Structural and other adaptation to long-term flooding by trees in Central Amazonia

Cross section discs were taken from 66 tree species at two sites in the Central Amazonian inundation forest, near Manaus (Brazil) and analysed macroscopically with respect to the occurrence and formation of growth zones. Dendroclimatological investigation and a succesfully applied dating survey using the 14C method (nuclear arms effect) showed, that trees in the igapó and várzea produce more or less distinct annual rings. The boundaries of the growth zones are marked mainly by marginal parenchyma bands and by the decreasing size and thickened walls of the fibre cells. These formations indicate deceleration, followed by suspension, of cambial activity as a reaction to unfavourable climatic conditions such as drought, low temperature or, in the present case, long term flooding. Adaptative strategies of trees to long term inundation are discussed. The formation of growth zones and the distinctiveness of the annual ring boundaries are related to defoliation behaviour, peculiar to each species

Diversity, abundance, and structure of tree communities in the Uluguru forests in the Morogoro region, Tanzania

Uluguru forests are globally recognized as important biodiversity hotspots, but anthropogenic pressure threatens their value. This study examined species diversity, abundance, and structure of trees in the Uluguru forests. All trees of diameter at breast height (DBH) ≥ 10 cm were inventoried in seven forests ranging from 3 to 995 ha in area. A total of 900 stems, 101 species and 34 families were inventoried. Fabaceae was the most speciose family. Ehretia amoena Klotzsch was the most abundant species with relative abundance of 9.22 %. The forests differed significantly in species richness (26–93 species ha−1), tree density (85–390 stems ha−1), basal area (3–24 m2 ha−1) and Shannon-Wiener diversity (2.50–4.02). Forest area was significantly and positively correlated with species richness (r = 0.92) and species diversity (r = 0.95). Tree density showed significant positive correlation with species richness (r = 0.80) and basal area (r = 0.85). Milawilila and Nemele forests had highest floristic similarity (0.55) followed by Kimboza and Kilengwe (0.54) while the rest had similarity coefficients of less than 0.50. Despite legislative protection, many forests remain at risk and therefore the possibility to conserve highly valuable tree species via enhanced protection or cultivation must be considered

Attaining the canopy in dry and moist tropical forests: strong differences in tree growth trajectories reflect variation in growing conditions

Availability of light and water differs between tropical moist and dry forests, with typically higher understorey light levels and lower water availability in the latter. Therefore, growth trajectories of juvenile trees—those that have not attained the canopy—are likely governed by temporal fluctuations in light availability in moist forests (suppressions and releases), and by spatial heterogeneity in water availability in dry forests. In this study, we compared juvenile growth trajectories of Cedrela odorata in a dry (Mexico) and a moist forest (Bolivia) using tree rings. We tested the following specific hypotheses: (1) moist forest juveniles show more and longer suppressions, and more and stronger releases; (2) moist forest juveniles exhibit wider variation in canopy accession pattern, i.e. the typical growth trajectory to the canopy; (3) growth variation among dry forest juveniles persists over longer time due to spatial heterogeneity in water availability. As expected, the proportion of suppressed juveniles was higher in moist than in dry forest (72 vs. 17%). Moist forest suppressions also lasted longer (9 vs. 5 years). The proportion of juveniles that experienced releases in moist forest (76%) was higher than in dry forest (41%), and releases in moist forests were much stronger. Trees in the moist forest also had a wider variation in canopy accession patterns compared to the dry forest. Our results also showed that growth variation among juvenile trees persisted over substantially longer periods of time in dry forest (>64 years) compared to moist forest (12 years), most probably because of larger persistent spatial variation in water availability. Our results suggest that periodic increases in light availability are more important for attaining the canopy in moist forests, and that spatial heterogeneity in water availability governs long-term tree growth in dry forests

Stand dynamics of the drought-affected floodplain forests of Araguaia River, Brazilian Amazon

