frankincense. Perfumer and Flavourist. 2019;December:47-55.
  8. Report on the Special Session on the Future of Frankincense and Myrrh at the WOCMAP VI in Northern Cyprus. Global Frankincense Alliance website. Available at: https://globalfrankincensealliance.com/wp-content/uploads/2020/07/WOCMAP-VI-report-final-PDF.pdf. Accessed January 29, 2021.
  9. Johnson S, Ablard K. Frankincense: Tapping into a sustainable future. International Journal of Professional Holistic Aromatherapy. 2020;9(3)45-56.
  10. Eslamieh J. The Genus Boswellia Preservation through Horticulture. Phoenix, AZ: A Book’s Mind; 2017.
  11. Thulin M, DeCarlo A, Johnson SP. Boswellia occulta (Burseraceae), a new species of frankincense tree from Somalia (Somaliland). Phytotaxa. 2019;394(3):219-224.
  12. Woolley CL, Suhail MM, Smith BL, et al. Chemical differentiation of Boswellia sacra and Boswellia carteri essential oils by gas chromatography and chiral gas chromatography-mass spectrometry. Journal of Chromatography A. 2012;1261:158-163.
  13. Ammon HPT. Weihrauch-Anwendung in der westlichen Medizin. New York, NY: Springer; 2018.
  14. Al-Harrasi A, Hussain H, Csuk R. Chemistry and Bioactivity of Boswellic Acids and Other Terpenoids of the Genus Boswellia. Amsterdam, the Netherlands: Elsevier; 2019.
  15. Frankincense Essential Oil Market Report. Market.US website. Available at: https://market.us/report/frankincense-essential-oil-market/request-sample/#overview. Accessed January 29, 2021.
  16. Bongers F, Groenendijk P, Bekele T. Frankincense in peril. Nature Sustainability. 2019;2:602-610.
  17. DeCarlo A, Ali S, Ceroni M. Ecological and economic sustainability of non-timber forest products in post conflict recovery: A case study of frankincense (Boswellia spp.) resin harvesting in Somaliland (Somalia). Sustainability. 2020;12(9):35-78.
  18. Soumya KV, Shackleton CM, Setty SR. Impacts of gum-resin harvest and Lantana camara invasion on the population structure and dynamics of Boswellia serrata in the Western Ghats, India. Forest Ecology and Management. 2019;453: 117618.
  19. Soumya KV, Shackleton CM, Setty SR. Harvesting and local knowledge of a cultural non-timber forest product (NTFP): Gum-resin from Boswellia serrata Roxb. in three protected areas of the Western Ghats, India. Forests. 2019;10:907 1-19.
  20. Mokria M, Tolera M, Sterck FJ, Gebrekirstos A, Bongers F, Decuyper M, Sass-Klaassen U. The frankincense tree Boswellia neglecta reveals high potential for restoration of woodlands in the Horn of Africa. Forest Ecology and Management. 2017;385:16-24.
  21. Klein J. Frankincense trees face collapse, a study warns. The New York Times. July 3, 2019.
  22. Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Notification to the Parties: Questionnaire on Decision 18.205 on Boswellia trees. February 10, 2020. CITES website. Available at: https://cites.org/sites/default/files/notif/E-Notif-2020-010.pdf. Accessed November 11, 2021.
  23. Girma A, de Bie CAJM, Skidmore AK, Venus V, Bongers F. Hyper-temporal SPOT-NDVI dataset parameterization captures species distribution. International Journal for Geographic Information Science. 2016;30:89-107.
  24. Deutsche Gesellschaft für Internationale Zusammenarbeit. Roots of Restoration: Sustainability through Community-Based Forest Landscape Recreation. Bonn, Germany: Global Landscapes Forum; 2021. Available at: www.globallandscapesforum.org/publication/roots-of-restoration-sustainability-through-community-based-forest-landscape-restoration/. Accessed November 17 2021.
