Starting a conservation project by buying a stretch of land to establish a rainforest seems a relatively easy undertaking. The legal aspects are clear, and the boundaries, at least on paper, obvious. In the field, the boundaries are less visible. To some, the acquisition might seem the end, the area is preserved by private ownership. But in reality, it is only the beginning. What is contained within that reserve, which plant species occur, and which ones might require further action? These questions are easier asked than answered. This second article about the Trésor Rainforest Project will clarify to the reader what it takes to identify plants, and will present some of the species encountered in the Trésor Nature Reserve. The first article was published in Myristica in August 2003.

The flora of French Guiana is still insufficiently known, and it is estimated to comprise about 5400 species (Boggan et al., 1997). However, species new for French Guiana, or even species new to science as a whole, continue to be discovered and the list is not near completion.

Plants are mostly collected as dried herbarium specimens. This routine is vital since identification in the field is only possible for the very typical species. Only through careful examination of the collected herbarium material and study of relevant literature is it possible to distinguish that plant from other very similar species. In some plant families, the species or even genera are extremely difficult to tell apart, and taxonomic study of certain families and genera by specialists is still in progress. In such cases even a trained botanist, due to the lack of existing specialist literature, is unable to identify such species. Herbarium material must then be sent to one of the few, or sometimes even the single specialist worldwide, to be identified. After every expedition, the 'Herbier de Cayenne' always receives a full set of duplicate herbarium vouchers to help document the botanical diversity in French Guiana.

Taxonomic knowledge is absolutely essential for conservation. Taxonomists provide the basic information regarding species composition and species abundance of a region, called floristics. This information forms the basis for any subsequent evaluation regarding the conservation status of each species, but also for ecological studies that are to provide the necessary insight in relationships and processes within the rainforest.

When coming up the road from Roura, the village near the Trésor Nature Reserve, one can easily encounter the Aroid Dracontium polyphyllum even near the road. The plant consists of just one leaf, developing from an underground rootstock, and can attain a hight of over 1.5 m. The inflorenscense, not present at the time the photograph was taken, is only about 15 cm and also originates from the rootstock. The Trésor Nature Reserve has a remarkably high diversity in Aroids. The reason for this is unclear; perhaps the extremely high annual rainfall, 4000-4500mm, the highest in all of French Guiana, has something to do with it.

Another plant that is difficult to miss is Passiflora coccinea. A casual look at the flowers is confusing. What is what? Only careful study of the flowers reveals how the flower is built up: the inner 5 corolla leaves are red, next the five calyx leaves with white markings on the inside and yellowish-green keels on the outside (most obvious in the closing flowers), and lastly, below the calyx, the red bracts. A whitish ring of filaments, the corona, surrounds the 5 stamens and style.

In general, lianas are most easily detected at the forest edges, and at the edges of forest gaps, where the light-hungry lianas can develop in larger numbers and are easy to spot. A absolutely spectacular example is Norantea guianensis, belonging to the Marcgraviaceae, a family of climbers restricted to Central and South America. What seem to be the flowers are actually nectar cups outside the flowers. The flowers are green-pink in colour and minute. The nectar cups are obviously to attract the pollinators, probably small bats or humming-birds.

Another beautiful climber is Combretum cacoucia, of the Combretaceae family, a family of predominantly lianas.

Lianas in the forest slowly make their way up to the canopy. Once they have reached the direct sunlight, growth increases rapidly. Their wiry stems grow from one tree to another, thus creating a maze of tough stems. When over time a huge tree dies and falls down, other less heavy trees are brought down as well due to the many lianas. Thus a single falling tree can cause a forest gap to form. In such gaps, the sunlight can reach the forest floor, where the seeds of pioneer species such as Cecropia obtusa lie waiting to germinate and the sunlight breaks the dormancy.

Cecropias produce very many very light seeds. As a result, these seeds lie everywhere, and when a gap forms, they quickly germinate. Cecropia growth rate is enormous, several meters per year, but they need full sun. They quickly establish a dappled shade over the forest floor, and as a consequence, the soil does not dry out in the sun. In such favourable conditions, primary forest tree species can slowly develop under the protective cover, but in the next decades these tall trees will surmount the Cecropia species, and eventually the latter will die due to lack of sunlight.

