953 resultados para plant communities
Resumo:
In tropical eastern Africa, vegetation distribution is largely controlled by regional hydrology, which has varied over the past 20 000 years. Therefore, accurate reconstructions of past vegetation and hydrological changes are crucial for a better understanding of climate variability in the tropical southeastern African region. We present high-resolution pollen records from a marine sediment core recovered offshore of the Rufiji River delta. Our data document significant shifts in pollen assemblages during the last deglaciation, identifying, through changes in both upland and lowland vegetation, specific responses of plant communities to atmospheric (precipitation) and coastal (coastal dynamics and sea-level changes) alterations. Specifically, arid conditions reflected by a maximum pollen representation of dry and open vegetation occurred during the Northern Hemisphere cold Heinrich event 1 (H1), suggesting that the expansion of drier upland vegetation was synchronous with cold Northern Hemisphere conditions. This arid period is followed by an interval in which forest and humid woodlands expanded, indicating a hydrologic shift towards more humid conditions. Droughts during H1 and the shift to humid conditions around 14.8 kyr BP in the uplands are consistent with latitudinal shifts of the intertropical convergence zone (ITCZ) driven by high-latitude Northern Hemisphere climatic fluctuations. Additionally, our results show that the lowland vegetation, consisting of well-developed salt marshes and mangroves in a successional pattern typical for vegetation occurring in intertidal habitats, has responded mainly to local coastal dynamics related to marine inundation frequencies and soil salinity in the Rufiji Delta as well as to the local moisture availability. Lowland vegetation shows a substantial expansion of mangrove trees after ~ 14.8 kyr BP, suggesting an increased moisture availability and river runoff in the coastal area. The results of this study highlight the decoupled climatic and environmental processes to which the vegetation in the uplands and the Rufiji Delta has responded during the last deglaciation.
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This collection contains measurements of environmental conditions measured on the plots of the different sub-experiments at the field site of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. The following series of datasets are contained in this collection: 1.Soil temperature measurements on plots of the Main Experiment; 2. Quantification of the duration that individual plots of the Main Experiment were submerged during a flooding event occurring in June 2013
Resumo:
Global air surface temperatures and precipitation have increased over the last several decades resulting in a trend of greening across the Circumpolar Arctic. The spatial variability of warming and the inherent effects on plant communities has not proven to be uniform or homogeneous on global or local scales. We can apply remote sensing vegetation indices such as the Normalized Difference Vegetation Index (NDVI) to map and monitor vegetation change (e.g., phenology, greening, percent cover, and biomass) over time. It is important to document how Arctic vegetation is changing, as it will have large implications related to global carbon and surface energy budgets. The research reported here examined vegetation greening across different spatial and temporal scales at two disparate Arctic sites: Apex River Watershed (ARW), Baffin Island, and Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, NU. To characterize the vegetation in the ARW, high spatial resolution WorldView-2 data were processed to create a supervised land-cover classification and model percent vegetation cover (PVC) (a similar process had been completed in a previous study for the CBAWO). Meanwhile, NDVI data spanning the past 30 years were derived from intermediate resolution Landsat data at the two Arctic sites. The land-cover classifications at both sites were used to examine the Landsat NDVI time series by vegetation class. Climate variables (i.e., temperature, precipitation and growing season length (GSL) were examined to explore the potential relationships of NDVI to climate warming. PVC was successfully modeled using high resolution data in the ARW. PVC and plant communities appear to reside along a moisture and altitudinal gradient. The NDVI time series demonstrated an overall significant increase in greening at the CBAWO (High Arctic site), specifically in the dry and mesic vegetation type. However, similar overall greening was not observed for the ARW (Low Arctic site). The overall increase in NDVI at the CBAWO was attributed to a significant increase in July temperatures, precipitation and GSL.
