Central French Guiana Research Articles

In remembrance of: Scott A. Mori (1941–2020), Tropical Botanist Extraordinaire

In remembrance of: Scott A. Mori (1941–2020), Tropical Botanist Extraordinaire

Unraveling pre-Columbian occupation patterns in the tropical forests of French Guiana using an anthracological approach

In Amazonia, a growing body of studies has shown that rainforests were affected by human occupation in many areas during pre-Columbian times, inducing changes in their floristic compositions. The northern part of Amazonia, and in particular the Guiana Shield, is much less studied, although past human occupations have also been documented in this region. Therefore, the actual impact of pre-Columbian societies on Guianan forests is still poorly known. Here we explore 12 sites in the dense forest of Nouragues, central French Guiana, ranging from a priori non-anthropogenic to clearly anthropogenic, using an anthracological approach. Soil charcoals were radiocarbon dated to assess the chronology of the past human occupations, and identified to determine shifts in vegetation cover. Our results show that two main periods of occupation can be distinguished on several sites in the Nouragues area: a first one between ca. 1,300 and 1,000 cal bp and a second one between ca. 600 and 400 cal bp. Charcoal identification reveals the presence of a secondary vegetation during this most recent period of occupation, as shown by the presence of pioneer and heliophilic taxa, suggesting that human activities induced and favored this kind of vegetation. The presence of valuable wood and edible species in the anthracological record could reflect selective exploitation of the former around dwelling areas and a concentration of the latter within anthropogenic sites. As shown by our anthracological results, all the sites which contained charcoal were once under forest cover, including those that are now covered by pseudo-bamboos or by liana forests. We therefore suggest that the type of human activity (e.g. dwelling or food production) may have had different impacts on the structure and composition of subsequent vegetation resulting either in anthropogenic forests or liana and pseudo-bamboo patches after land abandonment.

On the brink of extinction: two new species of Anomaloglossus from French Guiana and amended definitions of Anomaloglossus degranvillei and A. surinamensis (Anura: Aromobatidae).

A large portion of the amphibian species occurring in Amazonia remains undescribed. A recent study on species delineation in Anomaloglossus, a genus endemic to the Guiana Shield, demonstrated the existence of two undescribed species previously identified as A. degranvillei, which we describe herein. In addition to divergence at the molecular level, these two new taxa are also distinguished by subtle morphological characters and substantial differences in the advertisement calls (note length, dominant frequency, note structure). One species occurs in the hilly lowlands of north-eastern French Guiana and is mainly distinguished from its closest relatives by a small body size (15.9-18.8 mm in males) and by vocalisations characterized by the emission of short notes of 0.09 s on average. The other species is only known from the Itoupé Massif in southern French Guiana and is mainly distinguished from its closest relatives by a moderate body size (19.4-20.4 mm in males) and by vocalisations characterized by the emission of long notes of 0.23 s on average. We also provide amended definitions for two previously described species in the A. degranvillei species group: A. degranvillei, which is endemic to a few massifs in central French Guiana, and A. surinamensis, which is distributed throughout Suriname and French Guiana. The new species described here and A. degranvillei have very narrow ranges within French Guiana and seem to have rapidly declined during the last decade. Therefore, we suggest A. degranvillei and A. dewynteri to be considered as "Critically Endangered" and A. blanci as "Vulnerable" according to the IUCN standards.

Arbuscular mycorrhizal community structure on co-existing tropical legume trees in French Guiana

