Notes on Oenocarpus (Palmae) in the Colombian Amazon

Five species ofOenocarpus from the Río Caquetá, in the Colombian Amazon, are discussed. Two of themOenocarpus simplex andOenocarpus makeru are described as new.Oenocarpus bacaba var.parvus is shown to be a synonym ofO. balickii; this species andO. minor are recorded for the first time in Colombia. Some comments on the poorly knownO. circumtextus are also given. The new findings support the inclusion ofJessenia inOenocarpus.     

Resource utilization and guild structure of small vertebrates in the Amazon forest leaf litter

Ten species of small vertebrates that occurred together in leaf litter of the Amazon tropical rainforest were studied during the dry season in Rondônia, western Brazil. This vertebrate assemblage consisted of two diurnal lizards, two diurnal frogs, one nocturnal frog, and five frog species that are active by day and night. All species feed on small invertebrates, primarily insects and arachnids. There are significant differences in prey types and sizes eaten, and overlap values among species are relatively low. Niche breadths vary from unity (extremely low) to high (> 9.0). A pseudocommunity analysis using two different algorithms indicated that structure exists in the prey resource matrix of the vertebrate assemblage. The zero structure of the community matrix contributes to the observed structure, i.e. prey items not taken by certain species are important in maintaining structure. Several well-defined feeding guilds are apparent, and the feeding guilds do not appear to follow taxonomic lines.     

The changing Amazon forest

Long-term monitoring of distributed, multiple plots is the key to quantify macroecological patterns and changes. Here we examine the evidence for concerted changes in the structure, dynamics and composition of old-growth Amazonian forests in the late twentieth century. In the 1980s and 1990s, mature forests gained biomass and underwent accelerated growth and dynamics, all consistent with a widespread, long-acting stimulation of growth. Because growth on average exceeded mortality, intact Amazonian forests have been a carbon sink. In the late twentieth century, biomass of trees of more than 10cm diameter increased by 0.62+/-0.23tCha-1yr-1 averaged across the basin. This implies a carbon sink in Neotropical old-growth forest of at least 0.49+/-0.18PgCyr-1. If other biomass and necromass components are also increased proportionally, then the old-growth forest sink here has been 0.79+/-0.29PgCyr-1, even before allowing for any gains in soil carbon stocks. This is approximately equal to the carbon emissions to the atmosphere by Amazon deforestation. There is also evidence for recent changes in Amazon biodiversity. In the future, the growth response of remaining old-growth mature Amazon forests will saturate, and these ecosystems may switch from sink to source driven by higher respiration (temperature), higher mortality (as outputs equilibrate to the growth inputs and periodic drought) or compositional change (disturbances). Any switch from carbon sink to source would have profound implications for global climate, biodiversity and human welfare, while the documented acceleration of tree growth and mortality may already be affecting the interactions among millions of species.     

Soil CO2 efflux in a tropical forest in the central Amazon

This study investigated the spatial and temporal variation in soil carbon dioxide (CO₂) efflux and its relationship with soil temperature, soil moisture and rainfall in a forest near Manaus, Amazonas, Brazil. The mean rate of efflux was 6.45±0.25 SE μmol CO₂ m^?2s^?1 at 25.6±0.22 SE°C (5 cm depth) ranging from 4.35 to 9.76 μmol CO₂ m^?2s^?1; diel changes in efflux were correlated with soil temperature (r²=0.60). However, the efflux response to the diel cycle in temperature was not always a clear exponential function. During period of low soil water content, temperature in deeper layers had a better relationship with CO₂ efflux than with the temperature nearer the soil surface. Soil water content may limit CO₂ production during the drying‐down period that appeared to be an important factor controlling the efflux rate (r²=0.39). On the other hand, during the rewetting period microbial activity may be the main controlling factor, which may quickly induce very high rates of efflux. The CO₂ flux chamber was adapted to mimic the effects of rainfall on soil CO₂ efflux and the results showed that efflux rates reduced 30% immediately after a rainfall event. Measurements of the CO₂ concentration gradient in the soil profile showed a buildup in the concentration of CO₂ after rain on the top soil. This higher CO₂ concentration developed shortly after rainfall when the soil pores in the upper layers were filled with water, which created a barrier for gas exchange between the soil and the atmosphere.     

