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PubMed2005

Mind the gap: how open were European primeval forests?

There are two competing hypotheses about the structure and dynamics of primeval forests in lowland Europe: the high-forest and the wood-pasture hypotheses, both of which influence current European forest conservation policies. In a recent study using pollen-analytical data from across lowland Europe, Mitchell provides support for rejecting the wood-pasture hypothesis. His study is important for future forest management planning and for showing how hypotheses about large herbivores as biotic factors can be tested using palaeoecological data.

Journal Article↗
PubMed1997

Diversity of Glossina in the forest belt of Côte d'Ivoire.

Collections of Glossina with a biconical trap have been made for 6 years in the forest area of Daloa in Côte d'Ivoire. Three species of Glossina have been identified in the village of Batéguédéa II as well as in the plantations and gallery forests. They are: G. palpalis, G. pallicera and G. nigrofusca. G. palpalis was predominant in the village in 1984, representing 74% of the collection, while the G. pallicera and G. nigrofusca types are more common in plantations and gallery forest. In 1987, 3 years after the first observation, G. palpalis was the most common species in each of the three biotopes. G. palpalis was even more common in 1990, following a decline in the population of G. pallicera and G. nigrofusca in the village (0.2% for G. pallicera; 0.8% for G. nigrofusca) and the plantations (0.7% for G. pallicera; 1.3% for G. nigrofusca). However, these two species were still found in small numbers in the gallery forest.

Animals↗
PubMedDate not supplied

Deforestation and the spatio-temporal distribution of savannah and forest members of the Simulium damnosum complex in southern Ghana and south-western Togo.

Spatio-temporal data on cytotaxonomic identifications of larvae of different members of the Simulium damnosum complex collected from rivers in southern Ghana and south-western Togo from 1975 until 1997 were analysed. When the data were combined, the percentages of savannah blackflies (S. damnosum sensu stricto and S. sirbanum) in the samples were shown to have been progressively increasing since 1975. The increases were statistically significant (P < 0.001), but the rates of increase were not linear. Further analyses were conducted according to the collection seasons and locations of the samples, to account for possible biases such as savannah flies occurring further south in the dry season or a preponderance of later samples from northern rivers having more savannah flies. These analyses showed that the increasing trend was statistically significant (P < 0.0001) only during the periods April to June and October to December. The presence of adult savannah flies carrying infective larvae (L3) indistinguishable from those of Onchocerca volvulus in the study zone was confirmed by examinations of captured flies. The percentages of savannah flies amongst the human-biting populations and the percentages with L3s in the head were higher during dry seasons than wet seasons and the savannah species were found furthest south (5 degrees 25'N) in the dry season. Comparisons of satellite images taken in 1973 and 1990 over a study area in south-western Ghana encompassing stretches of the Tano and Bia rivers demonstrated that there have been substantial increases in urban and savannah areas, at the expense of forest. This was so not only for the whole images but also for subsamples of the images taken at 1, 2, 4, 8 and 16 km distant from sites alongside the River Tano. At every distance from the river, the percentages of pixels classified as urban or savannah have increased in 1990 compared with 1973, while those classified as degraded or dense forest have decreased. The possibility that the proportionate increases in savannah forms of the vectors of onchocerciasis, and hence in the likelihood of the transmission of savannah strains of the disease in formerly forested areas, were related to the decreases in forest cover is discussed.

Animals↗
PubMedDate not supplied

Characteristics of PAHs, PCDD/Fs and PCBs in sediment following forest fires in northern Alberta.

Extensive forest fires occurred in northern Alberta, Canada, in 1998. Polynuclear aromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs) were studied following these forest fires in order to explore natural and anthropogenic influences on the affected forest fire area. Specifically, concentrations and profiles of these compounds were determined in sediment samples. A predominance of alkylated PAH derivatives over parent PAHs were observed at the burned and reference sites. Naturally dervied PAHs were abundant at all sites. A high proportion and concentration of retene was observed at the totally burned site and indicates some inputs from forest fires. Very low concentrations of PCDD/Fs and PCBs were observed at all sites, and the profiles were very similar. This likely reflects common atmospheric contributing sources to the study area.

