932 resultados para Vegetation succession
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We studied the succession of small mammal species after fire in the cerrado (Neotropical savanna) of Central Brazil. Populations of small mammals were sampled with live-trapping techniques in a series of nine sites of different successional age, ranging from 1 to 26 years after fire. Ten species of small mammals were captured through all the seral stages of succession. Species richness ranged from two to seven species by seral stage. The species were arranged in different groups with respect to abundance along the succession: the first was composed of early successional species that peaked <2 years after fire (Calomys callosus, C. tener, Thalpomys cerradensis, Mus musculus, Thylamys velutinus); the second occurred or peaked 2-3 years after fire (Necromys lasiurus, Gracilinanus sp., Oryzomys scoth). Gracilinanus agilis peaked in the last seral stage. Species richness of small mammals showed an abrupt decrease from an average of four species immediately after fire to two species 5-26 years after the last fire. We propose a simple graphical model to explain the pattern of species richness of small mammals after fire in the cerrado. This model assumes that the occurrence of species of small mammals is determined by habitat selection behavior by each species along a habitat gradient. The habitat gradient is defined as the ratio of cover of herbaceous to woody vegetation. The replacement of species results from a trade-off in habitat requirements for the two habitat variables.
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In the Cerrado savannas from Brazil fire events are common and strongly influence the vegetation structure and, consequently, the associated small mammals. In this paper, we investigate changes in the structure of small mammal communities related to sites of different post-fire ages. Mammals were captured in similar Cerrado sites that differed in time since the last burn ( 1 to 26 yr). We sampled six sites in the wet season of 1997 ( phase 1) and, three years later, six sites in the wet and dry seasons ( phase 2). Six rodent species and four marsupials were captured. Community composition changed drastically as a function of time since fire. The diversity and abundance of small mammals reached maximum values in the early successional stages. The rodent Calomys tener was present only in early seral stages. The rodent Bolomys lasiurus was more frequent in mid-successional stages and decreased in later seral stages, and the rodent Oryzomys subflavus occupied all successional stages. The marsupial Gracilinanus agilis was dominant in the area that did not burn for at least 23 yr. Changes in composition of the community of small mammals were more accelerated in early successional stages, when there are more drastic vegetational changes. The ability of small mammals to cope with Cerrado fires and the great dissimilarity among post-burning seral stages suggest that a mosaic of areas representing different post-fire seral stages could increase the regional diversity of this group.
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Conselho Nacional de Desenvolvimento Cientfico e Tecnolgico (CNPq)
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The transition from the Oldest Dryas to the Blling around 14,685 cal yr BP was a period of extremely rapid climatic warming. From a single core of lake marl taken at Gerzensee (Switzerland) we studied the transition in stable isotopes of oxygen and carbon on bulk sediment and charophyte remains, as well as on monospecific samples of ostracods, after Pisidium a; in addition pollen, chironomids, and Cladocera were analyzed. The 18O record serves as an estimate of mean air temperature, and by correlation to the one from NGRIP in Greenland it provides a timescale. The timing of responses: The statistically significant zone boundaries of the biostratigraphies are telescoped at the rapid increase of about 3 in 18O at the onset of Blling. Biotic responses may have occurred within sampling resolution (8 to 16 years), although younger zone boundaries are less synchronous. Gradual and longer-lasting responses include complex processes such as primary or secular succession. During the late-glacial interstadial of Blling and Allerd, two stronger and two weaker cool phases were found. Biological processes involved in the responses occurred on levels of individuals (e.g. pollen productivity), of populations (increases or decreases, immigration, or extinction), and on the ecosystem level (species interactions such as facilitation or competition). Abiotic and biotic interactions include pedogenesis, nitrogen-fixation, nutrient cycling, catchment hydrology, water chemistry of the lake and albedo (controlled by the transition from tundra to forest). For the Swiss Plateau this major change in vegetation induced a change in the mammal fauna, which in turn led to changes in the tool-making by Paleolithic people.
