Succession and management of tropical dry forests in the Americas: Review and new perspectives

Understanding tropical forest succession is critical for the development of tropical forest conservation strategies worldwide, given that tropical secondary forests can be considered the forests of the future. Tropical dry forests (TDF) are among the most threatened tropical ecosystems, there are more secondary forests and forest restoration efforts that require a better understanding of successional processes. The main goal of this synthesis for this special issue on the ecology and management of tropical dry forests in the Americas is to present a summarized review of the current knowledge of the ecology and management implications associated to TDF succession. We explore specific issues associated to tropical dry forest succession with emphasis on the use of chronosequences, plant diversity and composition, plant phenology and remote sensing, pollination, and animal-plant interactions; all under the integrating umbrella of ecosystem succession. We also emphasize the need to conduct socio-ecological research to understand changes in land-use history and its effects on succession and forest regeneration of TDF. We close this paper with some thoughts and ideas associated with the strong need for an integrating dimension not considered until today: the role of cyberinfrastructure and eco-informatics as a tool to support sound conservation, management and understanding of TDF in the Americas. (C) 2009 Elsevier B.V. All rights reserved.

Spatio-temporal distribution of calling male frogs in Morro do Diabo State Park (Southeastern Brazil): implications for conservation and management in a seasonally dry tropical forest

The aims of this study are to determine how anuran calling males are spatially and temporally distributed in the Morro do Diabo State Park (MDSP), and to test for indicator species in different breeding habitats. We found high species turnover among breeding habitats of different hydroperiods. Our results indicate that spatial partitioning is more important than seasonal occurrence in permitting species coexistence at MDSP. Indicator Species Analysis identified one species associated with a local stream, one species associated with permanent ponds, two species associated with temporary ponds, and three species associated with a semipermanent pond. Guilds of species do not appear to stratify their distributions throughout the year, since most species occur during the rainy and warm months and are thus temporally overlapping. The main conservation implication of our work is the need to protect the different areas of the park where these unique breeding habitats, and their associated anuran assemblages, are found.

The role of tree size in the leafing phenology of a seasonally dry tropical forest in Belize, Central America

Leafing phenology of two dry-forest sites on soils of different depth (S = shallow, D = deep) at Shipstern Reserve, Belize, were compared at the start of the rainy season (April-June 2000). Trees greater than or equal to 2.5 cm dbh were recorded weekly for 8 wk in three 0.04-ha plots per site. Ten species were analysed individually for their phenological patterns, of which the three most common were Bursera simaruba, Metopium brownei and Jatropha gaumeri. Trees were divided into those in the canopy (> 10 cm dbh) and the subcanopy (less than or equal to 10 cm dbh). Site S had larger trees on average than site D. The proportion of trees flushing leaves at any one time was generally higher in site S than in site D, for both canopy and subcanopy trees. Leaf flush started 2 wk earlier in site S than site D for subcanopy trees, but only 0.5 wk earlier for the canopy trees. Leaf flush duration was 1.5 wk longer in site S than site D. Large trees in the subcanopy flushed leaves earlier than small ones at both sites but in the canopy just at site D. Large trees flushed leaves earlier than small ones in three species and small trees flushed leaves more rapidly in two species. Bursera and Jatropha followed the general trends but Metopium, with larger trees in site D than site S, showed the converse with onset of flushing I wk earlier in site D than site S. Differences in response of the canopy and subcanopy trees on each site can be accounted for by the predominance of spring-flushing or stem-succulent species in site S and a tendency for evergreen species to occur in site D. Early flushing of relatively larger trees in site D most likely requires access to deeper soil water reserves but small and large trees utilize stored tree water in site S.

