The area evaluated in this study was a continuous stretch comprising three vegetation formations: gallery forest, semideciduous seasonal forest and cerradão (woodland savanna). The aim of this study was to examine the tree community dynamics in a forest gradient-from gallery forest to cerradão-at Panga Ecological Station, in the city of Uberlandia, located in the state of Minas Gerais, Brazil. The study was based on data from a previous inventory of the continuous forest conducted in 211 permanent 10 × 10 m sample plots in eight parallel transect running perpendicular to Panga Creek. Trees with a diameter at breast height ≥ 4.77 cm were sampled in 1997, 2002 and 2007. With the exception of the cerradão, there was a net reduction in tree density over the studied period of ten years, because mortality rates were higher than the recruitment rates. The basal area increased during the period of the study, especially at cerradão. The mean mortality rate in the studied area was 2.64%.yr , respectively. In general, mortality rates and recruitment rates have increased during the two successive periods of measurement and showed an imbalance in favor of mortality for the semideciduous seasonal forest and the gallery forest. This fact, added to the low density and high basal area, suggest that there was a process of thinning in the tree community. However, at cerradão, there was an imbalance in favor of recruitment, with a consequent increase in density and basal area, indicating that the cerradão is in a construction phase, which was further favored by a decrease in the occurrence of fire and other anthropogenic disturbances. When the turnover rates are taken into consideration, the global dynamics of the study area over the ten years evaluated can be expressed as cerradão > semideciduous seasonal forest > gallery forest.

Studies report the forest expansion process toward open savanna areas; however, most of them were conducted by means of satellite images and aerial photographs. This study has investigated the forest expansion process through community dynamics over 15 years of permanent plots monitoring. The study was conducted at a forest continuum of three distinct phytophysiognomies (riparian forest, dry forest, and woodland savanna), sampling the trees with diameter at breast height C4.77 cm, distributed into 211 plots (10 m 9 10 m). Density and basal area were compared using a paired t test, and Shannon-Wiener diversity was determined through Hutcheson's t test. The number of dead and recruit trees, and basal area increment and decrement were compared among the phytophysiognomies using variance analysis, followed by Tukey's test. Dynamics rates were calculated for the interval of 15 years, as well as Jaccard and Morisita-Horn's similarity indices among phytophysiognomies. In woodland savanna, density and basal area increased and richness and diversity decreased, whereas in dry forest density decreased and richness and diversity increased. No changes in floristic parameters were observed for riparian forest. The similarity among phytophysiognomies increased over time due to advance of typical dry forests species toward woodland savanna and riparian forest; and local decrease in richness of typical savanna species in woodland savanna (decline of 13 species) and riparian species in the riparian forest (three species). From floristic analysis, our results support the dry forests expansion process toward woodland savanna and riparian forest, which seems to be strongly related to the control of fire and decrease in river flow, respectively.

No abstract

This study evaluated the impacts of water fl ow reduction in soil moisture and changes in the arboreal community in a riparian forest in Minas Gerais. Our hypothesis is that few years after river fl ow reduction can alter soil moisture and change tree community structure. We performed soil moisture analyses to confi rm reduction in soil moisture and a four-year-monitoring of the tree community structure in 1.1 ha of riparian forest. Soil moisture was reduced, especially during the dry season at the sector located near the original river fl ow. In this sector we found higher mortality and broken stems of living trees, strongly reducing basal area and causing a little reduction in trees density. This study highlights the strong impacts of dams' construction in the fl ora and water availability downstream from the dam.RESUMO -Mudanças na umidade do solo e na estrutura da fl oresta ripária após a construção de barragem. Este estudo avaliou os impactos da redução do fl uxo das águas do rio na umidade do solo e mudanças na comunidade arbórea pós-represamento em uma fl oresta ciliar em Minas Gerais. Nossa hipótese é que poucos anos após a redução do fl uxo do rio pode alterar a umidade do solo e, por consequência, mudar a estrutura da comunidade arbórea. Realizamos análises de umidade do solo para confi rmar a redução na umidade do solo e um monitoramento de quatro anos da estrutura da comunidade arbórea em 1,1 ha de mata ciliar. A umidade do solo foi reduzida, especialmente durante a estação seca no setor localizado próximo ao fl uxo original do rio. Neste setor encontramos maior mortalidade e fustes quebrados de árvores vivas, reduzindo fortemente a área basal e causando uma pequena redução na densidade de árvores. Este estudo destaca os fortes impactos da construção de barragens na fl ora e disponibilidade de água a jusante da barragem.Palavras-chave: dinâmica, modifi cações fl orísticas, represamento, mortalidade

As Florestas de Galeria (FG) estão sob intenso processo de antropização, reduzindo drasticamente seu potencial ecológico antes que se conheçam seus componentes bióticos e sua importância para a conservação dos recursos hídricos. Este estudo objetivou investigar a população de X. emarginata. Os indivíduos adultos foram quantificados e medidos em altura e DAP, em 62 parcelas de 10x10m. Arvoretas e plântulas foram quantificadas e tiveram as medidas de alturas e DAS aferidas em 2001 e 2002, em 20 parcelas sorteadas de 10x10m e 5x5m, respectivamente. Foram analisados: distribuição espacial (índice de Morisita); estruturas de altura e diâmetro (distribuição em classes e comparação das medidas nos dois anos por teste t pareado); crescimento em tamanho (diferença de medidas nos dois anos); e taxa de recrutamento e mortalidade. Foram registrados 1706 indivíduos em 2001 (432 plântulas, 734 arvoretas e 540 adultos) e 1007 em 2002 (359 plântulas e 648 arvoretas), com altas densidades. A distribuição foi agregada. Houve crescimento em quase todas as classes. A taxa de recrutamento foi de 0% (plântula) e 1,8% (arvoreta) e a taxa de mortalidade 19,7 % e 10,1%, respectivamente. A população de X. emarginata estudada pode estar sofrendo um processo de declínio na área de estudo, sendo necessário acompanhamento a longo prazo.