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High-resolution pollen analyses made on the same samples on which the ratios of oxygen isotopes were measured that provided the time scale and a temperature proxy after correlation to NorthGRIP. (1) A primary succession: The vegetation responded to the rapid rise of temperatures around 14,685 yr BP, with a primary succession on a decadal to centennial time scale. The succession between ca 15,600 and 13,000 yr BP included: (1.1.) The replacement of shrub-tundra by woodland of Juniperus and tree birch (around 14,665 yr BP) (1.2.) The response of Juniperus pollen to the shift in oxygen isotopes in less than 20 yr, (1.3.) A sequence of population increases of Hippopha rhamnoides (ca 14,600 yr BP), Salix spp. (ca 14,600 yr BP), Betula trees (ca.14,480 yr BP), Populus cf. tremula (ca. 14,300 yr BP), and Pinus cf. sylvestris (ca. 13,830 yr BP). (2) Biological processes: Plants responded to the rapid increase of summer temperatures on all organisational levels: (2.1) Individuals may have produced more pollen (e.g. Juniperus); (2.2) Populations increased or decreased (e.g. Juniperus, Betula, later Pinus), and (2.3) Populations changed their biogeographical range and may show migrational lags. (2.4) Plant communities changed in their composition because the species pools changed through immigration and (local) extinction. Some plant communities may have been without modern analogue.These mechanisms require increasing amounts of time. (2.5) Processes on the level of ecosystems, with species interactions, may involve various time scales. Besides competition and facilitation, nitrogen fixation is discussed. (3) The minor fluctuations of temperature during the Late-Glacial Interstadial, which are recorded in 18O, resulted in only very minor changes in pollen during the Aegelsee Oscillation (Older Dryas biozone, GI-1d) and the Gerzensee Oscillation (GI-1b). (4) Biodiversity: The afforestation at the onset of Blling coincided with a gradual increase of taxonomic diversity up to the time of the major Pinus expansion.
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To understand succession in dipterocarp rain forest after logging, the structure, species composition and dynamics of primary (PF) and secondary (SF) forest at Danum were compared. In 10 replicate 0.16-ha plots per forest type trees >= 10 cm gbh (3.2 cm dbh) were measured in 1995 and 2001. The SF had been logged in 1988, which allowed successional change to be recorded at 8 and 13 years. In 2001, saplings (1.0-3.1 cm dbh) were measured in nested quadrats. The forest types were similar in mean radiation at 2 m height, and in density, basal area and species number of all trees. Among small (10 <= 31.4) and large ( >= 31.4 cm gbh) trees, in both 1995 and 2001, there were 10- and 3-fold more dipterocarps in SF than PF respectively; and averaging over the two dates, there were correspondingly ca. 10- and 18-fold more pioneers. Mortality was ca. 60% higher in SF than PF, largely due to a seven-fold difference for pioneers: for dipterocarps there was little difference. Recruitment was similar in PF and SE Stem growth rates were 37% higher in SF than PF for all trees, although dipterocarps showed the opposite trend. Among saplings, dipterocarps dominated SF with a 10-fold higher density than in PF. For dipterocarps, the light (LH) and medium-heavy (MHH) canopy hardwoods, and the shade-tolerant, smaller-stature other (OTH) species (e.g. Hopea and Vatica) were in the ratios ca. 40:15:45 in SF and 85: < 1:15 in PF. LHs had higher mortality than OTHs in SE In PF ca. 80% of the saplings were LH: in SF ca. 70% were OTH. The predominance of OTHs in SF is explained by the logging of primary rain forest which was in a likely late stage of recovery from natural disturbance, plus the continuing shaded conditions in the understorey promoted by dense pioneer vegetation. At 13 years after logging succession appeared to be inhibited: LHs were being suppressed but MHHs and OTHs persisted. Succession in lowland dipterocarp, rain forests may therefore depend on the successional state of the primary forest when it is logged. A review of logged versus unlogged studies in Borneo highlights the need for more detailed ecological comparisons.