We aimed to characterise the arbuscular mycorrhizal fungal (AMF) community structure and potential edaphic determinants in the dominating, but poorly described, root-colonizing Paris-type AMF community on co-occurring Amazonian leguminous trees. Three highly productive leguminous trees (Dicorynia guianensis, Eperua falcata and Tachigali melinonii were targeted) in species-rich forests on contrasting soil types at the Nouragues Research Station in central French Guiana. Abundant AMF SSU rRNA amplicons (NS31-AM1 & AML1-AML2 primers) from roots identified via trnL profiling were subjected to denaturing gradient gel electrophoresis (DGGE), clone library sequencing and phylogenetic analysis. Classical approaches targeting abundant SSU amplicons highlighted a diverse root-colonizing symbiotic AMF community dominated by members of the Glomeraceae. DGGE profiling indicated that, of the edaphic factors investigated, soil nitrogen was most important in influencing the AMF community and this was more important than any host tree species effect. Dominating Paris-type mycorrhizal leguminous trees in Amazonian soils host diverse and novel taxa within the Glomeraceae that appear under edaphic selection in the investigated tropical forests. Linking symbiotic diversity of identified AMF taxa to ecological processes is the next challenge ahead.

SAR tomography for the retrieval of forest biomass and height: Cross-validation at two tropical forest sites in French Guiana

Developing and improving methods to monitor forest carbon in space and time is a timely challenge, especially for tropical forests. The next European Space Agency Earth Explorer Core Mission BIOMASS will collect synthetic aperture radar (SAR) data globally from employing a multiple baseline orbit during the initial phase of its lifetime. These data will be used for tomographic SAR (TomoSAR) processing, with a vertical resolution of about 20 m, a resolution sufficient to decompose the backscatter signal into two to three layers for most closed-canopy tropical forests. A recent study, conducted in the Paracou site, French Guiana, has already shown that TomoSAR significantly improves the retrieval of forest aboveground biomass (AGB) in a high biomass forest, with an error of only 10% at 1.5-ha resolution. However, the degree to which this TomoSAR approach can be transferred from one site to another has not been assessed. We test this approach at the Nouragues site in central French Guiana (ca 100 km away from Paracou), and develop a method to retrieve the top-of-canopy height from TomoSAR. We found a high correlation between the backscatter signal and AGB in the upper canopy layer (i.e. 20–40 m), while lower layers only showed poor correlations. The relationship between AGB and TomoSAR data was found to be highly similar for forests at Nouragues and Paracou. Cross validation using training plots from Nouragues and validation plots from Paracou, and vice versa, gave an error of 16–18% of AGB using 1-ha plots. Finally, using a high-resolution LiDAR canopy model as a reference, we showed that TomoSAR has the potential to retrieve the top-of-canopy height with an error to within 2.5 m. Our analyses show that the TomoSAR-AGB retrieval method is accurate even in hilly and high-biomass forest areas and suggest that our approach may be generalizable to other study sites, having a canopy taller than 30 m. These results have strong implications for the tomographic phase of the BIOMASS spaceborne mission.

Black-throated Antshrike preys on nests of social paper wasps in central French Guiana

We studied predation by birds on nests of neotropical social paper wasps at the Inselberg camp of the Nouragues Reserve in Central French Guiana, an minimally-disturbed lowland rainforest habitat. Seven meters above ground, we built recording arenas and fitted them with motion-detecting video cameras. We transferred active wasp nests from surrounding forest to the arenas to film bird predators of wasps. In a video recording taken on 13 April 2010, we documented predation by a male Black-throated Antshrike, Frederickena viridis, on nests of Polybia scrobalis and P. bistriata. In rapid fly-bys, the antshrike repeatedly struck the wasp nests with his beak and in the process knocked parts of the nest to the ground. After the wasps absconded, he perched next to the nest of P. bistriata and fed on the wasp larvae and pupae. This predation tactic and type of prey was previously not known for F. viridis. Also, F. viridis apparently forages in higher strata of the forest than previously recorded.

In memoriam: Eric Alston Christenson (1956-2011)

