Página 1 dos resultados de 478 itens digitais encontrados em 0.003 segundos

A MODIS-Based Energy Balance to Estimate Evapotranspiration for Clear-Sky Days in Brazilian Tropical Savannas

Ruhoff, Anderson L.; Paz, Adriano R.; Collischonn, Walter; Aragao, Luiz E. O. C.; Rocha, Humberto R.; Malhi, Yadvinder S.
Fonte: MDPI AG; BASEL Publicador: MDPI AG; BASEL
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.18%
Evapotranspiration (ET) plays an important role in global climate dynamics and in primary production of terrestrial ecosystems; it represents the mass and energy transfer from the land to atmosphere. Limitations to measuring ET at large scales using ground-based methods have motivated the development of satellite remote sensing techniques. The purpose of this work is to evaluate the accuracy of the SEBAL algorithm for estimating surface turbulent heat fluxes at regional scale, using 28 images from MODIS. SEBAL estimates are compared with eddy-covariance (EC) measurements and results from the hydrological model MGB-IPH. SEBAL instantaneous estimates of latent heat flux (LE) yielded r(2) = 0.64 and r(2) = 0.62 over sugarcane croplands and savannas when compared against in situ EC estimates. At the same sites, daily aggregated estimates of LE were r(2) = 0.76 and r(2) = 0.66, respectively. Energy balance closure showed that turbulent fluxes over sugarcane croplands were underestimated by 7% and 9% over savannas. Average daily ET from SEBAL is in close agreement with estimates from the hydrological model for an overlay of 38,100 km(2) (r(2) = 0.88). Inputs to which the algorithm is most sensitive are vegetation index (NDVI), gradient of temperature (dT) to compute sensible heat flux (H) and net radiation (Re). It was verified that SEBAL has a tendency to overestimate results both at local and regional scales probably because of low sensitivity to soil moisture and water stress. Nevertheless the results confirm the potential of the SEBAL algorithm...

Do extrafloral nectaries present a defensive role against herbivores in two species of the family Bignoniaceae in a Neotropical savannas?

Nogueira, Anselmo; Guimaraes, Elza; Machado, Silvia Rodrigues; Lohmann, Lucia Garcez
Fonte: SPRINGER; DORDRECHT Publicador: SPRINGER; DORDRECHT
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.18%
Despite the general belief that the interaction between extrafloral nectaries (EFNs) and ants is mutualistic, the defensive function of EFNs has been poorly documented in South American savannas. In this article, we evaluate the potential impact of EFNs (benefits and costs) on two species of plants from the dry areas of Central Brazil, Anemopaegma album and Anemopaegma scabriusculum (Bignoniaceae). In particular, we characterize the composition of substances secreted by the EFNs, test whether EFNs attract ants, and whether ants actually present a defensive role, leading to reduced herbivory and increased plant fitness. Histochemical analyses indicated that EFNs from both species of Anemopaegma secrete an exudate that is composed of sugars, and potentially lipids and proteins. Furthermore, EFNs from both species were shown to present a significant role in ant attraction. However, contrary to common expectations, ants were not found to protect plants against herbivore attack. No effect was found between ant visitation and flower or fruit production in A. album, while the presence of ants led to a significant decrease in flower production in A. scabriusculum. These results suggest that EFNs might present a similar cost and benefit in A. album...

Identifying the areas to preserve passion fruit pollination service in Brazilian Tropical Savannas under climate change

