Welcome To The Jungle: pt. 1
The first part of the capstone to my twitter thread series on the stunning ecosystems of Reunion island with a look at the lowland rainforest ecosystem.
PS: before we start the post is a little too long for email, so please be aware of that if you’re reading directly in your inbox.
For a few months now I’ve periodically shared my travels across the lush subtropical island of Reunion and the myriad beautiful species I saw there. This post will be dedicated to a topic that couldn’t be done justice with just one thread, the main draw for many a tourist to that wonderful location: the rainforests and cloudforests at the centre of the island. For those who feel like catching up, all my previous twitter threads on the island are linked at the bottom of this post.1
But first, as I’ve done in all my threads so far, I post a music video and invite you to immerse yourself in the holiday mood with the relaxing sounds of créole Sega Maloya music.
As stated in my first thread on the topic, Reunion is climatically cut in two parts: the “windward” part, which broadly represents the Eastern half of the island, is subject to frequent and heavy rainfall for most of the year, even the dry season (Austral winter). The “windless” part is bone dry for most of the year. This also broadly delineates the distribution of biomes on the island. Obviously, rainforests require lots of water: at least 2000mm of precipitation per year, in fact (to give you an idea, only a handful of the wettest areas in metropolitan France equal this). However, water isn’t the only ingredient required, and this is where it gets a little technical.
The second factor which cuts Reunion’s rainforests in two is altitude, through its proxy, temperature. The “megathermal” (very warm) level is the warmest and essentially stretches from roughly 100 metres to 1200 metres above sea level. Beyond this altitude, the lowland species will have trouble adapting to the larger daily and seasonal temperature swings and become outcompeted by “mesothermal” (medium heat) species. In layman’s terms, this means the biome is divided between lowland rainforest and high altitude cloud forest. Today, we’ll learn about the lowland forest.
The destruction of the lowland rainforest:
Reunion’s lowland rainforest is characterised by the presence of a canopy of evergreen leafy plants dominated by the families Sapotaceae (which includes the zapote and shea trees) and Arecaceae (palm trees). The native species of the former family are by far the largest contributors to the canopy, with others being rarer. They are not particularly large trees as their average size is between 10 and 20 metres in ordinary conditions.
Unfortunately, during the past two centuries, this lowland forest (called in French technical terms “Forêt mégatherme hygrophile” which essentially means a very warm and wet forest) has been increasingly fragmented by agriculture and urbanisation. All the major settlements of the island are coastal, or near-coastal, as the terrain in the centre of the island is too mountainous and rugged to build cities. This also means that nearby lowland forests are under intense anthropic pressure, and much of their superficy has been given over to agricultural uses, chiefly clear-cutting for the creation of cow pastures and plantation of cane sugar. This valuable crop is the island’s main export and also requires both warm temperatures and plentiful water. As it’s the only place in the EU where the plant can be grown in natural conditions, France encourages its production.
Today, the only significant lowland forest which is easily accessible for visitors is the Mare Longue forest of Saint-Philippe, in the South-Eastern corner of the island (which I unfortunately was unable to visit during my stay). It is managed as a tourism area with marked trails, picnic amenities, information signs, etc. The remaining forests are circumscribed to the steep mountainsides of the inner island, rarely served by asphalted roads and far from the cities. They are classified as “national forests” because of their notable biological value.
Emblematic of this destruction is the plateau known as the “Plaine des Palmistes”, “palmiste” being the name for indigenous palm tree species found on the island. This forested area was first colonised very slowly during the early 19th century after an inn was opened in the area (“Bon Accueil”, or good welcome), prompting several families from nearby Sainte-Rose to move in along the road. As it boasted (and still boasts) the only major road crossing the island’s centre, it was investigated by the army for its potential in agricultural development and facilitating troop movements. A large area at the heart of the forest was clear-cut to make place for a small camp housing 15 soldiers and as many convict workers. Shortly after, plots of land would be granted for the purposes of subsistence agriculture, and soon the location became a fully fledged city with a church and local authorities.