Seed Dispersal Spectrum of Woody Species in South Ecuadorian Dry Forests: Environmental Correlates and the Effect of Considering Species Abundance

This study examines the seed dispersal spectrum of the tropical dry forests of Southern Ecuador, in an effort to contribute to the knowledge of the complex dynamics of tropical dry forests. Seed dispersal spectrum was described for a total number of 160 species. Relationships of dispersal syndromes with plant growth form and climatic seasonality were explored. For a subset of 97 species, we determined whether dispersal spectrum changes when species abundance, in addition to species number, is taken into account. The same subset was used to relate dispersal syndromes with the environmental conditions. Zoochorous species dominated in the studied community. When considering the individual abundance of each species, however, anemochory was the prevalent dispersal syndrome. We found a significant difference in the frequency of dispersal syndromes among plant growth forms, with epizoochory only occurring in shrub species. The dispersal spectrum was dependent on climatic seasonality. The largest proportion of anemochorous species fructified during the dry season, while zoochorous diaspores dominated during the rainy season. A fourth-corner analysis indicated that the seed dispersal spectrum of Southern Ecuador dry forests is controlled by environmental conditions such as annual precipitation, annual temperature range or topography. Our results suggest that spatio-temporal changes in the environmental conditions may affect important ecological processes for dispersal. Thus, the predominance of one syndrome or another may depend on the spatial variation of environmental conditions.

Biodiversity conservation in human-modified Amazonian forest landscapes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Two new species of Mezilaurus (Lauraceae) from Brazil

Ongoing taxonomic work on Mezilaurus has revealed two new species of the genus in Brazil, which are here described and illustrated. The first one, Mezilaurus glabriantha, from the state of Espirito Santo, represents the third endemic species known from the Brazilian Atlantic Forest, and Mezilaurus microphylla occurs in seasonally dry forests from the central Brazilian state of Tocantins. A key to distinguish the extra-Amazonian species of Mezilaurus from Brazil is provided.

Diversidad funcional y diversidad filogenética en los bosques secos del sur del Ecuador

