Nutrient dynamics within amazonian forests

Summary Relationships between fine root growth, rates of litter decomposition and nutrient release were analysed in a mixed forest on Tierra Firme, a Tall Amazon Caatinga and a Low Bana on podsolized sands near San Carlos de Rio Negro. Fine root growth in the upper soil layers (root mat+10 cm upper soil) was considerably higher in the Tierra Firme forest (1117 g m^-2 yr^-1) than in tall Cattinga (120) and Bana (235). Fine root growth on top of the root mat was stimulated significantly by added N in Tall Caatinga and Low Bana forests, by P in Tierra Firme and Bana forests, and by Ca only in the Tierra Firme forest. Rate of fine root growth in Tierra Firme forest on fresh litter is strongly correlated with the Mg and Ca content of litter. Rate of litter decomposition was inversely related to % lignin and the lignin/N ratio of litter. Litter contact with the dense root mat of the Tierra Firme increased rates of disappearance for biomass, Ca and Mg as compared with litter permanently separated or lifted weekly from the root mat to avoid root attachment. Nitrogen concentration of decomposing litter increased in all forests, net N released being observed only in Caryocar glabrum and Aspidosperma megalocarpum of the Tierra Firme forest after one year of exposure. Results emphasize the differences in limiting nutrients in amazonian forest ecosystems on contrasting soil types: Tierra Firme forests are particularly limited by Ca and Mg, while Caatinga and Bana forests are limited mainly by N availability.     

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.     

Phytomass structure of natural plant communities on spodosols in southern Venezuela: the Bana woodland

Bana, or Low Amazon Caatinga is an evergreen sclerophyllous woodland. It occurs on bleached quartz sands in the lowlands of SW Venezuela, where it occupies relatively small ‘islands’ amidst Tall Amazon Caatinga which is exclusively developed on tropaquods. There is an outer vegetation belt about 20 m in width in which trees over 10 m in height occur (Tall Bana); its structure and floristic composition resemble Tall Amazon Caatinga. Low Bana (maximum tree height usually below 5 m) follows next. The central part is occupied by Open Bana in which even lower trees are very widely spaced. Destructive phytomass sampling was carried out for chemical analyses in seven plots along a 150 m line across the zonation. The total dry matter of living plants including roots of Tall Bana (30–32 kg/m²) compares rather well with 41 kg/m² in Tall Amazon Caatinga. This is only 9–14 kg/m² in Low Bana, and 4–6 kg/m² in Open Bana. The average root % of total phytomass increases from 41% in Tall Bana to 63% in Low Bana, and is 88% in Open Bana. Average total dry dead above-ground phytomass (including standing trees and stumps) declines from 1 kg/m² in Tall Bana to 0.2 kg/m² in Open Bana. An accumulation of dead matter in Low and Open Bana, relative to the above-ground phytomass of living plants, is noted and this contrasts with the general absence of raw humus in the soil. Eighty-two species of woody plants (dbh≥1 cm) were recorded on the total plot area (640 m²); 90% of the species are also known to occur in Tall Amazon Caatinga. The species number declines from 59 in Tall Bana to 18 in Open Bana. Mesophylls sensu strictu dominate in Tall Bana, while notophylls are dominant in Low and Open Bana. Herbaceous species are less numerous: most of them belong to the Araceae, Bromeliaceae, Orchidaceae, Droseraceae, Eriocaulaceae and Xyridaceae.     