Macrofungal diversity in Colombian Amazon forests varies with regions and regimes of disturbance

Here we present the results of fungal biodiversity studies from some selected Colombian Amazon forests in relationship to plant biodiversity and successional stages after slash and burn agriculture. Macrofungal diversity was found to differ between forests occurring in two regions (Araracuara vs Amacayacu) as well as between flooded forests and terra firme forests in the Amacayacu region. Macrofungal biodiversity differed between regeneration states of different age in the Araracuara region. Suitable substrates, especially dead wood that occurred as a result of recent slash and burn agriculture, resulted in the formation of many sporocarps of wood-inhabiting species. Putative ectomycorrhizal species were found in a dipterocarp forest. Fifty two percent of the macrofungal species could not be identified to the species level, but could be assigned to a genus, and it is likely that a significant portion of these represent species new to science. Long term studies are needed to obtain a comprehensive and complete understanding of the diversity and functioning of mycobiota in Amazon forest ecosystems.     

Ecological aspects of swidden cultivation among the Andoke and Witoto Indians of the Colombian Amazon

The investigation of crop and soil-crop conditions among Andoke and Witoto cultivators in southeast Colombia is used as a basis for assessing Geertz' (1963) model of swidden cultivation. In this respect, the extent to which maniocdominated swiddens in the study area simulate the structure and composition of the forest climax community is questioned. As Geertz (1963) indicates, an initial nutrient boost for crop cultivation results from the preliminary burning of forest debris, but weed competition, rather than progressive loss of soil fertility, is reported to be the primary cause of abandoning manioc cultivation after 2–3 years. While the Andoke and Witoto crop system remains adaptive at the individual field level, particularly in its constituent species, its fundamental adaptation is considered to be its integration into the broader field and fallow system that juxtaposes crop production with extended periods of forest regeneration.     

Valuing the rain forest: Economic strategies by small-scale forest extractivists in the Amazon estuary

The current interest in non-timber forest products as an economic option for the Brazilian Amazon represents a radical departure from the policies that have guided development in the region during recent decades. Despite this interest, little is currently known about the forms of resource management or economic strategies practiced by populations dependent on such resources. In this study, we measured the annual income and expenditures of ten households on Combu Island, located in the Amazon estuary near the major port city of Belém; in addition, we documented local uses and management of natural resources on the island Average annual income per household was found to be over U.S. $4000, derived primarily from the harvest and sale of non-timber forest products. The results of this study show that the combination of proximity to a major market and appropriate resource management can lead to high and apparently sustainable economic returns.Formerly Senior Researcher at the Museu Paraense Emílio GoeldiFormerly Student Fellow at the Museu Paraense Emílio Goeldi     

Gallery forest types and their environmental correlates in a Colombian savanna landscape

Savanna regions may contain significant areas of forest, usually in riparian environments. We described forest composition and quantified environmental variables for 80 plots in the watershed of the Yucao River (2550 km²), a tributary to the Meta River (Orinoco basin) in the eastern plains of Colombia. The total sampled area of 3.2 ha contained 147 tree species (110 genera and 45 families) with diameter at breast height >5 cm. The families represented by most species were Leguminosae (15 species), Arecaceae (11 species), Rubiaceae (9), Chrysobalanaceae (7), Euphorbiaceae (7), Melastomataceae (7) and Myrtaceae (7). Although most of the tree species have wide distribution ranges in humid neotropical forests, and few are endemic to the region, comparison with other neotropical forests suggests that the combination of taxa is characteristic for neotropical gallery forests. Cluster analysis allowed the definition of five forest types. They show important differences in a number of environmental variables, especially those related to inundation regimes and soil properties. Canonical correspondence analysis indicates good correlation of the first ordination axis with the size of the stream with which the forest is associated, the height to which the water rises during floods and variables related to soil fertility. The second ordination axis differentiates between soils with high or low water content in the dry season, high or low organic matter content and low or high bulk density. The results demonstrate the role of spatial variability and interactions of floodplain morphology, hydrological regime, and soil properties in structuring this important riparian community.     

