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188 records · Page 11Linked to original sources
PubMed2006

Fuel breaks affect nonnative species abundance in Californian plant communities.

We evaluated the abundance of nonnative plants on fuel breaks and in adjacent untreated areas to determine if fuel treatments promote the invasion of nonnative plant species. Understanding the relationship between fuel treatments and nonnative plants is becoming increasingly important as federal and state agencies are currently implementing large fuel treatment programs throughout the United States to reduce the threat of wildland fire. Our study included 24 fuel breaks located across the State of California. We found that nonnative plant abundance was over 200% higher on fuel breaks than in adjacent wildland areas. Relative nonnative cover was greater on fuel breaks constructed by bulldozers (28%) than on fuel breaks constructed by other methods (7%). Canopy cover, litter cover, and duff depth also were significantly lower on fuel breaks constructed by bulldozers, and these fuel breaks had significantly more exposed bare ground than other types of fuel breaks. There was a significant decline in relative nonnative cover with increasing distance from the fuel break, particularly in areas that had experienced more numerous fires during the past 50 years, and in areas that had been grazed. These data suggest that fuel breaks could provide establishment sites for nonnative plants, and that nonnatives may invade surrounding areas, especially after disturbances such as fire or grazing. Fuel break construction and maintenance methods that leave some overstory canopy and minimize exposure of bare ground may be less likely to promote nonnative plants.

Biodiversity↗
PubMed2006

Neighborhood analyses of canopy tree competition along environmental gradients in New England forests.

We use permanent-plot data from the USDA Forest Service's Forest Inventory and Analysis (FIA) program for an analysis of the effects of competition on tree growth along environmental gradients for the 14 most abundant tree species in forests of northern New England, USA. Our analysis estimates actual growth for each individual tree of a given species as a function of average potential diameter growth modified by three sets of scalars that quantify the effects on growth of (1) initial target tree size (dbh), (2) local environmental conditions, and (3) crowding by neighboring trees. Potential growth of seven of the 14 species varied along at least one of the two environmental axes identified by an ordination of relative abundance of species in plots. The relative abundances of a number of species were significantly displaced from sites where they showed maximum potential growth. In all of these cases, abundance was displaced to the more resource-poor end of the environmental gradient (either low fertility or low moisture). The pattern was most pronounced among early successional species, whereas late-successional species reached their greatest abundance on sites where they also showed the highest growth in the absence of competition. The analysis also provides empirical estimates of the strength of intraspecific and interspecific competitive effects of neighbors. For all but one of the species, our results led us to reject the hypothesis that all species of competitors have equivalent effects on a target species. Most of the individual pairwise interactions were strongly asymmetric. There was a clear competitive hierarchy among the four most shade-tolerant species, and a separate competitive hierarchy among the shade-intolerant species. Our results suggest that timber yield following selective logging will vary dramatically depending on the configuration of the residual canopy, because of interspecific variation in the magnitude of both the competitive effects of different species of neighbors and the competitive responses of different species of target trees to neighbors. The matrix of competition coefficients suggests that there may be clear benefits in managing for specific mixtures of species within local neighborhoods within stands.

Ecosystem↗
PubMed2000

[Application of competition index in assessing intraspecific and interspecific spatial relations between manchurian ash and dahurian larch].

The competition among trees within a stand includes aboveground and underground parts. How to determine the zone of competition influence is important for predicting tree growth. We divide the zone into two parts: one part is defined as inside radius, the distance from nearest competitors to subject tree, in which, the competition influence is the sum of both aboveground and underground; the another part is defined as outside radius, the distance of competitors to subject tree, where the competition influence comes mostly from underground. Thus, the competition index, based upon the divided two radii, could be decomposed into different components. We used the data of manchurian ash(MA) (Fraxinus mandshurica) and dahurian larch(DL) (Larix gmelini) from pure and mixed stands to analyze the competition influence of aboveground and underground in inside and of underground in outside radius. The results show that for MA in pure stand, the competition effect was 59.06% from inside radius, and 40.94% from outside radius. For DL in pure stand, the competition effects in both radii were 71.31% and 28.69%, respectively. There was a stronger competition influence in inside than in outside radius. Underground competitions were the important issues for both species in pure stands. In a mixed stand of MA and DL, there were two species in both radii, and the effects of competition came from intraspecific and interspecific competitors. For subject tree of MA, the effect of interspecific competition was 49.55%, and that of intraspecific was 50.45%. For subject tree of DL, the effects were 81.11% and 18.89%, respectively. DL displayed a stronger interspecific competition than MA in the zone of competition influence, and was a main effect of competition on MA. For subject tree of MA, the effect of competition from inside radius was 25.33%, which was the sum of competition influence from aboveground and underground, and about 74.67% was from outside radius. For subject tree of DL, both in inside and outside radii were 55.37% and 44.64%, respectively. Comparing with the information from both species and two radii, the root-root competition from underground was an important component. DL grew well, and could reduce the impact of intraspecific competition for MA when both species mixed in a stand.