El concepto tradicional de reglas de ensamblaje refleja la idea de que las especies no co-ocurren al azar sino que están restringidos en su co-ocurrencia por la competencia interespecífica o por un filtrado ambiental. En está tesis abordé la importancia de los procesos que determinan el ensamble de la comunidad en la estructuración de los Bosques Secos en el Sur del Ecuador. Este estudio se realizó en la región biogeográfica Tumbesina, donde se encuentra la mayor concentración de bosques secos tropicales bien conservados del sur de Ecuador, y que constituyen una de las áreas de endemismo más importantes del mundo. El clima se caracteriza por una estación seca que va desde mayo a diciembre y una estación lluviosa de enero a abril, su temperatura anual varía entre 20°C y 26°C y una precipitación promedio anual entre 300 y 700 mm. Mi primer tema fue orientado a evaluar si la distribución de los rasgos funcionales a nivel comunitario es compatible con la existencia de un filtro ambiental (filtrado del hábitat) o con la existencia de un proceso de limitación de la semejanza funcional impuesta por la competencia inter-específica entre 58 especies de plantas leñosas repartidas en 109 parcelas (10x50m). Para ello, se analizó la distribución de los valores de cinco rasgos funcionales (altura máxima, densidad de la madera, área foliar específica, tamaño de la hoja y de masa de la semilla), resumida mediante varios estadísticos (rango, varianza, kurtosis y la desviación estándar de la distribución de distancias funcionales a la especies más próxima) y se comparó con la distribución esperada bajo un modelo nulo con ausencia de competencia. Los resultados obtenidos apoyan que tanto el filtrado ambiental como la limitación a la semejanza afectan el ensamble de las comunidades vegetales de los bosques secos Tumbesinos. Un segundo tema fue identificar si la diversidad funcional está condicionada por los gradientes ambientales, y en concreto si disminuye en los ambientes más estresantes a causa del filtrado ambiental, y si por el contrario aumenta en los ambientes más benignos donde la competencia se vuelve más importante, teniendo en cuenta las posibles modificaciones a este patrón general a causa de las interacciones de facilitación. Para abordar este estudio analizamos tanto las variaciones en la diversidad funcional (respecto a los de los cinco rasgos funcionales empleados en el primer capítulo de la tesis) como las variaciones de diversidad filogenética a lo largo de un gradiente de estrés climático en los bosques tumbesinos, y se contrastaron frente a las diversidades esperadas bajo un modelo de ensamblaje completamente aleatorio de la comunidad. Los análisis mostraron que tan sólo la diversidad de tamaños foliares siguió el patrón de variación esperado, disminuyendo a medida que aumentó el estrés abiótico mientras que ni el resto de rasgos funcionales ni la diversidad funcional multivariada ni la diversidad filogenética mostraron una variación significativa a lo largo del gradiente ambiental. Un tercer tema fue evaluar si los procesos que organizan la estructura funcional de la comunidad operan a diferentes escalas espaciales. Para ello cartografié todos los árboles y arbustos de más de 5 cm de diámetro en una parcela de 9 Ha de bosque seco y caractericé funcionalmente todas las especies. Dicha parcela fue dividida en subparcelas de diferente tamaño, obteniéndose subparcelas a seis escalas espaciales distintas. Los resultados muestran agregación de estrategias funcionales semejantes a escalas pequeñas, lo que sugiere la existencia bien de filtros ambientales actuando a escala fina o bien de procesos competitivos que igualan la estrategia óptima a dichas escalas. Finalmente con la misma información de la parcela permanente de 9 Ha. Nos propusimos evaluar el efecto y comportamiento de las especies respecto a la organización de la diversidad taxonómica, funcional y filogenética. Para ello utilicé tres funciones sumario espaciales: ISAR- para el nivel taxonómico, IFDAR para el nivel funcional y IPSVAR para el nivel filogenética y las contrastamos frente a modelos nulos que describen la distribución espacial de las especies individuales. Los resultados mostraron que en todas las escalas espaciales consideradas para ISAR, IFDAR y IPSVAR, la mayoría de las especies se comportaron como neutras, es decir, que están rodeados por la riqueza de diversidad semejante a la esperada. Sin embargo, algunas especies aparecieron como acumuladoras de diversidad funcional y filogenética, lo que sugiere su implicación en procesos competitivos de limitación de la semejanza. Una pequeña proporción de las especies apareció como repelente de la diversidad funcional y filogenética, lo que sugiere su implicación en un proceso de filtrado de hábitat. En este estudio pone de relieve cómo el análisis de las dimensiones alternativas de la biodiversidad, como la diversidad funcional y filogenética, puede ayudarnos a entender la co-ocurrencia de especies en diversos ensambles de comunidad. Todos los resultados de este estudio aportan nuevas evidencias de los procesos de ensamblaje de la comunidad de