Air Pollutants↗
PubMed2000

Mercury methylation along a lake-forest transect in the Tapajós river floodplain, Brazilian Amazon: seasonal and vertical variations.

The seasonal and spatial variations of net methylmercury production in sediments, soils and other sites were evaluated by assays with 203Hg at different depths and locations along a lake-forest transect at lake Enseada Grande, Tapajós river. Soil and sediment samples were taken at the surface and at different depths up to 9 cm. Fresh samples and acidified controls (1-3 g dry wt.) were slurried with local water and incubated in the dark at 25-28 degrees C for 3 days with 0.5-1.6 microg Hg g(-1) (dry wt.) added as 203HgCl2. CH3 203Hg was extracted and measured in scintillation cocktail after acid leaching. Methylmercury production varied by orders of magnitude among sites and among sediment or soil layers. Seasonal variations were smaller than those with sample depth and location. In both seasons, MeHg formation in sediment and soil or flooded soil decreased with depth and was, in the top layers, one order of magnitude higher in the C-rich littoral macrophyte zone (2.3-8.9%) and flooded forest (3.2-4.5%) than in the center of the lake (0.2-0.56%). Similar MeHg production was found in slurried dry soils (dry season) and in soils already flooded for months. In the macrophyte zone soil (dry season), methylation was mainly associated with the thin Paspalum sp. rootlet layer. In the forest site, vertical variation in methylation was less pronounced in flooded than in dry soils and during the inundation the higher methylation rate was found in the flocculent sediment settled over the litter layer. The roots of floating Paspalum sp. were an important Hg methylation site, particularly those heavily colonized with periphyton (3.4-5.4%). Methylation in surface or near-bottom water was undetectable (< 3 x 10(-2)%) at all sites. Flooded forests and macrophyte mats are specific features of the Amazon and are important links between Hg inputs from natural and manmade sources and MeHg exposure of local populations through fish intake.

Brazil↗
PubMed2001

137Cs availability for soil to understory transfer in different types of forest ecosystems.

A quantitative analysis of 137Cs bioavailability in forest soils in the long term after the Chernobyl NPP accident based on a 3-year (1996-1998) investigation is presented. Five forest sites with different trees, composition and properties of soil were studied to identify factors determining radiocaesium transfer to different understory species. The following parameters were investigated: 137Cs activity concentrations and its speciation in various horizons of forest soil, accumulation of this radionuclide by different species of understory vegetation and distribution of root biomass in the soil profile. It has been shown that one decade after the deposition maximum 137Cs activity in soil of the experimental sites considered is located in different soil layers dependent on moisture regime, characteristics of litter and soil properties. A linear dependence between aggregated transfer factors for different species and groups of species of understory vegetation and exchangeable and available fractions of radiocaesium in soil was found. The vertical distribution of 137Cs activity, percentage of exchangeable radiocaesium in each horizon of litter and soil, as well as distribution of root systems (mycelia) over the soil profile are key factors governing variations in the availability of 137Cs for transfer to all forest understory components.

Biological Availability↗
PubMed2002

Human ecological intervention and the role of forest fires in human ecology.

The present text is a summary of research on the relationship between forest fires and human activities. Numerous theories have been created to explain changes in forests during the late Pleistocene and early Holocene, and a general understanding has developed in the past 50 years regarding natural fire regimes. The present summary is directed to assess the validity of these theories. A re-analysis of the literature argues that the intense forest fires we experience today are an artifact of human intervention in forest ecology, especially by the reduction of herbivores and are relatively recent, approximately 100,000-250,000 BP. The history of fire, especially in the context of the increased dominance of humans, has produced a progressively fire-adapted ecology, which argues for human-free wildlife areas and against prescribed burns under many circumstances.

Adaptation, Physiological↗
PubMed2006

Random forests for microarrays.

Random Forests is a powerful multipurpose tool for predicting and understanding data. If gene expression data come from known groups or classes (e.g., tumor patients and controls), Random Forests can rank the genes in terms of their usefulness in separating the groups. When the groups are unknown, Random Forests uses an intrinsic measure of the similarity of the genes to extract useful multivariate structure, including clusters. This chapter summarizes the Random Forests methodology and illustrates its use on freely available data sets.