Nutrient dynamics within amazonian forest ecosystems

Summary A comparative analysis on the rate of fine litterfall and its associated nutrient fluxes was carried out in a mixed forest on Tierra Firme, a tall Amazon Caatinga and a Bana on podsolized sands near San Carlos de Rio Negro. There was seasonality in leaf fall and total litterfall in mixed forest and tall Amazon Caatinga forest but no definite trend in the Bana. Litterfall curves were significantly correlated among sites indicating common regulating factors in the three forests. Leaf litter from mixed forest on Tierra Firme was richer in N with extremely low Ca and Mg concentrations; tall Amazon Caatinga litter had higher P and Mg concentration, while Bana litter was low in N but K concentration was twice as high as in the other two forests. Annual fine litterfall in Tierra Firme mixed forest was nearly 4 times higher than in Bana, But N flux was 10 times higher, while Ca and Mg fluxes were similar. Tall Amazon Caatinga had Ca and Mg fluxes in litterfall 2–3 times higher than the other two forests. Within-stand efficiency of nitrogen, calcium and magnesium use, as measured by biomass/nutrient ratios, differentiates Tierra Firme from Caatinga and Bana forest: Tierra Firme has the lowest N, but the highest Ca and Mg use efficiencies. Higher P use efficiency was measured in Bana followed by Tierra Firme and Caatinga; while Tierra Firme and Caatinga showed similar higher K use efficiencies than Bana. N/P ratios indicates that Tierra Firme forest is limited by P availability, while low N availability predominates in Caatinga. Bana appears limited by both N and P. These differences probably relate to variations in degree of sclerophylly and leaf duration which determine leaf nutrient concentrations in the ecosystems studied.     

Phosphorus and nitrogen status in soils and vegetation along a toposequence of dystrophic rainforests on the upper Rio Negro

Amazon forests along a toposequence at San Carlos de Rio Negro (Venezuela) show distinct nutrient limitations depending on slope position. Soils were collected by genetic horizons and analysed to provide information on the relationships between soil P and N status and the nutrition of natural forest at three locations along the toposequence. The upper-slope tierra firme sites had total P concentrations between 100 and 200 g g^–1 in the mineral soil fines and between 700 and 1100 g g^–1 in lateritic nodules. Hyphae were seen to explore lateritic nodules and may contribute to P nutrition. Total P in the mineral soil of the lower slope ranged from only 3 to 130 g g^–1. In both the organic mats of the tierra firme and the humic horizon at the lower-slope tall Amazon caatinga site, 50–60% of the P was in inorganic forms, which, in the absence of P-fixing mineral soil, maintain high levels of plant-available P. As a result, the litter mats and humic horizon accounted for over 70% of the total available P in these soils. The proportion of available P increased, and P sorption decreased, downslope, supporting ecological studies which found that tall Amazon caatinga was least P-limited. Soil N and C levels show a maximum at the mid-slope and a minimum at the lower slope. Distributions of biomass C, N and P closely follow those of soil C, N and available (but not total) P along the slope.     

Woody life-form composition and association on rainfall and soil fertility gradients in Ghana

The hypothesis that treelets/shrubs are more sensitive than trees to drought and low soil fertility was tested by analysing species densities (species per unit area) in 155 tropical forest plots (0.0625 ha) in Ghana, West Africa. Species densities of both life forms decreased with increasing dryness and with increasing soil fertility, which were correlated. Goodness of fit tests detected species preferences for four combinations of rainfall (dry: <1500 mm yr^-1, wet: 1500 mm yr^-1) and soil fertility (two classes based on a composite variable with high weightings for total exchangeable bases and pH), and a meta-analysis of these results compared life forms. The results contradicted the hypothesised response of life forms in two ways: (i) species densities of treelets/shrubs were comparably or relatively less reduced by dry conditions than were tree species densities, and (ii) treelet/shrub species did not show a more frequent preference for wet or fertile sites than did tree species. Light availability and rooting depth are discussed as explanations for the sensitivity of understorey plants to water and nutrient stress, and for the data's failure to support the hypothesis.     

