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PubMed2004

Stature of sub-arctic birch in relation to growth rate, lifespan and tree form.

BACKGROUND AND AIMS: Sub-arctic mountain birch Betula pubescens var. pumila communities in the North Atlantic region are of variable stature, ranging from prostrate scrubs to forests with trees up to 12 m high. Four hypotheses were tested, relating growth and population characteristics of sub-arctic birch woodland and scrub to tree stature; i.e. the variable stature of birch woods is due to differences in (1) the mean growth rate; (2) the age-related patterns of growth rate; (3) the life expectancy of stems; or (4) the tree form. METHODS: A stratified random sample of 300 birch trees was drawn from the total population of indigenous birch woodlands and scrub in Iceland, yielding 286 valid sample genets. The population was divided into three sub-populations with dominant trees 0-2, 2-4 and 4-12 m tall, referred to as birch scrub, birch scrub-woodland and birch forest, respectively. KEY RESULTS: Trees in the scrub population were of more contorted growth form than birch in the scrub-woodland and forest populations. Mean growth rates, mean age and median life expectancies increased significantly with sub-population of greater tree stature. At the population level, annual increment and longevity of birch stems was apparently interrelated as the stems in vigorously growing birch sub-populations had a longer life expectancy than those of slower growth. However, no difference was observed between sub-populations in age-related patterns of extension growth rate. CONCLUSIONS: The results were consistent with hypotheses (1), (3) and (4), but hypothesis (2) was rejected. Hence, mountain birch of more vigorous growth attains a greater stature than birch of lesser increment due to faster extension growth rate and a longer lifespan. In addition, the more contorted stem form of scrub populations contributes to their low stature.

Betula↗

PubMed2006

Seroprevalence of leptospirosis among high-risk population of Andaman Islands, India.

Leptospirosis is a severe spirochetal zoonosis in the world. It is considered an occupational disease of persons engaged in agriculture, sewage works, forestry, and animal slaughtering. A study was conducted with an objective of assessing the seroprevalence of leptospirosis among the high-risk groups of Andaman Islands. A total of 611 sera samples from different high-risk populations were collected and tested by microscopic agglutination test (MAT). Genetic characterization of the isolate was done by randomly amplified polymorphic DNA (RAPD) fingerprinting, and serological characterization was done using monoclonal antibody technique. Antibodies to leptospires were detected in 322 samples giving an overall seroprevalence of 52.7%. The seroprevalence was highest among agriculture workers (62.5%) followed by sewage workers (39.4%), animal handlers (37.5%), forest workers (27.3%), and butchers (30.0%). Seroprevalence among control population was 14.7%, which was comparatively less than that of the high-risk population groups. Subject sera were most commonly reacted with organisms of the serogroup Grippotyphosa followed by Australis, and the pattern was similar in control group. Four leptospires were isolated from agriculture workers who were admitted to the public health center (PHC) with complaints of fever and body ache. Human isolates were compared with two rodent (Rattus norvegicus) isolates from the same area of agriculture workers to get initial information about the transmission cycle of leptospirosis in the study community. Randomly amplified polymorphic DNA fingerprinting pattern of the strains recovered from the rodents and human patients were identified as belonged to genomo-species Leptospira interrogans. The antigenic characterization of the strains recovered from them belonged to serovar Valbuzzi of serogroup Grippotyphosa. The study showed that people engaged in high-risk activities such as agriculture, sewage cleaning, animal handling, animal slaughtering, and forestry are frequently exposed to leptospirosis, and hence control strategies targeting these populations could be more effective.

Adult↗

PubMed2004

Interaction between ants and fruits of Guapira opposita (Nyctaginaceae) in a Brazilian sandy plain rainforest: ant effects on seeds and seedlings.