The story about Cecropia doesn't end here. The Cecropia tree has a hollow stem with chambers, much like bamboo has. These chambers are connected to the outside by a small hole, big enough to give access to tiny insects. The chambers are often occupied by tiny Azteca ants, which grow fungi inside the chambers on debris that they carry inside. The fungi are food for the ants. The Azteca ants are very agressive and their bytes painful, a reason why Cecropia species have not been collected very often in the past; cutting them down is not a good idea! As a consequence, Cecropia species are rarely seen in botanic gardens.

The link between this tree and the ants is a typical example of mutualism, a form of cooperation from which both types of organisms benefit. The ants benefit from the dry and protected surroundings in which to grow their food, and the agressive ants protect the tree against any damage by voracious animals. One might argue that the tree has little choice and that the ants simply conquer the tree. But this is not the case. The tree has an additional adaptation to attract the ants that seems to have no function other than to attract the ants. At the base of the leaf stalks, a gland is present that exudes a substance that the ants feed on. Such a structure indicates the evolution of symbiosis.

Beyond the gaps, under a closed canopy on the forest floor, we can come across herbs that have adapted to the low light levels and high humidity. An example is Nautilocalyx pictus, a member of the Gesneriaceae, a family that is better known by such indoor plants as Saintpaulia and Gloxinia.

Another well-known family is Marantaceae, represented a.o. by Calathea microcephala. All these plants used to be quite desirable indoor plants in the past, since our houses have similar poor light conditions as does the forest floor, and used to be heated by coal- or wood-fuelled stoves. As a result, the relative humidity indoors was higher than it is today. Central heating, and the accompanying lower relative humidity, has caused most of these humidity-dependent plants to disappear from our window sills.

Beauty is in the eye of the beholder. This is a saying that much applies to the gentians in the rainforest. Here and there small white-flowerered plants can be observed, but only a well-trained eye will spot them. Hidden behind a fallen tree grow three plants of Voyria coerulea, a saprophytic Gentiana. It feeds on decaying leaf litter and does not require green leaves to turn sunlight into energy.

Another species is Voyria corymbosa. They lack leaves and could easily be mistaken for parasitic plants who also have no green leaves

Helosis cayennensis is a very peculiar plant species. It is hard to imagine that this plant is actually a flowering plant, rather than a mushroom, but it is a member of the Balanophoraceae, a family of parisitic/saprophytic plants. Helosis cayennensis has been surrounded by mystery. For years little was known about this plant. However, during the 1996 expedition, the botanists were joined for a few days by entomologists, who were catching insects during the night. One night the botanists noticed a Helosis cayennensis in flower, covered by ants.

As a result, it is now believed to be an ant-pollinated species. Such facts often remain hidden, since botanists are not in the habit of collecting plants after dark. Lack of eyesight and snake hazard - quite many South American venomous snakes are nocturnal hunters - render such activities ineffective and inadvisable compared to daytime collecting.

An Aroid that lives on the forest floor is Anaphyllopsis americana, the species that is depicted in the logo of the Trésor Foundation. This aroid has a corm 40-50 cm below the surface. The spathe of the inflorescense is curiously twisted.

The forest floor quite often reveals what trees are present. Freshly fallen flowers or fruits tell their tale, but it remains difficult to detect flowering trees in the canopy. Looking up towards the canopy, we can detect some smaller trees and shrubs. This is called the understory. Here is it easier to detect which tree or shrub is flowering. When in flower, the shrubby Palicourea is quite an eyecatcher. This is a member of the Rubiaceae, in South America a very abundant family of mostle trees and shrubs in terms of species and number of plants. In Europe this family is predominantly represented by herbs.

On the forest floor, open fruits reveal the presence of Clusia grandiflora. The ellipsoid seeds have fallen out of the soft tissue in the middle of the fruit. When the fruits are dried, they close in the process. Clusia is now sold as indoor plant and remotely resemble Ficus, yet are easy to distinguish since Clusia has opposite leaves (as opposed to alternate in Ficus).

In some parts of the forest, stands of Euterpe oleacea occur. This palm produces the well-known palm-hearts. This palm with its pendant leaflets is quite distinct.

Another easy-to-recognise palm is Mauritia flexuosa. It is a robust palm and an indicator for the presence of water. In (former British) Guyana, on the open savannas, they typically line creeks and waterways. In the forest, they prefer the open swampy patches. The dark red-brown scaly fruits are dispearsed by the water.