Dr Eric Christenson was a well-known research taxonomist with a strong interest in orchids, f lor is t ics , nomencla ture , conservat ion and horticultural taxonomy. He was a leading orchid expert who published numerous research papers in which he described hundreds of new species. His death is a great loss to the field of botany, which has lost one of its foremost experts on orchids. Eric died in April 2011 in his home in Bradenton, Florida. Eric Christenson’s monographic works focused mainly on Asian orchids, and he is probably best known for his monograph on the commonly cultivated genus Phalaenopsis (Christenson 2001). He travelled to numerous herbaria around the world to study original orchid collections, and he frequented South America, where his floristic works on orchids were focused. For instance, he authored the orchid treatment in the Vascular Flora of Central French Guiana (Mori et al. 1997) following fieldwork in the Guianas. His long term collaboration with the late David Bennett in Peru resulted in the impressive 600 plates of the Icones Orchidacearum Peruvianum (Bennett & Christenson 1993–2001), in which numerous species were illustrated, many new records for Peru were listed and for which a great number of species new to science were published. He additionally wrote a bilingual flora to the orchids of Machu Picchu (Christenson 2003). Eric’s research articles often bridged the gap between taxonomy and horticulture. He applied his extensive knowledge of horticultural and taxonomic literature to provide stable names for orchid enthusiasts. He worked closely together with orchid growers to establish ex-situ propagation programmes for conservation of rare species, working actively with commercial growers and botanical gardens to that end. His studies often focused on widespread species complexes and species thought to be highly variable, to come to a more detailed definition of taxa and their distribution. This aided in many cases the identification of rare species and resulted in the redefining of conservation strategies in Latin America.

Epiphyte Biomass and Canopy Microclimate in the Tropical Lowland Cloud Forest of French Guiana

Recent work on bryophyte diversity in lowland forests of northern South America has suggested the existence of a new type of cloud forest, the ‘tropical lowland cloud forest’ (LCF). LCF occurs in river valleys in hilly areas with high air humidity and morning fog, and is rich in epiphytes. We explored epiphyte abundance and canopy microclimate of LCF in a lowland area (200–400 m asl) near Saul, central French Guiana. We analyzed the vertical distribution of epiphytic cover and biomass on 48 trees, in LCF and in lowland rain forest (LRF) without fog. Trees in LCF had significantly more epiphytic biomass than in LRF; mean total epiphytic biomass in LCF was about 59 g/m2, and 35 g/m2 in LRF. In all height zones on the trees, total epiphyte cover in LCF exceeded that in LRF, with ca 70 percent mean cover in LCF and ca 15 percent in LRF. During both wet and dry seasons, mean diurnal relative air humidity (RH) was higher in LCF than in LRF, and persistence of high RH after sunrise significantly longer in LCF. We suggest that the prolonged availability of high air humidity in LCF and the additional input of liquid water through fog, enhance epiphyte growth in LCF by shortening the desiccation period and lengthening the period of photosynthetic activity of the plants.

Canopy level fog occurrence in a tropical lowland forest of French Guiana as a prerequisite for high epiphyte diversity

Fog frequency and the meteorological processes leading to fog formation have never been studied in depth in tropical lowland forest areas. This study provides detailed evidence of frequent fog occurrence in lowland valleys of central French Guiana. Fog frequency showed a clear diurnal course, with a maximum before sunrise; average fog duration was 4.6 h. The diurnal course of visibility was positively correlated with the diurnal course of humidity in the above-canopy air. Fog persistence correlated significantly with atmospheric parameters during the dry season, but not during the rainy season. The main trigger of fog development in the lowland forest seemed to be precipitation, leading to higher soil moisture, greater evapotranspiration and, thus, higher water content of air. An increasing temperature difference between valley and hill sites after sunset, together with more frequent down-slope winds during nights with long fog periods, points at some influence of katabatic flows. The frequent occurrence of fog in the valleys correlated with significantly higher epiphyte diversities in valley forests as compared to hill forests, and supported the occurrence of the hitherto undescribed, epiphyte-rich “tropical lowland cloud forest” (LCF) in the valleys. The higher epiphyte diversity in LCF coincided with significantly higher relative air humidity in LCF than in hill forest. The ecological benefits of fog for the epiphytes in LCF are surplus of moisture and delayed onset of the stress period, particularly in the dry season.