Abstract Background The floodplain forests of Araguaia River, a clear-water river in the southeastern Amazon (Tocantins State, Brazil), are characterized by seasonal flooding up to 3.5 m height, low nutrient levels in the water, and seasonal drought periods of 4–5 months. Methods We studied the forest dynamics (tree diameter growth, tree mortality and recruitment) of this unique forest ecosystem over a 5-year period by repeated censuses in 12 permanent plots established along a flooding gradient. Results The cumulative basal area in the plots increased by 0.84 (±0.45) m2∙ha–1∙yr–1 (mean ±SD) in the annually-flooded (AF) plots in lower terrain and by 0.69 (±1.00) m2∙ha–1∙yr–1 in the higher non-annually flooded (NAF) plots, corresponding to an aboveground biomass increase of 0.81 (±0.57) and 0.69 (±1.58) Mg∙ha–1∙yr–1 in the AF and NAF plots, indicating a recent carbon sink in the biomass. Mean diameter growth rate was 1.8 (±0.44) mm∙yr–1 in the AF and 2.0 (±0.56) mm∙yr–1 in the NAF plots (corresponding to a coarse wood production of 1.53 (±1.29) and 2.02 (±0.52) Mg∙ha–1∙yr–1), indicating no flooding effect on radial growth. Mean mortality rates in the 5-year period were 1.9 (±0.37)%∙yr–1 in the AF plots and 1.8 (±0.87)%∙yr–1 in the NAF plots with no differences along the flooding gradient. Highest mortalities were registered in the AF plots for the 10–20 cm dbh class (2.4%∙yr–1), likely as a consequence of flooding, and in the NAF plots for the 40–50 cm dbh class (3.0%∙yr–1), probably mainly caused by ENSO-related droughts. Conclusions We conclude that these drought-affected tropical floodplain forests have a lower standing biomass and aboveground productivity than central Amazonian floodplain forests in more humid climates, and the imprint of the flooding gradient on stand dynamics is relatively weak, which may result from the lower flooding height and the interaction of flooding with low nutrient supply and periodic drought

Feeding of Triportheus angulatus (Spix & Agassiz, 1829) in the Camaleão lake, Manaus, Amazonas state, Brazil

Periodical flooding cause strong modifications in Central Amazonian floodplain. Periodical rising and decreasing of the water level influences abiotic and biotic factors of the aquatic environments. During the flooding season, there is a high feed availability, in contrast with dry season in which feed availability is at the lowest level. Limnological parameters also change seasonally. Oxygen concentrations vary both daily and seasonally, sometimes even showing hypoxic conditions. Despite these alterations, floodplain lakes are inhabited by several fish species, having the most diverse and abundant fish fauna among the Amazonian environments. This study focused on Triportheus angulatus feeding in temporal distribution in order to understand the influences of hydrological changes on individual size, diet composition and feeding even in low oxygen concentrations. In rising waters season, small individuals are predominant while the decreasing and the dry seasons there are mostly larger ones. There is a seasonal change on diet composition and this is related to feed type that is more available: during the rising, fishes eat mainly insects and zooplankton; in the flood season and drying season, seeds and fruits are predominant, and at the dry season they eat mainly insects. Feed ingestion was higher in the rising waters and mostly in the flood, and it was lower in the drying season. Feeding activity was not related with oxygen concentrations.As inundações periódicas na Amazônia Central causam profundas modificações no meio ambiente. A alternância dos períodos de cheias e secas tem influência nos fatores bióticos e abióticos do meio aquático. Na enchente e na cheia é alta a oferta de alimentos, ampliando o espectro alimentar que é restrito na seca. As variáveis limnológicas também sofrem modificações. As concentrações de oxigênio têm variações sazonais e diárias, às vezes com períodos de hipoxia. Apesar dessas alterações, os lagos de várzea são habitados por muitas espécies de peixes e estão entre os ambientes de maior abundância e riqueza de peixes na Amazônia. A distribuição temporal e a alimentação de Triportheus angulatus (Spix & Agassiz, 1829) foi estudada em um lago de várzea da Amazônia Central para entender a influência das modificações hídricas sobre o tamanho dos indivíduos, a composição da dieta e a ingestão dos alimentos mesmo em condições de baixas concentrações de oxigênio. Na enchente predominam os indivíduos menores, enquanto que na cheia, vazante e seca os maiores. Houve mudança sazonal na composição da dieta que foi relacionada com a disponibilidade de alimentos no ambientena enchente os peixes ingerem principalmente insetos e zooplâncton; na cheia e vazante frutos e sementes, e na seca insetos. O consumo de alimento foi alto na enchente e cheia, decrescendo na vazante e atingindo as menores quantidades na seca. A atividade alimentar, no período estudado, não foi influenciada pelas baixas concentrações de oxigênio existentes no lago