Structure and dynamics of the mangrove forest in the Rancheria River delta, Colombian Caribbean

We registered seedling survival and biomass increase for Rhizophora mangle L., Avicennia germinans L. and Laguncularia racemosa (L.) Gaertn. f, main mangrove species in the Rancheria River delta, Colombia. Only seedlings of R. mangle were found to survive. We also measured maximum rate of litterfall. We estimated annual litterfall through interpolation within an exponential regression performed with maximum and annual litterfall data published in other sources; the value of annual litterfall for the area was estimated to be 12.9 mgha(-1)y(-1). We found a 7.4 mgha(-1)y(-1)(-1) increase in biomass. Litterfall constitutes the larger fraction of the 20.2 mgha(-1)y(-1) productivity of this mangrove. We believe this is a very high value for a forest under unfavorable natural and human conditions, such as high seasonality and continuous use of the forest to feed goats and sheep. We consider that the high productivity is a response to both natural and anthropogenic stress.     

Phytomass structure of natural plant communities on spodosols in southern Venezuela: The tall Amazon Caatinga forest

The phytomass structure of the evergreen lowland forest vegetation (Tall Amazon Caatinga) supported by tropaquods near San Carlos de Rio Negro, Federal Amazon Territory of Venezuela was studied in 13 10 m× 10 m plots. The plots were laid out subjectively to cover a low topographical gradient along which the forest on tropaquod is grading into a low woodland (Bana, or Low Amazon Caatinga). The phytomass was estimated by destructive sampling. The total living phytomass (dry matter) varies between 199 t/ha in one plot including a natural gap, to 822 t/ha in a plot located near a blackwater creek draining the 10 ha study site in which the vegetation was surveyed. Dead aboveground phytomass (dry matter) varies between 2 and 37 t/ha. The average leaf area index is 5.1. Leaves are sclerophyllous. The mesophyll leaf size class is dominant. Compared with other Amazonian rainforests the Tall Amazon Caatinga is lower in aboveground phytomass and wood volume, respectively, but its root average proportion is 2.4 times greater. One hundred and thirty species (dbh≥1 cm) were recorded in all plots. 14–45 species per plot composed the aboveground phytomass. 20 species each had a relative frequency of 50 or more percent. 7 of these species plus 10 less frequent ones each represented 10 or more percent of the basal area in at least 1 plot. Sixteen species each contributed 10 or more percent to the aboveground phytomass, in at least 1 plot. There is only 1 species (Micranda sprucei, Euphorbiaceae) which was observed in all plots. Its contribution to basal area and aboveground phytomass is considerable. M. sprucei is also the dominant species of the top canopy layer. Eperua leucantha, Caesalpiniaceae, is subdominant.     

Soil characteristics influence species composition and forest structure differentially among tree size classes in a Bornean heath forest

Plant and Soil - To investigate how different tree species affect the composition of SOM and its mineralization in boreal forest ecosystems. We used pyrolysis GC–MS for molecular-level...     

The relationship between soil variables and leafcutter ant (Atta sexdens) nest distribution in the Colombian Amazon

We determined the relationships between several soil variables and the distribution of leafcutter ant (Atta sexdens) nests on the Colombian shore of the Amazon River. Seven habitats were identified in which nests were consistently present or absent. Soil samples for physiochemical analysis were taken near nest sites in three habitats where nests were present and from randomly selected sites in four other habitats where nests were absent. Percent canopy cover and soil resistance were also measured for each site. Almost all of the 20 identified soil variables were significantly different between habitats with and without A. sexdens nests, and the values of all variables were heterogeneous between the seven habitats. The most important variables correlated with leafcutter ant nest presence were percent canopy cover (positively), percent silt, soil resistance at 0–20 cm, and pH (all negatively). We deduced a binomial and a multinomial logistic regression which showed how each of these variables was related to nest presence and habitat, respectively. We describe how each variable may affect leafcutter ant nest development, especially in its earliest stages, and therefore influences nest distribution. We propose a suitable-soil hypothesis which, complementary to the palatable forage hypothesis, aims to explain patterns in leafcutter ant nest demography based on soil conditions.     