This study examines the dispersal system of Guapira opposita in a tropical sandy rainforest in southeast Brazil. Guapira trees produce small fruits with a high protein content (28.4%) and low lipid content (0.3%), and the plant is primarily dispersed by birds. Mature fruits of G. opposita can fall spontaneously with the pulp intact, or be dropped by birds with bits of pulp attached. In either case, ground-dwelling ants rapidly remove the fruits to their nest (93% after 12 h). The ponerine ants Odontomachus chelifer and Pachycondyla striata are the main seed vectors among the ants, and together account for 56% (20 of 36) of the ant-fruit interactions recorded on the forest floor. Individual workers of O. chelifer and P. striata transport single fruits to their nests. Bits of pulp are fed to larvae and worker nestmates, and intact seeds are discarded outside the nest. Germination success in Guapira is higher for cleaned seeds (pulp removed) than for seeds coated by pulp. Guapira seedlings and juveniles are more frequent close to Odontomachus nests than at sites without such nests. Soil samples from Odontomachus nests had greater penetrability, and higher concentrations of P, K, and Ca than random soil samples. Field experiments suggest that the association between G. opposita seedlings and O. chelifer nests can potentially render the plant some protection against herbivores. Results indicate that fruit displacement by ponerine ants play an important role in the biology of G. opposita seeds and seedlings in the sandy forest, and illustrate the complex nature of the dispersal ecology of tropical tree species.

Animals↗

PubMed1998

Directed seed dispersal by bellbirds in a tropical cloud forest.

A fundamental goal of plant population ecology is to understand the consequences for plant fitness of seed dispersal by animals. Theories of seed dispersal and tropical forest regeneration suggest that the advantages of seed dispersal for most plants are escape from seed predation near the parent tree and colonization of vacant sites, the locations of which are unpredictable in space and time. Some plants may gain in fitness as a fortuitous consequence of disperser behavior if certain species of dispersers nonrandomly place seeds in sites predictably favorable for seedling establishment. Such patterns of directed dispersal by vertebrates long have been suggested but never demonstrated for tropical forest trees. Here we report the pattern of seed distribution and 1-year seedling survival generated by five species of birds for a neotropical, shade-tolerant tree. Four of the species dispersed seeds to sites near the parent trees with microhabitat characteristics similar to those at random locations, whereas the fifth species, a bellbird, predictably dispersed seeds under song perches in canopy gaps. The pattern of seedling recruitment was bimodal, with a peak near parent trees and a second peak, corresponding to bellbird song perches, far (>40 m) from parent trees. Seedling survival was higher for seeds dispersed by bellbirds than by the other species, because of a reduction in seedling mortality by fungal pathogens in gaps. Thus, bellbirds play a significant role in seed dispersal by providing directed dispersal to favorable sites and therefore may influence plant recruitment patterns and species diversity in Neotropical forests.

Journal Article↗

PubMedDate not supplied

Statins and cholesterol lowering after a cancer diagnosis: why not?

The pleiotropic effects of statins continue to garner attention. One area of interest that requires more attention is their potential, or that of another heart healthy agent, to impact favorably or inhibit the progression of numerous cancers, especially prostate cancer. Statins have accumulated a plethora of data in the area of general cancer cell line inhibition, and the potential to have a synergistic impact in patients receiving a variety of conventional treatments for a diversity of cancers is endorsed at least by laboratory and some preliminary small clinical studies. However, prostate cancer is unique compared to other cancers because, despite a high prevalence, some men choose watchful waiting or no treatment, especially if they are older and/or have a well-differentiated tumor. Thus, prostate cancer is a good candidate for the potential investigation of statins after diagnosis, with or without standard therapy. Regardless, because the number 1 or 2 cause of death in men with prostate cancer is cardiovascular disease than even in the worst-case scenario, these agents appear attractive for more immediate clinical study because they could impact a major cause of morbidity and mortality in these men. It is time to see the forest over the tree, and statins seem to have an argument as good as many other agents for allocating more money and time to test their ability as adjuvant therapy in a randomized trial or, in some cases, of nonaggressive disease as a potential monotherapy.

Anticarcinogenic Agents↗

PubMed2005

[A meta-analysis of treatment of infantile diarrhea with bifid triple viable bacterial tablet].