Photosynthesis in an Australian rainforest tree,Argyrodendron peralatum,during the rapid development and relief of water deficits in the dry season

Summary Rates of apparent photosynthesis were measured in situ at five positions between the upper crown and a lower branch of a 34 m tall Argyrodendron peralatum (F.M. Bailey) H.L. Edlin ex I.H. Boas tree, and on an understorey sapling of the same species growing in a northern Australian rainforest. At the end of the dry season, rapid reductions in photosynthetic rates occurred in the upper crown within three days after a rain event, but changes in the lower crown and the sapling were less marked. Complete recovery of photosynthesis followed a second rain event. At high photon flux densities, stomatal conductance to water vapour decreased in a curvilinear fashion as the vapour pressure difference between leaf and air increased. Apparent photosynthesis was linearly related to stomatal conductance on the first clear day after each rain event, but there was no relationship between these parameters at the end of a brief natural drying cycle. Under conditions of adequate water supply, stomatal conductances of both upper crown and understorey leaves increased linearly with increasing photon flux density up to about 300 mol m^-2 s^-1. During water deficits, stomatal conductances in leaves from the understorey increased much more rapidly at very low photon flux densities than did conductances in leaves from the upper canopy.     

Structure and dynamics of a tropical dry forest in Ghana

Forest under low rainfall (averaging 745 mm yr^-1) on the Shai Hills in S.E. Ghana has redeveloped following cessation of farming in the 1890s. Forest stature is low, with a canopy at about 11 m, principally of three species, Diospyros abyssinica, D. mespiliformis and Millettia thonningii. Drypetes parvifolia and Vepris heterophylla are common understorey trees. Twelve species of woody liane were recorded. Species of thicket vegetation in the area were also present at low density. Most species are evergreen.Tree mortality averaged 2.3% yr^-1 and exceeded recruitment (1.5% yr^-1). Differences between species in mortality and recruitment were pronounced: canopy species showed a small decline in density; understorey species increased markedly and the thicket species declined. Seed production was very variable, but seedling establishment was very poor for all species. Seedling mortality was high (11% yr^-1) especially for small seedlings. These population trends probably represent the latter stages of succession of forest regrowth after farming about 100 years ago.Compared with tropical rain forest, Shai Hills forest has similar relative tree diameter growth (1–3.5% yr^-1), mortality and recruitment rates, and small-litter fall (5.52 t ha^-1 yr^-1).Shai Hills forest differs from rain forest by its short stature, relatively few (evergreen) tree species, poor regeneration from seed, high soil nutrient status and low rainfall. Similar forests have been reported in east Africa and in parts of New Guinea.Abbreviations dbh diameter at breast height (1.3 m) - gbh girth at breast height died May 1984     

Lowland floristic assessment of Pico da Neblina National Park,Brazil

Pico da Neblina National Park, located in north-western Amazonia,Brazil, is characterized by considerable habitat diversity resulting from anorographic zonation of vegetation (from 100 to 3,014 m above sealevel) and a mosaic pattern of soil types with lowland primary tropicalrainforest being the predominant ecosystem. A tree inventory of the lowlandareas of the Park was conducted as part of an ecological study of primates. Twohectares of forest were inventoried within the limits of a 500 hectare studysite. There were 1569 trees with diameter at breast height 10 cm in the sample (minimum of 229 species in 45 families). Thetree species Eperua leucantha and Hevea cf.brasiliensis dominated the forest accounting for 29% of thesampled trees. Three forest types were represented: chavascal, terra firme andcaatinga. Caatinga was the least diverse forest (H = 0.9), andterrafirme the most diverse (H = 1.5). Low diversity in caatinga wasassociated with high species dominance by Eperua leucantha, Micrandrasprucei and Hevea cf. brasiliensis whichtogether accounted for 66% of all sampled trees in one caatinga plot.Compared to Amazonian forests elsewhere, the ranking order of plant families inPico da Neblina was peculiar in that Leguminosae sensulatuand Euphorbiaceae dominated the sample accounting for 52% of all markedtrees. Such families were represented by few tree species, all of which werecharacterized by dry, large-seeded sclerocarpic fruits. The consequentlow availability of fleshy fruits in the forest is suggested as a possiblecontributing factor to the observed low abundance and diversity of primates inthe lowlands of Pico da Neblina.     

