1,721,062 research outputs found
Propagation of keystone-woody species as a first step in restoration of an overgrazed seasonal dry forest
No full textAbstract In degraded forest ecosystems, reintroduction of keystone-woody species is an important step for restoration because it provides regeneration niches. However, lack of information on how to propagate species restricts the use of native species; specially in tropical dry forests where seed germination is seasonal and is synchronized with the onset of the wet season. We evaluated the dormancy-breaking and germination requirements of nine keystone-woody species from Dry Chaco Forest. Most fresh viable seeds of the keystone species are nondormant, but viability decreases during dry-cold storage restricting the use of some species. Seeds of three keystone species germinated to higher percentages in light than darkness and those of five species germinated equally well in light and darkness; seeds of Castela coccinea germinated to higher percentages in darkness than in light. Alternating vs. constant temperatures had no effect on germination in seven species. Seeds of Anisocapparis speciosa and Cynophalla retusa were nondormant and remained viable for only 1 month during cold-dry storage; and 62–95% of the seeds of the other seven species were nondormant. Dormancy-break was studied in five of the seven species; seeds of four species had physiological dormancy and one had physical dormancy. Dormancy-breaking was promoted by environmental conditions in the habitat, i.e. warm stratification, after seed dispersal. Castela coccinea , Achatocarpus praecox , Mimosa detinens , and Capparicordis tweedieana are the most suitable keystone species for the restoration of overgrazed areas in the Dry Chaco Forest because their seeds germinate to a high percentage and retain viability during dry storage at low temperatures. Seeds of Mimosa detinens and Capparicordis tweedieana required mechanical scarification and 6-weeks of warm stratification, respectively, for dormancy-break.Fulbright Association http://dx.doi.org/10.13039/100010629Georg-August-Universität Göttingen 50110000338
Deep simple epicotyl morphophysiological dormancy in seeds of two Viburnum species, with special reference to shoot growth and development inside the seed
No full textEffect of climate change on regeneration of plants from seeds in tropical wet forests
No full textTropical forests account for more than half of the above-ground carbon on planet earth. Changes in species and trait composition resulting from climate change may strongly influence this carbon pool and therefore the global carbon cycle. We highlight how climate change may impact forest regeneration processes in tropical wet forests by altering the frequency of environmental cues for flowering, seed provisioning, seed germination success, and seedling survival. Furthermore, we emphasize the potential for alterations to seedling community composition via interspecific variation in sensitivity to elevated temperatures, trade-offs between shade and drought tolerance, and species differences in the ability to overcome nutrient limitation under elevated CO2. Understanding the importance of each of these mechanisms will require a new generation of in situ experiments that account for the direct effects of climatic drivers and indirect effects arising from complex interactions between plants and their suites of mutualists and natural enemies
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
An Overview of Environmental Cues That Affect Germination of Nondormant Seeds
No full textFor a successful germination and plant growth, seeds must germinate at the right time. Seeds must become nondormant and must fulfill the seed germination requirements. These requirements include light/dark, moisture, temperature, and other environmental cues (e.g., ethylene, exudate from host roots, or chemicals from fire) in the habitat. Seeds come out from dormancy in response to environmental cues, but depending on the species, they may need to be exposed to a second set of environmental cue to germinate. That is, nondormant seeds require specific temperature and water conditions to germination, and sometimes unfavorable temperature and water conditions will cause seeds to enter secondary dormancy. There are still mysteries about how/what environmental cues help seeds detect the right time/conditions for germination after dormancy is broken. Our knowledge of species-specific conditions is incomplete and further studies are needed
Recommended from our members
Seed Dynamics and Seedling Establishment of Woody Species in the Tropical Savannas of Central Brazil (Cerrado)
No full textStudies of seed dynamics and seedling establishment at the community level in savanna ecosystems are scant, particularly in the tropical savannas of Central Brazil. The Brazilian savannas (cerrado) have the largest diversity of plant species among Neotropical savannas. Cerrado vegetation exhibits consistent changes in tree density and tree size along shallow topographic gradients. Vegetation types differ from closed savannas with high tree density, and a nearly continuous canopy cover in the uppermost portions, to open savannas with scattered short trees in the low portions of the topographic gradients. Whether or not dynamics of seeds and seedlings of woody species are consistent with variations in tree density and tree canopy cover across the cerrado landscape has not been determined, but could potentially influence such spatial patterns of tree density and canopy cover. The main objective of this study was to evaluate seed dynamics (i.e., seed rain, soil seed banks, and seed characteristics) and seedling establishment of woody species in three major cerrado vegetation types (closed, intermediate and open savannas) which differ in tree canopy cover and tree height. These vegetation types are located along topographic gradients of approximately 30 m in elevation and 1000 m in length. I conducted field work from June 2005 to August 2008 at the Instituto Brasileiro de Geografia e Estatística (IBGE) reserve, a field experimental station located 35 Km south of Brasilia, Brazil (15˚ 56' S, 47˚ 63' W, altitude 1100 m). I established permanent plots in each of the three vegetation types to assess seed rain, seed limitation, seed predation, and seed removal. I also quantified density and composition of the soil seed bank in each vegetation type and studied seed characteristics (i.e., kind of dormancy, moisture content, longevity) of 14 common cerrado woody species. In the field, I quantified establishment of woody seedlings in fire-protected savannas as well as in accidentally burned and frequently burned savannas. In the greenhouse I performed experiments to evaluate the effect of litter cover and light level on seedling emergence of 9 common cerrado woody species. Finally, I evaluated the effect of pulses of heat on seed germination of 5 common cerrado woody species under controlled conditions. The overall results of this study show that regardless of tree canopy cover, cerrado vegetation types are limited in seeds and seedlings of woody species, but these limitations are higher in open than in closed savannas. Most woody species do not form persistent soil seed banks along cerrado vegetation types because their seeds are short-lived, predated and quickly removed from the ground. In addition, dispersal season and dormancy appear to control timing of germination at the onset of the rainy season to ensure survival of seedlings in the field. In the absence of fire, establishment of woody seedlings is higher in closed than in open savannas because canopy cover mitigates the stressful environmental conditions of open savannas and thus facilitates establishment of woody seedlings. As a result, closed savannas are likely to maintain higher density of woody elements over time than open savannas. In burned savannas, however, species composition of woody and herbaceous seedlings is significantly affected because establishment of seedlings of woody and herbaceous species decreases but vegetative reproduction increases. This dissertation study indicates that interactions of early life-history stages of woody species with environmental and disturbance factors appear to play a more significant role in maintaining woody cover variations along cerrado topographic gradients than previously recognized.</p
- …