  25. Munyua SJM, Mbiru S, eds. Report on formulating a strategy for production, value addition and marketing of products from arid and semi-arid (ASAL) in the IGAD region. Nairobi, Kenya: ICPALD; 2015.
  26. Tolera M, Menger D, Sass-Klaassen U, Sterck FJ, Copini P, Bongers F. Resin secretory structures of Boswellia papyrifera and implications for frankincense yield in Ethiopia. Annals of Botany. 2013;111:1-8.
  27. Deutsche Gesellschaft für Internationale Zusammenarbeit. Partnership Ready Ethiopia: Gums and resins. Eschborn, Germany: Global Business Network Programme; 2020.
  28. Negusse A, Gebrehiwot K, Yohannes M, Norgrove L, Aynekulu A. Continuous resin tapping for frankincense harvest increases susceptibility of Boswellia papyrifera (Del.) Hochst trees to longhorn beetle damage. Heliyon. 2021;7(2):e06250.
  29. Mengistu, T, Sterck FJ, Fetene M, Bongers F. Frankincense tapping reduces the carbohydrate storage of Boswellia trees. Tree Physiology. 2013; 33(6):601-608.
  30. Rijkers T. Ogbazghi W, Wessel M, Bongers F. The effect of tapping for frankincense on sexual reproduction in Boswellia papyrifera. Journal of Applied Ecology. 2006;43:1188-1195.
  31. Ghazanfar SA. Boswellia – the trees that produce frankincense. Presentation for Leeds University Language and/or Nature in Southern Arabia Programme. CELCE July 14, 2020. London, UK: Royal Botanic Gardens, Kew.
  32. Global Frankincense Alliance. The Main Outcomes and Roadmap: Proceedings for the Future of Frankincense Online Workshop 2021. March 2021. Available at: https://globalfrankincensealliance.com/. Accessed November 11, 2021.
  33. Abdalla MMA, Gessmala AF. Economic net return analysis of Boswellia papyrifera (Del.) Hochst in the Blue Nile State Sudan. Horticulture International Journal. 2018;2(5):281-285.
  34. Abtew AA, Pretzsch J, Mohmoud TE, Adam YO. Commodity chain of frankincense from the dry woodlands of Nuba Mountains South Kordofan State, Sudan. Small Scale Forestry. 2012;(11):365-388.
  35. Woldeamanuel T. Dryland resources, livelihoods and institutions. Diversity and dynamics in use and management of gum and resin trees in Ethiopia. PhD thesis. Wageningen, the Netherlands: Wageningen University; 2011.
  36. FAO FSNAU. East Golis Frankincense, Goats and Fishing Livelihood Zone Baseline Report. Technical Series Report No. VI. 66. Food and Agriculture Organization of the United Nations. May 18, 2016:1-28
  37. Mekonnen Z, Worku A, Bahru T, Teketay D. Economic contribution of gum and resin resources to household livelihoods in selected regions and the national economy of Ethiopia. Ethnobotany Research and Applications. 2013;11:273-288.
  38. Global Frankincense Alliance. ‘Future of Frankincense’ Online Survey Final Results. 2021
  39. Muse OA. Market Potential of Frankincense Gum for Rahan Trading LLC. Bachelor thesis. Helsinki, Finland: Haaga-Helia University of Applied Sciences; 2018.
  40. Martinetz D, Lohs K, Janzen J. Weihrauch und Myrrhe: Kulturgeschichte und wirtschaftliche Bedeutung, Botanik, Chemie, Medizin. Stuttgart, Germany: Wissenschaftliche Verlangsgesellschaft mbH Stuttgart; 1988.
  41. Farah AY. Milk of the Boswellia Forests: Frankincense Production among the Pastoralist Somali. Uppsala, Sweden: Reprocentralen HSC; 1994.