Tree species of the warm rainforest:
This is an appropriate juncture to segue into proper botany. In this forest were likely found three species of “palmistes” indigenous to the Mascareignes archipelago. They are today some of the rarest trees on the island, as unfortunately part of their core is considered not only edible, but a coveted delicacy, which led to tremendous over-harvesting. The edible part is the apical meristem near the leafy crown of the plant, and cutting it off always results in its demise. The harvesting of the plants is described as follows in contemporary accounts of the island’s forests:
“In truth, I’ve several times harboured regrets when I thought about the fact that, to satisfy my appetite, I destroyed in an instant the fruit of thirty and fifty years of vegetation, which had endured a thousand storms and protected with its errant shadow the trees and shrubs above which it rose so majestically. (…) The maroon negroes make of it their main sustenance; sometimes not having an instrument to fell the tree, or fearing that the sound of its fall would attract the hunter, they climb on its plain trunk, and with a sharpened knife separate the head from the place where it’s united to the wood.”
Bory de Saint-Vincent, Voyage dans les quatre îles principales des mers d’Afrique (Travel through the four main islands of Africa’s seas) - 1804
The most widely distributed species on the archipelago is the white palmiste, Dictyosperma album, which is present on all three islands. It grows in both the wet and dry forests from sea level to 600 metres of altitude and has a maximum height of over 20 metres, allowing it to rise above the surrounding canopy. The tenderest part of the plant is the “palmiste heart” which is located near the top of the trunk. It’s the softest part of the plant and its crunchy texture, combined with its rich but understated taste, led to it being considered the best vegetable on the island. Because only one heart can be extracted per plant, which takes years to become large enough to be useable, once the human population reached a certain point, demand was bound to outstrip supply. And so, as the dry forests were obliterated and the lowest levels of the lowland rainforests were heavily encroached upon, D. album almost disappeared. To preserve the species, seeds were taken from botanical gardens to create plantations where the trees are grown for culinary purposes. Their sale is heavily controlled by the ONF (national forestry organism), with each heart being branded with a mark to ensure its provenance before selling. Because of its high cost, this prized vegetable is now only used to cook during major celebrations. It can be prepared in salads, gratinated, or grated and used as an accompaniment to créole “carry” staple dishes. Unfortunately even the plantation system doesn’t completely discourage poaching of the few remaining or reintroduced wild specimens.
Acantophoenix rubra, the red palmiste, boasts a similar edible core although it’s smaller (maximum 12 metres) and more restricted in its habitat, strictly requiring rainforest and only within altitudes of 100 to 600 metres. Its name comes from the fact that, while D. album has grey or light brown hairs on the tough sheath protecting its crown, A. rubra has chestnut-brown or orange hairs. A final species, Hyophorbe indica, or pig-palmiste, is the smallest palmiste in the list at 10 metres tall, endemic to Reunion only, and is the most common one still seen in the wild as it is inedible by humans. As its name suggests, it’s still sometimes poached for use as pig feed. It’s easy to recognise compared to the other two species as its sheath is matte green.
The other notable family of lowland rainforests, the Sapotaceae, which comprises most of the canopy, is composed mainly in this environment of “natte” and “bois de fer” (ironwoods), both categories containing two major species. Labourdonnaisia calophylloides (‘ti natte in créole, meaning little natte) and Mimusops balata (grand natte) can both reach 20 metres tall, although the former has a shorter trunk which spreads into a more ramified network of branches. Their trunks both naturally grow very straight and with a dense, red, high quality wood used to build traditional créole houses, known as “cases”, with wooden plank floors and supporting beams. The ironwoods are part of the genus Sideroxylon, with the most notable species being S. majus, white ironwood, which also reaches close to 20 metres tall, with a wide trunk flanked by noticeable buttress roots, making it one of the largest endemic trees on the island. Its name isn’t just for show: this ironwood is extremely tough, and naturally rot-proof, even in wet tropical conditions, and was used in ship building, construction and woodworking. The final species, S. borbonicum, bastard ironwood, is small (8 metres maximum), with a thick but tortuous trunk, saving it from being as overexploited as its congener. All these species generally live between sea-level and 5-1200 metres of altitude and suffered greatly from habitat destruction but also (all but the last species) logging. They are all now beneficiaries of reintroduction programs based on plantation-bred specimens.
A few other smaller yet nonetheless emblematic species of the understory of lowland rainforests include Chassalia corallioides, or coral wood, so-called because of its delicately branched inflorescence which blooms during the austral summer (our winter), Gaertnera vaginata, or losto café, a member of the Rubiaceae family just like coffee plants whose fruits bear a passing ressemblence to those of the latter, hence its name, Syzygium cymosum, a member of the Gondwanan plant family Myrtaceae which produces pink spherical fruits (colloquially known as apples in the créole language) attached directly to the trunk. Although not generally considered edible, anecdotal internet reports from island inhabitants seem to indicate the fruits aren’t dangerous, just rather flavourless.
