No description available.

Natural tropical deciduous forest (TDF) is considered with a medium to small height (< 15 m). Particularly, in Mexico TDF shows a remnant of 36.2% of primary forest driving changes in the structure and species composition. This vegetation in Mexico is mainly transformed into grassland for cattle raising, and agriculture, primarily for self-consumption. More information about the ecology and the social pressures on this vegetation can be seen in Chapter I. The general methods, including sampling allocation and collection, characteristics of the study site, as well the procedure of the research proposal is presented in Chapter II. The main aim of this thesis is to improve the accuracy of predictions of net carbon emissions and the spatial distribution of AGB in the Tropical Deciduous Forest of Mexico. To address this aim, it is important to take into consideration the forest structure, spatial patterns and processes in a natural forest in a multi-scale analysis; also, it is necessary to characterize the spatial socio-economic drivers that influence current AGB losses. With the understanding of such elements, it is possible to reconstruct the potential carbon stocks and estimate the allocation of net carbon emissions due to deforestation and forest degradation. This study shows that it is possible to count net carbon emissions caused by deforestation and forest degradation at a landscape scale. To come to such estimates, it was necessary to reduce the different sources of uncertainty. Chapter III explores different elements that drive the AGB allocation in a mature forest. The AGB in the mature forest was considered as the potential AGB that the forest could get assuming that it has reached its steady state. Different field sampling strategies and allometric equations were evaluated to account for uncertainty in the AGB estimations. The results showed that small sampling design (300-400 m2) and large-sized plots (4 ha) produce the same tree distribution for trees: ≥30 cm in DBH as well as in AGB. These results contradict what has been reported for others (Chave et al., 2004 and 2005) when they refer to the general definition of tropical forest. However, those other studies referred to forests with a much higher precipitation and which can be classified as tropical rain (perennial) forest (Chave et al., 2004). In the tropical deciduous forest, the kind considered in this study, AGB tends to be allocated in small-sized trees. Diverse biophysical characteristics that may drive AGB allocation were considered over different spatial scales. Water stress was the main driver for AGB density at different spatial scales. Nutrients showed little significance to explain AGB as other studies have suggested in secondary forests and/or chronosequences. With this understanding, Chapter IV shows the use of different multi-variable models. Parsimonious models were the result of the variables selection and sensitivity test. Most of the methodologies showed a better performance to explain AGB allocation than a null-model. However, when they were contrasted with independent observations over different spatial resolutions, it was possible to conclude that only GLM was capable of reproducing the spatial patterns, and its estimations were close to observations. Nevertheless, some observations with very large AGB densities were underestimated by the model. This underestimation was related to the presence of few very large-sized trees. These two chapters depict the possibility of accounting for the potential AGB, and the uncertainty, namely whether the landscape could reach it with the absence of human disturbance. Once the potential AGB map was built and validated, it was transformed to carbon stock, using a local carbon concentration estimate. This potential carbon stock map was contrasted to the different available maps of current carbon stocks. Consequently, it was possible to estimate net carbon emissions due to deforestation and forest degradation (Chapter V), suggesting that the general models tend to agree in the total carbon loss. However, there are some spatial discrepancies in the magnitudes of change. Main differences between maps can be reduced by diverse socio-ecological constraints that dominate the landscape. This is important because it may be possible to make future adjustments that would reduce variability, enabling more accurate AGB estimations. However, to individually account for deforestation and forest degradation, more detailed sources of local information are necessary, such as socio-economic variables. Therefore models with a bottom-up perspective would lead to a better understanding and representation of the landscape. Finally, the growing rural population will have larger demands for wood and food, so while remote or protected areas may have the potential for storing high AGB, forest close to settlements and access routes are likely to continue being disturbed, unless affordable alternatives are available for the sustainable use of the forest. In conclusion, the estimation of spatial heterogeneity of AGB in the landscape is of great importance when measuring carbon stocks and ecological dynamics. Various elements influence the AGB allocation in the mature forest. Among all of them, water availability played the most decisive part of various spatial scales. My models support the hypothesis that water availability plays the major role in explaining AGB in Mexico on a local, sub-regional and landscape scale. Model selection produced contrasting AGB estimates and patterns. Moreover, the results of this study tell us that there is not a clear consensus among various current AGB maps. However, they also show that with a multi-model comparison it is possible to identify carbon emissions drivers and calculate total carbon emissions due to forest disturbances. Socio-economic variables played the major role in explaining AGB losses. Therefore, future studies should look into a bottom-up approach for a better understanding and representation of current AGB.