Ecosystem↗
PubMed2000

[Individual tree growth-competition model in mixed plantation of manchurian ash and dahurian larch].

Based on distance-dependent competition models and neighborhood interference models, the competition index components and competition effect coefficients were used to quantify the spatial competition among trees in the mixed plantation of ash(Fraxinus mandshurica) and larch(Larix gmelini). Taking each component of competition index as independent variables and the yearly volume growth as dependent variable, the competition-growth model was established with good regression result. The study provided a new approach to deal with the further improvement of spatial competition models and the plant competition-growth relationship ecological study.

Ecosystem↗
PubMedDate not supplied

[Prophylactic efficacy of aerosol preparations based on Abies siberica polyprenols in experimental influenza infection].

Preliminary investigations showed high preventive activity of two of three aerosol preparations of Abies sibirica polyprenols with nonionic surface active substances towards influenza infection. At least 2 aerosol administrations are needed to attain a high protective effect, the second dose depending on the first. Relationship between animal reaction to influenza virus infection changed in a nonmonotonous mode, depending on the drug dose injected during the first treatment: as the dose increased, the death rate first decreased and reached the minimum and then increased again. Such a reaction to aerosol treatment can be explained by the hypothesis of hyperstimulation followed by exhaustion of the host defense systems after high doses of the preparation.

Aerosols↗
PubMedDate not supplied

[Mechanisms of action of aerosol preparations based on Abies siberica polyprenols in experimental influenza infection].

Humoral and cellular mechanisms of Abies sibirica polyprenol effects on nonspecific resistance of mice to influenza A/Aichi/2/68 virus were investigated. Two aerosol doses of polyprenols had a high protective effect in mice challenged with influenza virus. Aerosol polyprenol preparations in the studied doses induced no interferon or tumor necrosis factor production in the lungs. Lung macrophage counts and capacity to produce superoxide anion radicals increased in survivors after influenza in comparison with intact animals. Double aerosol administration of polyprenols prior to influenza infection promoted an increase in the thymus weight, bronchoalveolar tract cell counts (predominantly at the expense of lymphocytes), and of superoxide-producing potential of macrophages, which, in turn, can contribute to improvement of the defense potential of the organism towards influenza virus.

Aerosols↗
PubMed2002

[Age structure and dynamics of Keteleeria davidiana var. chien-peii population in Guizhou Province].

Type and dynamics of age structure of Keteleeria davidiana var. chien-peii population and its relationship to community succession and environment were analyzed. The results showed that the age structures were classified into four types:growing, stable, initial and middle sensecent types. The survival curves had concave, convex, disconnected and dotted shapes. Along with development and succession of community, the age structure changes from growing, stabilized, senescent to residual type. The important factors causing change to the age structure were biological features of Keteleeria davidiana var. chien-peii, development of broad-leaved tree species, geographic isolation, and human disturbance.

Aging↗
PubMed2005

[Pseudolaric acid B induces human melanoma A375-S2 cell apoptosis in vitro].

OBJECTIVE: To study the mechanisms of pseudolaric acid B-induced apoptosis on A375-S2 cells. METHOD: MTT, fluorescence microscope observation, DNA agarose gel electrophoresis and Western blot analysis wereused. RESULT: Pseudolaric acid Binduces A375-S2 cell apoptosis in a time and dose-dependent manner. Apoptotic bodies and DNA ladder were observed in 5 micromol x L(-1) pseudolaric acid B-treated A375-S2 cells for 36 h. The expression of Bcl-2, Bcl-xL and ICAD was reduced time dependently, whereas the expression of Bax was increased. CONCLUSION: The major cause of pseudolaric acid B induced cytotoxicity on A375-S2 cells was apoptosis. Mitochondria proteins and ICAD might be involved in the apoptotic pathways of pseudolaric acid B-treated A375-S2 cells.

Apoptosis↗