los Bosques Estacionalmente secos y como las variables ambientales y la competencia juegan un papel importante en la estructuración de la comunidad. ABSTRACT The traditional concept of the rules assembly for species communities reflects the idea that species do not co-occur at random but are restricted in their co-occurrence by interspecific competition or an environmental filter. In this thesis, I addressed the importance of the se processes in the assembly of plant communities in the dry forests of southern Ecuador. This study was conducted in the biogeographic region of Tumbesina has the largest concentration of well-conserved tropical dry forests of southern Ecuador, and is recognized as one of the most important areas of endemism in the world. The climate is characterized by a dry season from May to December and a rainy season from January to April. The annual temperature varies between 20 ° C and 26 ° C and an average annual rainfall between 300 and 700 mm. I first assessed whether the distribution of functional traits at the level of the community is compatible with the existence of an environmental filter (imposed by habitat) or the existence of a limitation on functional similarity imposed by interspecific competition. This analysis was conducted for 58 species of woody plants spread over 109 plots of 10 x 50 m. Specifically, I compared the distribution of values of five functional traits (maximum height, wood density, specific leaf area, leaf size and mass of the seed), via selected statistical properties (range, variance, kurtosis and analyzed the standard deviation of the distribution of the closest functional species) distances and compared with a expected distribution under a null model of no competition. The results support that both environmental filtering and a limitation on trait similarity affect the assembly of plant communities in dry forests Tumbesina. My second chapter evaluated whether variation in functional diversity is conditioned by environmental gradients. In particular, I tested whether it decreases in the most stressful environments because of environmental filters, or if, on the contrary, functional diversity is greater in more benign environments where competition becomes more important (notwithstanding possible changes to this general pattern due to facilitation). To address this theme I analyzed changes in both the functional diversity (maximum height, wood density, specific leaf area, leaf size and mass of the seed) and the phylogenetic diversity, along a gradient of climatic stress in Tumbes forests. The observed patterns of variation were contrasted against the diversity expected under a completely random null model of community assembly. Only the diversity of leaf sizes followed the hypothesis decreasing in as trait variation abiotic stress increased, while the other functional traits multivariate functional diversity and phylogenetic diversity no showed significant variation along the environmental gradient. The third theme assess whether the processes that organize the functional structure of the community operate at different spatial scales. To do this I mapped all the trees and shrubs of more than 5 cm in diameter within a plot of 9 hectares of dry forest and functionally classified each species. The plot was divided into subplots of different sizes, obtaining subplots of six different spatial scales. I found aggregation of similar functional strategies at small scales, which may indicate the existence of environmental filters or competitive processes that correspond to the optimal strategy for these fine scales. Finally, with the same information from the permanent plot of 9 ha, I evaluated the effect and behavior of individual species on the organization of the taxonomic, functional and phylogenetic diversity. The analysis comprised three spatial summary functions: ISAR- for taxonomic level analysis, IFDAR for functional level analysis, and IPSVAR for phylogenetic level analysis, in each case the pattern of diversity was contrasted against null models that randomly reallocate describe the spatial distribution of individual species and their traits. For all spatial scales considering ISAR, IFDAR and IPSVAR, most species behaved as neutral, i.e. they are surrounded by the diversity of other traits similar to that expected under a null model. However, some species appeared as accumulator of functional and phylogenetic diversity, suggesting that they may play a role in competitive processes that limiting similarity. A small proportion of the species appeared as repellent of functional and phylogenetic diversity, suggesting their involvement in a process of habitat filtering. These analysis highlights that the analysis of alternative dimensions of biodiversity, such as functional and phylogenetic diversity, can help us understand the co-occurrence of species in the assembly of biotic communities. All results of this study provide further evidence of the processes of assembly of the community of the seasonally dry forests as environmental variables and competition play an important role in structuring the community.