Species richness and distribution of understorey bryophytes in different forest types in Colombian Amazonia

Abstract

The first bryophyte survey results from Colombian Amazonia are presented. Bryophyte species, differentiated into mosses and liverworts, and further into four life-form classes, were sampled in 0.1-ha plots. These plots were distributed over four landscape units in the middle Caquetá area: floodplains, swamps, terra firme forests and white-sand areas. The total numbers of bryophyte species in the units were 50, 45, 45 and 32, respectively. The plots in floodplains and swamps were richer in moss species than the terra firme and white-sand plots, suggesting that coexistence of many moss species is favoured by high humidity. Moss species with fan life-forms preferred floodplains. On the other hand, liverwort species richness was highest in white-sand plots, which suggests that light incidence controls liverwort species-richness, perhaps more than humidity. All plots from the floodplain of the Caquetá River differed remarkably in species composition (of both mosses and liverworts) from the other landscape units. This may be due to the unique properties of this varzea system where, during yearly flooding events, soil, dead logs and stems are covered with a fresh layer of nutrient-rich fine silt, enhancing the surface for colonization and improving the conditions for productive bryophyte growth compared with elsewhere in the middle Caquetá area.     

Pollination of Bactris (Palmae) in an Amazon forest

Phenology, inflorescence behavior, and pollination of 10 sympatric taxa ofBactris were studied in a lowland Amazon forest. Taxa flowered over an eight month period during the rainy season and early dry season, but individual taxa flowered for one to a few months. Related taxa had mostly non-overlapping flowering periods. Inflorescence behavior was similar for all taxa, with nocturnal pistillate anthesis and temperature elevation, followed 24 hours later by rapid, nocturnal staminate anthesis. Pollinators of all taxa were small weevilsPhyllotrox (Curculionidae) and nitidulidsColopterus (Nitidulidae), although various other insect visitors were recorded. Large numbers ofPhyllotrox were recorded on inflorescences, but weevil sex ratios were highly skewed.     

Gaseous and fluvial carbon export from an Amazon forest watershed

The transfer of carbon (C) from Amazon forests to aquatic ecosystems as CO₂ supersaturated in groundwater that outgases to the atmosphere after it reaches small streams has been postulated to be an important component of terrestrial ecosystem C budgets. We measured C losses as soil respiration and methane (CH₄) flux, direct CO₂ and CH₄ fluxes from the stream surface and fluvial export of dissolved inorganic C (DIC), dissolved organic C (DOC), and particulate C over an annual hydrologic cycle from a 1,319-ha forested Amazon perennial first-order headwater watershed at Tanguro Ranch in the southern Amazon state of Mato Grosso. Stream pCO₂ concentrations ranged from 6,491 to 14,976 ??atm and directly-measured stream CO₂ outgassing flux was 5,994 ± 677 g C m^?2 y^?1 of stream surface. Stream pCH₄ concentrations ranged from 291 to 438 ??atm and measured stream CH₄ outgassing flux was 987 ± 221 g C m^?2 y^?1. Despite high flux rates from the stream surface, the small area of stream itself (970 m², or 0.007% of watershed area) led to small directly-measured annual fluxes of CO₂ (0.44 ± 0.05 g C m² y^?1) and CH₄ (0.07 ± 0.02 g C m² y^?1) per unit watershed land area. Measured fluvial export of DIC (0.78 ± 0.04 g C m^?2 y^?1), DOC (0.16 ± 0.03 g C m^?2 y^?1) and coarse plus fine particulate C (0.001 ± 0.001 g C m^?2 y^?1) per unit watershed land area were also small. However, stream discharge accounted for only 12% of the modeled annual watershed water output because deep groundwater flows dominated total runoff from the watershed. When C in this bypassing groundwater was included, total watershed export was 10.83 g C m^?2 y^?1 as CO₂ outgassing, 11.29 g C m^?2 y^?1 as fluvial DIC and 0.64 g C m^?2 y^?1 as fluvial DOC. Outgassing fluxes were somewhat lower than the 40?C50 g C m^?2 y^?1 reported from other Amazon watersheds and may result in part from lower annual rainfall at Tanguro. Total stream-associated gaseous C losses were two orders of magnitude less than soil respiration (696 ± 147 g C m^?2 y^?1), but total losses of C transported by water comprised up to about 20% of the ± 150 g C m^?2 (±1.5 Mg C ha^?1) that is exchanged annually across Amazon tropical forest canopies.     