Giannini, Tereza Cristina; Acosta, André Luis; Silva, Cláudia Inês da; Oliveira, Paulo Eugênio Alves Macedo de; Fonseca, Vera Lucia Imperatriz; Saraiva, Antonio Mauro
Fonte: Biblioteca Digital da Produção Intelectual da USP Publicador: Biblioteca Digital da Produção Intelectual da USP
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.35%
The aim of this study was to identify future distribution areas and propose actions to preserve passion fruit pollination service under a scenario of future climate change. We used four species of Xylocopa bees that are important for passion fruit pollination in Brazilian Tropical Savannas. We also used the known forage plant species (33 species) that are associated with this same area, since passion fruit flowers provide only nectar for bees and only during their blossoming period. We used species distribution modeling to predict the potential areas of occurrence for each bee and plant based on the current day distribution and a future climate scenario (moderate projections of climate change to 2050). We used a geographic information system to classify the models and to analyze the future areas for both groups of species. The current day distribution map showed that Xylocopa and plant species occurred primarily in the southern and central-eastern areas of the Brazilian Tropical Savannas. In the north, Xylocopa species only occurred in a small area between the states of Maranhão and Piauí while forage plant species were only observed in the northern part of the Tocantins State. However...

Do extrafloral nectaries present a defensive role against herbivores in two species of the family Bignoniaceae in a Neotropical savannas?

Nogueira, Anselmo; Guimaraes, Elza; Machado, Silvia Rodrigues; Lohmann, Lucia G.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 289-301
ENG
Relevância na Pesquisa
27.18%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 07/55433-8; Processo FAPESP: 07/54917-1; Despite the general belief that the interaction between extrafloral nectaries (EFNs) and ants is mutualistic, the defensive function of EFNs has been poorly documented in South American savannas. In this article, we evaluate the potential impact of EFNs (benefits and costs) on two species of plants from the dry areas of Central Brazil, Anemopaegma album and Anemopaegma scabriusculum (Bignoniaceae). In particular, we characterize the composition of substances secreted by the EFNs, test whether EFNs attract ants, and whether ants actually present a defensive role, leading to reduced herbivory and increased plant fitness. Histochemical analyses indicated that EFNs from both species of Anemopaegma secrete an exudate that is composed of sugars, and potentially lipids and proteins. Furthermore, EFNs from both species were shown to present a significant role in ant attraction. However, contrary to common expectations, ants were not found to protect plants against herbivore attack. No effect was found between ant visitation and flower or fruit production in A. album, while the presence of ants led to a significant decrease in flower production in A. scabriusculum. These results suggest that EFNs might present a similar cost and benefit in A. album...

Can savannas become forests? A coupled analysis of nutrient stocks and fire thresholds in central Brazil

Silva, Lucas C.R.; Hoffmann, William A.; Rossatto, Davi R.; Haridasan, Mundayatan; Franco, Augusto C.; Horwath, William R.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1-14
ENG
Relevância na Pesquisa
27.55%
Aims: The effects of fire ensure that large areas of the seasonal tropics are maintained as savannas. The advance of forests into these areas depends on shifts in species composition and the presence of sufficient nutrients. Predicting such transitions, however, is difficult due to a poor understanding of the nutrient stocks required for different combinations of species to resist and suppress fires. Methods: We compare the amounts of nutrients required by congeneric savanna and forest trees to reach two thresholds of establishment and maintenance: that of fire resistance, after which individual trees are large enough to survive fires, and that of fire suppression, after which the collective tree canopy is dense enough to minimize understory growth, thereby arresting the spread of fire. We further calculate the arboreal and soil nutrient stocks of savannas, to determine if these are sufficient to support the expansion of forests following initial establishment. Results: Forest species require a larger nutrient supply to resist fires than savanna species, which are better able to reach a fire-resistant size under nutrient limitation. However, forest species require a lower nutrient supply to attain closed canopies and suppress fires; therefore...