Woody plant seedling distribution under invasive Lantana camara thickets in a dry-forest plot in Mudumalai, southern India

Lantana camara, a shrub of Central and South American origin, has become invasive across dry forests worldwide. The effect of the thicket-forming habit of L. camara as a dispersal and recruitment barrier in a community of native woody seedlings was examined in a 50-ha permanent plot located in the seasonally dry forest of Mudumalai, southern India. Sixty 100-m(2) plots were enumerated for native woody seedlings between 10-100 cm in height. Of these, 30 plots had no L. camara thickets, while the other 30 had dense thickets. The frequency of occurrence and abundance of seedlings were modelled as a function of dispersal mode (mammal, bird or mechanical) and affinities to forest habitats (dry forest, moist forest or ubiquitous) as well as presence or absence of dense L. camara thickets. Furthermore, frequency of occurrence and abundance of individual species were also compared between thickets and no L. camara. At the community level, L. camara density, dispersal mode and forest habitat affinities of species determined both frequency of occurrence and abundance of seedlings, with the abundance of dry-forest mammal-dispersed species and ubiquitous mechanically dispersed species being significantly lower under L. camara thickets. Phyllanthus emblica and Kydia calycina were found to be significantly less abundant under L. camara, whereas most other species were not affected by the presence of thickets. It was inferred that, by affecting the establishment of native tree seedlings, L. camara thickets could eventually alter the community composition of such forests.

Effects of Nutrition and Time of Weaning on Dry Season Liveweight Loss of Breeder Cows

In the seasonally dry tropics of northern Australia, breeder cows may lose up to 30% liveweight during the dry season when pasture is of low nutritive value. This is a major cause of low reproductive rates and high mortality. Weaning early in the dry season is effective to reduce this liveweight loss of the breeder (Holroyd et al. 1988). An experiment examined the dry season liveweight loss of breeders for a range of weaning times and levels of nutrition. From April to October through the dry season, 209 Bos indicus x Shorthorn cross cows 4-6 years of age grazed speargrass pastures in north Queensland. The cows had been joined with bulls from late January until April. Twenty-nine breeders had not suckled a calf during the previous wet season (DRY cows). In addition 180 cows lactating in April were weaned in late April, mid July or early September. The cows were allocated by stratified randomisation based on lactational status, stage of pregnancy and body condition to 15 x 40 ha paddocks. Five paddocks with low fertility soils provided LOW nutrition, while 10 paddocks with medium fertility soils and no supplementation or with supplementation provided MEDIUM and HIGH nutrition, respectively. The supplement consisted of molasses containing 14% urea offered ad libitum. Liveweight was measured at intervals and conceptus-free liveweight (CF-LW) calculated. Data were analyses by AOV within groups of paddocks. Animal production for a consuming world : proceedings of 9th Congress of the Asian-Australasian Association of Animal Production Societies [AAAP] and 23rd Biennial Conference of the Australian Society of Animal Production [ASAP] and 17th Annual Symposium of the University of Sydney, Dairy Research Foundation, [DRF]. 2-7 July 2000, Sydney, Australia.