Seven new genera of dorylaimid nematodes from Colombian rain forest

Summary New genera described from soil in Colombian rain forest are Fuscheila (Thornenematidae), Capilonchus (Tylencholaiminae, Tylencholaimidae), Caveonchus (Tyleptinae, Leptonchidae), Coronatyleptus (Belonenchinae, Leptonchidae), Promumtazium (Mumtaziinae, Tylencholaimidae), Tantunema (Thorniinae, Tylencholaimidae) and Zalophidera (Xiphinemellinae, Tylencholaimidae). 12 new species belonging to these genera described and illustrated are: Fuscheila citrifera (type species), F. godmanae, Capilonchus lineatus (type-species), Caveonchus colombicus (type species), C. brevisaccus, Coronatyleptus barbarae, C. curvus, C. robustus, Promumtazium pyxidorum (type species), Tantunema bothriocephalum (type species), Zalophidera tylocephala (type species) and Z. idiostoma. Caveonchus saccatus (Goseco, Ferris & Ferris, 1981) n. comb. and Coronatyleptus coronatus (Siddiqi & Khan, 1965) n. comb. (type-species) are made for Basirotyleptus saccatus and B. coronatus, respectively. The composition of the families Leptonchidae and Tylencholamidae is discussed and Leptonchoidae Thorne, 1935 (Ferris, 1970) is made a junior synonym of Tylencholaimoidea Filipjev, 1934 (n.rank). ac]19810621     

15N natural abundance in forest and pasture soils of the Brazilian Amazon Basin

The natural abundance of ¹⁵N was examined in soil profiles from forests and pastures of the Brazilian Amazon Basin to compare tropical forests on a variety of soil types and to investigate changes in the sources of nitrogen to soils following deforestation for cattle ranching. Six sites in the state of Rondônia, two sites in Pará and one in Amazonas were studied. All sites except one were chronosequences and contained native forest and one or more pastures ranging from 2 to 27 years old. Forest soil ¹⁵N values to a depth of 1 m ranged from 8 to 23 and were higher than values typically found in temperate forests. A general pattern of increasing ¹⁵N values with depth near the soil surface was broadly similar to patterns in other forests but a decrease in ¹⁵N values in many forest profiles between 20 and 40 cm suggests that illuviation of ¹⁵N-depleted nitrate may influence total soil ¹⁵N values in deeper soil where total N concentrations are low. In four chronosequences in Rondônia, the ¹⁵N values of surface soil from pastures were lower than in the original forest and ¹⁵N values were increasingly depleted in older pastures. Inputs of atmospheric N by dinitrogen fixation could be an important N source in these pastures. Other pastures in Amazonas and Pará and Rondônia showed no consistent change from forest values. The extent of fractionation that leads to ¹⁵N enrichment in soils was broadly similar over a wide range of soil textures and indicated that similar processes control N fractionation and loss under tropical forest over a broad geographic region. Forest ¹⁵N profiles were consistent with conceptual models that explain enrichment of soil ¹⁵N values by selective loss of ¹⁴N during nitrification and denitrification.