Animals↗
PubMed2004

Phytotoxicity and bioaccumulation of copper and chromium using barley (Hordeum vulgare L.) in spiked artificial and natural forest soils.

The toxicities of two heavy metals, copper (Cu2+) and chromium (Cr6+), to barley (Hordeum vulgare L.) were evaluated using two types of substrates: artificial and natural forest soils. Phytotoxicity was assessed using a standardized toxicity test. Endpoints included plant emergence and shoot and root growth. Shoot and root concentrations of Cu and Cr were also measured. Data indicated that the root biomass was the most sensitive endpoint. The results showed that toxicity of Cr to root growth (IC50=6.6 microg/g in artificial soil; IC50=61.8 microg/g in forest soil) was higher than that of Cu (IC50=13.7 microg/g in artificial soil; IC50>322 microg/g in forest soil). Data also indicated that the toxicity of Cu and Cr was significantly decreased in the spiked forest soil, suggesting lower metal bioavailability to barley in the natural soil. Analysis of tissue concentrations in barley showed that Cu and Cr were mainly accumulated in the roots. Toxicity was correlated with Cr residues in shoots (< or =11.2 microg Cr/g and < or =5.3 microg Cr/g for artificial and natural soils, respectively) and roots (< or =161 microg Cr/g and < or =51.7 microg Cr/g for artificial and natural soils, respectively) and Cu residues in roots (< or =61.8 microg Cu/g and < or =91.3 microg Cu/g for artificial and natural soils, respectively). Cu concentration in shoot tissues was < or =61.8 microg Cu/g. Since it may overestimate toxicity, effect and risk assessment using spiked soils, particularly in artificial soil, must be used with diligence.

Biomass↗
PubMed2001

A cost-benefit analysis of long-term management options for forests following contamination with 137Cs.

This paper provides a description of a cost-benefit analysis applied to determine the cost effectiveness, or otherwise, of nine management strategies potentially applicable to forests contaminated with 137Cs. The management strategies were considered singly and in a number of likely combinations. A management strategy was considered to be cost-effective if it resulted in a lower overall monetary detriment than was incurred if use of the contaminated forest was continued on a 'business as usual' basis. Only the banning of mushroom collection and restriction of public access proved to be cost-effective management strategies on the basis of this definition. However, even these strategies only proved cost-effective at high levels of 137Cs contamination, at which net savings in detriment in the form of public dose were achieved. Cost-effective savings of doses to forest workers were never achieved at any of the contamination levels considered in this study. It is suggested that novel alternative uses of contaminated forests are required which could provide added value to the standing crop in return for small increases in public and worker doses. One such use might be biofuel production.

Cesium Radioisotopes↗
PubMed2002

Soil organic horizons as a major source for radiocesium biorecycling in forest ecosystems.

Here we review some of the main processes and key parameters affecting the mobility of radiocesium in soils of semi-natural areas. We further illustrate them in a collection of soil surface horizons which largely differ in their organic matter contents. In soils, specific retention of radiocesium occurs in a very small number of sorbing sites, which are the frayed edge sites (FES) born out of weathered micaceous minerals. The FES abundance directly governs the mobility of trace Cs in the rhizosphere and thus its transfer from soil to plant. Here, we show that the accumulation of organic matter in topsoils can exert a dilution of FES-bearing minerals in the thick humus of some forest soils. Consequently, such accumulation significantly contributes to increasing 137Cs soil-to-plant transfer. Potassium depletion and extensive exploration of the organic horizons by plant roots can further enhance the contamination hazard. As humus thickness depends on both ecological conditions and forest management. our observations support the following ideas: (1) forest ecosystems can be classified according to their sensitivity to radiocesium bio-recycling, (2) specific forest management could be searched to decrease such bio-recycling.

Biological Availability↗
PubMed2002

In situ gamma-ray spectrometry in forests: determination of kerma rate in air from 137Cs.