No description available.

Leaf traits have long been used to classify and characterise species in natural ecosystems. In addition, leaf traits provide important information about plants’ strategies for the use of resources and can be used to improve our understanding of ecosystem level processes such as nutrient cycling and carbon allocation. To explore the linkages between leaf traits and productivity, we worked in two resource-limited ecosystems (a grassland and a forest), and used leaf traits to understand how species respond to changes in available resources and their relationship to ecosystem processes. We worked in a species rich limestone-grassland located in central England, which has been subjected to long-term climatic manipulation (winter warming, summer drought and extra summer rainfall). We characterised species composition in terms of their identity, abundance and leaf structural properties (nitrogen content and leaf mass per area (LMA)) in the main treatments and the control. We found that change in species abundance was the most important factor to understand the differences in productivity (above ground biomass and total foliar nitrogen). We then measured CO2 exchange at ecosystem level, using a chamber technique, and assessed the treatments’ effect on the gross primary productivity (GPP) and ecosystem respiration (Reco). GPP and Reco were controlled by soil moisture and above ground biomass but also influenced by the conditions experienced during the growing season prior to the measuring period. Our second location was a post-disturbance chronosequence in a seasonally dry tropical forest in Costa Rica and we used leaf level gas exchange measurements to explore the role of nitrogen (N) and phosphorus (P) on the temporal-spatial variation of photosynthesis of dominant species. We found that photosynthetic efficiency was strongly linked to leaf N and P content, but that there was an important seasonal pattern on this relationship likely associated to P remobilization. Additionally we found seasonal changes in resources (water, nutrients) had a larger impact on the photosynthetic parameters than changes along the chronosequence. The two ecosystems studied for this thesis are contrasting in their physiognomy, species composition and climate, but are also characterised by species whose structural traits (high LMA and high C:N ratio) are likely to have a significant impact on the nutrient cycling processes. We learned that leaf traits provide important information about species strategies and their usage of resources and they can also aid to address questions at ecosystem level in time and space, either through simple aggregation or as emergent properties. Additionally, the traits explored are important input information to up-scale processes from leaf to the ecosystem level, a step needed to address the effect changes in resources will have on the seasonally dry tropical forest and grasslands, which represent a significant fraction of the total global carbon storage.

Os objetivos do presente trabalho foram avaliar o potencial de acúmulo de carbono (C) em solos de cerrado sob diferentes usos florestais (Eucalyptus, Pinus versus vegetação natural) e as possíveis alterações ocorridas na ciclagem de nutrientes sob esse tipo de coberturas. Para isso, foram coletadas 30 amostras de solo (0-5, 10-25 e 35-50 cm) e de serrapilheira acumulada em plantios de Eucalyptus, Pinus e remanescentes de cerradão em quatro municípios do estado de SP, nas quais se determinou: pH, matéria orgânica (MO), C, macronutrientes e densidade, além da granulometria no solo. Os estoques de C do solo foram calculados através do ajuste e integração de equações exponenciais, obtendo-se valores entre 3,4 e 8,6 kgC.m-2.(na camada de 0 a 30 cm) e entre 5,7 e 11,3 kgC.m-2.