Actes du colloque de Digne-les-Bains (Alpes-de-Haute-Provence), 28 septembre 2012

Delnatte César. Actes du colloque de Digne-les-Bains (Alpes-de-Haute-Provence), 28 septembre 2012. In: Bulletin mensuel de la Société linnéenne de Lyon, 82ᵉ année, n°3-4, Mars-avril 2013. pp. 71-86

Actes du colloque de Digne-les-Bains (Alpes-de-Haute-Provence), 28 septembre 2012

Delnatte César. Actes du colloque de Digne-les-Bains (Alpes-de-Haute-Provence), 28 septembre 2012. In: Bulletin mensuel de la Société linnéenne de Lyon, 82ᵉ année, n°3-4, Mars-avril 2013. pp. 71-86

Le gradient altitudinal sur les sommets tabulaires de Guyane (basé sur l'étude des Arecaceae, des Melastomataceae et des Ptéridophytes)

Amazonia is mainly covered by lowland forest, however it presents some reliefs. Previous works have shown two types of relief in French Guiana : Inselbergs and plateaus on basic volcanic rocks known as tabular summits. Regarding the latter two, vegetation is quite uniform within mountains with comparable altitude and geomorphology. The present research deals mainly cith studying floristic composition along an altitudinal gradient with several bioindicators. For this, the study relies on using three vascular plant groups : Arecaceae, Melastomateceae and Pteridophytes. The present research confirms the existence of variation in floristic composition at around 500 meters a.s.l., but also below and above depending on the selected group.L Amazonie, bien qu elle soit essentiellement couverte par une forêt de basse altitude, possède quelques reliefs. Les travaux précédents ont montré que la Guyane en présentait deux types : les inselbergs et les sommets tabulaires sur roches basiques. Sur ces derniers, la végétation y est relativement uniforme entre les reliefs d altitude et de nature géomorphologique comparables. Notre travail vise principalement à étudier la composition floristique le long d un gradient altitudinal en s appuyant sur plusieurs bioindicateurs. Pour se faire, notre étude s appuie sur l utilisation de trois groupes de végétaux vasculaires : les Arecaceae, les Melastomataceae et les Ptéridophytes. L étude confirme une variation de la composition à 500 mètres d altitude mais également à des altitudes inférieures et supérieures en fonction des groupes étudiés.CAYENNE-BU (973022101) / SudocSudocFranceFrench GuianaFRG

Periodicity and growth pattern variability for six Cecropia sciadophylla populations in the Amazon basin and Guiana shield

International audienceThe genus Cecropia Loefl. includes pioneer trees that colonize canopy gaps and cleared areas. It is widely distributed from Mexico to Northern Argentina and the West Indies. The simple architecture of Cecropia conforms to the model of Rauh; that is, it has orthotropic axes with lateral flowering and rhythmic branching. In a recent study it was found that C. obtusa in French Guiana, have a strong annual periodicity for growth, branching and flowering processes, with annual emission of 35 nodes. To determine the ages of Cecropia trees would help to pinpoint the date of the area’s disturbance, and for this, one possibly is to understand their developmental and architectural changes over time. Axes are made of a succession of nodes and internodes whose length and associated lateral productions remain visible and measurable over years. Thus, by describing the tree trunk node by node it is possible to depict the sequence of events involved in tree development. In this work we have focused on /Cecropia sciadophylla/, a species found throughout the Amazon basin, the Guiana region, and the Llanos region in Colombia. For 89 trees of C. sciadophylla, from two populations in French Guiana and four populations in Colombia, we recorded internode length and any presence of branches and flowers for each node. Using autocorrelation coefficients, we found a high periodicity in elongation, flowering and branching processes. An alternation of long and short nodes with a period that varies between 23 and 25 nodes, flowering processes with a period that varies between 22 and 25 nodes, and stages of branches produced each 23 and 25 nodes, or its multiples, were founded. We found differences in the average height and average number of nodes at which first branches and inflorescences were produced in all populations but the maximum annual elongation was similar among the populations. Considering that flowering is annual for many species of this genus, the main conclusion of this work is that strong annual growth, branching, and flowering rhythms exist for this tropical species. Although our results show a strongly rhythmic and clear topological periodicity, several elements, like the height and number of nodes at which the first branch and first inflorescence are produced, differentiate the six studied populations. This suggest that in spite of a strong ontogenetic restriction for the annual average number of nodes emitted, different environmental factors, like rainfall and soil fertility, could be the cause of the variation seen in the growth pattern

The genus Cecropia: a biological clock to estimate the age of recently disturbed areas in the Neotropics.