Along the rivers, the smaller trees and shrubs receive more light and the water supply for the plants is abundant and constant. Pachira aquatica was depicted in the first article. It is sometimes refered to as Bombax aquaticum, a synonym.
Topobea parasitica also has quite attractive flowers. Contrary to what might be deduced from its name, this is not a parasyte but a semi-parasite. Its green leaves turn sunlight into energy, it only steals minerals from host plants.

Along the river, the trees of Eperua rubiginosa are quite easy to detect. This species is locally abundant in riverine forests (Roosmalen, 1985). The big brown pods hang down from stems several meters long, as did the flowers before the fruits were formed. Thus these hang well below the branches and leaves. We can only guess what the reason might be for the long stems on which flowers and fruits sangle down from. Most likely it either will have something to do with the pollination of the flowers, or with the seed dispersal by water. But it could also have something to do with diminishing predation by herbivores. Where in taxonomy there is still much to be discovered in the rainforest, pollination biology is even less advanced, since this science requires long-term observations to record visits of animals, and to find out which ones are the pollinators. The detection of nocturnal pollinators is even more complicated. It is easy to understand why so little is known about the pollinators of rainforest plants. To a lesser extent this also applies to disperal biology.

Water plants by the very nature of their environment are less known than terrestrial plants, except for those plants that can be collected either from the shore or from a boat. An additional complication is that water plants seldom produce good herbarium material, since their fibre component is obviously much less than in terrestrial plants. This requires conserving these specimens in alchohol, which is more difficult to transport and keep from damage than is the case with herbarium material. Cabomba aquatica is such a water plant, though this particular plant species is well-known since it is widely cultivated as aquarium plant. Under those conditions it rarely flowers, due to the low light intensity. In the tropical waters, light levels are very much higher and the plants flower freely.

Another fairly well-known genus is Utricularia. Utricularias are carnivorous water plants or bog plants. The water plants catch their prey, small water insects, in equally small bladders. These can be observed when the plant is viewed against the light. Quite surprisingly, even the terrestrial species of Utricularias have retained these bladders, although this structure is disfunctional in the soil. It seems therefore obvious that Utricularia has evolved in the water, and that the terrestrial species have evolved later along the evolutionary path, retaining the trap bladders.

The three major botanical expeditions that were organised and coordinated by the Dutch National Herbarium, Utrecht section, and the inventory made by the Botany laboratory of the National Natural History Museum in Paris, have up till now resulted in a list of 934 plant species. This list is certainly not complete. Earlier estimates suggest that 1,500 species is a more likely number for the plant species that grow inside the Trésor Nature Reserve. This is also supported by the increase of new plants on the list following every single expedition. Species that may be new to French Guiana, or even new to science. Such species, new to science, have indeed been found. At least one new palm (perhaps even two, still to be described) was found in the reserve, and a new bromeliad that was described in 1996 was found outside the reserve, but in the Montagnes de Kaw. It has not been found inside the reserve yet. For the Trésor Nature Reserve this means that further studies are warranted, to learn more about the plants inside the Trésor Nature Reserve, about their abundance per species, and about the dynamics in the forest. And that information again is the basis for improving the conservation effort that the Trésor project was and is all about.

One cannot protect what one does not know.

References

• Boggan, J., V. Funk, C. Kelloff (Smithsonian Institute) and M. Hoff, G. Cremers, C. Feuillet (ORSTOM), 1997. Checklist of the plants of the Guianas. Dept. of Botany, Smithsonian Institute, Washington DC. 2nd edition.
• Herbier de Guyane - www.cayenne.ird.fr/aublet2/
• Roosmalen, M.G.M. van, 1985. Fruits of the guianan flora. Institute for Systematic Botany, Utrecht University. ISBN 90-9000987-6.
• Smithsonian Institute - Tropicos Image Index - mobot.mobot.org/W3T/Search/image/imagefr.html
• Utrecht University - The Trésor Rainforest Project in French Guyana, www.bio.uu.nl/tresor/, last update unknown, accessed 29 october 2003.
• Utrecht University - Virtual Tree Guide of the Guianas - www.bio.uu.nl/~herba/VTGG/Main.htm. The Virtual Tree Guide of the Guianas may assist researchers in finding a quick match of those species that were considered to be able to reach sizes over 10 cm DBH
• Wollenberg, L.J.W. van den, 2003. The Trésor Rainforest Project: a botanic garden involved in habitat conservation. Myristica 20, last update 25 August 2003.