A Holocene pollen record of savanna establishment in coastal Amapá

Toledo,Mauro B. de; Bush,Mark B.
Fonte: Academia Brasileira de Ciências Publicador: Academia Brasileira de Ciências
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2008 EN
Relevância na Pesquisa
27.18%
The main goal of this study was to investigate how climate and human activities may have influenced ecotonal areas of disjoint savannas within Brazilian Amazonia. The fossil pollen and charcoal records of Lake Márcio (Amapá) were used to provide a Holocene palaeoecological history of this region. Detrended correspondence analysis (DCA) was used to enhance the patterns of sample distribution along the sediment core. A marked vegetation change from closed forests with swamp elements to open flooded savanna at c. 5000 yrs BP was evident from the pollen record. Charcoal analysis revealed a pattern of increased accumulation of particles coincident with the establishment of savannas, suggesting higher fire frequency and human impacts near the lake. A 550-year sedimentary hiatus suggests that the lake depended heavily on floodwaters from the Amazon River, and that it became suddenly isolated from it. When sedimentation restarted in the lake, the environment had changed. A combination of factors, such as reduced river flooding, palaeofires and human occupation may have had a tremendous impact on the environment. As there are no other major changes in vegetation, after 4700 yrs BP, it is plausible to assume that the modern mosaic vegetation formed at that time.

Dispersal modes and fruiting periods in hyperseasonal and seasonal savannas, central Brazil

Silva,Igor Aurélio; Cianciaruso,Marcus Vinicius; Batalha,Marco Antônio
Fonte: Sociedade Botânica de São Paulo Publicador: Sociedade Botânica de São Paulo
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2009 EN
Relevância na Pesquisa
27.35%
Seasonal savannas are characterized by an intense drought that influences their functioning. Hyperseasonal savannas experience additionally a waterlogging during the rainy season. In South America, the largest savanna environment is the Brazilian cerrado. To assess whether a particular dispersal mode or fruiting period is associated to the waterlogging, we examined dispersal and phenological groups in hyperseasonal and seasonal cerrado plant species. We compared the proportion of species and individuals in these groups with G-tests for independence in contingency tables. We did not find differences in the proportion of species; however, based on the proportion of individuals, the main dispersal strategy was anemochory in the hyperseasonal cerrado and zoochory in the seasonal cerrado. Phenological strategies of fruiting in safe periods of the year were differently selected in both cerrados. In the hyperseasonal cerrado, most individuals fruited in non-waterlogged periods, whereas in the seasonal cerrado, most individuals fruited in wetter periods. Thus, waterlogging may drive important modifications in the efficiency of the dispersal and phenological strategies of hyperseasonal savannas plants.

Abundance distribution of common and rare plant species of Brazilian savannas along a seasonality gradient

Silva,Igor Aurélio; Cianciaruso,Marcus Vinicius; Batalha,Marco Antônio
Fonte: Sociedade Botânica do Brasil Publicador: Sociedade Botânica do Brasil
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2010 EN
Relevância na Pesquisa
27.18%
We examined the species abundance distribution (SAD) of plant communities in: (1) a wet grassland, waterlogged throughout most of the year; (2) a seasonal savanna, with an annual dry season; and (3) a hyperseasonal savanna, with alternating drought and waterlogging over the year. We searched for differences in the abundance distributions of all species, as well as of the common and rare species. We tested whether the SADs fitted the lognormal, log-series, power fraction, and random assortment models. We found that environmental constraints may reduce the evenness of plant communities and change the SADs in savannas. We observed a lognormal abundance distribution in the wet grassland and a random abundance distribution in the hyperseasonal cerrado. The SAD of the seasonal savanna did not follow any model. The common species in the three communities were better fitted by the lognormal model. The rare species in the wet grassland and the hyperseasonal cerrado were better fitted by the random assortment model. The SAD of the rare species of the seasonal savanna did not follow any model. Seasonality seems to modify the lognormal distribution of the overall plant community, generating abundance distributions indistinguishable from random. However...