OBJECTIVE: To assess the efficacy and safety of bifid triple viable bacterial tablet in treatment of infantile diarrhea. METHODS: According to the requirements of Cochrane systematic review, a thorough literature search was performed among Chinese Digital Hospital Library (www.chkd.cnki.net) and Chinese Biomedical Literature Disk Database (CBMdisk). A meta analysis was performed on a total of 1326 patients involved in 12 papers which met the inclusion criteria. RESULTS: Publication bias analysis showed that the funnel plot was symmetrical. Test for heterogeneity showed that the groups treated with bifid triple viable bacterial tablet and antibiotics or anti-viral agents or placebo control had clinical homogeneity and statistical homogeneity (P = 0.66, 0.67, 0.85, respectively, I(2) = 0%), which allowed to use fixed effect model analysis. The bifid triple viable bacterial tablet and Smecta did not have statistical homogeneity (P = 0.02, I(2) = 70.9%), therefore random effect model analysis was applied. Incorporation analysis showed that in comparison of the bifid triple viable bacterial tablet versus antibiotics or anti-viral agents or placebo control, the odds ratios were 5.34, 4.74 and 6.43, respectively, and 95% CIs were [2.81, 10.16], [2.47, 9.09], and [2.61, 15.83], on test for overall effect, Z = 5.11, 4.67 and 4.04, P < 0.00001. In the forest plot the 95% CI horizontal line of incorporation odds ratio droped to the right side of the vertical line indicating the border of effectiveness. However, no statistically significant difference was found between bifid triple viable bacterial tablet and Smecta. CONCLUSION: The clinical evidences available so far indicated that treatment of infantile diarrhea with bifid triple viable bacterial tablet is safe and effective although rigorously designed large sample size randomized double blind clinical trials are required to further demonstrate and support the conclusion.

Administration, Oral↗

PubMed2006

Movement trajectories and habitat partitioning of small mammals in logged and unlogged rain forests on Borneo.

1. Non-volant animals in tropical rain forests differ in their ability to exploit the habitat above the forest floor and also in their response to habitat variability. It is predicted that specific movement trajectories are determined both by intrinsic factors such as ecological specialization, morphology and body size and by structural features of the surrounding habitat such as undergrowth and availability of supportive structures. 2. We applied spool-and-line tracking in order to describe movement trajectories and habitat segregation of eight species of small mammals from an assemblage of Muridae, Tupaiidae and Sciuridae in the rain forest of Borneo where we followed a total of 13,525 m path. We also analysed specific changes in the movement patterns of the small mammals in relation to habitat stratification between logged and unlogged forests. Variables related to climbing activity of the tracked species as well as the supportive structures of the vegetation and undergrowth density were measured along their tracks. 3. Movement patterns of the small mammals differed significantly between species. Most similarities were found in congeneric species that converged strongly in body size and morphology. All species were affected in their movement patterns by the altered forest structure in logged forests with most differences found in Leopoldamys sabanus. However, the large proportions of short step lengths found in all species for both forest types and similar path tortuosity suggest that the main movement strategies of the small mammals were not influenced by logging but comprised generally a response to the heterogeneous habitat as opposed to random movement strategies predicted for homogeneous environments. 4. Overall shifts in microhabitat use showed no coherent trend among species. Multivariate (principal component) analysis revealed contrasting trends for convergent species, in particular for Maxomys rajah and M. surifer as well as for Tupaia longipes and T. tana, suggesting that each species was uniquely affected in its movement trajectories by a multiple set of environmental and intrinsic features.

Animals↗

PubMed1999

Spectroscopic limits on the distance and energy release of GRB 990123

An optical spectrum of the afterglow from the unusually bright gamma-ray burst GRB 990123 obtained on 24.25 January 1999 universal time showed an absorption system at a redshift of z = 1.600. The absence of a hydrogen Lyman alpha forest sets an upper limit of z < 2.17, whereas ultraviolet photometry indicates an upper limit of z < 2.05. The probability of intersecting an absorption system as strong as the one observed along a random line of sight out to this z is at most a few percent, implying that GRB 990123 was probably at z = 1. 600. Currently favored cosmological parameters imply that an isotropic energy release equivalent to the rest mass of 1.8 neutron stars (4.5 x 10(54) erg) was emitted in gamma rays. Nonisotropic emission, such as intrinsic beaming, may resolve this energy problem.

