Periodicidade dos anéis de crescimento de Araucaria angustifolia no nordeste do Rio Grande do Sul

48

Climatic signals on phenological patterns among tree species in a subtropical forest community

The study of vegetative and reproductive phenophases of plants is critical for understanding aspects related to plant behavior in different environments. In the tropics, there is a gap of understanding related to plant phenology since the theoretical framework on the topic has been built from perspectives of the temperate region. Furthermore, there are few studies in tropical regions influenced by anthropic conditions, which may be important for understanding these issues in the face of future climate scenarios. This study aimed to describe the vegetative and reproductive phenology of trees in an urban subtropical forest community and to test the influence of climatic variables on the tree community. In an urban forest fragment in Rio Grande do Sul, Brazil, eight individuals of locally dominant species were monitored: Allophylus edulis, Casearia sylvestris, Guarea macrophylla, Mimosa bimucronata, Myrsine coriacea, Myrsine umbellata, Schinus glandulosum, and Schinus terebinthifolia. The monitoring occurred every two weeks, for two years, with the recording of the presence of leaf flushing, leaf shedding, flowering, and fruiting phenophases for each tree. The seasonality of the species was tested using the Rayleigh test. We described the common pattern of community phenological activity by a Principal Component Analysis. Finally, we correlated the common patterns of each phenophase in the community with climatic variables of total precipitation, average temperature, and day length. All species showed a non-uniform phenological pattern for the evaluated phenophases despite the variable intensity. We evidenced common patterns for the community only for the vegetative phenophases. The reproductive phenophases of flowering and fruiting present themselves independently among species in the community. Finally, we identified influences only of temperature and day length on the vegetative phenophases

Growth rings of Araucaria angustifolia (Bertol.) O. Kuntze : fundamentals of dendroecology in subtropical moutain ecosystems in Brazil

Determinadas espécies arbóreas apresentam ciclos anuais de crescimento e dormência, registrados no lenho por conspícuas estruturas anatômicas – os anéis de crescimento. Nessas árvores pode-se determinar a idade e taxas de crescimento, com resolução calendária anual, através da análise temporal dos anéis de crescimento (dendrocronologia), bem como estudar a variação dessas estruturas segundo as condições ambientais (dendroecologia). Pesquisas recentes têm descrito anéis de crescimento anuais num grande número de espécies tropicais e subtropicais. A exemplo do que ocorre em zonas temperadas e áridas, o desenvolvimento da dendroecologia pode contribuir substancialmente ao conhecimento da dinâmica do clima e da vegetação em ecossistemas tropicais e subtropicais. Nesta tese eu reviso e desenvolvo estudos dendroecológicos em biomas brasileiros, principalmente, em ecossistemas subtropicais montanos, visando solidificar a dendroecologia no país. Segundo ampla revisão bibliográfica, estudos relacionados à dendroecologia nos biomas brasileiros, em sua maioria, versam sobre a anatomia e periodicidade de formação de anéis de crescimento na flora; poucos efetivamente relacionam séries anuais de anéis de crescimento com variações do ambiente. As pesquisas estão concentradas em biomas florestais, notadamente na Amazônia. No intuito de facilitar estudos futuros, apresento uma compilação de 124 espécies que formam anéis anuais. Pesquisas inéditas sobre anéis de crescimento em Araucaria angustifolia, espécie típica de formações florestais e campestres em regiões montanas do sul e sudeste do Brasil, comprovam seu potencial dendroecológico. Através de análise da atividade cambial demonstro que esta espécie forma anéis de crescimento anuais, relacionados à variação sazonal de temperatura e fotoperíodo. Estudando séries temporais de largura de anéis de crescimento verifiquei a existência de padrões regionais de crescimento, relacionados à variação interanual do clima, principalmente da temperatura. Regionalmente, A. angustifolia parece sensível a déficit hídrico em Dezembro e Janeiro, bem como responde de forma complexa às condições térmicas em Maio e Junho. Padrões de crescimento divergente entre árvores de campo e de floresta podem estar relacionados ao regime de queimada da vegetação campestre, por sua vez, moderado pela precipitação no mês de ignição de queimadas (Agosto).Certain tree species present annual cycles of growth and dormancy, imprinted in wood as conspicuous anatomical structures – the growth rings. Temporal analysis of annual growth rings (dendrochronology) allows the determination of tree age and growth rate, with calendar year resolution, and to study long-term relationship between tree-growth and environmental conditions (dendroecology). Recent studies have found annual growth rings in many tropical and subtropical species. As in temperate and arid zones, dendroecological investigations may contribute for understanding the dynamics of climate and vegetation in tropical and subtropical ecosystems. Here, I review and develop dendroecological studies in biomes of Brazil, aiming to support further advances. According to a broad literature review, dendroecological studies in Brazilian Biomes have focused mostly on anatomy and periodicity of growth ring formation; few of them relate growth ring time-series to environmental conditions. The studies are concentrated in forested biomes, noticebly in Amazonia. In order to assist future studies I present a compilation of 124 species that produce annual growth rings. Novel studies on Araucaria angustifolia, a typical conifer growing in forest and grassland ecosystems of south and southeast Brazilian highlands, confirm its dendroecological potential. By means of cambium activity examination I show that this species produces annual growth rings, related to seasonal variations of temperature and photoperiod. Analyses of ring-width time series revealed regional growth patterns related to inter-annual climate variations. In a regional extent, A. angustifolia trees are, probably, sensitive the water deficit in December and January, as well respond to thermal conditions of May and June, in a complex manner. Divergent patterns between grassland and forest trees may be related to grassland fire regimes, moderated by rainfall during the fire ignition period (August)

Heraldo de Zamora : Diario de la tarde. Defensor de los intereses morales y materiales de la provincia: Siglo II Año XLVI Número 14471 - 1942 Mayo 12

Copia digital. Madrid : Ministerio de Cultura. Subdirección General de Coordinación Bibliotecaria, 200