Poaceae communities in the savannas of the Amazon Estuary in Brazil

Rocha,Antônio Elielson Sousa; Miranda,Izildinha Souza
Fonte: Sociedade Botânica do Brasil Publicador: Sociedade Botânica do Brasil
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2014 EN
Relevância na Pesquisa
27.35%
We sought to identify the major environmental factors that affect the diversity and distribution of Poaceae in the savannas of the Amazon Estuary. The study was conducted across seven areas of savanna in the Amazon Estuary, within which 160 subplots of 1 m² each were established within four 10 × 100 m plots. Soil samples were collected at a depth of 0-20 cm. A total of 24 Poaceae species were recorded. Only two were common to all of the areas studied (Axonopus aureus P. Beauv. and Anthaenantia lanata (Kunth) Benth). The edaphic factors that most influenced the Poaceae in the savannas studied were organic matter, coarse sand, and silt contents. Conversely, rainfall had no effect. The floristic and structural characteristics of the savannas studied suggest that Poaceae communities exhibit low diversity and a peculiar distribution pattern in which a group of species predominate in a given stretch, creating a homogeneous physiognomy. Our findings suggest that the structure of these communities is related to a gradient of soil texture, the percentage of Axonopus and Trachypogon coverage increasing and decreasing, respectively, along that gradient. These data can contribute to the understanding of plant-soil interactions in this environment...

Fire-free land use in pre-1492 Amazonian savannas

Iriarte, José; Power, Mitchell J.; Rostain, Stéphen; Mayle, Francis E.; Jones, Huw; Watling, Jennifer; Whitney, Bronwen S.; McKey, Doyle B.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.46%
The nature and scale of pre-Columbian land use and the consequences of the 1492 “Columbian Encounter” (CE) on Amazonia are among the more debated topics in New World archaeology and paleoecology. However, pre-Columbian human impact in Amazonian savannas remains poorly understood. Most paleoecological studies have been conducted in neotropical forest contexts. Of studies done in Amazonian savannas, none has the temporal resolution needed to detect changes induced by either climate or humans before and after A.D. 1492, and only a few closely integrate paleoecological and archaeological data. We report a high-resolution 2,150-y paleoecological record from a French Guianan coastal savanna that forces reconsideration of how pre-Columbian savanna peoples practiced raised-field agriculture and how the CE impacted these societies and environments. Our combined pollen, phytolith, and charcoal analyses reveal unexpectedly low levels of biomass burning associated with pre-A.D. 1492 savanna raised-field agriculture and a sharp increase in fires following the arrival of Europeans. We show that pre-Columbian raised-field farmers limited burning to improve agricultural production, contrasting with extensive use of fire in pre-Columbian tropical forest and Central American savanna environments...

Parent Genotype and Environmental Factors Influence Introduction Success of the Critically Endangered Savannas Mint (Dicerandra immaculata var. savannarum)

Peterson, Cheryl L.; Kaufmann, Gregory S.; Vandello, Christopher; Richardson, Matthew L.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 09/04/2013 EN
Relevância na Pesquisa
27.18%
Species previously unknown to science are continually discovered and some of these species already face extinction at the time of their discovery. Conserving new and rare species in these cases becomes a trial-and-error process and conservationists will attempt to manage them by using knowledge of closely related species, or those that fill the same ecological niche, and then adapting the management program as needed. Savannas Mint (Dicerandra immaculata Lakela var. savannarum Huck) is a perennial plant that was discovered in Florida scrub habitat at two locations in 1995, but is nearly extinct at these locations. We tested whether shade, leaf litter, propagation method, parent genotype, parent collection site, planting date, and absorbent granules influenced survival, reproduction, and recruitment of Savannas Mint in a population of 1,614 plants that we introduced between June 2006 and July 2009 into a state protected site. Survival and reproduction of introduced plants, and recruitment of new plants, was higher in microhabitats in full sun and no leaf litter and lower in partially shaded habitats. The two sites from which parent plants were collected differentially influenced survival and reproduction of introduced plants. These differences in survival and reproduction are likely due to underlying genetic differences. Differential survival of progeny from different parent genotypes further supports the idea that underlying genetics is an important consideration when restoring plant populations. The most successful progeny of parent genotypes had survival rates nearly 12 times higher than the least successful progeny. We speculate that many of these environmental and genetic factors are likely to influence allopatric congeners and other critically endangered gap specialists that grow in Florida scrub and our results can be used to guide their conservation.