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The aim of this thesis was to evaluate historical change of the landscape of Madeira Island and to assess spatial and temporal vegetation dynamics. In current research diverse retrospective techniques, such as landscape repeat photography, dendrochronology, and research of historical records were used. These, combined with vegetation relevs, aimed to gather information about landscape change, disturbance history, and vegetation successional patterns. It was found that landscape change, throughout 125 years, was higher in the last five decades manly driven by farming abandonment, building growth and exotic vegetation coverage increase. Pristine vegetation was greatly destroyed since early settlement and by the end of the nineteenth century native vegetation was highly devastated due to recurrent antropogenic disturbances. These actions also helped to block plant succession and to modify floristical assemblages, affecting as well as species richness. In places with less hemeroby, although significant growth of vegetation of lower seral stages was detected, the vegetation of most mature stages headed towards unbalance between recovery and loss, being also very vulnerable to exotic species encroachment. Recovery by native vegetation also occurred in areas formerly occupied by exotic plants and agriculture but it was almost negligible. Vegetation recovery followed the successional model currently proposed, attesting the model itself. Yet, succession was slower than espected, due to lack of favourable conditions and to recurrent disturbances. Probable tempus of each seral stage was obtained by growth rates of woody taxa estimated through dendrochronology. The exotic trees which were the dominant trees in the past (Castanea sativa and Pinus pinaster) almost vanished. Eucalyptus globulus, the current main tree of the exotic forest is being replaced by other cover types as Acacia mearnsii. The latter, along with Arundo donax, Cytisus scoparius and Pittosporum undulatum are currently the exotic species with higher invasive behaviour. However, many other exotic species have also proved to be highly pervasive and came together with the ones referred above to prevent native vegetation regeneration, to diminish biological diversity, and to block early successional phases delaying native forest recovery.
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"March 2001"--P. [2] of cover.
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The maintenance of species richness is often a priority in the management of nature reserves, where consumptive use of resources is generally prohibited. The purpose of this research was to improve management by understanding the vegetation dynamics in the lowlands of Nepal. The objectives were to determine vegetation associations in relation to environments and human-induced disturbances that affect vegetation dynamics on floodplains, where upstream barrages had altered flooding patterns, and consumptive use of plant resources was influencing natural processes. Floodplain vegetation in relation to physical environments and disturbances were studied along transects, perpendicular to the course of the Mahakali River in the western Terai, Nepal. Forest structural changes were studied for three years in ten plots. A randomized split-block experiment with nine burning and grazing treatments was performed in seasonally flooded grasslands. A semi-structured questionnaire was used to assess people's socio-economic status, natural resource use patterns and conservation attitudes. ^ Elevation, soil organic matter, nitrogen, percentage of sand and grazing intensity were significant in delineating herbaceous vegetation assemblages, whereas elevation and livestock grazing were significant in defining forest type boundaries. On the floodplain islands, highly grazed Dalbergia sissoo-Acacia catechu forests were devoid of understory woody vegetation, but the lightly grazed D. sissoo-mixed forests had a well-developed second canopy layer, comprising woody species other than D. sissoo and A. catechu. In grasslands, species richness and biomass production were highest at intermediate disturbance level represented by the lightly grazed and ungrazed early-burned treatments. Ethnicity, education and resource use patterns were important in influencing conservation attitudes. A succession towards the mixed forests would occur in D. sissoo-dominated floodplain forests, where dams and barrages reduce flooding and associated fluvial processes, and if livestock grazing is stopped, as occasionally suggested by nature conservationists. In seasonally flooded grasslands, early burning with moderate grazing would enhance the species diversity and productivity. There is a need to implement a participatory integrated wetland management plan, to include community development, education and off farm income generation, to assure participatory conservation and management of wetlands in Nepal. ^
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This report examines the interaction between hydrology and vegetation over a 10-year period, between 2001/02 and 2012 within six permanent tree island plots located on three tree islands, two plots each per tree island, established in 2001/02, along a hydrologic and productivity gradient. We hypothesize that: (H1) hydrologic differences within plots between census dates will result in marked differences in a) tree and sapling densities, b) tree basal area, and c) forest structure, i.e., canopy volume and height, and (H2) tree island growth, development, and succession is dependent on hydrologic fluxes, particularly during periods of prolonged droughts or below average hydroperiods.
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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:
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.