Relationship between annual rainfall and tree mortality in a tropical dry forest: Results of a 19-year study at Mudumalai, southern India

Variability in rainfall is known to be a major influence on the dynamics of tropical forests, especially rates and patterns of tree mortality. In tropical dry forests a number of contributing factors to tree mortality, including dry season fire and herbivory by large herbivorous mammals, could be related to rainfall patterns, while loss of water potential in trees during the dry season or a wet season drought could also result in enhanced rates of death. While tree mortality as influenced by severe drought has been examined in tropical wet forests there is insufficient understanding of this process in tropical dry forests. We examined these causal factors in relation to inter-annual differences in rainfall in causing tree mortality within a 50-ha Forest Dynamics Plot located in the tropical dry deciduous forests of Mudumalai, southern India, that has been monitored annually since 1988. Over a 19-year period (1988-2007) mean annual mortality rate of all stems >1 cm dbh was 6.9 +/- 4.6% (range = 1.5-17.5%); mortality rates broadly declined from the smaller to the larger size classes with the rates in stems >30 cm dbh being among the lowest recorded in tropical forest globally. Fire was the main agent of mortality in stems 1-5 cm dbh, elephant-herbivory in stems 5-10 cm dbh, and other natural causes in stems > 10 cm dbh. Elephant-related mortality did not show any relationship to rainfall. On the other hand, fire-related mortality was significantly negatively correlated to quantity of rainfall during the preceding year. Mortality due to other causes in the larger stem sizes was significantly negatively correlated to rainfall with a 2-3-year lag, suggesting that water deficit from mild or prolonged drought enhanced the risk of death but only with a time lag that was greater than similar lags in tree mortality observed in other forest types. In this respect, tropical dry forests growing in regions of high rainfall variability may have evolved greater resistance to rainfall deficit as compared to tropical moist or temperate forests but are still vulnerable to drought-related mortality.

Vegetation structure and floristic composition of a tropical dry deciduous forest in Bhadra Wildlife Sanctuary, Karnataka, India

A permanent 2 ha (200 m x 100 m) plot was established for long-term monitoring of plant diversity and dynamics in a tropical dry deciduous forest of Bhadra Wildlife Sanctuary, Karnataka, southern India. Enumeration of all woody plants >= 1 cm DBH (diameter at breast height) yielded a total of 1766 individuals that belonged to 46 species, 37 genera and 24 families. Combretaceae was the most abundant family in the forest with a family importance value of 68.3. Plant density varied from 20 - 90 individuals with an average 35 individuals/quadrat (20 m x 20 m). Randia dumetorum, with 466 individuals (representing 26.7 % of the total density 2 ha(-1)) with species importance value of 36.25, was the dominant species in the plot. The total basal area of the plot was 18.09 m(2) ha(-1) with a mean of 0.72 m(2) quadrat(-1). The highest basal area of the plot was contributed by Combretaceae (12.93 m(2) 2 ha(-1)) at family level and Terminalia tomentosa (5.58 m(2) 2 ha(-1)) at species level. The lowest diameter class (1-10 cm) had the highest density (1054 individuals 2 ha(-1)), but basal area was highest in the 80 - 90 cm diameter class (5.03m(2) 2 ha(-1)). Most of the species exhibited random or aggregated distribution over the plot. This study provides a baseline information on the dry forests of Bhadra Wildlife Sanctuary.

