By Alba Costa, a 4th year PhD Student with Chris Kaiser-Bunbury, researching the effects of habitat restoration on plant-animal mutualistic and antagonistic interaction networks in Seychelles inselberg plant communities.
Carrot cakes, chai lattes, buns and mulled cider wouldn’t be the same without the unmistakable sweet and woody aroma of cinnamon. This versatile spice is a favourite across the world in both savoury and sweet dishes, and was once so highly sought after that it was used as a currency, with wars fought over it. But where does this spice come from and how is it linked to the conservation of our natural world?
Where does cinnamon come from?
Cinnamon is the bark of several tree species from the genus Cinnamomum in the family Lauraceae and it is native to Sri Lanka (Ceylon). Ceylon cinnamon (Cinnamomum verum), also called ‘true cinnamon’ is a bushy evergreen tree that grows to 15 m in height, with creamy-yellowish flowers and purple fleshy fruits or drupes, each containing one seed. After growing the tree for two years, branches are cut at an angle to encourage the plant to regrow. The cut branches are then soaked in water to facilitate the peeling process, during which peelers shave off first the outer bark and then the inner bark, which is the cinnamon layer. In a final step, the inner bark is dried and naturally curls up into the characteristic reddish brown quills.
Ceylon cinnamon (Cinnamomum verum) leaves and flower buds. Photo: A. Costa
The role of cinnamon on a remote island
In 1772 Ceylon cinnamon was introduced as an exportable crop to the Seychelles, a group of 155 islands in the Western Indian Ocean. However, following the boom in tourism over the past 50 years, the production of cinnamon leaf oil and the export of bark are no longer central to the islands’ economy. Although cinnamon harvesting is only done for the local and tourism market, cinnamon trees dominate forests across the main island of Mahé, where more than 80% of the forest canopy consists of this most successful invasive species.
The key to successful invasion
A species is classified as an ‘invasive alien’ when its introduction causes or is likely to cause ecological or economic damage, or harm to human health. Cinnamon is well adapted to different conditions and thrives in tropical climates; this means that it can quickly colonise large areas and compete with native plant species for light and nutrients. By forming dense thickets of vegetation, cinnamon trees shade out other plant species and prevent light from reaching their leaves. Once established, adult trees create a dense root mat on the surface of the soil that suppresses the growth of young trees by competing for scarce nutrients. In addition to its rapid and vigorous growth, the invasion success of cinnamon is also thanks to the quantity and characteristics of its fruits. Trees produce large fruit crops that are highly attractive to birds due to their high nutritional content compared to those of native species. Cinnamon fruits are therefore a favoured food source for frugivorous birds such as the Seychelles bulbul (Hypsipetes crassirostris) and the Seychelles blue pigeon (Alectroenas pulcherrimus) which then disperse their seeds and consequently contribute to cinnamon’s spread and colonisation success.
Left: Ceylon cinnamon (Cinnamomum verum) ripe (dark purple) and unripe (green) fruit. Right: One of the main dispersers of cinnamon fruits in the Seychelles, the Seychelles blue pigeon (Alectroenas pulcherrimus). Photos: A. Costa
Why is the presence of cinnamon out of its native range a conservation issue?
The spread of Ceylon cinnamon has altered and degraded Seychelles native habitats and affected endemic fauna including several endangered snails, endemic geckos, the tiger chameleon (Archaius tigris), the Seychelles house snake (Lamprophis geometricus, which is also a forest dweller) and the Seychelles wolf snake (Lycognathophis seychellensis) (see the Global Invasive Species Database for further impact information). Moreover, cinnamon competes with many endemic plant species, such as the critically endangered bois de montagne (Campnosperma seychellarum). Furthermore, cinnamon’s invasion not only threatens individual species but entire communities of plants and animals by altering plant-animal interactions such as pollination and seed dispersal. Consequently, such invasive species can alter biological processes that are essential for the functioning and persistence of ecosystems, such as pollination and seed dispersal. Specifically, at sites without invasive plants, the number of pollinator species, the number of visits to flowers and the diversity of interactions between pollinators and plants are higher than in invaded forests. As a result, native flowering plants received more pollen and produced more fruit in the absence of invasive plants. More recently, similar negative effects have been shown for seed dispersal. In cinnamon-dominated forests the dispersal of native seeds is reduced, compromising the regeneration and long-term survival of native plants (unpublished data). These impacts of invasive alien plants on individual species and ecosystem functions is a problem for the conservation of native biodiversity.
How is the Seychelles dealing with this environmental threat?
Today, cinnamon is only one of many invasive alien species in the Seychelles, and the problems caused by such species have been widely recognised. For instance, the active management of invasive alien plants was listed as a main target in the Seychelles’ National Strategy for Plant Conservation developed under the Global Strategy for Plant Conservation. Moreover, with the aim of developing active measures against the spread of cinnamon, the Indian Ocean Commission (IOC) tested different physical methods, such as uprooting, girdling or ring-barking and replanting for the control of this species. To date, various scientific studies have provided excellent data that can be used as guidance for future control and management programmes (see Rocamora and Henriette 2017, for more information on the management of invasive alien species in Seychelles). Recently, however, with the Covid-19 pandemic having highlighted the vulnerability of the tourism industry, the Seychelles’ government is considering bringing back the cultivation and exportation of cinnamon.
Restoration team from the Seychelles National Parks Authority (SNPA) eliminating invasive plants on the island of Mahé, Seychelles. Photo: C. Kaiser-Bunbury.
Could cinnamon harvesting be the solution?
Harvesting cinnamon again could benefit Seychelles’ economy by providing a new source of revenue in addition to the Seychelles main income from fisheries and tourism. But how likely is it that harvesting cinnamon would contribute to control the spread of the species and become a solution to the pressure exerted by cinnamon on native ecosystems? Given the rarity of invasive species being successfully controlled via economic exploitation, the consequences for conservation are more likely to be negative. Turning cinnamon into a commodity, and thereby increasing its value, comes with the risk of the control of this species becoming contentious, promoting its spread, and with it, aggravating the impacts of the invasion.
So the next time you smell or taste cinnamon, think about the past and present ecological stories behind the spices we use, like this one about the challenges posed to a small island by plant invasion.