A new species of Neobaryssinus Monné & Martins, and two new species of Baryssiniella new genus (Coleoptera: Cerambycidae), reared from trees in the Brazil nut family (Lecythidaceae)

Neobaryssinus altissimus new species is described from central French Guiana; a key to the four species of the genus is given. Baryssiniella new genus is described, including two new species: B. hieroglyphica new species from southeastern Peru, and B. tavakiliani new species from central French Guiana. Comparisons among Neobaryssinus, Baryssiniella, and several other genera in the tribe Acanthocinini are presented. All three new species were reared from trees in the Brazil nut family (Lecythidaceae). Two of these species emerged preferentially from bait branches at canopy stratum.

Diversity and vertical distribution of epiphytic macrolichens in lowland rain forest and lowland cloud forest of French Guiana

Abstract Recent work on bryophyte diversity in lowland forests of northern South America has suggested the existence of a new type of cloud forest, the “tropical lowland cloud forest” (LCF). LCF occurs in river valleys with high air humidity and radiation fog, and is rich in epiphytes. We explored the lichenological characteristics of putative LCF in a lowland area (200–400 m a.s.l.) near Saul, central French Guiana, using macrolichens (including large crustose species) as indicator taxa. We analyzed macrolichen diversity on 16 trees in two 1 ha plots, in LCF and in lowland rain forest without fog (LRF). Sampling efficiency was ca. 80% in both forest types. Canopies of both LRF and LCF were richer in lichen species than understory trunks. Species richness of macrolichens was rather similar in the two forest types but species composition was significantly different. Cyanolichen richness in LCF was ca. 2.5 times higher than in LRF; in contrast, LRF had 4 times more species of green-algal Parmeliaceae. Our study suggests that cyanolichens except for Coccocarpiaceae serve as indicators of LCF. We explain the detected diversity patterns by differences in water availability due to fog precipitation and higher humidity. This is indicated by the higher relative air humidity in the lowland cloud forest, which was >6% higher than in the rain forest.

Developmental plasticity and biomechanics of treelets and lianas in Manihot aff. quinquepartita (Euphorbiaceae): a branch-angle climber of French Guiana.

Most tropical lianas have specialized organs of attachment such as twining stems, hooks or tendrils but some do not. Many climbers also have an early self-supporting phase of growth and in some species this can produce treelet-sized individuals. This study focuses on how a liana can climb without specialized attachment organs and how biomechanical properties of the stem are modulated between self-supporting treelets and canopy-climbing lianas. Biomechanics and stem development were investigated in self-supporting to climbing individuals of Manihot aff. quinquepartita (Euphorbiaceae) from tropical rain forest at Saül, central French Guiana. Bending tests were carried out close to the site of growth. Mechanical properties, including Young's elastic modulus, were observed with reference to habit type and changes in stem anatomy during development. This liana species can show a remarkably long phase of self-supporting growth as treelets with stiff, juvenile wood characterizing the branches and main stem. During the early phase of climbing, stiff but unstable stem segments are loosely held in a vertical position to host plants via petiole bases. The stiffest stems--those having the highest values of Young's modulus measured in bending--belonged to young, leaning and climbing stems. Only when climbing stems are securely anchored into the surrounding vegetation by a system of wide-angled branches, does the plant develop highly flexible stem properties. As in many specialized lianas, the change in stiffness is linked to the development of wood with numerous large vessels and thin-walled fibres. Some angiosperms can develop highly effective climbing behaviour and specialized flexible stems without highly specialized organs of attachment. This is linked to a high degree of developmental plasticity in early stages of growth. Young individuals in either open or closed marginal forest conditions can grow as substantial treelets or as leaning/climbing plants, depending on the availability of host supports. The species of liana studied differs both in terms of development and biomechanics from many other lianas that climb via twining, tendrils or other specialized attachment organs.