Journal Article↗

PubMed2002

A spatially explicit neutral model of beta-diversity in tropical forests.

To represent species turnover in tropical rain forest, we use a neutral model where a tree's fate is not affected by what species it belongs to, seeds disperse a limited distance from their parents, and speciation is in equilibrium with random extinction. We calculate the similarity function, the probability F(r) that two trees separated by a distance r belong to the same species, assuming that the dispersal kernel P(r), the distribution of seeds about their parents and the prospects of mortality and reproduction, are the same for all trees regardless of their species. If P(r) is radially symmetric Gaussian with mean-square dispersal distance sigma, F(r) can be expressed in closed form. If P(r) is a radially symmetric Cauchy distribution, then, in two-dimensional space, F(r) is proportional to 1/r for large r. Analytical results are compared with individual-based simulations, and the relevance to field observations is discussed.

Ecosystem↗

PubMed2006

Structured additive regression for categorical space-time data: a mixed model approach.

Motivated by a space-time study on forest health with damage state of trees as the response, we propose a general class of structured additive regression models for categorical responses, allowing for a flexible semiparametric predictor. Nonlinear effects of continuous covariates, time trends, and interactions between continuous covariates are modeled by penalized splines. Spatial effects can be estimated based on Markov random fields, Gaussian random fields, or two-dimensional penalized splines. We present our approach from a Bayesian perspective, with inference based on a categorical linear mixed model representation. The resulting empirical Bayes method is closely related to penalized likelihood estimation in a frequentist setting. Variance components, corresponding to inverse smoothing parameters, are estimated using (approximate) restricted maximum likelihood. In simulation studies we investigate the performance of different choices for the spatial effect, compare the empirical Bayes approach to competing methodology, and study the bias of mixed model estimates. As an application we analyze data from the forest health survey.

Bayes Theorem↗

PubMed2004

Diversity and molecular relationships of endophytic Colletotrichum isolates from the Iwokrama Forest Reserve, Guyana.

The diversity and host specificity were studied of a collection of Colletotrichum strains derived from endophytic colonies in leaves of 12 tree species in the Iwokrama Forest Reserve, Guyana. Analysis included ISSR-PCR and RAPD molecular fingerprinting techniques, rDNA ITS sequencing and morphological and cultural characterization. Most strains belonged to one of two species, C. gloeosporioides and a further taxon which is probably referable to C. boninense. Almost no strains were found to be genetically identical, indicating that clonal reproduction does not play a prominent role. No degree of host specificity could be detected even at molecular fingerprint level. The implications for estimation of fungal diversity in closed tropical forests may be profound.

Colletotrichum↗

PubMed1989

Regional variation in surface properties of Norway spruce and scots pine needles in relation to forest decline.

Measurements of leaf wettability (contact angle), amounts of epicuticular wax and of surface dust are reported for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L) Karst) trees growing at 12 sites in Europe from SW Germany to NE Scotland. At each site, three year classes (current year, 1 and 2-year-old) of needles were sampled from the mid-crown of up to 12 trees. Trees were selected at random from two strata, those showing visible decline symptoms (i.e. loss of needles or discoloration) and those apparently healthy. Needles for analysis were taken from apparently healthy (green) shoots in both cases. There were no significant differences between 'declining' and 'healthy' trees within sites, suggesting that leaf surface properties reflect environmental exposure rather than plant response. There were significant differences between sites, particularly for Norway spruce, which may be related to environmental factors including air pollution. Contact angles were consistently smaller at low-altitude sites in Britain and The Netherlands than at high-altitude sites in Germany where forests show decline symptoms. Leaf wettability decreased (contact angles increased) with wax amount and increased with dust amount. Leaf surface properties integrate environmental influences over long periods, and may be useful in identifying sites 'at risk' of developing decline symptoms, but causal relationships cannot be deduced without further direct experimentation.

