Directional changes in the species composition of a tropical forest

Long-term studies have revealed that the structure and dynamics of many tropical forests are changing, but the causes and consequences of these changes remain debated. To learn more about the forces driving changes within tropical forests, we investigated shifts in tree species composition over the past 25 years within the 50-ha Forest Dynamics Plot on Barro Colorado Island (BCI), Panama, and examined how observed patterns relate to predictions of (1) random population fluctuations, (2) carbon fertilization, (3) succession from past disturbance, (4) recovery from an extreme El Ni?o drought at the start of the study period, and (5) long-term climate change. We found that there have been consistent and directional changes in the tree species composition. These shifts have led to increased relative representations of drought-tolerant species as determined by the species' occurrence both across a gradient of soil moisture within BCI and across a wider precipitation gradient from a dry forest near the Pacific coast of Panama to a wet forest near its Caribbean coast. These nonrandom changes cannot be explained by stochastic fluctuations or carbon fertilization. They may be the legacy of the El Ni?o drought, or alternatively, potentially reflect increased aridity due to long-term climate change. By investigating compositional changes, we increased not only our understanding of the ecology of tropical forests and their responses to large-scale disturbances, but also our ability to predict how future global change will impact some of the critical services provided by these important ecosystems.     

Can spatial isolation help predict dispersal-limited sites for native species restoration?

When the distribution of species is limited by propagule supply, new populations may be initiated by seed addition, but identifying suitable sites for efficiently targeted seed addition remains a major challenge for restoration. In addition to the biotic or abiotic variables typically used in species distribution models, spatial isolation from conspecifics could help predict the suitability of unoccupied sites. Site suitability might be expected to increase with spatial isolation after other factors are accounted for, since isolation increases the chance that a site is unoccupied only because of propagule limitation. For two native annual forbs in Californian grasslands, we combined experimental seeding and niche modeling to ask whether suitability of unoccupied sites could be predicted by spatial variables (either distances from, or densities of, conspecific populations), either by themselves or in combination with niche models. We also asked whether experimental tests of these predictions held up not only in the short term (one year), but also in the longer term (three years). For Lasthenia californica, seed additions were only successful relatively near existing populations. For Lupinus nanus, seeding success was low and was positively related to the number of conspecifics within 1 km. For both species, a few previously unoccupied sites remained occupied three years after seeding, but this subset was not predictable based on either spatial or niche variables. Seed addition alone may be a limited means of native forb restoration if suitable unoccupied sites are either rare or unpredictable, or if they tend to be close to where the species already occurs.     

An explanation for the apparent losses of metals in a long-term field experiment with sewage sludge

Large losses of metals applied to soil in metal-contaminated sewage sludge have been reported. The potential pathways of loss, including lateral movement from treated plot areas, have not been examined. A field experiment, which started in 1942, was investigated to determine the amount of lateral movement of zinc, cadmium, copper, nickel, chromium and lead due to conventional cultivation processes. A two-dimensional 'dispersion' model (i.e. movement of soil due to cultivation) fitted well to the observed movement of metals, and gave coefficients for movement of 0.24 and 0.13 m(2) per tillage operation in dimensions parallel or perpendicular to the direction of ploughing, respectively. For testing purposes, the model was used to predict the concentrations of metals in specific areas of a plot or average concentrations for whole plots at different points in time. The concentrations measured in soil samples agreed well with the predicted values. Finally, the model was also used to estimate the proportion of the metal load applied between 1942 and 1961 that remained in the 0-27 cm cultivated layer in 1985. About 80% was accounted for: this large recovery is of great relevance to the long-term disposal of metal-contaminated wastes to land. Detailed analyses of soil profile samples showed that approximately 1% of the metals applied had moved 3.5 cm below the plough layer or less, but there was no evidence of accumulation of metals in deeper horizons down to 46 cm. These results are discussed in relation to the other potential losses of metals in the experiment.     

The last “pelycosaur”: a varanopid synapsid from the <Emphasis Type="Italic">Pristerognathus</Emphasis> Assemblage Zone,Middle Permian of South Africa

We report on a partial varanopid skull and mandible from the Pristerognathus Assemblage Zone of the Beaufort Group, in the South African Karoo Basin, which is probably latest Middle Permian (Capitanian) in age. This mycterosaurine is not only the youngest known varanopid from the Southern Hemisphere, but it is also the youngest known “pelycosaur” (i.e., non-therapsid synapsid). Like all other members of this clade of hypercarnivores, the teeth are strongly flattened, recurved, and have finely serrated cutting edges. The anterior dentary teeth form a caniniform region, and the splenial features a foramen intermandibularis oralis, the first ever to be described in a “pelycosaur.” The last varanopids were the smallest carnivores of latest Middle Permian continental faunas. Occupation of the small carnivore guild appears to have allowed varanopids to achieve a nearly cosmopolitan distribution throughout the Middle Permian, between the great Early Permian radiation of basal synapsids and the spectacular diversification of therapsid synapsids in the Late Permian and Early Triassic.     