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In this study, we investigated the relationship between vegetation and modern-pollen rain along the elevational gradient of Mount Paggeo. We apply multivariate data analysis to assess the relationship between vegetation and modern-pollen rain and quantify the representativeness of forest zones. This study represents the first statistical analysis of pollen-vegetation relationship along an elevational gradient in Greece. Hence, this paper improves confidence in interpretation of palynological records from north-eastern Greece and may refine past climate reconstructions for a more accurate comparison of data and modelling. Numerical classification and ordination were performed on pollen data to assess differences among plant communities that beech (Fagus sylvatica) dominates or co-dominates. The results show a strong relationship between altitude, arboreal cover, human impact and variations in pollen and nonpollen palynomorph taxa percentages.
Resumo:
Les cosystmes dunaires remplissent plusieurs fonctions cologiques essentielles comme celle de protger le littoral grce leur capacit damortissement face aux vents et vagues des temptes. Les dunes jouent aussi un rle dans la filtration de leau, la recharge de la nappe phratique, le maintien de la biodiversit, en plus de prsenter un attrait culturel, rcratif et touristique. Les milieux dunaires sont trs dynamiques et incluent plusieurs stades de succession vgtale, passant de la plage de sable nu la dune bordire stabilise par lammophile ligule courte, laquelle permet aussi ltablissement dautres herbaces, darbustes et, ventuellement, darbres. Or, la survie de ces vgtaux est intimement lie aux microorganismes du sol. Les champignons du sol interagissent intimement avec les racines des plantes, modifient la structure des sols, et contribuent la dcomposition de la matire organique et la disponibilit des nutriments. Ils sont donc des acteurs cls de lcologie des sols et contribuent la stabilisation des dunes. Malgr cela, la diversit et la structure des communauts fongiques, ainsi que les mcanismes influenant leur dynamique cologique, demeurent relativement mconnus. Le travail prsent dans cette thse explore la diversit des communauts fongiques travers le gradient de succession et de conditions daphiques dun cosystme dunaire ctier afin damliorer la comprhension de la dynamique des sols en milieux dunaires. Une vaste collecte de donnes sur le terrain a t ralise sur une plaine de dunes reliques se trouvant aux les de la Madeleine, Qc. Jai chantillonn plus de 80 sites rpartis sur lensemble de ce systme dunaire et caractris les champignons du sol grce au squenage haut dbit. Dans un premier temps, jai dress un portait densemble des communauts fongiques du sol travers les diffrentes zones des dunes. En plus dune description taxonomique, les modes de vie fongiques ont t prdits afin de mieux comprendre comment les variations au niveau des communauts de champignons du sol peuvent se traduire en changements fonctionnels. Jai observ un niveau de diversit fongique lev (plus de 3400 units taxonomiques oprationnelles au total) et des communauts taxonomiquement et fonctionnellement distinctes travers un gradient de succession et de conditions daphiques. Ces rsultats ont aussi indiqu que toutes les zones des dunes, incluant la zone pionire, supportent des communauts fongiques diversifies. Ensuite, le lien entre les communauts vgtales et fongiques a t tudi travers lensemble de la squence dunaire. Ces rsultats ont montr une augmentation claire de la richesse spcifique vgtale, ainsi quune augmentation de la diversit des stratgies dacquisition de nutriments (traits souterrains li la nutrition des plantes, soit mycorhizien arbuscule, ectomycorhizien, mycorhizien ricoide, fixateur dazote ou non spcialis). Jai aussi pu tablir une forte corrlation entre les champignons du sol et la vgtation, qui semblent tous deux ragir de faon similaire aux conditions physicochimiques du sol. Le pH du sol influenait fortement les communauts vgtales et fongiques. Le lien observ entre les communauts vgtales et fongiques met lemphase sur limportance des interactions biotiques positives au fil de la succession dans les environnements pauvres en nutriments. Finalement, jai compar les communauts de champignons ectomycorhiziens associes aux principales espces arborescentes dans les forts dunaires. Jai observ une richesse importante, avec un total de 200 units taxonomiques oprationnelles ectomycorhiziennes, appartenant principalement aux Agaricomyctes. Une analyse de rseaux na pas permis de dtecter de modules (c'est--dire des sous-groupes despces en interaction), ce qui indique un faible niveau de spcificit des associations ectomycorhiziennes. De plus, je nai pas observ de diffrences en termes de richesse ou de structure des communauts entre les quatre espces htes. En conclusion, jai pu observer travers la succession dunaire des communauts diversifies et des structures distinctes selon la zone de la dune, tant chez les champignons que chez les plantes. La succession semble toutefois moins marque au niveau des communauts fongiques, par rapport aux patrons observs chez les plantes. Ces rsultats ont aliment une rflexion sur le potentiel et les perspectives, mais aussi sur les limitations des approches reposant sur le squenage haut-dbit en cologie microbienne.
