Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The Schinopsis brasiliensis Engl. (braúna) is a long-lived species with wide distribution in phytogeographical areas of caatinga and cerrado. Due to uncontrolled exploitation of its timber and the environmental devastation of the caatinga is currently a threatened species. However, these trees have higher dimensions than other species of this environment and, therefore, have higher ecological importance. The biological and ecological characteristics of this species highlights the need of studies about theirs structures and reaction to environmental and climatic changes, among these wood anatomy and dendrochronology. The present study collected specimens of S. brasilienis from São Pedro Farm, in the municipality of Porto da Folha/SE. Living wood and construction wood samples were collected in June and July, 2013, through a non-destructive method, afterwards the samples were kept in the UFS Plant Anatomy and Dendroecology Laboratory, for sample preparations and data analisys. The heartwood and sapwood were significantly different in structure (p<0.05 for all analysis), which revealed that the structure of the heartwood is more resistant to environmental weathering, justifying its use for rural constructions in areas of caatinga. It has growth rings limited by marginal parenchyma band and/or thickness of the fiber walls; small vessels, and tyloses when in the heartwood; rays with procumbent and square cells that store many calcium oxalate crystals; and short and thick fibers. The cross-dating of growth rings series showed correlation of 0.52 between their live individuals and 0.49 among the construction wood. The chronology showed positive correlations with rainfall in the beginning and ending of the rainy season, and fall in the increase rate in the warmer and drier periods of the year, coinciding with the leaf fall and consequent disruption of metabolic activity in new xylem cells´ generation. The analysis of the rings in construction woods allowed new chronology expansion in Brazil, for the previous 20 years to the formation of the first growth ring of the older sample of S. brasiliensis. / A Schinopsis brasiliensis Engl. (braúna) é uma espécie longeva com ampla distribuição nos domínios fitogeográficos da caatinga e cerrado. Por conta da exploração sem controle de sua madeira e da devastação ambiental que assola a caatinga, encontra-se atualmente ameaçada de extinção. Porém, é uma espécie que se destaca por possuir indivíduos com dimensões superiores às geralmente encontradas em outras espécies deste ambiente, e por isso foi classificada como de alta importância ecológica. Suas características biológicas e ecológicas enfatizam a necessidade de estudos sobre suas estruturas e reações às mudanças ambientais e climáticas, dentre estes os de anatomia da madeira e dendrocronologia. O estudo foi realizado com indivíduos de S. brasiliensis provenientes da Fazenda São Pedro, município de Porto da Folha/SE. Amostras de árvores e de madeiras de construção foram coletadas nos meses de junho e julho de 2013, através de método não destrutivo, e posteriormente foram armazenadas no Laboratório de Anatomia Vegetal e Dendroecologia da UFS, para preparo e análise dos dados. A madeira de S. brasiliensis apresentou cerne e alburno significativamente distintos estruturalmente (p<0,05), houve destaque para as características estruturais que tornam o cerne a região mais resistente e duradoura, justificando seu uso em construções rurais em áreas de caatinga. Apresentou anéis de crescimento delimitados por banda de parênquima marginal e/ou espessamento das paredes das fibras; vasos pequenos, com tiloses quando no cerne; raios formados por células procumbentes e quadradas que armazenam muitos cristais de oxalato de cálcio; e fibras curtas e grossas. A espécie foi passível de datação cruzada com 0,52 de correlação entre seus indivíduos vivos e 0,49 entre as árvores e madeiras de construção. Apresentou correlações positivas com a precipitação no início e final do período chuvoso e queda na taxa de incremento nos períodos mais quentes e secos do ano, coincidindo com a queda foliar e consequente interrupção das atividades metabólicas de formação de novas células xilemáticas. A análise dos anéis das madeiras de construção permitiu a inédita expansão de uma cronologia no Brasil, com a inclusão de 20 anos de medidas anteriores à formação do primeiro anel de crescimento da árvore mais velha amostrada na área de estudo.

Thesis (MSc. Agriculture (Pasture Science)) -- University of Limpopo, 2016. / The relationships between tree age, growth rings, and stem circumference correlated with establishment patterns may be a valuable instrument to reveal the functioning of woody species in the Savanna Biome. A study on tree age and establishment patterns of Acacia tortilis in the semi-arid regions of the Limpopo Province was conducted to aid an understanding of the causes of encroachment in savanna vegetation. This study aimed to determine the periodicity of growth ring formation at two study areas, correlate the number of growth rings with different tree characteristics and document tree population establishment patterns of Acacia tortilis, using stem circumferences. This was done in order to predict long-term bush encroachment using the interaction between rainfall and soil on the age, growth and establishment patterns of Acacia tortilis. Data was collected at three sites representing two study areas, two sites at the University of Limpopo’s Syferkuil Agricultural Experimental Farm and one site at the Sondela Nature Reserve in the Limpopo Province. The study incorporated two different soil forms and two rainfall regimes. Trees were divided into five height classes; namely, <0.5 m, >0.5 – 1.5 m, >1.5 – 2.0 m, >2.0 – 3.0 m and >3m. Fifty trees (ten in each class) were felled at each site, and the following recordings were made: tree height, stem circumference and crown diameter. Furthermore, each felled stump was taken to the laboratory and examined for growth rings. The results indicated that growth pattern of Acacia tortilis stems were more influenced by soil form than the amount of rainfall. Tree height was not significantly affected by soil form. However, rainfall proved to have a significant effect on the final height of the plant. Both rainfall and soil form did not have a substantial effect on the number of growth rings. Crown diameter was affected by soil form but rainfall did not prove to have the same effect. Correlations between growth rings and stem circumferences, tree height and crown diameter, proved to have significant relationships. However, the relationship between stem circumference and the number of growth rings was the most significant. iv A prediction model was created using the relationship between stem size and growth rings. Using this model tree age can be determined in a non-destructive manner. However, the absence of a correlation between rainfall and establishment strongly suggests that rainfall cannot be used, on its own, to determine the establishment sequence and the pattern of bush encroachment. The study suggests that natural developments responsible for establishment patterns and population dynamics of woody species are complex, and their effects are visible after an extensive period. Therefore, to understand these influential processes comprehensively, several seasons of observations and monitoring would be recommended. Future research on this particular topic should include more than one encroaching species, because this will provide a broader perspective on the encroachment patterns of bush communities. However, the focus should be on studying the influence of growth limiting factors such as soil and climatic impacts, as well as area-specific environmental factors on the growth of encroaching species, such as Acacia tortilis. Key words: Bush encroachment, dendrochronology, growth rings, tree age, savanna, stem circumference Note: The candidate and the supervisors are aware of the fact that the Acacia genus has been revised. However, in this dissertation, the genus and species Acacia tortilis is still used. Relevant changes will be used in future publications. / University of Limpopo’s Department of Agriculture and National Research Foundation