The ecology of very small-seeded shade-tolerant trees and shrubs in lowland rain forest in Singapore

A study was made in Bukit Timah Nature Reserve of niche differentiation among 11 woody species that have very small seeds (22–460 µg) and establish in deep shade, i.e., where the indirect site factor (isf) under cloudy conditions is 2%, and one taxonomically related light-demander (seed mass 33 µg). Comparative observations were made on changing light requirement with age. The species varied from shrubs and treelets (Urophyllum) via small to medium-height trees (Ficus, Pternandra) to tall trees (Gynotroches and Pellacalyx). In general, the shorter species fruited in deep shade while the taller needed direct irradiance. All produced ripe fruit at least once a year.In 1–3% isf seedling mortality over 11 months was 24% for Urophyllum hirsutum and 57% for Pternandra echinata (two strongly shade-tolerant species); survivors produced appreciable new stem and leaf tissue. For two more light-demanding species (Ficus grossularioides and F. fistulosa) mean lamina area was much larger in small gaps (10% isf) than in the understorey (<3% isf), while for Urophyllum hirsutum it was much smaller. These three species showed the greatest difference in SLA. There were few significant intraspecific differences between gaps and understorey in concentrations of N, P or K. In a valley where there was no significant difference in isf between a path and adjacent understorey, seedlings of species with seeds <1 mg mean dry mass were five times as dense on transects along steep pathside banks as in the understorey 5 m upslope. The mean mid-bank slope was 66° (cf. 20° upslope). On mid-bank transects litter had a cover of 36% (cf. 95% upslope), and was thinner (0.8 vs 3.2 cm). The soil at 0–7 cm depth into the mid-bank had much lower concentrations of organic matter, total N and P (but not total K) and fine roots than that of upslope transects. All species were found to have vesicular-arbuscular mycorrhiza when 1–2 m tall in deep shade, several having very dense infections. Seedling form and responses are discussed in relation to potential adaptive value and possible evolutionary origin.     

Distribution,production, and age structure of slimy sculpin in an Arctic lake

Synopsis Slimy sculpins (Cottus cognatus) were caught in the littoral region of Toolik Lake, an arctic lake. These sculpins grew slower and lived longer (71 mm at 8⁺ years) than more southerly populations. Sculpin distribution along the slope of the rocky littoral zone was greatest at the 3.5 m depth and coincided with the rock-mud interface. The hypothesis that this preferred area provided both increased prey and reduced predation was advanced. Yearly production estimate of littoral sculpins was 0.40 g · m^–2 · yr^–1 with a P/B ratio of 0.36. This is considerably less than estimates for more southerly populations of the same species.     

Primary lowland dipterocarp forest at Danum Valley, Sabah, Malaysia. Species composition and patterns in the understorey

The spatial distributions of species of tree 10 cm gbh were examined in two 4 ha plots and related to the local variation in topography and soil chemistry. The plots were similar in their species composition, particularly in terms of the densities of small trees, and they showed very similar edaphic characteristics. Size class distributions varied little within and between plots. Ordination of 0.25 ha subplots highlighted parallel gradients in the vegetation of both plots when the densities of trees 10 cm gbh were considered. Focusing on understorey trees in the 10-<50 cm gbh class at the 0.04 ha subplot scale showed a similar vegetation gradient in both plots closely associated with change from lower slope to ridge. No relationship with soil chemistry was found. On the ridges a special group of understorey species formed clumps and these species contributed importantly to the ordinations. Borneo has a regional history of occasionally severe droughts. It is suggested here that the observed patterns in the understorey are due to differential responses to low soil water supply, the ridges probably tending to dryness more than the lower slopes. Within the large and diverse family Euphorbiaceae, which dominates the understorey at Danum, there may be ecophysiological groupings of species. The long-term effects of disturbance interacting with local edaphic factors on forest structure and composition are discussed.     