Tree Cover Bimodality in Savannas and Forests Emerging from the Switching between Two Fire Dynamics

De Michele, Carlo; Accatino, Francesco
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 24/03/2014 EN
Relevância na Pesquisa
27.18%
Moist savannas and tropical forests share the same climatic conditions and occur side by side. Experimental evidences show that the tree cover of these ecosystems exhibits a bimodal frequency distribution. This is considered as a proof of savanna–forest bistability, predicted by dynamic vegetation models based on non-linear differential equations. Here, we propose a change of perspective about the bimodality of tree cover distribution. We show, using a simple matrix model of tree dynamics, how the bimodality of tree cover can emerge from the switching between two linear dynamics of trees, one in presence and one in absence of fire, with a feedback between fire and trees. As consequence, we find that the transitions between moist savannas and tropical forests, if sharp, are not necessarily catastrophic.

Guide to the Vascular Flora of the Savannas and Flatwoods of Shaken Creek Preserve and Vicinity (Pender & Onslow Counties, North Carolina, U.S.A.)

Thornhill, Robert; Krings, Alexander; Lindbo, David; Stucky, Jon
Fonte: Pensoft Publishers Publicador: Pensoft Publishers
Tipo: Artigo de Revista Científica
Publicado em 16/05/2014 EN
Relevância na Pesquisa
27.18%
Shaken Creek Preserve (“SCP”) is a 2,448 ha (6,050 ac) natural area in Pender and Onslow Counties, North Carolina (U.S.A). Best known for its high-quality longleaf pine savanna habitat, the site contains seven savanna or savanna-like plant community types (i.e., flatwoods or sandhills), three of which are globally critically imperiled (G1): Sandy Pine Savanna (Rush Featherling subtype), Wet Loamy Pine Savanna, and Very Wet Loamy Pine Savanna. SCP hosts three Federally Endangered plant species and six Federal Species of Concern. Formerly a private hunting club, the site was virtually unknown to scientists until the 1990s; consequently, few biological inventories of SCP have been conducted. In particular, no systematic floristic inventories of the species-rich savannas have been undertaken, despite the fact that floristic data is critical to the effective management of any natural area. The goals of this study were to (1) inventory the vascular flora of the savannas, flatwoods, and sandhill community types on site through the collection of voucher specimens; (2) provide a comprehensive checklist of the flora based on collections and reports made from the site and from the same or similar habitats in the vicinity (i.e., within 2 miles of SCP); and (3) create an illustrated guide based on the checklist. In order to increase the usefulness of the guide...

Fire in Australian savannas: from leaf to landscape

Beringer, Jason; Hutley, Lindsay B; Abramson, David; Arndt, Stefan K; Briggs, Peter; Bristow, Mila; Canadell, Josep G; Cernusak, Lucas A; Eamus, Derek; Edwards, Andrew C; Evans, Bradley J; Fest, Benedikt; Goergen, Klaus; Grover, Samantha P; Hacker, Jorg;
Fonte: John Wiley & Sons Ltd Publicador: John Wiley & Sons Ltd
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.35%
Savanna ecosystems comprise 22% of the global terrestrial surface and 25% of Australia (almost 1.9 million km2) and provide significant ecosystem services through carbon and water cycles and the maintenance of biodiversity. The current structure, composition and distribution of Australian savannas have coevolved with fire, yet remain driven by the dynamic constraints of their bioclimatic niche. Fire in Australian savannas influences both the biophysical and biogeochemical processes at multiple scales from leaf to landscape. Here, we present the latest emission estimates from Australian savanna biomass burning and their contribution to global greenhouse gas budgets. We then review our understanding of the impacts of fire on ecosystem function and local surface water and heat balances, which in turn influence regional climate. We show how savanna fires are coupled to the global climate through the carbon cycle and fire regimes. We present new research that climate change is likely to alter the structure and function of savannas through shifts in moisture availability and increases in atmospheric carbon dioxide, in turn altering fire regimes with further feedbacks to climate. We explore opportunities to reduce net greenhouse gas emissions from savanna ecosystems through changes in savanna fire management.

