751 resultados para BURN
Resumo:
In order to influence global policy effectively, conservation scientists need to be able to provide robust predictions of the impact of alternative policies on biodiversity and measure progress towards goals using reliable indicators. We present a framework for using biodiversity indicators predictively to inform policy choices at a global level. The approach is illustrated with two case studies in which we project forwards the impacts of feasible policies on trends in biodiversity and in relevant indicators. The policies are based on targets agreed at the Convention on Biological Diversity (CBD) meeting in Nagoya in October 2010. The first case study compares protected area policies for African mammals, assessed using the Red List Index; the second example uses the Living Planet Index to assess the impact of a complete halt, versus a reduction, in bottom trawling. In the protected areas example, we find that the indicator can aid in decision-making because it is able to differentiate between the impacts of the different policies. In the bottom trawling example, the indicator exhibits some counter-intuitive behaviour, due to over-representation of some taxonomic and functional groups in the indicator, and contrasting impacts of the policies on different groups caused by trophic interactions. Our results support the need for further research on how to use predictive models and indicators to credibly track trends and inform policy. To be useful and relevant, scientists must make testable predictions about the impact of global policy on biodiversity to ensure that targets such as those set at Nagoya catalyse effective and measurable change.
Resumo:
We present a well-dated, high-resolution, ~ 45 kyr lake sediment record reflecting regional temperature and precipitation change in the continental interior of the Southern Hemisphere (SH) tropics of South America. The study site is Laguna La Gaiba (LLG), a large lake (95 km2) hydrologically-linked to the Pantanal, an immense, seasonally-flooded basin and the world's largest tropical wetland (135,000 km2). Lake-level changes at LLG are therefore reflective of regional precipitation. We infer past fluctuations in precipitation at this site through changes in: i) pollen-inferred extent of flood-tolerant forest; ii) relative abundance of terra firme humid tropical forest versus seasonally-dry tropical forest pollen types; and iii) proportions of deep- versus shallow-water diatoms. A probabilistic model, based on plant family and genus climatic optima, was used to generate quantitative estimates of past temperature from the fossil pollen data. Our temperature reconstruction demonstrates rising temperature (by 4 °C) at 19.5 kyr BP, synchronous with the onset of deglacial warming in the central Andes, strengthening the evidence that climatic warming in the SH tropics preceded deglacial warming in the Northern Hemisphere (NH) by at least 5 kyr. We provide unequivocal evidence that the climate at LLG was markedly drier during the last glacial period (45.0–12.2 kyr BP) than during the Holocene, contrasting with SH tropical Andean and Atlantic records that demonstrate a strengthening of the South American summer monsoon during the global Last Glacial Maximum (~ 21 kyr BP), in tune with the ~ 20 kyr precession orbital cycle. Holocene climate conditions occurred as early as 12.8–12.2 kyr BP, when increased precipitation in the Pantanal catchment caused heightened flooding and rising lake levels in LLG. In contrast to this strong geographic variation in LGM precipitation across the continent, expansion of tropical dry forest between 10 and 3 kyr BP at LLG strengthens the body of evidence for widespread early–mid Holocene drought across tropical South America.
Resumo:
An ongoing controversy in Amazonian palaeoecology is the manner in which Amazonian rainforest communities have responded to environmental change over the last glacial–interglacial cycle. Much of this controversy results from an inability to identify the floristic heterogeneity exhibited by rainforest communities within fossil pollen records. We apply multivariate (Principal Components Analysis) and classification (Unweighted Pair Group with Arithmetic Mean Agglomerative Classification) techniques to floral-biometric, modern pollen trap and lake sediment pollen data situated within different rainforest communities in the tropical lowlands of Amazonian Bolivia. Modern pollen rain analyses from artificial pollen traps show that evergreen terra firme (well-drained), evergreen terra firme liana, evergreen seasonally inundated, and evergreen riparian rainforests may be readily differentiated, floristically and palynologically. Analogue matching techniques, based on Euclidean distance measures, are employed to compare these pollen signatures with surface sediment pollen assemblages from five lakes: Laguna Bella Vista, Laguna Chaplin, and Laguna Huachi situated within the Madeira-Tapajós moist forest ecoregion, and Laguna Isirere and Laguna Loma Suarez, which are situated within forest patches in the Beni savanna ecoregion. The same numerical techniques are used to compare rainforest pollen trap signatures with the fossil pollen record of Laguna Chaplin.
