Structure and Floristic Composition of Flood Plain Forests in the Peruvian Amazon. II. The Understorey of Restinga Forests

Structure and floristic composition of small trees and shrubs (1.5 m height to 10 cm diameter at breast height was described in two flood plain forests of the lower Ucayali river, Peruvian Amazon. The forests were of the high and low restinga type, on an annual average flooded around 1 and 2 months, respectively. The soils were nutrient rich entisols, and the vegetation forms closed high canopy forests with presence of emergents. A total of 25 permanent sample plots covering 0.64 ha were established. They were nested within six quadratic 1 ha permanent sample plots where large individuals (>10 cm DBH) were inventoried. Overall average density and basal area of the understorey were 4458 ha and 5.0 m2 /ha, respectively. The families of Moraceae, Leguminosae, Annonaceae, Euphorbiaceae, and Lauraceae were among the most important tree families, while important shrub and small tree families were Violaceae, Rubiaceae, Melastomataceae, and Olacaceae. Two hundred eight and 204 tree species were registered in the restinga forest overstories and understories, respectively. Fifty-six percent of the species were shared between the two forest strata, while around 22% were confined to each of them. Species present only in the understorey were predominantly shrubs or treelets, while some of the species with a presence only in the overstorey were probably early succession species about to disappear from the forests

Structure and Floristic Composition of Flood Plain Forests in the Peruvian Amazon I. Overstorey

Three Peruvian flood plain forests adjacent to the Ucayali river were sampled using nine 1 ha permanent sample plots in which stems exceeding 10 cm DBH were identified and measured. These plots were measured four times during 1993-1997. Three plots were established in each of the three forest types high restinga, low restinga, and tahuampa, characterised in part by an annual inundation of one, two and four months per year, respectively. Stem density varied from 446 to 601 per hectare, and the basal area ranged between 20 and 29 m2/ha. A total of 321 species were recorded in the nine hectare sample, with 88-141 species in each 1 ha plot. Species composition indicated a relatively low similarity between the forest types. Plots with the longest flooding contained the most species, expressed both as per unit area as well as per 1000 stems. The flood plain forests contained fewer tree species than adjacent non-flooded terra firme forest. Family importance values were calculated for each forest. In all three forests Leguminosae, Euphorbiaceae, Annonaceae and Lauraceae were important. The Moraceae family was conspicuous in both high restinga and low restinga. The Arecaceae and Meliaceae were notable in high restinga, as was Rubiaceae in low restinga. Lecythidaceae, Sapotaceae and Chrysobalanaceae exhibited relatively high values in the tahuampa forest. High species importance values were obtained for Maquira coriacea, Guarea macrophylla, Terminalia oblonga, Spondias mombin, Ceiba pentandra, Hura crepitans, Eschweilera spp., Canipsiandra angustifolia, Pouteria spp., Licania micrantha, Parinari excelsa and Calycophyllum spruceanum. Among the species of smaller stature, Drypetes amazonica, Leonia glycicarpa, Theobroma cacao and Protium nodulosum attained high values

Influence comparée de la saison sur la phénologie et sur les dégâts d'insectes phyllophages chez de jeunes individus d'arbres de forêt tropicale en Guyane française

Influence of season on phenology and insect herbivory on saplings of tropical rain forest trees in French Guiana. Leaf herbivory by insects as a function of season was quantified for saplings of five major tree species of a tropical rain forest in French Guiana. We determined the impact of herbivory based on the observed ratio of leaf area eaten to total leaf area (attack ratio) in a study of individual leaves on young saplings naturally established in undisturbed and adjacent logged forest. Measurements were conducted during the strongly contrasted dry and rainy seasons over a period of 10 months. The five species chosen for the study are Dicorynia guianensis, Eperua falcata, Eperua grandiflora, Goupia glabra and Qualea rosea. For four of the five species, leaf production varies significantly with season. D. guianensis is the only species of the five for which leaf production is maintained throughout the dry season. This has the effect of diminishing the relative impact of herbivory during a period when ground water deficits create conditions unfavorable for plant growth. Three other species experiencing high levels of herbivory during the dry season have significantly lower mean height growth than during the rainy season. In contrast, D. guianensis and G. glabra have similar height growths regardless of season. Seasonal variation in leaf production and leaf attack also occur in similar proportions. The resulting attack ratios, with the exception of E. grandiflora, are not significantly different between the rainy season and dry season observations. This supports the hypothesis that, for the tropical rain forest, the rainy season is the more favorable period for leaf-eating insect activity. The influence of leaf production phenology on the population dynamics of leaf-eating insects in this community is also discussed. (© Inra/Elsevier, Paris.)Des observations conduites en forêt tropicale humide, dans la zone littorale de la Guyane Française, ont permis de quantifier, en fonction des saisons, les attaques par les insectes phyllophages et la phénologie de jeunes individus de cinq espèces d'arbres (Dicorynia guianensis, Eperua falcata, Eperua grandiflora, Goupia glabra, Qualea rosea). D guianensis est la seule des cinq espèces étudiées chez laquelle la production foliaire est maintenue en saison sèche, ce qui tend à diminuer l'impact des phyllophages durant une période où l'alimentation hydrique des plantes est généralement peu favorable à la croissance. Les espèces ayant de fortes proportions de feuilles attaquées en saison sèche ont durant cette saison une croissance en hauteur significativement plus faible qu'en saison des pluies (E. falcata, G. glabra et Q. rosea). Au contraire D. guianensis et G. glabra présentent des croissances en hauteur semblables en saison des pluies et en saison sèche. Les variations saisonnières de production foliaire et d'attaques d'insectes phyllophages s'effectuent dans des proportions semblables. Le taux de défoliation qui en résulte (sauf pour E. grandiflora) n'est pas significativement différent entre la saison sèche et la saison des pluies. Notre étude conforte l'hypothèse selon laquelle la saison des pluies serait favorable à l'activité des insectes phyllophages en forêt tropicale humide. L'impact de la phénologie de la production foliaire sur la dynamique des populations de phyllophages est également discuté. (© Inra/Elsevier, Paris.