A method is presented to determine the kerma rate in air from 137Cs due to Chernobyl fallout in forests. In situ gamma-ray spectra from several forest sites in Russia, in the Ukraine and in Southern Germany are evaluated with the aim of deducing the ratio of primary and forward scattered photons for 137Cs. With this ratio and the results of Monte-Carlo simulations of photon transport the contribution of scattered photons to the total kerma is assessed successfully. Scattered photons contribute between 42% and 50% to the total kerma rate from radiocesium, which is less than according values for grassland areas. The contribution of radiocesium to the total kerma rate varies between 40% and 90%. whereas radiocesium stored in the forest biomass contributes only a few percent. The mean mass depth of radiocesium ranges from 2.6 to 6.4 g cm(-2) in the forest soils.

Biomass↗
PubMed2002

Distribution of ozone and other air pollutants in forests of the Carpathian Mountains in central Europe.

Ozone (O3) concentrations were monitored during the 1997-1999 growing seasons in 32 forest sites of the Carpathian Mountains. At all sites (elevation between 450 and 1320 m) concentrations of O3, nitrogen dioxide (NO2), and sulfur dioxide (SO2) were measured with passive samplers. In addition, in two western Carpathian locations, Vychodna and Gubalówka, ozone was continuously monitored with ultraviolet (UV) absorption monitors. Highest average hourly O3 concentrations in the Vychodna and Gubałówka sites reached 160 and 200 microg/m3 (82 and 102 ppb), respectively (except for the AOT40 values, ozone concentrations are presented as microg/m3; and at 25 degrees C and 760 mm Hg, 1 microg O3/m3 = 0.51 ppb O3). These sites showed drastically different patterns of diurnal 03 distribution, one with clearly defined peaks in the afternoon and lowest values in the morning, the other with flat patterns during the entire 24-h period. On two elevational transects, no effect of elevation on O3 levels was seen on the first one, while on the other a significant increase of O3 levels with elevation occurred. Concentrations of O3 determined with passive samplers were significantly different between individual monitoring years, monitoring periods, and geographic location of the monitoring sites. Results of passive sampler monitoring showed that high O3 concentrations could be expected in many parts of the Carpathian range, especially in its western part, but also in the eastern and southern ranges. More than four-fold denser network of monitoring sites is required for reliable estimates of O3 distribution in forests over the entire Carpathian range (140 points). Potential phytotoxic effects of O3 on forest trees and understory vegetation are expected on almost the entire territory of the Carpathian Mountains. This assumption is based on estimates of the AOT40 indices for forest trees and natural vegetation. Concentrations of NO2 and SO2 in the entire Carpathian range were typical for this part of Europe and below the expected levels of phytotoxicity.

Air Pollutants↗
PubMed2002

Using forest health monitoring data to integrate above and below ground carbon information.

The national Forest Health Monitoring (FHM) program conducted a remeasurement study in 1999 to evaluate the usefulness and feasibility of collecting data needed for investigating carbon budgets in forests. This study indicated that FHM data are adequate for detecting a 20% change over 10 years (2% change per year) in percent total carbon and carbon content (MgC/ha) when sampling by horizon, with greater than 80% probability that a change in carbon content will be determined when a change has truly occurred (P < or = 0.33). The data were also useful in producing estimates of forest floor and soil carbon stocks by depth that were somewhat lower than literature values used for comparison. The scale at which the data were collected lends itself to producing standing stock estimates needed for carbon budget development and carbon cycle modeling. The availability of site-specific forest mensuration data enables the exploration of above ground and below ground linkages.

Biomass↗
PubMed2002

Use of pyrolysis molecular beam mass spectrometry (py-MBMS) to characterize forest soil carbon: method and preliminary results.