Resumo:
La vgtation riveraine et littorale de lest du Canada a t svrement altre par la drave et plusieurs barrages lacustres subsistent, mais leurs effets et ceux de leur retrait sont peu documents. Cette tude visait : i) mesurer les changements de la structure et de la composition vgtale des zones riveraines et littorales en fonction de llvation par rapport au plan deau, ii) valuer le temps de retour de la vgtation son tat de rfrence naturel suite au retrait de barrages et iii) dterminer les facteurs rgissant les rponses de la vgtation ces variations de niveaux deau. La structure et la composition vgtale suite la restauration dun barrage a t compare sur deux lacs : un tmoin et un comprenant quatre bassins prsentant un gradient dinfluence du barrage. Suite au retrait de barrage, la vgtation a t examine sur quatre lacs, dont un tmoin. Les principaux facteurs qui influenaient la vgtation riveraine et littorale en prsence dun barrage taient llvation actuelle par rapport au lac et lampleur de linfluence du barrage. Suite un dmantlement de barrage, les principaux facteurs dinfluence taient llvation par rapport au rivage et le nombre dannes depuis le retrait de barrage. En prsence dun barrage, la vgtation riveraine tait caractrise par la transformation de hautes terres en fort humide riveraine qui partageait des caractristiques avec le tmoin. partir de 1 m dlvation, la vgtation tait caractrise par une fort sche. Dans les premires annes suivant le retrait de barrage, la vgtation littorale tait compose dherbiers submergs mixtes faible densit avec une forte diversit spcifique prs du rivage. La structure et la composition vgtale taient similaires au tmoin aprs 16 ans. Il ny avait pas dvidence que les communauts vgtales dviaient de leur trajectoire successionnelle naturelle sous linfluence des nouvelles conditions environnementales.
Resumo:
Among insects, which are the most diverse eukaryotic group on earth, Lepidoptera is one of four enormously diverse orders, with approximately 10,000 described species in North America. Within the order, Nearctic microlepidoptera, which represent an overwhelmingly large percentage of diversity within the order, remain poorly known despite their ecological importance in many plant communities. In this thesis, I undertook several studies of microlepidoptera diversity in a natural community type (hill prairie) and a managed community type (biofuel feedstock). In two Illinois hill prairies differing in size, latitude, and plant composition, alpha diversity of Pyraloidea and Tortricidae was similar, but the prairies were found to support different sets of species of these moth groups. It is concluded that the similarity in alpha diversity occurs because the larger prairie supports primarily a complement of moth species that feed as larvae on prairie plants (especially species of Asteraceae and Fabaceae), whereas the moths collected in the small prairie represent relatively few prairie-associated species, plus a large component of species that feed as larvae on deciduous trees that surround the prairie. This agrees with the finding of high beta diversity of moths between the sites, which reflects a high level of larval hostplant specificity in most species of Pyraloidea and Tortricidae. Based on published information plus observations made on microlepidoptera collected during the course of this study, 31 families of basal microlepidoptera were reviewed with an aim toward evaluating the likelihood of their including species that are dependent on tallgrass prairie. Of these families, 12 were evaluated as possible, and two as likely or certain, to include prairie-dependent species. In a comparison of moth diversity in light-trap samples from corn, miscanthus, switchgrass, and native prairie, alpha diversity was highest in prairie and was higher in switchgrass than in the other two biofuel crops. Moth species complements generally were similar among the biofuel crops, and prairie shared higher species complementarity with switchgrass than with corn or miscanthus. These findings suggest that large-scale conversion of land to biofuel crops may, to a substantial degree, detrimentally affect arthropod biodiversity, with a resulting loss of valuable arthropod-derived ecosystem services both within the cropping systems and in the surrounding landscape. During the course of this study, rearing efforts yielded two species of moths of the family Gelechiidae, both of which are monophagous leaf feeders on leadplant, Amorpha canescens (Fabaceae). Because these moths are restricted to tallgrass prairie, they are likely to be of interest to conservation biologists. In the interest of naming the moths to facilitate communication regarding them, and to augment our taxonomic knowledge of their respective genera, the moths are described, and diagnoses are provided to differentiate them from similar, related species.