Predicting the Effects of Woody Encroachment on Mammal Communities, Grazing Biomass and Fire Frequency in African Savannas

Smit, Izak P. J.; Prins, Herbert H. T.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 17/09/2015 EN
Relevância na Pesquisa
27.18%
With grasslands and savannas covering 20% of the world’s land surface, accounting for 30–35% of worldwide Net Primary Productivity and supporting hundreds of millions of people, predicting changes in tree/grass systems is priority. Inappropriate land management and rising atmospheric CO2 levels result in increased woody cover in savannas. Although woody encroachment occurs world-wide, Africa’s tourism and livestock grazing industries may be particularly vulnerable. Forecasts of responses of African wildlife and available grazing biomass to increases in woody cover are thus urgently needed. These predictions are hard to make due to non-linear responses and poorly understood feedback mechanisms between woody cover and other ecological responders, problems further amplified by the lack of long-term and large-scale datasets. We propose that a space-for-time analysis along an existing woody cover gradient overcomes some of these forecasting problems. Here we show, using an existing woody cover gradient (0–65%) across the Kruger National Park, South Africa, that increased woody cover is associated with (i) changed herbivore assemblage composition, (ii) reduced grass biomass, and (iii) reduced fire frequency. Furthermore, although increased woody cover is associated with reduced livestock production...

The role of topography in the emergence of African savannas

Kim, Yeonjoo, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 96 leaves
ENG
Relevância na Pesquisa
27.46%
The coexistence of trees and grasses in savannas are not well understood even though savannas occupy a wide area of West Africa. In this study, a hypothesis is proposed to investigate the question of how trees and grasses coexist in a region. The hypothesis suggests that the variation in elevation leads to the variation in soil moisture, which in turn can explain the coexistence of trees and grasses in savannas. To test this hypothesis, experimental simulations are performed using biospheric model, IBIS, and distributed hydrologic model, SHE. We, first, estimate the amount of rainfall required for trees and grasses under a certain atmospheric condition. Here, the variation of rainfall is prescribed to force a similar variation of soil moisture. A 30% decrease in rainfall is sufficient to simulate grasses at 9°N. A 100% increase in rainfall is sufficient to simulate trees at II°N. However, even with a five fold increase in rainfall, the model fails to simulate trees at 13°N. To study the influences of topography explicitly, a distributed hydrologic modeling is performed using SHE. The results suggest that the variation of the depth to water table induced by the varying elevation is highly correlated with the variation of soil moisture. Consequently...

State of the art-developing grain cultivars for acid savannas of Brazil.

BAHIA FILHO, A.F.C.; LOPES, M.A.
Fonte: In: WORKSHOP TO DEVELOP A STRATEGY FOR COLLABORATIVE RESEARCH AND DISSEMINATION OF TECHNOLOGY IN SUSTAINABLE CROP PRODUCTION IN ACID SAVANNAS AND OTHER PROBLEM SOILS OF THE WORLD, 1998, [West Lafayette], USA. Proceedings. [West Lafayette]: Purdue University, [1998?]. p. 27-45. Publicador: In: WORKSHOP TO DEVELOP A STRATEGY FOR COLLABORATIVE RESEARCH AND DISSEMINATION OF TECHNOLOGY IN SUSTAINABLE CROP PRODUCTION IN ACID SAVANNAS AND OTHER PROBLEM SOILS OF THE WORLD, 1998, [West Lafayette], USA. Proceedings. [West Lafayette]: Purdue University, [1998?]. p. 27-45.
Tipo: Artigo em anais de congresso (ALICE)
EN
Relevância na Pesquisa
37.18%
1998

Mammals of Australia's Tropical Savannas: A Conceptual Model of Assemblage Structure and Regulatory Factors in the Kimberley Region