(até 1m). Os resultados mostraram que a silvicultura de Eucalyptus e Pinus afeta o acúmulo de C e a ciclagem de nutrientes em áreas de cerrado. As alterações nos estoques de C ocorreram principalmente nos horizontes orgânicos e na camada superficial do solo em decorrência da substituição da MO original por outra de pior qualidade química. A influência do tipo de vegetação sobre o C da camada superficial do solo variou em função de características do sítio, verificando ganhos em alguns dos locais estudados, perdas em outros e ainda diferenças não significativas. Em profundidades maiores, o conteúdo de C mostrou-se fortemente relacionado com o teor de argila e diminuiu sob cultura de Eucalyptus e Pinus, sendo mais fortes as depleções sob Pinus. Nos plantios houve formação de horizontes orgânicos espessos, com concentrações de C elevadas. A concentração de nitrogênio (N), cálcio, magnésio e potássio do material aí acumulado foi menor do que nas áreas naturais, enquanto que a acidez e a relação C/N foram maiores. Isso pode inibir a decomposição, o que explicaria o maior armazenamento de C na serapilheira. A incorporação desse material ao solo implica em alterações da MO, que é um dos principais fatores de estruturação e fertilidade dos solos tropicais e foi afetada em quantidade e qualidade. As relações C/N quantificadas na camada superficial do solo foram significativamente maiores do que em áreas de vegetação natural, indicando substituição da MO nessa camada no tempo de vida dos plantios (~40 anos). Os resultados demonstram a ocorrência de alterações na qualidade química da MO na serapilheira e no solo superficial sob uso silvicultural, as quais podem originar maiores estoques e tempos de residência do C, mas também diminuições de recursos tróficos para a comunidade decompositora, com implicações no resto do ecossistema. Os resultados sugerem que a dinâmica do carbono do solo varia ao longo do perfil, sendo necessário esclarecer melhor os fatores que definem o carbono da camada superficial, maior em quantidade e mais sensível aos efeitos do manejo. / Effects on soil organic carbon storage potential and possible biogeochemical changes of established forest plantations were assessed in southeast Brazil, in Eucalyptus and Pinus plantations compared with natural areas of native dry forest (cerradão). 30 plots were randomly distributed for soil (0-5, 10-25 and 35-50 cm) and forest floor litter collection in mature plantations (~40 years old) and adjacent native forest. The design was replicated in 4 localities in Sao Paulo, southeast Brazil. Organic matter, organic carbon, macro nutrients, pH, density, and soil texture were determined. Soil organic carbon stocks were calculated through exponential equations adjustment and integration, values ranged from 3,4 to 8,6 kgC.m-2.(on the 0 and 30 cm layer) and from 5,7 to 11,3 kgC.m-2.(up to 1m). Soil organic carbon and biogeochemical features were affected under Eucalyptus and Pinus plantations. Changes in carbon stocks were stronger in organic layers and topsoil, due to the replacement of the original organic matter, causing chemical quality decrease. Effects of vegetation on topsoil organic carbon were site dependent, as plantations results in gains, losses and no remarkable differences between natural and forested areas. Eucalyptus and Pinus establishment led to organic carbon losses, which possibly conducted by soil disturbances at implementation of plantations. Carbon content was strongly related to clay at deeper layers, but not at shallower ones. Thicker organic layers with higher carbon content were found under plantations. Lower calcium, magnesium and potassium concentrations and higher acidity and C/N (carbon to nitrogen) ratios were measured at implanted forest floor litter layers. These changes could inhibit decomposition, explaining larger litter carbon storage. Soil organic matter is an important factor in maintaining tropical soil structure and fertility. It was affected by Eucalyptus and Pinus forestation. While litter organic mater is incorporated into the soil, it leads to soil organic matter chemical quality decreases. The topsoil C/N ratio measured in plantations was significantly higher than in natural vegetation areas, indicating organic matter replacement on this layer in plantations lifetime (~40 years). We concluded that litter and topsoil organic matter chemical properties were affected by forestation with Eucalyptus and Pinus, which could result in larger C stocks and residence times, but could also decrease trophic resources for decomposers, with implications on the whole ecosystem. The results suggest that soil carbon dynamics changes along the soil profile. Factors controlling surface soil carbon dynamics must be clarified further, as they contained high carbon amounts, the most sensible to management practices.