Resumo:
Os Charcos temporrios mediterrnicos (3170*) so habitats prioritrios devido enorme biodiversidade que albergam e ao grau de ameaa sob o qual que se encontram. A singularidade deste habitat resulta da coexistncia de diferentes comunidades de plantas no mesmo espao mas em perodos de tempo diferentes, o que viabilizado pela existncia de bancos de sementes abundantes e diversificados. A avaliao da composio especfica e abundncia do banco de sementes do solo permitiu determinar a distribuio espacial das sementes e o potencial de recuperao dos charcos. Com esta avaliao concluiu-se que existe uma maior riqueza especfica nas cinturas externa e mdia dos charcos do que na cintura interna. Concluiu-se tambm que o conhecimento do banco de sementes dos charcos pode contribuir para a definio de estratgias de gesto/recuperao dos charcos, nomeadamente daqueles que possuem grau de conservao intermdio, funcionando como um valioso instrumento de gesto; The soil seed bank - a tool for assessing the conservation status of Mediterranean temporary ponds Abstract: Mediterranean temporary ponds (3170*) are priority habitats due to the huge biodiversity they shelter and because they are menaced. The uniqueness of this habitat results from the coexistence of different plant communities in the same space at different time periods, what is allowed by the existence of abundant and diversified soil seed banks. The assessment of the specific composition and abundance of soil seed bank, made possible to ascertain the spatial distribution of seeds within ponds and their recovery potential. This assessment showed that there is more specific richness in intermediate and outer belts of ponds than in the inner belt. It also showed how valuable can this information be regarding the design of management or recovery strategies for ponds, particularly for those with intermediate degree of conservation.
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Wydzia Biologii
Resumo:
Les cosystmes dunaires remplissent plusieurs fonctions cologiques essentielles comme celle de protger le littoral grce leur capacit damortissement face aux vents et vagues des temptes. Les dunes jouent aussi un rle dans la filtration de leau, la recharge de la nappe phratique, le maintien de la biodiversit, en plus de prsenter un attrait culturel, rcratif et touristique. Les milieux dunaires sont trs dynamiques et incluent plusieurs stades de succession vgtale, passant de la plage de sable nu la dune bordire stabilise par lammophile ligule courte, laquelle permet aussi ltablissement dautres herbaces, darbustes et, ventuellement, darbres. Or, la survie de ces vgtaux est intimement lie aux microorganismes du sol. Les champignons du sol interagissent intimement avec les racines des plantes, modifient la structure des sols, et contribuent la dcomposition de la matire organique et la disponibilit des nutriments. Ils sont donc des acteurs cls de lcologie des sols et contribuent la stabilisation des dunes. Malgr cela, la diversit et la structure des communauts fongiques, ainsi que les mcanismes influenant leur dynamique cologique, demeurent relativement mconnus. Le travail prsent dans cette thse explore la diversit des communauts fongiques travers le gradient de succession et de conditions daphiques dun cosystme dunaire ctier afin damliorer la comprhension de la dynamique des sols en milieux dunaires. Une vaste collecte de donnes sur le terrain a t ralise sur une plaine de dunes reliques se trouvant aux les de la Madeleine, Qc. Jai chantillonn plus de 80 sites rpartis sur lensemble de ce systme dunaire et caractris les champignons du sol grce au squenage haut dbit. Dans un premier temps, jai dress un portait densemble des communauts fongiques du sol travers les diffrentes zones des dunes. En plus dune description taxonomique, les