Radford, Ian J.; Dickman, Christopher R.; Start, Antony N.; Palmer, Carol; Carnes, Karin; Everitt, Corrin; Fairman, Richard; Graham, Gordon; Partridge, Thalie; Thomson, Allan
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 26/03/2014 EN
Relevância na Pesquisa
27.46%
We construct a state-and-transition model for mammals in tropical savannas in northern Australia to synthesize ecological knowledge and understand mammalian declines. We aimed to validate the existence of alternative mammal assemblage states similar to those in arid Australian grasslands, and to speculate on transition triggers. Based on the arid grassland model, we hypothesized that assemblages are partitioned across rainfall gradients and between substrates. We also predicted that assemblages typical of arid regions in boom periods would be prevalent in savannas with higher and more regular rainfall. Data from eight mammal surveys from the Kimberley region, Western Australia (1994 to 2011) were collated. Survey sites were partitioned across rainfall zones and habitats. Data allowed us to identify three assemblage states: State 0:- low numbers of mammals, State II:- dominated by omnivorous rodents and State III:- dominated by rodents and larger marsupials. Unlike arid grasslands, assemblage dominance by insectivorous dasyurids (State I) did not occur in savannas. Mammal assemblages were partitioned across rainfall zones and between substrates as predicted, but—unlike arid regions—were not related strongly to yearly rainfall. Mammal assemblage composition showed high regional stability...

Spatio-temporal dynamics of woody plant-cover in Argentine savannas: encroachment, agriculture conversion and changes in carbon stocks at varying scales

Gonzalez-Roglich, Mariano
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2015
Relevância na Pesquisa
27.35%

Land use and land cover changes significantly affect C storage in terrestrial ecosystems. Programs intended to compensate land owners for the maintenance or enhancement to C stocks are promising, but require detailed and spatially explicit C distribution estimates to monitor the effectiveness of management interventions. Savanna ecosystems are significant components of the global C cycle, however, they have not received much attention for the development of C monitoring approaches. In this dissertation I have investigated three of the aspects related to woody plant cover dynamics in semiarid savannas of central Argentina: spatio-temporal dynamics, precise field surveying and scaling from field to region with the use of freely available remotely sense data.

To examine the long term changes in woody plant cover, I first carefully extracted information from historical maps of the Caldenal savannas of central Argentina (190,000 km2) in the 1880s to generate a woody cover map that was compared to a 2000s dataset. Over the last ~120 years, woody cover increased across ~12,200 km2 (14.2 % of the area). During the same period, ~5,000 km2 of the original woody area was converted to croplands and ~7,000 km2 to pastures, about the same total land area as was affected by woody plant encroachment. A smaller area...

Landscape Supplementation in Adjacent Savannas and its Implications for the Design of Corridors for Forest Birds in the Central Cerrado, Brazil

Tubelis, Darius; Cowling, Ann; Donnelly, Christine
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.55%
We examined landscape supplementation (sensu [Oikos 65 (1992) 169]) by forest birds along forest/savanna boundaries in central Brazil to: (1) verify the role of savanna vegetation in providing resources to forest bird communities; (2) suggest minimum amounts of savannas to be conserved within corridors, to provide adequate foraging habitat for forest birds outside reserves. Transect counts parallel (n=64) and perpendicular (n=64) to forests were conducted in eight savannas (cerrado sensu stricto) between February 2000 and January 2001. Patterns of species richness and abundance of birds in relation to distances from forests were examined using Generalised Linear Mixed Models. Omnivores were the most abundant birds foraging in savannas, followed by insectivores and frugivores. Landscape supplementation in savannas was proportional to the density of savanna vegetation. Also, it was higher in the breeding season than in the non-breeding period. These two patterns suggest that surrounding savannas play a major role in providing additional foraging areas for forest bird species. We suggest that the environmental policy currently protecting 20 m of gallery forests along each side of rivers be modified to include at least 60 m of savanna along these forests through central Brazil. The study suggests that appropriate conservation efforts should also encompass the surrounding matrix to which the home ranges of target species are expanded...