Physical damage on tropical tree saplings: quantification and consequences for competition through height growth in a neotropical rain forest of French Guiana

This paper deals with the quantification and the effects of physical damage on tree regeneration dynamics in the tropical rain forest. We define physical damage as breakage resulting in a greater than 20 % reduction in stem diameter and its associated effects. A study of physical damage at the community level was made in March 1994 in primary forest and forest disturbed by silvicultural treatments at the Paracou research site in French Guiana. The frequency of damage varies with diameter class and the degree of forest disturbance due to the silvicultural treatments, ranging from 14.9 % for saplings greater than 6 cm DBH in undisturbed forest to over 50 % for smaller saplings in disturbed forest. Study at the specific level was made at the same site on saplings of three tree species with contrasting ecological temperaments, Bocoa prouacensis, Pradosia cochlearia and Goupia glabra, from March 1994 to March 1996. Damage frequencies varied from 34 % for saplings of the pioneer species Goupia glabra to 64 and 60 %, respectively, for the more shade tolerant species Bocoa prouacensis and Pradosia cochlearia. Physical damage does not directly influence height or diameter growth rates nor mortality within a species except for Pradosia cochlearia. However, diameter growth rates irrespective of damage are significantly different between species. Under certain circumstances, stem breakage may be an influential factor affecting the long term survival of pioneer species saplings because it modifies their social status. (© Inra/Elsevier, Paris.)Casse mécanique sur des jeunes arbres tropicaux : quantification et conséquences sur la compétition par la croissance en hauteur dans une forêt néotropicale humide de Guyane française. Ce travail portant sur la quantification et les effets de la casse mécanique sur la dynamique de la régénération des arbres en forêt dense humide tropicale, a été envisagé à deux niveaux de perception sur le dispositif de recherche de Paracou, en Guyane française. Une étude au niveau peuplement sans prise en compte des espèces a été réalisée en mars 1994 en forêt primaire et en forêt perturbée par des traitements sylvicoles. Le pourcentage de casse varie selon les classes de diamètre et l'importance de la perturbation due aux traitements, depuis 14,9 % pour les jeunes arbres de DBH supérieur à 6 cm en forêt naturelle, à plus de 50 % pour ceux de petits diamètres dans des sites perturbées. L'étude au niveau spécifique a été réalisée sur trois espèces aux tempéraments écologiques contrastés, Bocoa prouacensis, Pradosia cochlearia et Goupia glabra, entre mars 1994 et mars 1996. Les jeunes arbres de l'espèce pionnière Goupia glabra sont moins fréquemment endommagées (34 %) que celles des espèces plus tolérantes d'ombre, Bocoa prouacensis (64 %) et Pradosia cochlearia (60 %). La casse mécanique n'influence pas directement les taux de croissance des tiges en hauteur ou en diamètre pour une espèce, sauf pour Pradosia cochlearia. Cependant, la croissance en diamètre, sans prendre en compte des dégâts mécaniques, est significativement différentes entre espèces. La casse mécanique, dans certaines circonstances, peut avoir une influence importante sur la survie à long terme des jeunes arbres d'espèces pionnières, car elle modifie leur statut social. (© Inra/Elsevier, Paris.

The effects of forest type, harvesting and stand refinement on early seedling recruitment in a tropical rain forest

International audienc

Predicting effects of habitat destruction on plant communities: A test of a model using Amazonian trees

We devised a 'random-clearing model' to predict effects of habitat loss on plant communities and populations. The model yields the probability that a species will be extirpated by land clearing, based on only two parameters: its density and the percentage of the landscape that has been cleared. It can also be used to predict species richness of plant communities following clearing, so long as densities of individual species are known. We tested the model using data on the distributions of 200 tree species (≥ 10 cm dbh) within two 9-ha experimental landscapes in central Amazonia. Deforestation levels ranging from 20% to 99% of the landscape were simulated randomly, with the actual persistence of each species being the number of times it remained in the landscape after 1000 runs. The model was effective in all cases, explaining 83-99% of the total variability in species persistence on each plot. Species' distribution patterns explained some residual variation in persistence but were of negligible importance compared to the predictions of the model. We also used the model to predict species richness, simulating both random and realistically contagious patterns of deforestation. Again, the model was highly effective, explaining 96% to 98% of the total variation in richness. Surprisingly, there was little difference in richness between random and contagious clearing patterns. These results suggest that, at least at the limited spatial scale of our analysis, the effects of deforestation on plant persistence and richness can be predicted using a simple model that assumes random species distributions and deforestation patterns. The model makes four predictions: (1) Density has an overriding influence on the susceptibility of species to clearing, while distribution patterns are usually of much lesser importance. (2) The relationship between density and persistence is nonlinear. (3) Rare species (≤1 tree/ha) become exceptionally vulnerable in heavily degraded landscapes and in small forest remnants. (4) The distinction between high (e.g., 95%) and very high (e.g., 99%) levels of habitat clearing in terms of species persistence is often dramatic