Zooplankton diversity and physico-chemical conditions in three perennial ponds of Virudhunagar district, Tamilnadu

Plankton diversity and physico-chemical parameters are an important criterion for evaluating the suitability of water for irrigation and drinking purposes. In this study we tried to assess the zooplankton species richness, diversity and evenness and to predict the state of three perennial ponds according to physico-chemical parameters. A total of 47 taxa were recorded: 24 rotifers, 9 copepods, 8 cladocerans, 4 ostracods and 2 protozoans. More number of zooplankton species were recorded in Chinnapperkovil pond (47 species) followed by Nallanchettipatti (39 species) and Kadabamkulam pond (24 species). Among the rotifers, Branchionus sp. is abundant. Diaphanosoma sp. predominant among the cladocerans. Among copepods, numerical superiority was found in the case of Mesocyclopes sp. Cypris sp. repeated abundance among ostracoda. Present study revealed that zooplankton species richness (R1 and R2) was comparatively higher (R1: 4.39; R2: 2.13) in Chinnapperkovil pond. The species diversity was higher in the Chinnapperkovil pond (H': 2.53; N1: 15.05; N2: 15.75) as compared to other ponds. The water samples were analyzed for temperature, pH, electrical conductivity alkalinity salinity, phosphate, hardness, dissolved oxygen and biological oxygen demand. Higher value of physico-chemical parameters and zooplankton diversity were recorded in Chinnapperkovil pond as compared to other ponds. The zooplankton population shows positive significant correlation with physico-chemical parameters like, temperature, alkalinity phosphate, hardness and biological oxygen demand, whereas negatively correlated with rainfall and salinity. The study revealed that the presence of certain species like, Monostyla sp., Keratella sp., Lapadella sp., Leydigia sp., Moinodaphnia sp., Diaptomus sp., Diaphanosoma sp., Mesocyclopes sp., Cypris sp. and Brachionus sp. is considered to be biological indicator for eutrophication.     

清洁生产—实施上海可持续发展战略的关键

上海市政府已经采取了一种可持续发展思路来实现其长远发展目标,清洁生产被认为是上海地区技术现代化的一个组成部分。上海市环保局和市经委目前正在编制“上海市促进清洁生产框架计划”。     

Measurements of benzene and formaldehyde in a medium sized urban environment. Indoor/outdoor health risk implications on special population groups

In the present study, the results of a measurement campaign aiming to assess cancer risk among two special groups of population: policemen and laboratory technicians exposed to the toxic substances, benzene and formaldehyde are presented. The exposure is compared to general population risk. The results show that policemen working outdoor (traffic regulation, patrol on foot or in vehicles, etc.) are exposed at a significantly higher benzene concentration (3-5 times) than the general population, while the exposure to carbonyls is in general lower. The laboratory technicians appear to be highly exposed to formaldehyde while no significant variation of benzene exposure in comparison to the general population is recorded. The assessment revealed that laboratory technicians and policemen run a 20% and 1% higher cancer risk respectively compared to the general population. Indoor working place air quality is more significant in assessing cancer risk in these two categories of professionals, due to the higher Inhalation Unit Risk (IUR) of formaldehyde compared to benzene. Since the origin of the danger to laboratory technicians is clear (use of chemicals necessary for the experiments), in policemen the presence of carbonyls in indoor air concentrations due to smoking or used materials constitute a danger equal to the exposure to traffic originated air pollutants.     

In situ fixation of metals in soils using bauxite residue: chemical assessment

Contamination of soils with heavy metals and metalloids is a widespread problem all over the world. Low cost, non-invasive, in situ technologies are required for remediation processes. We investigated the efficiency of a bauxite residue (red mud) to fix heavy metals in two soils, one contaminated by industrial activities (French soil), and one by sewage sludge applications (UK soil). This Fe-oxide rich material was compared with lime, or beringite, a modified aluminosilicate that has been used for in situ fixation processes. Four different crop species were successively grown in pots. Metal concentrations in the soil pore waters were analyzed during the growing cycles. At the end of the experiment fluxes of heavy metals were measured using a diffusive gradient in thin film technique (DGT). Furthermore, a sequential extraction procedure (SEP) and an acidification test were performed to investigate the mechanisms of metal fixation by different soil amendments. In both soils, the concentrations of metals in the soil pore water and metal fluxes were greatly decreased by the amendments. An application of 2% red mud performed as well as beringite applied at 5%. Increasing soil pH was a common mechanism of action for all the amendments. However, the red mud amendment shifted metals from the exchangeable to the Fe-oxide fraction, and decreased acid extractability of metals. The results suggest that specific chemisorption, and possibly metal diffusion into oxide particles could also be the mechanisms responsible for the fixation of metals by red mud.     

Responses of hybrid poplar clones and red maple seedlings to ambient O(3) under differing light within a mixed hardwood forest

The responses of ramets of hybrid poplar (Populus spp.) (HP) clones NE388 and NE359, and seedlings of red maple (Acer rubrum, L.) to ambient ozone (O(3)) were studied during May-September of 2000 and 2001 under natural forest conditions and differing natural sunlight exposures (sun, partial shade and full shade). Ambient O(3) concentrations at the study site reached hourly peaks of 109 and 98 ppb in 2000 and 2001, respectively. Monthly 12-h average O(3) concentrations ranged from 32.3 to 52.9 ppb. Weekly 12-h average photosynthetically active radiation (PAR) within the sun, partial shade and full shade plots ranged from 200 to 750, 50 to 180, and 25 to 75 micromol m(-2) s(-1), respectively. Ambient O(3) exposure induced visible foliar symptoms on HP NE388 and NE359 in both growing seasons, with more severe injury observed on NE388 than on NE359. Slight foliar symptoms were observed on red maple seedlings during the 2001 growing season. Percentage of total leaf area affected (%LAA) was positively correlated with cumulative O(3) exposures. More severe foliar injury was observed on plants grown within the full shade and partial shade plots than those observed on plants grown within the sun plot. Lower light availability within the partial shade and full shade plots significantly decreased net photosynthetic rate (Pn) and stomatal conductance (g(wv)). The reductions in Pn were greater than reductions in g(wv), which resulted in greater O(3) uptake per unit Pn in plants grown within the partial shade and full shade plots. Greater O(3) uptake per unit Pn was consistently associated with more severe visible foliar injury in all species and/or clones regardless of differences in shade tolerance. These studies suggest that plant physiological responses to O(3) exposure are likely complicated due to multiple factors under natural forest conditions.