Resumo:
We used fossil pollen to investigate the response of the eastern Chiquitano seasonally-dry tropical forest (SDTF), lowland Bolivia, to high-amplitude climate change associated with glacial–interglacial cycles. Changes in the structure, composition and diversity of the past vegetation are compared with palaeoclimate data previously reconstructed from the same record, and these results shed light on the biogeographic history of today’s highly disjunct blocks of SDTF across South America. We demonstrate that lower glacial temperatures limited tropical forest in the Chiquitanía region, and suggest that SDTF was absent or restricted at latitudes below 17°S, the proposed location of the majority of the hypothesized ‘Pleistocene dry forest arc’ (PDFA). At 19500 yrs b.p., warming supported the establishment of a floristically-distinct SDTF, which showed little change throughout the glacial–Holocene transition, despite a shift to significantly wetter conditions beginning ca. 12500–12200 yrs b.p. Anadenanthera colubrina, a key SDTF taxon, arrived at 10000 yrs b.p., which coincides with the onset of drought associated with an extended dry season. Lasting until 3000 yrs b.p., Holocene drought caused a floristic shift to more drought-tolerant taxa and a reduction in α-diversity (shown by declining palynological richness), but closed-canopy forest was maintained throughout. In contrast to the PDFA, the modern distribution of SDTF most likely represents the greatest spatial coverage of these forests in southern South America since glacial times. We find that temperature is a key climatic control upon the distribution of lowland South American SDTF over glacial-interglacial timescales, and seasonality of rainfall exerts a strong control on their floristic composition.
Resumo:
The Moraceae family is one of the most abundant and ecologically important families in Neotropical rainforests and is very well-represented in Amazonian fossil pollen records. However, difficulty in differentiating palynologically between the genera within this family, or between the Moraceae and Urticaceae families, has limited the amount of palaeoecological information that can be extracted from these records. The aim of this paper is to analyse the morphological properties of pollen from Amazonian species of Moraceae in order to determine whether the pollen taxonomy of this family can be improved. Descriptive and morphometric methods are used to identify and differentiate key pollen types of the Moraceae (mulberry) and Urticaceae (nettle) families which are represented in Amazonian rainforest communities of Noel Kempff Mercado National Park (NKMNP), Northeast Bolivia. We demonstrate that Helicostylis, Brosimum, Pseudolmedia, Sorocea and Pourouma pollen can be identified in tropical pollen assemblages and present digital images of, and a taxonomic key to, the Moraceae pollen types of NKMNP. Indicator species, Maquira coriacea (riparian evergreen forest) and Brosimum gaudichaudii (open woodland and upland savanna communities), also exhibit unique pollen morphologies. The ability to recognise these ecologically important taxa in pollen records provides the potential for much more detailed and reliable Neotropical palaeovegetation reconstructions than have hitherto been possible. In particular, this improved taxonomic resolution holds promise for resolving long-standing controversies over the interpretation of key Amazonian Quaternary pollen records.