Journal Article↗

PubMed2006

Ectomycorrhizal community structure varies among Norway spruce (Picea abies) clones.

In northern boreal forests, the diversity of ectomycorrhizal (ECM) species is much greater than that of their host trees. This field study investigated the role of individual trees in shaping the ECM community. We compared ECM communities of eight Norway spruce (Picea abies) clones planted in a clear-cut area in 1994 with a randomized block design. In 2003, the ECM fungi were identified from randomly sampled root tips using denaturing gradient gel electrophoresis (DGGE) and rDNA internal transcribed spacer (ITS) sequence similarity. ECM diversity varied among clone groups, showing twofold growth differences. Moreover, according to detrended correspondence analysis (DCA), ECM community structure varied not only among but also within slow-growing or fast-growing clones. Results suggest that ECM diversity and community structure are related to the growth rate or size of the host. A direct or indirect influence of host genotype was also observed, and we therefore suggest that individual trees are partly responsible for the high diversity and patchy distribution of ECM communities in boreal forests.

Ecosystem↗

PubMed2004

Open-nucleus breeding strategies compared with population-wide positive assortative mating: I. Equal distribution of testing efforts.

Positive assortative mating (PAM) can enhance the additive genetic variance in a breeding population(BP). This increases the potential for gains in the production population (PP, selected subset of the BP) for recurrent selection programs in forest trees. The assortment of mates can be either: (1) by individual tree rank across the whole BP (PAM), or (2) trees of similar rank can be merged into larger hierarchical groups and then mated randomly within group ("open"-nucleus breeding,NB). The objective of this study was to compare PAM and NB in quantitative terms. The NB simulation model assumed two tiers (nucleus, main) with unrestricted migration between the tiers. Clonal tests were used to predict breeding values and test resources per mate were kept constant for all mates. Both gain and diversity were combined into a single selection criterion, "group-merit selection." Alternatives were compared over five breeding cycles by considering genetic gain and diversity in a selected PP established in a seed orchard. The assortment of mates in both alternatives enhanced additive variance and increased the additive effect in the BP, leading to additional gain in the PP. Gains generated under PAM always exceeded gains under NB. Thus, the main message from this study is that PAM in both the short- and long-term results in more gain at any target level of diversity in the PP (the breeder's target) than is achieved by the NB alternative. The optimum size of the nucleus varies with the desired level of seed orchard diversity. At lower target diversity, smaller nucleus sizes are favorable, while larger sizes result in more gain when seed orchard diversity is considered more important.

Breeding↗

PubMed1998

A randomized trial comparing prostaglandin E(2) vaginal insert (Cervidil) to vaginal gel for cervical ripening before induction of labor.

Objective: To compare the efficacy and safety of a controlled release vaginal insert (Cervidil) with hospital compounded prostaglandin E(2) vaginal gel for cervical ripening before labor induction.Methods: A prospective randomized study was performed between July 1996 and August 1997 on 200 patients undergoing cervical ripening before induction of labor. The efficacy and safety of a 12-hour controlled release 10-mg vaginal insert (Cervidil, Forest Pharmaceuticals) was compared with two 4-mg doses of prostaglandin E(2) gel.Results: The study groups did not differ by parity, estimated gestational age, indications for induction, and initial Bishop scores. No differences were noted in Bishop score at 12 hours or change in Bishop score. No statistically significant differences were noted in the successful inductions, additional days of induction, and the number of patients discharged undelivered. There were no differences in mean time to active labor, cesarean section, meconium staining, 1 and 5 minute Apgar scores, cord pH values, NICU admissions, and incidence of hyperstimulation.Conclusions: Two 4-mg doses of prostaglandin vaginal gels are equally effective to a Cervidil vaginal insert for preinduction cervical ripening.

Journal Article↗

PubMed2005

Using ergodic theory to assess the performance of ecosystem models.