modes de vie fongiques ont t prdits afin de mieux comprendre comment les variations au niveau des communauts de champignons du sol peuvent se traduire en changements fonctionnels. Jai observ un niveau de diversit fongique lev (plus de 3400 units taxonomiques oprationnelles au total) et des communauts taxonomiquement et fonctionnellement distinctes travers un gradient de succession et de conditions daphiques. Ces rsultats ont aussi indiqu que toutes les zones des dunes, incluant la zone pionire, supportent des communauts fongiques diversifies. Ensuite, le lien entre les communauts vgtales et fongiques a t tudi travers lensemble de la squence dunaire. Ces rsultats ont montr une augmentation claire de la richesse spcifique vgtale, ainsi quune augmentation de la diversit des stratgies dacquisition de nutriments (traits souterrains li la nutrition des plantes, soit mycorhizien arbuscule, ectomycorhizien, mycorhizien ricoide, fixateur dazote ou non spcialis). Jai aussi pu tablir une forte corrlation entre les champignons du sol et la vgtation, qui semblent tous deux ragir de faon similaire aux conditions physicochimiques du sol. Le pH du sol influenait fortement les communauts vgtales et fongiques. Le lien observ entre les communauts vgtales et fongiques met lemphase sur limportance des interactions biotiques positives au fil de la succession dans les environnements pauvres en nutriments. Finalement, jai compar les communauts de champignons ectomycorhiziens associes aux principales espces arborescentes dans les forts dunaires. Jai observ une richesse importante, avec un total de 200 units taxonomiques oprationnelles ectomycorhiziennes, appartenant principalement aux Agaricomyctes. Une analyse de rseaux na pas permis de dtecter de modules (c'est--dire des sous-groupes despces en interaction), ce qui indique un faible niveau de spcificit des associations ectomycorhiziennes. De plus, je nai pas observ de diffrences en termes de richesse ou de structure des communauts entre les quatre espces htes. En conclusion, jai pu observer travers la succession dunaire des communauts diversifies et des structures distinctes selon la zone de la dune, tant chez les champignons que chez les plantes. La succession semble toutefois moins marque au niveau des communauts fongiques, par rapport aux patrons observs chez les plantes. Ces rsultats ont aliment une rflexion sur le potentiel et les perspectives, mais aussi sur les limitations des approches reposant sur le squenage haut-dbit en cologie microbienne.
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Members of the oomycete cause extensive losses in agriculture and widespread degradation in natural plant communities, being responsible for the death of thousands of trees every year. Two of the representative species are Phytophthora infestans, which causes late blight of potato, and Phytophthora cinnamomi, which causes chestnut ink disease, responsible for losses on sweet chestnut production in Europe. Genome sequencing efforts have been focused on the study of three species: P. infestans, P. sojae and P. ramorum. Phytophthora infestans has been developed as the model specie for the genus, possessing excellent genetic and genomics resources including genetic maps, BAC libraries, and EST sequences. Our research team is trying to sequence the genome of P. cinnamomi in order to gain a better understanding of this oomycete, to study changes in plant-pathogen relationships including those resulting from climate change and trying to decrease the pathogens impact on crops and plants in natural ecosystems worldwide. We present here a preliminary report of partially sequenced genomic DNA from P. cinnamomi encoding putative protein-coding sequences and tRNAs. Database analysis reveals the presence of genes conserved in oomycetes.