Resumo:
The peroxisomal proliferating-activated receptors (PPARs) are lipid-sensing transcription factors that have a role in embryonic development, but are primarily known for modulating energy metabolism, lipid storage, and transport, as well as inflammation and wound healing. Currently, there is no consensus as to the overall combined function of PPARs and why they evolved. We hypothesize that the PPARs had to evolve to integrate lipid storage and burning with the ability to reduce oxidative stress, as energy storage is essential for survival and resistance to injury/infection, but the latter increases oxidative stress and may reduce median survival (functional longevity). In a sense, PPARs may be an evolutionary solution to something we call the 'hypoxia-lipid' conundrum, where the ability to store and burn fat is essential for survival, but is a 'double-edged sword', as fats are potentially highly toxic. Ways in which PPARs may reduce oxidative stress involve modulation of mitochondrial uncoupling protein (UCP) expression (thus reducing reactive oxygen species, ROS), optimising forkhead box class O factor (FOXO) activity (by improving whole body insulin sensitivity) and suppressing NFkB (at the transcriptional level). In light of this, we therefore postulate that inflammation-induced PPAR downregulation engenders many of the signs and symptoms of the metabolic syndrome, which shares many features with the acute phase response (APR) and is the opposite of the phenotype associated with calorie restriction and high FOXO activity. In genetically susceptible individuals (displaying the naturally mildly insulin resistant 'thrifty genotype'), suboptimal PPAR activity may follow an exaggerated but natural adipose tissue-related inflammatory signal induced by excessive calories and reduced physical activity, which normally couples energy storage with the ability to mount an immune response. This is further worsened when pancreatic decompensation occurs, resulting in gluco-oxidative stress and lipotoxicity, increased inflammatory insulin resistance and oxidative stress. Reactivating PPARs may restore a metabolic balance and help to adapt the phenotype to a modern lifestyle.
Resumo:
There is considerable controversy over whether pre-Columbian (pre-A.D. 1492) Amazonia was largely “pristine” and sparsely populated by slash-and-burn agriculturists, or instead a densely populated, domesticated landscape, heavily altered by extensive deforestation and anthropogenic burning. The discovery of hundreds of large geometric earthworks beneath intact rainforest across southern Amazonia challenges its status as a pristine landscape, and has been assumed to indicate extensive pre-Columbian deforestation by large populations. We tested these assumptions using coupled local- and regional-scale paleoecological records to reconstruct land use on an earthwork site in northeast Bolivia within the context of regional, climate-driven biome changes. This approach revealed evidence for an alternative scenario of Amazonian land use, which did not necessitate labor-intensive rainforest clearance for earthwork construction. Instead, we show that the inhabitants exploited a naturally open savanna landscape that they maintained around their settlement despite the climatically driven rainforest expansion that began ∼2,000 y ago across the region. Earthwork construction and agriculture on terra firme landscapes currently occupied by the seasonal rainforests of southern Amazonia may therefore not have necessitated large-scale deforestation using stone tools. This finding implies far less labor—and potentially lower population density—than previously supposed. Our findings demonstrate that current debates over the magnitude and nature of pre-Columbian Amazonian land use, and its impact on global biogeochemical cycling, are potentially flawed because they do not consider this land use in the context of climate-driven forest–savanna biome shifts through the mid-to-late Holocene.
Resumo:
Reliable evidence of trends in the illegal ivory trade is important for informing decision making for elephants but it is difficult to obtain due to the covert nature of the trade. The Elephant Trade Information System, a global database of reported seizures of illegal ivory, holds the only extensive information on illicit trade available. However inherent biases in seizure data make it difficult to infer trends; countries differ in their ability to make and report seizures and these differences cannot be directly measured. We developed a new modelling framework to provide quantitative evidence on trends in the illegal ivory trade from seizures data. The framework used Bayesian hierarchical latent variable models to reduce bias in seizures data by identifying proxy variables that describe the variability in seizure and reporting rates between countries and over time. Models produced bias-adjusted smoothed estimates of relative trends in illegal ivory activity for raw and worked ivory in three weight classes. Activity is represented by two indicators describing the number of illegal ivory transactions--Transactions Index--and the total weight of illegal ivory transactions--Weights Index--at global, regional or national levels. Globally, activity was found to be rapidly increasing and at its highest level for 16 years, more than doubling from 2007 to 2011 and tripling from 1998 to 2011. Over 70% of the Transactions Index is from shipments of worked ivory weighing less than 10 kg and the rapid increase since 2007 is mainly due to increased consumption in China. Over 70% of the Weights Index is from shipments of raw ivory weighing at least 100 kg mainly moving from Central and East Africa to Southeast and East Asia. The results tie together recent findings on trends in poaching rates, declining populations and consumption and provide detailed evidence to inform international decision making on elephants.