And yet it shrinks: A novel method for correcting bias in forest tree growth estimates caused by water-induced fluctuations

Accuracy in tree woody growth estimates is important to global carbon budget estimation and climate-change science. Tree growth in permanent sampling plots (PSPs) is commonly estimated by measuring stem diameter changes, but this method is susceptible to bias resulting from water-induced reversible stem shrinkage. In the absence of bias correction, temporal variability in growth is likely to be overestimated and incorrectly attributed to fluctuations in resource availability, especially in forests with high seasonal and inter-annual variability in water. We propose and test a novel approach for estimating and correcting this bias at the community level. In a 50-ha PSP from a seasonally dry tropical forest in southern India, where tape measurements have been taken every four years from 1988 to 2012, for nine trees we estimated bias due to reversible stem shrinkage as the difference between woody growth measured using tree rings and that estimated from tape. We tested if the bias estimated from these trees could be used as a proxy to correct bias in tape-based growth estimates at the PSP scale. We observed significant shrinkage-related bias in the growth estimates of the nine trees in some censuses. This bias was strongly linearly related to tape-based growth estimates at the level of the PSP, and could be used as a proxy. After bias was corrected, the temporal variance in growth rates of the PSP decreased, while the effect of exceptionally dry or wet periods was retained, indicating that at least a part of the temporal variability arose from reversible shrinkage-related bias. We also suggest that the efficacy of the bias correction could be improved by measuring the proxy on trees that belong to different size classes and census timing, but not necessarily to different species. Our approach allows for reanalysis - and possible reinterpretation of temporal trends in tree growth, above ground biomass change, or carbon fluxes in forests, and their relationships with resource availability in the context of climate change. (C) 2014 Elsevier B.V. All rights reserved.

Systématique et biogéographie du groupe Caesalpinia (famille Leguminosae)

Parmi les lignées des Caesalpinioideae (dans la famille des Leguminosae), l’un des groupes importants au sein duquel les relations phylogénétiques demeurent nébuleuses est le « groupe Caesalpinia », un clade de plus de 205 espèces, réparties présentement entre 14 à 21 genres. La complexité taxonomique du groupe Caesalpinia provient du fait qu’on n’arrive pas à résoudre les questions de délimitations génériques de Caesalpinia sensu lato (s.l.), un regroupement de 150 espèces qui sont provisoirement classées en huit genres. Afin d’arriver à une classification générique stable, des analyses phylogénétiques de cinq loci chloroplastiques et de la région nucléaire ITS ont été effectuées sur une matrice comportant un échantillonnage taxonomique du groupe sans précédent (~84% des espèces du groupe) et couvrant la quasi-totalité de la variation morphologique et géographique du groupe Caesalpinia. Ces analyses ont permis de déterminer que plusieurs genres du groupe Caesalpinia, tels que présentement définis, sont polyphylétiques ou paraphylétiques. Nous considérons que 26 clades bien résolus représentent des genres, et une nouvelle classification générique du groupe Caesalpinia est proposée : elle inclut une clé des genres, une description des 26 genres et des espèces acceptées au sein de ces groupes. Cette nouvelle classification maintient l’inclusion de douze genres (Balsamocarpon, Cordeauxia, Guilandina, Haematoxylum, Hoffmanseggia, Lophocarpinia, Mezoneuron, Pomaria, Pterolobium, Stenodrepanum, Stuhlmannia, Zuccagnia) et en abolit deux (Stahlia et Poincianella). Elle propose aussi de réinstaurer deux genres (Biancaea et Denisophytum), de reconnaître cinq nouveaux genres (Arquita, Gelrebia, Hererolandia, Hultholia et Paubrasilia), et d’amender la description de sept genres (Caesalpinia, Cenostigma, Coulteria, Erythrostemon, Libidibia, Moullava, Tara). Les résultats indiquent qu’il y aurait possiblement aussi une 27e lignée qui correspondrait au genre Ticanto, mais un échantillonage taxonomique plus important serait nécéssaire pour éclaircir ce problème. Les espèces du groupe Caesalpinia ont une répartition pantropicale qui correspond presque parfaitement aux aires du biome succulent, mais se retrouvent aussi dans les déserts, les prairies, les savanes et les forêts tropicales humides. À l’échelle planétaire, le biome succulent consiste en une série d’habitats arides ou semi-arides hautement fragmentés et caractérisés par l’absence de feu, et abrite souvent des espèces végétales grasses, comme les Cactacées dans les néo-tropiques et les Euphorbiacées en Afrique. L’histoire biogéographique du groupe Caesalpinia a été reconstruite afin de mieux comprendre l’évolution de la flore au sein de ce biome succulent. Ce portrait biogéographique a été obtenu grâce à des analyses de datations moléculaires et des changements de taux de diversification, à une reconstruction des aires ancestrales utilisant le modèle de dispersion-extinction-cladogenèse, et à la reconstruction de l’évolution des biomes et du port des plantes sur la phylogénie du groupe Caesalpinia. Ces analyses démontrent que les disjonctions trans-continentales entre espèces sœurs qui appartiennent au même biome sont plus fréquentes que le nombre total de changements de biomes à travers la phylogénie, suggérant qu’il y a une forte conservation de niches, et qu’il est plus facile de bouger que de changer et d’évoluer au sein d’un biome différent. Par ailleurs, contrairement à nos hypothèses initiales, aucun changement de taux de diversification n’est détecté dans la phylogénie, même lorsque les espèces évoluent dans des biomes différents ou qu’il y a changement de port de la plante, et qu’elle se transforme, par exemple, en liane ou herbacée. Nous suggérons que même lorsqu’ils habitent des biomes très différents, tels que les savanes ou les forêts tropicales humides, les membres du groupe Caesalpinia se retrouvent néanmoins dans des conditions écologiques locales qui rappellent celles du biome succulent. Finalement, bien que la diversité des espèces du biome succulent ne se compare pas à celle retrouvée dans les forêts tropicales humides, ce milieu se distingue par un haut taux d’espèces endémiques, réparties dans des aires disjointes. Cette diversité spécifique est probablement sous-estimée et mérite d’être évaluée attentivement, comme en témoigne la découverte de plusieurs nouvelles espèces d’arbres et arbustes de légumineuses dans la dernière décennie. Le dernier objectif de cette thèse consiste à examiner les limites au niveau spécifique du complexe C. trichocarpa, un arbuste des Andes ayant une population disjointe au Pérou qui représente potentiellement une nouvelle espèce. Des analyses morphologiques et moléculaires sur les populations présentes à travers les Andes permettent de conclure que les populations au Pérou représentent une nouvelle espèce, qui est génétiquement distincte et comporte des caractéristiques morphologiques subtiles permettant de la distinguer des populations retrouvées en Argentine et en Bolivie. Nous décrivons cette nouvelle espèce, Arquita grandiflora, dans le cadre d’une révision taxonomique du genre Arquita, un clade de cinq espèces retrouvées exclusivement dans les vallées andines.