Entre as principais oleaginosas eleitas para a produção de biodiesel, encontra-se a mamona (Ricinus communis L.), por possuir elevado teor de óleo, conhecido como óleo de rícino, extraído pela prensagem das sementes, contendo 90% de ácido graxo ricinoléico, o qual confere ao óleo suas características singulares, possibilitando ampla gama de utilização industrial. A produção brasileira de mamona concentra-se na caatinga baiana. A agricultura desta região, embora seja feita sem o uso de insumos agrícolas mantém uma produtividade regular. Com isso, tornou-se importante avaliar o efeito ambiental desta cultura sobre os estoques de C (carbono) e N (nitrogênio) no solo e os mecanismos de sua manutenção. Este trabalho foi realizado em solos de uma fazenda na região de Irecê-BA, tendo como objetivos calcular os estoques de C e N no solo; calcular o fluxo de gases do efeito estufa dos resíduos de mamona; calcular os valores C e N da biomassa microbiana no solo (BMS) e analisar o perfil da comunidade de bactérias fixadoras de N2 no solo por PCR-DGGE. Os resultados indicaram a ausência de variações nos estoques de C entre os tratamentos de mamona com 10, 20 e 50 anos de cultivo (48 Mg ha-1) sendo superados pelos valores encontrados na caatinga (90 Mg ha-1); mesma condição para o estoque de N (5,3 Mg ha-1 nos tratamentos de mamona e 8 Mg ha-1 na caatinga). Já os valores de C-microbiano foram superiores na caatinga, mas não apresentaram diferenças entre os cultivos de mamona; para o N-microbiano, os valores não sofreram diferenças entre as camadas, porém foram inferiores no tratamento de mamona com 10 e 50 anos de cultivo. O fluxo de gases de N-N2O e C-CO2 foram maiores para o tratamento com aplicação de resíduos orgânicos de mamona chegando a 160 mg m-2 h-1 de C-CO2 e 600 mg m-2 h-1 de N-N2O. O teste de redução de acetileno (ARA) e a análise de DGGE indicaram que o perfil da comunidade de bactérias diazotróficas do solo nos diferentes tratamentos sofreu alteração e permitiu a estocagem de N no solo durante os 50 anos de cultivo viabilizando, ambientalmente, a produção de mamona nesta região. / Among the main oils elected for biodiesel production is the castor bean (Ricinus communis L.) for its high oil content, known as castor oil extracted by pressing the seeds containing 90% ricinoleic acid, which gives the oil its unique features, allowing a wide range of industrial use. Brazilian production of castor oil is concentrated in the tropical dry forest of Bahia. Farming in this region, although it is made without the use of agricultural inputs remains a regular productivity. With this, it became important to assess the \"environmental effect\" of this culture on the stocks of C (carbon) and N (nitrogen) in soil and the mechanisms for its maintenance. This work was carried out in soils of a farm in Irecê-BA, aimed to calculate the stocks of C and N in soil, calculated the flows of greenhouse gases from oil waste; to figure out the values of carbon (C) and nitrogen (N) of microbial biomass in soil (BMS and to analyze the profile of the community of N2-fixing bacteria in soil through denaturing gradient gel electrophoresis (DGGE). Results indicated the absence of changes in C stocks between treatments of castor oil with 10, 20 and 50 years of cultivation (about 48 Mg ha-1) being outweighed by values found in the tropical dry forest (90 Mg ha-1); same condition verified for the stock of N (5.3 Mg ha-1 treatments of castor and 8 Mg ha-1 in tropical dry forest). As for values of microbial-C, they were higher in the tropical dry forest and did not present differences between the cultures of castor oil; regarding microbial-N values, there have not been differences between the layers, but they were lower for castor oil with 10 and 50 years of cultivation. The gases flow accumulated N-N2O was significantly higher than that of CCO2 and higher for the treatment of soil with organic fertilizer castor reaching 160 mg m- 2 h-1 of C-CO2 and 600 mg m-2 h-1 of N-N2O. ARA analysis and DGGE indicated that the profile of the diazotrophic community of soil in different treatments had change, allowing the storage of N in soil during the 50 years of cultivation enabling, in environmental terms, the production of castor oil in this region.

No description available.