Above-ground biomass and productivity in a rain forest of eastern South America

AbstractThe dynamics of tropical forest woody plants was studied at the Nouragues Field Station, central French Guiana. Stem density, basal area, above-ground biomass and above-ground net primary productivity, including the contribution of litterfall, were estimated from two large permanent census plots of 12 and 10 ha, established on contrasting soil types, and censused twice, first in 1992–1994, then again in 2000–2002. Mean stem density was 512 stems ha−1 and basal area, 30 m2 ha−1. Stem mortality rate ranged between 1.51% and 2.06% y−1. In both plots, stem density decreased over the study period. Using a correlation between wood density and wood hardness directly measured by a Pilodyn wood tester, we found that the mean wood density was 0.63 g cm−3, 12% smaller than the mean of wood density estimated from the literature values for the species occurring in our plot. Above-ground biomass ranged from 356 to 398 Mg ha−1 (oven-dry mass), and it increased over the census period. Leaf biomass was 6.47 Mg ha−1. Our total estimate of aboveground net primary productivity was 8.81 MgC ha−1 y−1 (in carbon units), not accounting for loss to herbivory, branchfalls, or biogenic volatile organic compounds, which may altogether account for an additional 1 MgC ha−1 y−1. Coarse wood productivity (stem growth plus recruitment) contributed to 4.16 MgC ha−1 y−1. Litterfall contributed to 4.65 MgC ha−1 y−1 with 3.16 MgC ha−1 y−1 due to leaves, 1.10 MgC ha−1 y−1 to twigs, and 0.39 MgC ha−1 y−1 to fruits and flowers. The increase in above-ground biomass for both trees and lianas is consistent with the hypothesis of a shift in the functioning of Amazonian rain forests driven by environmental changes, although alternative hypotheses such as a recovery from past disturbances cannot be ruled out at our site, as suggested by the observed decrease in stem density.

Mast Fruiting Is a Frequent Strategy in Woody Species of Eastern South America

BackgroundIt is thought that mast seeding is a rare reproductive strategy in the tropics, since tropical climates are less variable, and fruit consumers tend to be more generalist in these regions. However, previous tests of this hypothesis were based on only few tropical datasets, and none from tropical South America. Moreover, reproductive strategies have been quantified based on the coefficient of variation of interannual seed production, an index that potentially confounds masting and high interannual variability in seed production.Methodology/Principal FindingsWe developed a new approach to model the monthly variability in seed production for 28 tree species, and 20 liana species monitored during 5 years in a tropical forest of Central French Guiana. We found that 23% of the species showed a masting pattern, 54% an annual fruiting pattern, and 23% an irregular fruiting pattern. The majority of masting species were trees (8 out of 11), most of them animal-dispersed. The classification into reproductive strategies based on the coefficient of variation was inconsistent with our results in nearly half of the cases.Conclusions/SignificanceOur study is the first to clearly evidence the frequency of the masting strategy in a tropical forest community of Eastern South America. The commonness of the masting strategy in tropical plants may promote species coexistence through storage dynamics.

Specific epithets of the flowering plants of central French Guiana

The epithets of the flowering plants of central French Guiana are classified into derivation categories. Specific epithets of the flowering plants of central French Guiana refer mostly to shapes (274 species), persons (252), places (212), appearance (146), and size (140). These categories account for 55% of names given to the plants of this flora. The most prolific publishers of names for the flora of central French Guiana are Aublet and Linnaeus, who were respectively the authors of 177 and 110 of the names of species (15% of the total) found in the flora of central French Guiana. Although many of the species names, such as those relating to place and person, are easy to categorize, many others are open to different interpretations. Specific epithets with different orthographies derived from Guiana or Guyana are discussed. In addition, problems in the use of diacritical marks and inconsistencies with spacing between the abbreviations of given names and surnames of authors of plant names are noted.

Using checklists and collections data to investigate plant diversity: II. An analysis of five florulas from northeastern South America

Abstract Five plant checklists from areas on and adjacent to the Guiana Shield were analyzed and used to test hypotheses of the salient properties of the flora of northeastern South America. Newly available checklists of Iwokrama, Mabura Hill, and Kaieteur Falls (all three in Guyana), Central French Guiana, and Reserva Ducke near Manaus, Brazil were compiled and their nomenclatural synonymies standardized. Data from checklists provide an attractive alternative to transect or plot data because they are based on rigorously determined plants of all habit types rather than the sterile vouchers of tree species often used in plot or transect studies. Descriptive data were compiled from the checklists regarding diversity, overlap, and endemism. Ranking of diversity at the family level was subjected to Kendall's coefficient of concordance of ranks test and Spearman rank correlation coefficients to evaluate similarities among the five sites. A UPGMA dendrogram was created from data for the presence or absence of s...