Forest successional processes following disturbance take decades to play out, even in tropical forests. Nonetheless, records of vegetation change in this ecosystem are scarce, increasing the importance of the chronosequence approach to study forest recovery. However, this approach requires accurate dating of secondary forests, which until now was a difficult and/or expensive task. Cecropia is a widespread and abundant pioneer tree genus of the Neotropics. Here we propose and validate a rapid and straightforward method to estimate the age of secondary forest patches based on morphological observations of Cecropia trees. We found that Cecropia-inferred ages were highly correlated with known ages of the forest. We also demonstrate that Cecropia can be used to accurately date disturbances and propose twenty-one species distributed all over the geographical range of the genus as potential secondary forest chronometer species. Our method is limited in applicability by the maximal longevity of Cecropia individuals. Although the oldest chronosequence used in this study was 20 years old, we argue that at least for the first four decades after disturbance, the method described in this study provides very accurate estimations of secondary forest ages. The age of pioneer trees provides not only information needed to calculate the recovery of carbon stocks that would help to improve forest management, but also provides information needed to characterize the initial floristic composition and the rates of species remigration into secondary forest. Our contribution shows how successional studies can be reliably and inexpensively extended without the need to obtain forest ages based on expensive or potentially inaccurate data across the Neotropics

Relationship between the estimated age of <i>Cecropia</i> trees obtained using the age estimation protocol (see <b>Fig. 1</b>) and real age of disturbances determined using multiple datasets from local interviews and ONF information.

<p>(a) Both ages were square-root-transformed to meet normality and homoscedasticity assumptions. The dotted line represents the equation adjusted by the linear mixed-effect model. For ease of interpretation by the reader we also present the untransformed data in the panel (b). Black diamonds represent <i>C. sciadophylla</i> and grey diamonds represent <i>C. obtusa</i> individuals. For the Colombian sites we described 52 <i>C. sciadophylla</i> individuals at Leticia, while 28 were described at La Primavera. For the French Guiana sites, we described 20 <i>C. sciadophylla</i> and 137 <i>C. obtusa</i> individuals at Sparwine, 84 <i>C. sciadophylla</i> and 82 <i>C. obtusa</i> individuals at Counamama, and 18 <i>C. sciadophylla</i> and 68 <i>C. obtusa</i> individuals at Coralie (see the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042643#s2" target="_blank">methods</a> section for a detailed study site description).</p

List of <i>Cecropia</i> annual flowering species that could be used to date perturbations in the Neotropics.

<p>The list was taken from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042643#pone.0042643-Zalamea3" target="_blank">[15]</a>. For each species, the distribution, altitude, geographic range and country presences were taken from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042643#pone.0042643-Berg1" target="_blank">[13]</a> and personal observations.</p>*<p>Arg = Argentina, Bar = Barbados, Bel = Belize, Ber = Bermuda, Bol = Bolivia, Bra = Brazil, Col = Colombia, Cos = Costa Rica, Cub = Cuba, Dom = Dominica, Ecu = Ecuador, Sal = El Salvador, Fgu = French Guiana, Gud = Guadeloupe, Gua = Guatemala, Guy = Guyana, Hai = Haiti, Hon = Honduras, Jam = Jamaica, Mar = Martinique, Mex = Mexico, Mon = Monserrat, Net = Netherland Antilles, Nic = Nicaragua, Pan = Panama, Par = Paraguay, Per = Peru, Pue = Puerto Rico, Doi = Dominican Republic, Sab = Saba, Cro = St. Croix, Joh = St. John, Luc = St. Lucia, Vin = St. Vincent, Sur = Suriname, Tor = Trotola, Tri = Trinidad, and Ven = Venezuela.</p

Geographic distributions of the annually flowering <i>Cecropia</i> species.

<p>The map illustrates the number of annually flowering <i>Cecropia</i> species identified by Zalamea et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042643#pone.0042643-Zalamea3" target="_blank">[15]</a>. The colors represent the number of species present in each hexagon of 4° side (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042643#pone-0042643-t001" target="_blank">Table 1</a> for a list of species).</p

Tree silhouette showing a 14.7-years-old individual of <i>C. sciadophylla</i>.

<p><i>Cecropia</i> age estimation protocol consists in dividing the total number of nodes on the main axis by 23 for <i>C. sciadophylla</i> or 35 for <i>C. obtusa</i>. In the pictures (a), (b), and (c) leaf and stipule scars are shown at different heights in the tree. (d) Relationship between the number of nodes on the borne axes (An) and that of their bearing axis (An-1) above their point of insertion, for the same individual. The comparison of A2 in relation to A1 is represented by circles, A3 in relation to A2 by squares, A4 in relation to A3 by triangles and A5 in relation to A4 by “x” symbols. The dotted line in the panel (d) represents the 1∶1 line. The human silhouette represents a 1.8 m height scale.</p