Phylogeographie und Populationsgenetik der Arten der Gattung Fosterella (Bromeliaceae) in den südamerikanischen Anden

Die tropischen Anden sind eines der artenreichsten Gebiete der Erde. Fast die Hälfte der 45.000 in diesem Gebiet vorkommenden Gefäßpflanzenarten sind in den Anden endemisch (Myers et al. 2000). Die Gattung Fosterella (Bromeliaceae) ist eine den Anden zugeordnete Pflanzengruppe, denn die meisten ihrer 31 Arten kommen in den Anden vor. Achtzehn Arten sind kleinräumige Endemiten. Fosterella hat damit Modellcharakter für diese Region. In der vorliegenden Arbeit wurde die Evolution der Gattung in Raum und Zeit mithilfe der vergleichenden Sequenzierung von sechs plastidären Loci (atpB-rbcL, matK, psbB-psbH, rpl32-trnL, rps16-trnK, rps16-Intron) und einem nukleären Marker (PHYC) untersucht. Es wurden über 90 Akzessionen von 24 Fosterella-Arten untersucht. Mit 5,6 % informativer Merkmale innerhalb der Gattung war rpl32-trnL der informativste Chloroplastenmarker. Es wurden mit den kombinierten Sequenzdaten eine Maximum Parsimony-, eine Maximum Likelihood- und eine Bayes´sche Analyse berechnet. Weiterhin wurden biogeographische und ultrametrische Untersuchungen durchgeführt. Die 6-Locus-Phylogenie zeigt eine Aufteilung der monophyletischen Gattung Fosterella in sechs Gruppen, von denen vier – die penduliflora-, weddelliana-, weberbaueri- und micrantha-Gruppe - klar monophyletisch und gut gestützt sind. Die albicans- und die rusbyi-Gruppe bilden hingegen einen Komplex. Ultrametrische Analysen legen ein Alter der Gattung von ca. 9,6 Mio. Jahren nahe. Der geographische Ursprung von Fosterella befindet sich nach den vorliegenden biogeographischen Analysen in den Anden und nach der Biom-Analyse zu gleicher Wahrscheinlichkeit entweder in andinen Trockenwäldern (seasonally dry tropical forests, SDTFs) oder in azonalen Standorten des amazonischen Tieflands östlich der Anden. Es gab mehrere Ausbreitungsereignisse, von denen die beiden Fernausbreitungsereignisse nach Mittelamerika (F. micrantha) und in das zentrale Amazonasgebiet (F. batistana) die auffälligsten sind. Die feuchten Bergregenwälder (Yungas) der Anden wurden offenbar mehrfach unabhängig von Fosterella-Arten besiedelt. Insgesamt wurden elf nukleäre Marker (XDH, GS, RPB2, MS, ADH, MS, GLO/PI, CHS, FLO/LFY, NIAi3 und PHYC) auf ihre Anwendbarkeit für molekularsystematische Studien in Fosterella getestet. Davon konnten acht Marker erfolgreich mithilfe einer PCR amplifiziert werden. Die Fragmentgrößen lagen zwischen 350 bp und 1.500 bp. Nur für drei Loci (FLO/LFY, NIAi3 und PHYC) konnten lesbare DNA-Sequenzen in Fosterella erzeugt werden. FLO/LFY zeigte nur 1,5 % Variabilität innerhalb der Gattung. Der NIA-Locus erzeugte bei der Amplifikation mehrere Fragmente, die separat voneinander sequenziert wurden. Der Locus PHYC konnte hingegen aufgrund der guten Amplifizier- und Sequenzierbarkeit für das gesamte Probenset sequenziert werden. Dieser Marker zeigte eine Variabilität innerhalb der Gattung von 10,2 %, davon waren 6,8 % informativ. In der Phylogenie basierend auf PHYC ist Fosterella klar monophyletisch, innerhalb der Gattung zeigt sich jedoch an der Basis eine unaufgelöste Polytomie. Es lassen sich neun mehr oder weniger gut gestützte Artengruppen definieren – rusbyi-, villosula-, albicans-, weddelliana-, penduliflora-, weberbaueri-, micrantha-, robertreadii- und spectabilis-Gruppe - die sich in ihrer Zusammensetzung mit Ausnahme der weddelliana-Gruppe von den nach Chloroplastendaten definierten Gruppen unterscheiden. Viele Arten sind para- oder polyphyletisch, so z. B. F. albicans, F. penduliflora und F. rusbyi. Bei den beiden erstgenannten Arten weisen die unterschiedlichen Stellungen in Chloroplasten- und Kernphylogenie auf Hybridisierungsereignisse hin.

Impact of a drier Early-Mid-Holocene climate upon Amazonian forests

This paper uses a palaeoecological approach to examine the impact of drier climatic conditions of the Early-Mid-Holocene (ca 8000-4000 years ago) upon Amazonia's forests and their fire regimes. Palaeovegetation (pollen data) and palaeofire (charcoal) records are synthesized from 20 sites within the present tropical forest biome, and the underlying causes of any emergent patterns or changes are explored by reference to independent palaeoclimate data and present-day patterns of precipitation, forest cover and fire activity across Amazonia. During the Early-Mid-Holocene, Andean cloud forest taxa were replaced by lowland tree taxa as the cloud base rose while lowland ecotonal areas, which are presently covered by evergreen rainforest, were instead dominated by savannahs and/or semi-deciduous dry forests. Elsewhere in the Amazon Basin there is considerable spatial and temporal variation in patterns of vegetation disturbance and fire, which probably reflects the complex heterogeneous patterns in precipitation and seasonality across the basin, and the interactions between climate change, drought- and fire susceptibility of the forests, and Palaeo-Indian land use. Our analysis shows that the forest biome in most parts of Amazonia appears to have been remarkably resilient to climatic conditions significantly drier than those of today, despite widespread evidence of forest burning. Only in ecotonal areas is there evidence of biome replacement in the Holocene. From this palaeoecological perspective, we argue against the Amazon forest 'dieback' scenario simulated for the future.