  42. Waheed Khan MA. Propagation of Boswellia papyrifera through branch-cuttings. The Indian Forester. 1972;98(7)437-440.
  43. Haile G, Gebrehiwot K, Lemenih M, Bongers F. Time of collection and cutting sizes affect vegetative propagation of Boswellia papyrifera (Del.) Hochst through leafless branch cuttings. Journal of Arid Environments. 2011;75(9):873-877.
  44. Eslamieh J. Cultivation of Boswellia: Sacred Trees of Frankincense. Phoenix, AZ: A Book’s Mind; 2011.
  45. Propagation of Boswellia sacra in Oman with Salah Agieb [video]. Global Frankincense Alliance website. Available at: https://globalfrankincensealliance.com/news-2/webinars/. Accessed January 29, 2021.
  46. About the farm. Balm of Gilead Farm website. Available at: www.balmofgileadfarm.com/. Accessed January 29, 2021.
  47. Yamamoto F, Iwanaga F, Al-Busaidi A, Yamanaka N. Roles of ethylene, jasmonic acid, and salicylic acid and their interactions in frankincense resin production in Boswellia sacra Flueck. trees. Scientific Reports. 2020;10(1):16760.
  48. Essential Oils and Oleoresins: Market Insider. Geneva, Switzerland: International Trade Centre; August 2015.
  49. Bongers F, FRAME. Keeping Frankincense Resources: What We Need to Know and Do. Presentation at the special session on the Future of Frankincense and Myrrh at WOCMAP VI. Nicosia, Northern Cyprus; November 2019.
  50. Khan AJ. Medicinal properties of frankincense. Int J Nutr Pharmacol Neurol Dis. 2012;2:79.
  51. Khan AL, Al-Harrasi A, Shahzad R, et al. Regulation of endogenous phytohormones and essential metabolites in frankincense-producing Boswellia sacra under wounding stress. Acta Physiologiae Plantarum. 2018;40(6):1-11.
  52. Schmiech M, Lang SJ, Werner K, et al. Comparative analysis of pentacyclic triterpenic acid compositions in oleogum resins of different Boswellia species and their in vitro cytotoxicity against treatment-resistant human breast cancer cells. Molecules. 2019;24(11):21-53.
  53. Al-Harrasi A, Khan Al, Al-Rawahi AS. Biology of Genus Boswellia. Basel, Switzerland: Springer Nature; 2019.
  54. Al-Harrasi A, Al-Saidi S. Phytochemical analysis of the essential oil from botanically certified oleogum resin of Boswellia sacra (Omni Luban). Molecules. 2008;13:2181-2189.
  55. DeCarlo A, Dosoky NS, Satyal P, Sorenson A, Setzer W. The essential oils of the Burseraceae. In: Malik S, ed. Essential Oil Research: Trends in Biosynthesis, Analytics, Industrial Applications and Biotechnological Production. London, UK: Springer International Publishing; 2019:61-14.
  56. Pappas R. Frankincense review: Classification by chemotype rather than just species. December 18, 2016. LinkedIn. Available at: www.linkedin.com/pulse/frankincense-review-classification-chemotype-rather-pappas-ph-d-. Accessed November 11, 2021.
  57. Gupta M, Rout PK, Misra LN, Gupta P, Singh N, Darokar MP. Chemical composition and bioactivity of Boswellia serrata Roxb. essential oil in relation to geographical variation. Plant Biosystems. 2017;151(4): 623-629.
  58. DeCarlo A, Johnson S, Poudel A, Satyal P, Bangerter L, Setzer WN. Chemical variation in essential oils from the oleo-gum resin of Boswellia carteri: A preliminary investigation. Chemistry and Biodiversity. 2018;15(6):e1800047.
  59. DeCarlo A, Johnson S, Okeke-Agulu KI, et al. Compositional analysis of the essential oil of Boswellia dalzielii frankincense from West Africa reveals two major chemotypes. Phytochemistry. 2019;164:24-32.