The emblematic fauna of lowland forests:
Being one of the most biodiverse biomes on the planet, rainforests are occupied by a large variety of animals, both vertebrate and invertebrate. As all the forest birds of Reunion thrive just as well in the lowlands as in the cloud forest, and this post is becoming long enough already, I’ll keep those for next time and focus on other animals. I’ll make an exception for the only strict lowland forest bird, unfortunately extinct on Reunion, the echo parakeet (Psittacula eques). This bird subsists mainly on fruits and leaves and lives today only in a single national park in Southern Mauritius. Thanks to a very intensive conservation program, its numbers rose from a few dozen in the 1990s to more than 700 today. Maybe one day we can hope for this emblematic species to be returned to Reunion?
There aren’t many mammals native to Reunion, and even fewer which frequent its forests. The most notable is the Mauritian flying fox (Pteropus niger). Despite its name, the species was originally present in the whole archipelago and quite abundant, but excessive deforestation and extermination hunting in the 18th and 19th centuries made it locally extinct on the island, with extremely threatened small populations remaining in Maurice and Rodrigues. After a powerful cyclone hit the area in 2007, a small group of fruit bats found their way back to the island, forming today a small community of no more than a few dozen individuals in the Eastern forests. A woodlands dweller which didn’t arrive naturally is the tailless tenrec (Tenrec ecaudatus), an animal that convergently evolved spikes similar to those of hedgehogs. This discreet burrowing animal from Madagascar is largely omnivorous and rarely seen, but it’s actively hunted for its meat which can be used in créole carry dishes.
A few other colourful notable inhabitants typical of the lower forest level include the Reunion day gecko (Phelsuma borbonica), which feeds off insects, soft fruit, tree sap and flower nectar, Papilio phorbanta, a forest butterfly whose larvae feed on the leaves of plants in the citrus family Rutaceae and is threatened by deforestation (and parasitic flies which were originally introduced to control populations of introduced pest butterflies), and the diminutive Omphalotropis rubens (or “Chinese hat snail” in créole) which breathes with gills and feeds by grazing on microscopic epiphytic algae which grow as a thin layer on top of rainforest foliage.
Finally, to speak of a few risks to these lowland forests today, we can mention the creation of plantations of the tree Cryptomeria japonica to use as construction wood, and the presence of invasive species which compete with the natire trees for light, such as giant bramble (Rubus alceifolius) which is undergoing a biological control campaign which has seen it almost cleared from forest areas below 600m thanks to the use of a leaf-eating fly, and guava (Psidium cattleianum), a fruit that’s much appreciated on the island, but unfortunately also a species which expands so aggressively that it can completely replace old-growth rainforest by an impenetrable thicket of the guava.
This concludes our visit through the lush lowland forests of Reunion, I hope this gave you enough of an insight into the structure and attributes of this ecosystem and its troubled history with human occupation of the island. Be on the lookout soon for the sequel about the island’s cloudforests, it’ll be filled to the brim with colourful and unique species!
Main sources:
La Flore et la Faune Originelles des Mascareignes, by Matthieu Saliman-Hitillambeau (éditions Orphie, 2020)
La Réunion: Faune et Flore - Le Guide Naturaliste, by Stéphane Bernard, Stéphanie Dalleau-Coudert, Maëla Winckler, Roland Benard (Austral éditions, 2016)
mi-aime-a-ou.com (an excellent resource maintained by passionate naturalists and historians from the area)
Previous threads on Reunion (teasers at the end of threads were non-binding):
Thread 1: Introduction to Reunion
Thread 2: The rocky coastal ecosystems
Thread 3: The sandy coastal ecosystems
Thread 4: The lost dry climate forests of Western Reunion
Thread 5: The concrete jungle, aka cities and their particular species
Thread 6: Continuation of the previous topic
Thread 7: Agriculture in Reunion, the sweet-scented geranium
Thread 8: Agriculture in Reunion, the extraordinary vanilla
Thread 9: Reunion’s volcanic moors and highlands
Thread 10: Agriculture in Reunion (kinda), the brewing of rum
More please! 😊👍