Grazing and an invasive grass confound spatial pattern of exotic and native grassland plant species richness

Previous work has shown exotic and native plant species richness are negatively correlated at fine spatial scales and positively correlated at broad spatial scales. Grazing and invasive plant species can influence plant species richness, but the effects of these disturbances across spatial scales remain untested. We collected species richness data for both native and exotic plants from five spatial scales (0.5–3000 m²) in a nested, modified Whittaker plot design from severely grazed and ungrazed North American tallgrass prairie. We also recorded the abundance of an abundant invasive grass, tall fescue (Schedonorus phoenix (Scop.) Holub), at the 0.5-m² scale. We used linear mixed-effect regression to test relationships between plant species richness, tall fescue abundance, and grazing history at five spatial scales. At no scale was exotic and native species richness linearly related, but exotic species richness at all scales was greater in grazed tracts than ungrazed tracts. Native species richness declined with increasing tall fescue abundance at all five spatial scales, but exotic species richness increased with tall fescue abundance at all but the broadest spatial scales. Severe grazing did not reduce native species richness at any spatial scale. We posit that invasion of tall fescue in this working landscape of originally native grassland plants modifies species richness-spatial scale relationships observed in less disturbed systems. Tall fescue invasion constitutes a unique biotic effect on plant species richness at broad spatial scales.     

Restoration experiment of Zostera marina L. in a subtropical coastal lagoon

Zostera marina is the dominant seagrass species in coastal lagoons on the western coast of Baja California Peninsula, and due to its coastal location it is threatened by natural and anthropogenic factors, as is happening in Puerto San Carlos, B.C.S., where a fish cannery unloads its wastewater to the beach. Apparently an extensive intertidal meadow replacement was established by great amounts of green macroalgae. We evaluated the possibility to mitigate the impacts of this cannery with transplants of Z. marina meadow using adult plants. The transplant experiment was made in two different seasons for which two undisturbed donor meadows were chosen: El Cuervo and San Carlitos. The winter one obtained a 30% and in San Carlitos 90% after 13 months and the autumn transplant in San Carlos obtained a 0% of survival after 3 months. The results of these transplant activities were reflected in the shoot density at the end of the experiment (San Carlos was of 482 shoots/m² and San Carlitos of 818 shoots/m²s and agree with the density of the natural meadows. This experiment shows that it is possible to develop a small-scale seagrass restoration as mitigation for Baja California coastal lagoons which are under severe threat for coastal development.     

Identity and relationships of the Arboreal Caatinga among other floristic units of seasonally dry tropical forests (SDTFs) of north-eastern and Central Brazil

The tree species composition of seasonally dry tropical forests (SDTF) in north-eastern and central Brazil is analyzed to address the following hypotheses: (1) variations in species composition are related to both environment (climate and substrate) and spatial proximity; (2) SDTF floristic units may be recognized based on peculiar composition and environment; and (3) the Arboreal Caatinga, a deciduous forest occurring along the hinterland borders of the Caatinga Domain, is one of these units and its flora is more strongly related to the caatinga vegetation than to outlying forests. The study region is framed by the Brazilian coastline, 50th meridian west and 21st parallel south, including the Caatinga Domain and extensions into the Atlantic Forest and Cerrado Domains. Multivariate and geostatistic analyses were performed on a database containing 16,226 occurrence records of 1332 tree species in 187 georeferenced SDTF areas and respective environmental variables. Tree species composition varied significantly with both environmental variables and spatial proximity. Eight SDTF floristic units were recognized in the region, including the Arboreal Caatinga. In terms of species composition, its tree flora showed a stronger link with that of the Cerrado Dry Forest Enclaves. On the other hand, in terms of species frequency across sample areas, the links were stronger with two other units: Rock Outcrops Caatinga and Agreste and Brejo Dry Forests. There is a role for niche-based control of tree species composition across the SDTFs of the region determined primarily by the availability of ground water across time and secondarily by the amount of soil mineral nutrients. Spatial proximity also contributes significantly to the floristic cohesion of SDTF units suggesting a highly dispersal-limited tree flora. These units should be given the status of eco-regions to help driving the conservation policy regarding the protection of their biodiversity.     