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Earth climate has changed significantly in the last century and the different models indicate that it will continue to change over the next decades, even if the emission of greenhouse gases stop immediately. These changes have impact on different plant populations, as well as in the actual distribution of several species. As plants, in general, have a smaller capacity of dispersion compared with the animals it is likely that they will suffer the impacts of the climate change more intensively.
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Boreal peatlands contain approximately one third of the global soil carbon and are considered net sinks of atmospheric CO2. Water level position is one of the main regulators of CO2 fluxes in northern peatlands because it controls both the thickness of the aerobic layer in peat and plant communities. However, little is known about the role of different plant functional groups and their possible interaction with changing water level in boreal peatlands with regard to CO2 cycling. Climate change may also accelerate changes in hydrological conditions, changing both aerobic conditions and plant communities. To help answer these questions, this study was conducted at a mesocosm facility in Northern Michigan where the aim was to experimentally study the effects of water levels, plant functional groups (sedges, shrubs and mosses) and the possible interaction of these on the CO2 cycle of a boreal peatland ecosystem. The results indicate that Ericaceous shrubs are important in the boreal peatland CO2 cycle. The removal of these plants decreased ecosystem respiration, gross ecosystem production and net ecosystem exchange rates, whereas removing sedges did not show any significant differences in the flux rates. The water level did not significantly affect the flux rates. The amount of aboveground sedge biomass was higher in the low water level sedge treatment plots compared to the high water level sedge plots, possibly because the lowered water level and the removal of Ericaceae released nutrients for sedges to use up.
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In recent decades the importance of structuring sciences such as botany or phytosociology faced a declining attention from the scientific community. This was accompanied by a growing interest in theoretical ecology. For such scenario greatly contributed an hypothetical exhaustion of research topics in these areas, but especially the introduction of new technologies that have provided powerful tools for data analysis. This allowed, for example, to make predictions about the impacts of climate change on species and plant communities and the consequent recognition of theoretical ecology, as one of the most prestigious pieces of current biological sciences. However, theoretical ecology has been facing serious knoledge gaps that greatly compromise their results, putting again the spotligth on structuring sciences. For example there are enourmous gaps in knowledge and data on dispersal, species and communities chorology and abundace, as well as in biological interactions. These data is essential, since they will determine ecological behavior of species. Its omission always limits the understanding and proper execution of the models generated by theoretical ecology. In this conference we will present a review on the gaps in knowledge and data in flora and vegetation fields in order to identify situations where geobotanical knowledge can make their major contribution. Furthermore, we will emphasize the need to reformulate objectives in geobotanical sciences in order to give it the deserved scientific recognition, considering the relationship between different scientific knowledges.
Resumo:
Vegetation series, defined as the sequence of stages in a sucession, and know as sigmetum (synassociation), describes the set of plant communities or stages that can be found in similar tesselar spaces as a result of the sucession process. This establishes the concept of vegetation series; a climatophilous series is one that depends on the climate, whereas an edaphoxerophilous series depends on the dryness of the soil, and is found on crests, spurs, ledges and limestone and siliceous rock fields. Edaphohygrophilous series are located in valleys, dry water courses and river terraces, and depend on the water present in the soil, which may become temporarily flooded and thus condition the temporihygrophilous series; they represent the transition between the clearly edaphohygrophilous and climatophilous series. The vegetation permaseries represents the perennial communities of permatesselae or similar permatesselar complexes, as occurs in polar territories, hyperdesert, high-mountain peaks, and non-stratified communities lacking in serial communities. The edaphoxerophilous series may include -in addition to the series head- permaseries (permanent communities) and other habitats, such as annual and crevice habitats. A territory behaves undergoes soil-loss phenomena it may become an edaphoseries, if the loss of the soil factor produces a situation of rocky crest. Thus the edaphoseries may act as dynamic transitional stage between the climatophilous series and the permaseries.