Ecosystem simulation models are designed to assess the flux of energy, water, carbon and nitrogen according to a given vegetation type. The reliability of the modeled results is determined by model validations. Model validations are typically done using classical statistical methods like regression analysis of predicted versus observed values, paired t statistics and error assessment procedures to characterize the quality of current and future model predictions. All these validation efforts concentrate on static aspects of the model but fail to describe the model dynamics. In this paper, we introduce methods from ergodic theory to analyze the dynamic behavior of ecosystem models. We describe (1) how the attractor representation of model behavior can be reconstructed from a time series of model outputs, and (2) what we can learn from the attractor to assess the model dynamics. As an application example, we provide simulation results for two important pine forest ecosystems in Austria, i.e., 23 Cembran pine and 16 Scots pine stands. These stands were simulated with three model parameterizations: one representing a generic, evergreen needle-leaf forest, and two species- specific parameter sets, one for Cembran pine and one for Scots pine. First, we applied standard validation methods to get static measures of model accuracy and precision. Next, we used ergodic theory to assess model dynamics. A comparison of both analyses reveals important issues related to model dynamics, such as the finding that the occurrence of instabilities in model behavior may not be detected by standard validation methods. Using ergodic theory, we were able to reconstruct the attractors of model behavior. In the attractor describing model dynamics for Cembran pine, simulated with the generic, evergreen needle-leaf forest parameter set, we detected instability in model behavior. We identified this instability as a riddled basin configuration, which is a strong indicator for the occurrence of a chaotic model behavior that may result in random predictions. Our results suggest that ergodic theory is a useful tool for assessing inconsistencies in the dynamics of ecosystem model simulations that have not been detected by standard statistical validation methods.

Climate↗

PubMed2006

Free-space optical communication through a forest canopy.

We model the effects of the leaves of mature broadleaf (deciduous) trees on air-to-ground free-space optical communication systems operating through the leaf canopy. The concept of leaf area index (LAI) is reviewed and related to a probabilistic model of foliage consisting of obscuring leaves randomly distributed throughout a treetop layer. Individual leaves are opaque. The expected fractional unobscured area statistic is derived as well as the variance around the expected value. Monte Carlo simulation results confirm the predictions of this probabilistic model. To verify the predictions of the statistical model experimentally, a passive optical technique has been used to make measurements of observed sky illumination in a mature broadleaf environment. The results of the measurements, as a function of zenith angle, provide strong evidence for the applicability of the model, and a single parameter fit to the data reinforces a natural connection to LAI. Specific simulations of signal-to-noise ratio degradation as a function of zenith angle in a specific ground-to-unmanned aerial vehicle communication situation have demonstrated the effect of obscuration on performance.

Journal Article↗

PubMed2003

Nitrogen limitation of growth and nutrient dynamics in a disturbed mangrove forest, Indian River Lagoon, Florida.

The objectives of this study were to determine effects of nutrient enrichment on plant growth, nutrient dynamics, and photosynthesis in a disturbed mangrove forest in an abandoned mosquito impoundment in Florida. Impounding altered the hydrology and soil chemistry of the site. In 1997, we established a factorial experiment along a tree-height gradient with three zones, i.e., fringe, transition, dwarf, and three fertilizer treatment levels, i.e., nitrogen (N), phosphorus (P), control, in Mosquito Impoundment 23 on the eastern side of Indian River. Transects traversed the forest perpendicular to the shoreline, from a Rhizophora mangle-dominated fringe through an Avicennia germinans stand of intermediate height, and into a scrub or dwarf stand of A. germinans in the hinterland. Growth rates increased significantly in response to N fertilization. Our growth data indicated that this site is N-limited along the tree-height gradient. After 2 years of N addition, dwarf trees resembled vigorously growing saplings. Addition of N also affected internal dynamics of N and P and caused increases in rates of photosynthesis. These findings contrast with results for a R. mangle-dominated forest in Belize where the fringe is N-limited, but the dwarf zone is P-limited and the transition zone is co-limited by N and P. This study demonstrated that patterns of nutrient limitation in mangrove ecosystems are complex, that not all processes respond similarly to the same nutrient, and that similar habitats are not limited by the same nutrient when different mangrove forests are compared.

Avicennia↗