Increasing drought pressure under anthropogenic climate change may jeopardize the potential of tropical forests to capture carbon in woody biomass and act as a long-term carbon dioxide sink. To evaluate this risk, we assessed drought impacts in 483 tree-ring chronologies from across the tropics and found an overall modest stem growth decline (2.5% with a 95% confidence interval of 2.2 to 2.7%) during the 10% driest years since 1930. Stem growth declines exceeded 10% in 25% of cases and were larger at hotter and drier sites and for gymnosperms compared with angiosperms. Growth declines generally did not outlast drought years and were partially mitigated by growth stimulation in wet years. Thus, pantropical forest carbon sequestration through stem growth has hitherto shown drought resilience that may, however, diminish under future climate change.

As Florestas Estacional Decidual Aluvial e Submontana encontram-se ao longo de um gradiente topográfico com variações geomorfológicas e pedológicas. Para entender as variações das guildas ecológicas e do contingente geográfico das comunidades florestais em uma microbacia do rio Jacuí, no Rio Grande do Sul, foram alocadas 200 parcelas de 100 m², distribuídas em 40 pontos amostrais, com 5 parcelas cada, desde as cabeceiras de drenagem até a planície de inundação do referido rio. Em cada unidade amostral foram medidos e identificados todos os indivíduos lenhosos com diâmetro à altura do peito de ≥5 cm. A partir da amostra total, foi realizada uma análise de agrupamento de similaridade florística, resultando em três comunidades florestais distintas. Elas foram nomeadas de formações aluvial e submontana e área dominada por ambas as formações. Para a amostra total e dos grupos obtidos, foram determinadas as porcentagens de contribuição das espécies e indivíduos, por meio da classificação de guildas ecológicas de dispersão de diásporos e grupos ecológicos, além dos contingentes fitogeográficos. O contingente geográfico de composição das comunidades florestais foi dominado por espécies de ampla distribuição. Os padrões das guildas ecológicas entre os grupos foram distintos. Entretanto, todos os grupos apresentaram maior contribuição de espécies zoocóricas. Palavras-chave: Comunidades florestais; fitogeografia; similaridades florísticas; ecologia florestal.   Abstract Floristic composition and dispersal and regeneration strategies of woody species in Deciduous Seasonal Forests. The connected fragments of submontane and alluvial deciduous forests are present along the topographic gradient with large pedological and geomorphological variations. In order to understand the variations of ecological guilds and geographical contingent of forest community in a watershed, 200 plots of 100 m² divided into 40 sampling points with five plots each were distributed from the headwaters to the floodplain of the Jacuí River. In each sampling unit were identified and measured all woody plants with diameter at breast height ≥ 5 cm. From the total sample was performed a cluster analysis of floristic similarity, resulting in three forest communities. These were termed formation, submontane and alluvial, and the area dominated by both formations.For the total sample and the groups was determined the percentage contribution of species and individuals, by classification of ecological guilds of dispersal of seeds and regeneration and geographic quotas. The geographic contingent composition of forest communities was dominated by species of wide distribution. The patterns of ecological guilds were different between groups. However, all groups revealed higher contribution of zoocoric species. Keywords: Forest communities; phytogeography; floristic similarity; forest ecology.

Araucaria angustifolia (Bertol.) Kuntze is a native tree species of major importance in southern Brazil. It is a regional symbol due to its iconic shape and stature in the landscape; its wood was once economically important and its seeds are an important source of food for the fauna and are presently used in regional cuisine. Despite its importance and apparent abundance, the species is facing extinction mainly as a result of unregulated exploitation and deforestation. This study catalogued the remaining individuals in order to add to the body of knowledge available on A. angustifolia, a species that has become rare across its historic range. The circumference at breast height (1.30 m), the total height, and the tree volume were measured (3,529 araucarias). We catalogued trees with a large diameter measuring them in loco over three years involving a journey of more than 6,800 km. The volumes of these old trees are very large, ranging from 38.2 m³ to 106.6 m³. The largest A. angustifolia individual is located in the state of Santa Catarina and measures 3.25 m in diameter. The giant araucarias with > 2.00 m in diameter are rare and only 13 individuals could be found in southern Brazil; a priority action at the governmental level is to recognize and preserve these monumental trees and together with a need for a public policy of drawing up specific inventories of large trees.

O presente estudo foi realizado em Frederico Westphalen, no Estado do Rio Grande do Sul, com a instalação de 10 parcelas de 20x50 m. Em cada parcela foram levantadas todas as plantas com diâmetro a altura do peito (DAP) ≥ 5 cm, totalizando 1.461 indivíduos amostrados no hectare. A florística da área inclui 79 espécies distribuídas em 31 famílias e 69 gêneros. A família Fabaceae, com 14 espécies, foi a mais diversa, seguido por Myrtaceae (8), Meliaceae (6), Euphorbiaceae (5), Sapindaceae (5), Rutaceae (4) e Salicaceae (4). As espécies com maior valor de importância (VI) foram Gymnanthes concolor, Nectandra megapotamica, Trichilia claussenii e Chrysophyllum marginatum. Os índices de diversidade de Shannon e equabilidade de Pielou foram respectivamente 3,49 nats. ind.-1 e 0,79. Na análise de agrupamento de Twinspan foi contatado pela florística três subformações no fragmento, e destas, uma foi fisionomicamente distinta pelo estrato inferior, com o predomínio de espécies arborescentes (xaxim), enquanto as demais foram caracterizadas por espécies arbóreas, sendo as espécies, Trichilia claussenii e Gymnanthes concolor, as responsáveis pelo grande grupo fisionômico, que caracterizou a sucessão florestal em secundária avançada.

Loss of large trees due to indiscriminate timber cutting and opening of new areas for human use is a global problem. Brazil is well known for tree species richness within its extensive forested areas composed of various biomes. Giant trees are “key” to recognize the original forest structure. Decline of their populations in Brazil may be estimated by comparing data of the National Forest Inventory (NFI) with those of regional data and other surveys. In fact, Santa Catarina is the first state in Brazil to have currently completed its forest inventory. However, only few large trees were sampled systematically. Recognition of the maximum tree growth is important for their ecological management and tourism potential. Public policies for cataloging and management of these resources must be developed before it is too late.