  60. Thulin M, DeCarlo A, Johnson SP. Boswellia occulta ( Burseraceae) A new species of Frankincense tree from Somalia (Somaliland). Phytotaxa. 2019;394(3):219-224.
  61. McCutcheon A. Boswellia serrata Adulteration. Austin, TX: ABC-AHP-NCNPR Botanical Adulterants Prevention Program. June 2018. Available at: www.herbalgram.org/resources/botanical-adulterants-prevention-program/adulterants-bulletins/boswellia-bulletin-june-2018/. Accessed November 11, 2021.
  62. Yang Y. Chinese Herbal Medicines Comparisons and Characteristics. London, UK: Churchill Livingstone; 2002.
  63. Engels G. Frankincense: Boswellia sacra (syn. B. carteri), B. serrata Burseraceae. HerbalGram. 2010;88:1-4.
  64. Al-Harrasi A. Distribution of the anti-inflammatory and anti-depressant compounds: Incensole and incensole acetate in genus Boswellia. Phytochemistry. 2019;161:28-40.
  65. Al-Harrasi A, Hussain H, Hussain J, et al. Two pyrolysate products from Omani frankincense smoke: First evidence of thermal aromatization of boswellic acids. Journal of Analytical and Applied Pyrolysis. 2014;110:430-434.
  66. Tisserand R. Frankincense Oil and Cancer in Perspective. Tisserand Institute website. Available at: https://tisserandinstitute.org/frankincense-oil-and-cancer-in-perspective/. Accessed November 11, 2021.
  67. Brendler T, Al-Harrasi A, Bauer R, et al. Botanical drugs and supplements affecting the immune response in the time of COVID-19: Implications for research and clinical practice. Phytotherapy Research. 2021;35(6):3013-3031.
  68. Di Stefano V, Schillaci D, Cusimano MG, Rishan M, Rashan L. In vitro antimicrobial activity of frankincense oils from Boswellia sacra grown in different locations of the Dhofar Region (Oman). Antibiotics (Basel). 2020;9(4):195. 1-9.
  69. Frank MB, Yang Q, Osban J, et al. Frankincense oil derived from Boswellia carteri induces tumor cell specific cytotoxicity. BMC Complement Altern Med. 2009;9 (6) 1-11.
  70. Vuuren SFV, Kamatou GPP, Viljoen AM. Volatile composition and antimicrobial activity of twenty commercial frankincense essential oil samples. South African Journal of Botany. 2010;76:686-691.
  71. Tisserand R, Young R. Essential Oil Safety: A Guide for Health Care Professionals. 2nd ed. London, UK: Churchill Livingstone; 2014:287-289.
  72. Harmon A. Circle H Institute ID# CHI1314 - 1316, 1173, 1096, 1153, 1372, 1408. Available at: https://circlehinstitute.com/chemistry/gc13/#CHI-1315. Accessed November 11, 2021.
  73. CBI Ministry of Foreign Affairs. Exporting Frankincense to Europe. CBI website. November 1, 2018. Available at: https://www.cbi.eu/node/1023/pdf. Accessed November 11, 2021.
  74. De Angelis P, Timoshyna A. Strengthening sustainable trade in medicinal and aromatic plants. HerbalGram. 2020;127:28-34.
  75. Raterman K. The potential of blockchain for herbal supply chain management. HerbalGram. 2019;123:52-61.
  76. DeCarlo A, Johnson S, Phillips D. Frankincense Geopolitics, Trade and Transparency, Part 1. Perfumer & Flavorist. September 2019;44:28–40.
  77. DeCarlo A, Johnson S, Phillips D. Frankincense Varieties and Habitats, Part 2. Perfumer & Flavorist. September 2019;44:DM1–DM8.
  78. Eslamieh J, Canney Davison S. Ensuring the Future of Boswellia. Perfumer & Flavorist. October 2019;44:45–50.
References