Life Form, Habitat, and Nutritional Mode of the Flowering Plants of Central French Guiana

MoRI, S. A., E. F HECKLAU, AND T. KIRCHGESSNER (The New York Botanical Garden, Bronx, New York 10458-5126). Life form, habitat, and nutritional mode of the flowering plants of central French Guiana. J. Torrey Bot. Soc. 129: 331-345. 2002.-The flowering plants of central French Guiana comprise 1918 native species, including 549 species of herbs, 44 species of vines, 45 species of subshrubs, 269 species of shrubs, 245 species of lianas, and 766 species of trees. The habitat of the flowering plants of central French Guiana is primarily terrestrial. A total of 1653 species or 86% of the flora occurs in this habitat. However, the reproductive cycles of a majority of the flowering plants of central French Guiana take place in the crowns of trees. When the number of species of trees is added to the numbers of epiphytes, hemi-epiphytes, and aerial endophytes, tree crowns are the site of about 68% of the flowering plant reproductive activity in this forest. Heterotrophic vascular plants, with 36 species, make up 1.9% of the flora; 98.1% of the flowering plants of central French Guiana are autotrophs. Because of differences in definitions and lack of standardization in sampling, it is difficult to make valid comparisons with studies made in other geographic areas. We address the first problem by providing a glossary of terms used to describe the life form, habitat, and nutritional mode of plants and urge others to develop standardized sampling protocols.

A new series and three new species of Passiflora subgenus Astrophea from the Guianas

A new series,Passiflora ser.Carneae, and three new species are described inPassiflora subg.Astrophea:P. ascidia from Guyana and Venezuelan Guayana;P. balbis from Guyana, Venzuelan Guayana, and Amazonian Brazil; andP. saulensis from central French Guiana. A key to the 19 Guiana species ofPassiflora subg.Astrophea is provided.

Notes on some South American species of Psychotria subgenus Heteropsychotria (Rubiaceae), with observations on rubiaceous taxonomic characters

During the preparation of a treatment of the Rubiaceae for theGuide to the Vascular Plants of Central French Guiana, several field and laboratory observations have contributed toward a better understanding of the morphological variation of certain species ofPsychotria and have stimulated a reevaluation of some morphological features used by previous authors in distinguishing taxa in thePsychotria. Typification for all taxa is provided, several new synonyms and one new combination,Psychotria carapichea (Poir.) Delprete, are proposed, and illustrations ofP. ligularis andP. carapichea are included.

Do Lecythidaceae Specialists (Coleoptera, Cerambycidae) Shun Fetid Tree Species?1

ABSTRACTCharacteristic secondary metabolites are currently acknowledged to play a pivotal role in the circumscription of a plant's insect fauna. A newly discovered association between wood–boring longicorn beetles (Cerambycidae) and their host trees belonging to the Brazil nut family (Lecythidaceae) inspired a yearlong rearing project in the lowland Neotropical rain forest of central French Guiana. Branches severed from five species of Lecythidaceae yielded 1813 cerambycids belonging to 37 species. Two of the five tree species, Couratari stellata and Gustavia hexapetala, yielded impoverished complements of cerambycids that included large percentages of generalists. Both tree species are characterized by fetid odors. Wood samples collected from the malodorous C. stellata, as well as from two well–colonized species, Lecythis poiteaui and Eschweilera coriacea, were analyzed for their volatile components. Sulfur compounds accounted for almost 15 percent of the volatiles detected from C. stellata, while they were at most minor components of the two well–colonized tree species. S–methylmethionine, isolated from a C. stellata wood sample, appeared to be the major sulfur compound contributing to the distinctive smell. We hypothesize that this foul odor is a deterrent to specialist cerambycids seeking oviposition sites.