Resumo:
The chapter examines how far medieval economic crises can be identified by analysing the residuals from a simultaneous equation model of the medieval English economy. High inflation, falls in gross domestic product and large intermittent changes in wage rates are all considered as potential indicators of crisis. Potential causal factors include bad harvests, wars and political instability. The chapter suggests that crises arose when a combination of different problems overwhelmed the capacity of government to address them. It may therefore be a mistake to look for a single cause of any crisis. The coincidence of separate problems is a more plausible explanation of many crises.
Resumo:
The nature and extent of pre-Columbian (pre-1492 AD) human impact in Amazonia is a contentious issue. The Bolivian Amazon has yielded some of the most impressive evidence for large and complex pre-Columbian societies in the Amazon basin, yet there remains relatively little data concerning the land use of these societies over time. Palaeoecology, when integrated with archaeological data, has the potential to fill these gaps in our knowledge. We present a 6,000-year record of anthropogenic burning, agriculture and vegetation change, from an oxbow lake located adjacent to a pre-Columbian ring-ditch in north-east Bolivia (13°15’44” S, 63°42’37” W). Human occupation around the lake site is inferred from pollen and phytoliths of maize (Zea mays L.) and macroscopic charcoal evidence of anthropogenic burning. First occupation around the lake was radiocarbon dated to ~2500 years BP. The persistence of maize in the record from ~1850 BP suggests that it was an important crop grown in the ringditch region in pre-Columbian times, and abundant macroscopic charcoal suggests that pre-Columbian land management entailed more extensive burning of the landscape than the slash-and-burn agriculture practised around the site today. The site was occupied continuously until near-modern times, although there is evidence for a decline in agricultural intensity or change in land use strategy, and possible population decline, from ~600-500 BP. The long and continuous occupation, which predates the establishment of rainforest in the region, suggests that pre-Columbian land use may have had a significant influence on ecosystem development at this site over the last ~2000 years.
Resumo:
Public and policy discourse about the content of history curricula is frequently contested, but the voice of history teachers is often absent from such debate. Drawing on a large scale on-line survey of history teachers in England, this paper explores their responses to major curriculum reforms proposed by the Coalition government in February 2013. In particular it examines teachers' responses to government plans to prescribe a list of topics, events and individuals to be taught chronologically that all students would be expected to study. Nearly 550 teachers responded to the survey, and more than two-thirds of them provided additional written comments on the curriculum proposals. This paper examines these comments, with reference to a range of curriculum models. The study reveals a deep antagonism towards the proposals for various reasons, including concerns about the extent and nature of the substantive content proposed and the way in which it should be sequenced. Analysis of these reactions provides an illuminating insight into history teachers’ perspectives. While the rationales that underpin their thinking seem to have connections to a variety of different theoretical models, the analysis suggests that more attention could usefully be devoted to the idea of developing frameworks of reference.
Resumo:
Brazilian Campos grasslands are rich in species and the maintenance of its diversity and physiognomy is dependent on disturbance (e.g. fire and grazing) Nevertheless, studies about fire intensity and severity are inexistent. The present paper describes fire parameters, using 14 experimental burn plots in southern Brazil (30 degrees 02` to 30 degrees 04`S, and 51 degrees 06` to 51 degrees 09`W. 311masl). Two sites under different fire histories were chosen: frequently burned and excluded since six years. Experimental burning was performed during summer (2006-2007), when most burning takes place in these grasslands. The following parameters were measured: air temperature and moisture, vegetation height, wind speed, fuel (fine, coarse), fuel moisture, fire temperatures (soil level and at 50cm), ash, residuals, flame freight, fire duration: burning efficiency and fire intensity were later calculated. Fuel load varied from 0.39 to 1.44kg.m(-2). and correlated positively with both fire temperature and fire intensity. Fire temperatures ranged 47 to 537.5 degrees C. being higher in the excluded site Fire intensity was low compared to grassland elsewhere (36 5-319.5kW.m(-1)), differing significantly between sties Fine fuel was the variable that best explained fire intensity. The results on fire intensity and severity in Campos grasslands can be considered a pilot study, since plots were very small. However the data provided can help other researchers to get permission for experimentation using larger plots The results provide support for further studies about the effects of fire on grassland vegetation and for studies involving fire models and fire risk prediction