Cold resistance mechanisms in high desert Andean plants

Freezing tolerance and freezing avoidance were studied, during the growing season, in plant species from two different elevations (3200 m and 3700 m) in a desert region of the high Andes (29° 45S, 69° 59W) in order to determine whether there was a relationship between plant height and cold resistance mechanisms. Freezing injury and supercooling capacity were determined in plants of different height, from ground-level (<20 cm tall) to tall shrubs (27–90 cm). All ground-level plants showed freezing tolerance as the main mechanism for resistance to freezing temperatures. Tall shrubs avoided freezing temperatures, mainly through supercooling. Supercooling was only present in plants occupying the lower elevation (i.e., 3200 m). Both avoidance and tolerance mechanisms are present in a single genus (i.e., Adesmia).     

Chitin production by Ampelisca (Amphipoda) populations from a fine sand community in the Bay of Morlaix (English channel)

We measured chitin biomass and production in five species of Ampelisca (Crustacea Amphipoda) living on a fine sand community at Pierre Noire Station in the Bay of Morlaix (Western English Channel, Brittany, France). Taking into account the maxima of their mean total production, the annual chitin production was estimated at between 600 and 900 mg m^–2 yr^–1. These values are close to those of the chitin production of pioneering benthic communities growing on naked substrates in the coastal waters of Calvi bay (Mediterranean, Corsica) between 7 to 28 meter depth, and of the zooplankton of that same area.     

Two New Species and New Occurrences of <Emphasis Type="Italic">Syneches</Emphasis> Walker for Brazilian Biome of Caatinga (Diptera: Hybotidae: Hybotinae)

Syneches from Brazilian biome of Caatinga were studied, two new species are described, Syneches atratus sp. nov. and Syneches limeirai sp. nov., and three species, Syneches annulipes Bezzi, 1909, Syneches moraballi Smith, 1963, and Syneches rafaeli Ale-Rocha & Vieira, 2008, are recorded for the biome. An identification key for the species of Syneches from Caatinga biome is provided.     

Dioecy in the Caatinga,a Brazilian tropical dry forest: typical reproductive traits of a low frequent sexual system

Dioecy is a rare sexual system among angiosperms whose occurrence and frequency depend on the kind and geographical location of the ecosystem. We evaluate the frequency of dioecy in the Caatinga, a special semi-arid vegetation type in Brazil. We compare the floral traits and other ecological characteristics usually related to dioecy between the Caatinga and other tropical ecosystems. Dioecious species of the Caatinga were compiled based on 24 published floristic lists including most of the Caatinga domain. These lists were compared with publications comprising data on sexual systems in different kinds of vegetation in the world. Sexual system confirmation and the database of the reproductive traits of the dioecious species were made by consulting herbaria, literature, and field observations. We registered 22 dioecious species occurring in the Caatinga. The overall dioecy frequency was 2.36 %, considering all Caatinga species, and 6.91 % within woody species. Most dioecious species exhibited traits related to this sexual system (e.g., woody habit, greenish inconspicuous flowers, generalistic pollination syndrome, and zoochory). The distribution of dioecy across the Caatinga plant community exhibited a very low level of phylogenetic signal (D = ?0.145), indicating a phylogenetic structure under Brownian evolution (p = 0.671). The frequency of dioecy in the Caatinga (2.36 %) proved lower than reported for angiosperms in general (ca. 6 %) and for other tropical ecosystems. This low frequency can be related to particular ecological characteristics of the Caatinga, such as low percentage of trees >3–4 m tall (13–18.7 %), low rainfall (50 % of the Caatinga vegetation with annual rainfall lower than 750 mm), and strong seasonality (6–9 months of dry season). Dioecious species of the Caatinga exhibited typical reproductive traits for this sexual system, similar to what has been reported for dioecious species of other tropical ecosystems in the world.