Dry forests of the Caribbean islands are regarded as highly disturbed ecosystems and have been characterized as having a high density of small diameter stems, a lower basal area at maturity and a lower species-richness than continental Neotropical dry forests. However, the emerging view regards these ecosystems as phenologically complex, where taxonomic and structural composition is variable over time and space, due to local hydraulic regimes induced by high topographic and climactic variability and varying forms and intensities of disturbance. The former view is derived from a few studies, the majority of which have been conducted in Puerto Rico and from one data review of small 0.1 ha plots representing 4 sites in the Antilles and 25 sits in the continental Neotropics. Overall, little is known about the less-disturbed dry forest formations of the Antilles. Given the emerging view and lack of research in less-disturbed Antillean dry forests, a case study of dry forest structure and composition on the island of St. Lucia is used to examine heterogeneity in dry forest floristic and structural composition on the topographically, floristically and climactically complex island of St. Lucia. Amongst twenty-two 15 x 15 m widely distributed plots, only 11/64 species/genera were found in >50\% of plots and clustering was observed amongst uncommon species, supporting evidence of floristic heterogeneity. Significant differences between the total basal area of each plot (Kruskal-Wallis test, p <0.05) were observed; each plot differed significantly with at least 2 other plots, 6 differed significantly with 10 or more plots, providing evidence for structural heterogeneity. Comparisons were also made with prior research to question generalizations about Antillean dry forests. Amongst large diameter stems, species richness and stem density was higher in this study, when compared to more-disturbed Antillean dry forests. The most speciose dry forest genus was Zanthoxylum, while four families were found to be equally speciose namely, Myrtaceae, Fabaceae, Rutaceae and Rubiaceae, highlighting inconsistencies with prior generalizations. Species-richness values reported amongst Neotropical dry forests were highly variable amongst similar regions, let alone the continental Neotropics, relative to the Antillean Archipelago. Stem density and basal area in St. Lucia was similar to ranges reported throughout the Neotropics, further supporting evidence for intra-island structural variability. The intra-region heterogeneity observed in Antillean and Neotropical continental dry forests indicates that results from localized plot-based studies of structure and composition, should not be extrapolated to broad geo-political regions.

Dry forests of the Caribbean islands are regarded as highly disturbed ecosystems and have been characterized as having a high density of small diameter stems, a lower basal area at maturity and a lower species-richness than continental Neotropical dry forests. However, the emerging view regards these ecosystems as phenologically complex, where taxonomic and structural composition is variable over time and space, due to local hydraulic regimes induced by high topographic and climactic variability and varying forms and intensities of disturbance. The former view is derived from a few studies, the majority of which have been conducted in Puerto Rico and from one data review of small 0.1 ha plots representing 4 sites in the Antilles and 25 sits in the continental Neotropics. Overall, little is known about the less-disturbed dry forest formations of the Antilles. Given the emerging view and lack of research in less-disturbed Antillean dry forests, a case study of dry forest structure and composition on the island of St. Lucia is used to examine heterogeneity in dry forest floristic and structural composition on the topographically, floristically and climactically complex island of St. Lucia. Amongst twenty-two 15 x 15 m widely distributed plots, only 11/64 species/genera were found in >50\% of plots and clustering was observed amongst uncommon species, supporting evidence of floristic heterogeneity. Significant differences between the total basal area of each plot (Kruskal-Wallis test, p <0.05) were observed; each plot differed significantly with at least 2 other plots, 6 differed significantly with 10 or more plots, providing evidence for structural heterogeneity. Comparisons were also made with prior research to question generalizations about Antillean dry forests. Amongst large diameter stems, species richness and stem density was higher in this study, when compared to more-disturbed Antillean dry forests. The most speciose dry forest genus was Zanthoxylum, while four families were found to be equally speciose namely, Myrtaceae, Fabaceae, Rutaceae and Rubiaceae, highlighting inconsistencies with prior generalizations. Species-richness values reported amongst Neotropical dry forests were highly variable amongst similar regions, let alone the continental Neotropics, relative to the Antillean Archipelago. Stem density and basal area in St. Lucia was similar to ranges reported throughout the Neotropics, further supporting evidence for intra-island structural variability. The intra-region heterogeneity observed in Antillean and Neotropical continental dry forests indicates that results from localized plot-based studies of structure and composition, should not be extrapolated to broad geo-political regions.