The components of soil organic matter (SOM) and their degradation dynamics in forest soils are difficult to study and thus poorly understood, due to time-consuming sample collection, preparation, and difficulty of analyzing and identifying major components. As a result, changes in soil organic matter chemical composition as a function of age, forest type, or disturbance have not been examined. We applied pyrolysis molecular beam mass spectrometry (py-MBMS), which provides rapid characterization of SOM of whole soil samples. to the Tionesta soil samples described by Hoover, C.M., Magrini, K.A., Evans, R.J., 2002. Soil carbon content and character in an old growth forest in northwestern Pennsylvania: a case study introducing molecular beam mass spectrometry (PY-MBMS). Environmental Pollution 116 (Supp. 1), S269-S278. Our goals in this work were to: (1) develop and demonstrate an advanced, rapid analytical method for characterizing SOM components in whole soils, and (2) provide data-based models to predict soil carbon content and residence time from py-MBMS analysis. Using py-MBMS and pattern recognition techniques we were able to statistically distinguish among four Tionesta sites and show an increase in pyrolysis products of more highly decomposed plant materials at increasing sample depth. For example, all four sites showed increasing amounts of older carbon (phenolic and aromatic species) at deeper depths and higher amounts of more recent carbon (carbohydrates and lignin products) at shallower depths. These results indicate that this type of analysis could be used to rapidly characterize SOM for the purpose of developing a model, which could be used in monitoring the effect of forest management practices on carbon uptake and storage.

Carbon↗
PubMed2003

Deposition to forests in Europe: most important factors influencing dry deposition and models used for generalisation.

Dry deposition of gases and particles to forests is influenced by factors influencing the turbulent transport, such as wind speed, tree height, canopy closure, LAI, etc. as well as by factors influencing surface condition, such as precipitation, relative humidity, global radiation, etc. In this paper, an overview of these factors is given and it is shown which are the most important determining temporal and spatial variation of dry deposition of sodium and sulphur. Furthermore, it is evaluated how well current deposition models are able to describe the temporal and spatial variation in dry deposition. It is concluded that the temporal variation is not modelled well enough, because of limited surface-wetness exchange parameterisations. The influence of forest characteristics are modelled reasonably well, provided enough data describing the forests and the spatial variation in concentration is available. For Europe these data are not available. The means to decrease the atmospheric deposition through forest management is discussed.

Air Pollutants↗
PubMed2003

The use of passive sampling to monitor forest exposure to O3, NO2 and SO2: a review and some case studies.

The use of passive sampler systems is reviewed and discussed. These devices are able to determine both spatial and temporal differences in canopy exposure, as is demonstrated by their use in extensive monitoring of air-pollution exposure in forest health plots. Categorising forest health monitoring plots according to air-pollution exposure permits cause-effect analysis of certain forest health responses. In addition, passive sampling may identify areas affected by interaction between different gaseous pollutants. Passive samplers at the stand level can be used to resolve vertical profiles of ozone within the stand, and edge effects, which are important in exposure of understorey and ground flora. Recent case studies using passive samplers to determine forest exposure to gaseous pollutants indicate a potential for the development of spatial models on regional-, landscape-, and stand-level scales and the verification of atmospheric transport models.

Air Pollutants↗
PubMed2004

Preliminary study of prairies forested with Eucalyptus sp. at the northwestern Uruguayan soils.

The land cover change of Uruguayan Forestal Plan provoked biogeochemical changes on horizon Au(1) of Argiudols; in native prairies which were replaced by monoculture Eucalyptus sp. plantation with 20 year rotations as trees. Five fields forested and six natural prairies were compared. The results not only show a statistical significant soil acidification, diminution of soil organic carbon, increase of aliphaticity degree of humic substances, and increase of affinity and capacity of hydrolytic activity from soil microbial communities for forested sites with Eucalyptus sp. but also, a tendency of podzolization and/or mineralization by this kind of land cover changes, with a net soil organic lost of 16.6 tons ha(-1) in the horizon Au(1) of soil under Eucalyptus sp. plantation compared with prairie. Besides, these results point out the necessity of correction of the methodology used by assigned Uruguayan commission to assess the national net emission of greenhouse gases, since the mineralization and/or podzolization process detected in forested soil imply a overestimation of soil organic carbon. The biochemical parameters show a statistical significant correlation between the soil organic carbon status and these parameters which were presented as essential for the correct evaluation of Uruguayan soil carbon sink.

Agriculture↗