Submitted by Lara Oliveira (lara@ufersa.edu.br) on 2017-03-23T19:49:11Z No. of bitstreams: 1 DayanneTSN_DISSERT.pdf: 1338268 bytes, checksum: 2ceb62e733ae7b4bf23609d3ab99716a (MD5) / Approved for entry into archive by Vanessa Christiane (referencia@ufersa.edu.br) on 2017-04-13T14:44:45Z (GMT) No. of bitstreams: 1 DayanneTSN_DISSERT.pdf: 1338268 bytes, checksum: 2ceb62e733ae7b4bf23609d3ab99716a (MD5) / Approved for entry into archive by Vanessa Christiane (referencia@ufersa.edu.br) on 2017-04-13T14:44:54Z (GMT) No. of bitstreams: 1 DayanneTSN_DISSERT.pdf: 1338268 bytes, checksum: 2ceb62e733ae7b4bf23609d3ab99716a (MD5) / Made available in DSpace on 2017-04-13T14:45:04Z (GMT). No. of bitstreams: 1 DayanneTSN_DISSERT.pdf: 1338268 bytes, checksum: 2ceb62e733ae7b4bf23609d3ab99716a (MD5) Previous issue date: 2016-05-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / During the process of germination, water absorption by the seeds is crucial in the recovery of metabolic activity, and all the factors that control the physiological events involved in the germination process are influenced by temperature. This process is also worth noting the degree of tolerance of seeds to salinity, and contaminants such as oil. Poincianella pyramidalis is endemic to the Caatinga and commonly indicated for recovery of degraded areas. This work aims to analyze the tolerance of this species to different electrical conductivities and temperatures during their soaking process water and germination, as well as their tolerance for different times of immersion in oil. The experiment absorption was developed under a completely randomized design in a factorial 5 x 7 x 3, 5 salinities, temperatures 7 and 3 repetitions. The seeds were weighed at various periods of time until the stabilization of the absorption curve. The germination experiment was conducted using the seeds from the water absorption test, developed under a completely randomized design in a factorial 5 x 5 x 3, 5 salinities, temperatures 5 and 3 repetitions. The germination evaluations were performed daily until the stabilization of the same. The experiment oil was developed under a completely randomized design in a factorial 5 x 4, 5 treatments and 4 repetitions. The periods of immersion times oil employed were 0; 5; 60; 720 and 1440 minutes. During the process of water absorption, the increase of EC caused a reduction of AAmax and TAAmáx, and the temperature increase caused reduction only tAA50%. In the process of germination, the increase of EC resulted in decreased Gmáx and increased TG50%, while increasing temperature had a positive influence to 27°C at Gmax and TGmax, however, reduced the TG50%, and t.TGmax. The oil seed negatively impacts, reduced Emax and TEmax, while t.E50% and t.TEmax were prolonged / Durante o processo de germinação, a absorção de água pelas sementes é fundamental na retomada das atividades metabólicas, e todos os fatores que controlam os eventos fisiológicos envolvidos no processo germinativo sofrem influência da temperatura. Nesse processo também é válido observar o grau de tolerância das sementes à salinidade, e à contaminantes como o petróleo. Poincianella pyramidalis é endêmica da Caatinga e comumente indicada para recuperação de áreas degradadas. Este trabalho tem como objetivo analisar a tolerância dessa espécie à diferentes condutividades elétricas e temperaturas durante seu processo de embebição de água e germinação, bem como sua tolerância a diferentes tempos de imersão em petróleo. O experimento de absorção foi desenvolvido sob o delineamento inteiramente casualizado em esquema fatorial 5 x 7 x 3, sendo 5 salinidades, 7 temperaturas e 3 repetições. As sementes foram pesadas em diversos períodos de tempo até a estabilização da curva de absorção. O experimento de germinação foi desenvolvido utilizando as sementes provenientes do teste de absorção de água, desenvolvido sob o delineamento inteiramente casualizado em esquema fatorial 5 x 5 x 3, sendo 5 salinidades, 5 temperaturas e 3 repetições. As avaliações da germinação foram efetuadas diariamente até a estabilização da mesma. O experimento com petróleo foi desenvolvido sob o delineamento inteiramente casualizado em esquema fatorial 5 x 4, sendo 5 tratamentos e 4 repetições. Os períodos de tempos de imersão em petróleo empregados foram de 0 ; 5 ; 60; 720 e 1440 minutos. Durante o processo de absorção de água, o aumento da CE ocasionou a redução da AAmáx e da TAAmáx, e o aumento da temperatura provocou redução apenas no tAA50%. No processo de germinação, o aumento da CE ocasionou decréscimo na Gmáx e aumento no tG50%, enquanto que o aumento da temperatura interferiu positivamente até 27°C na Gmáx e na TGmáx, porém, reduziu o tG50%, e o tTGmáx. O petróleo afetou negativamente as sementes, reduziu a Emáx e a TEmáx, enquanto que o t.E50%, e o t.TEmáx foram prolongados / 2017-03-23