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141.
Air pollution has become an actual problem in Balikesir because of rapid urbanisation and increasing of the polluting sources. Air pollutionproblems occur under the unfavorable meteorological conditions which increase in frequency of occurrence in winter due to use of low quality lignite coals for heating. The `Protection of Air Quality' in Turkey dated 1986 is based on the human health criteria. But the critical limit values are lethal for the forest trees as far as SO2 is concerned. The field observations showed that leaves of the trees have yellow spots indicating acid burns in Balikesir. This study aims at determining the relationships between the SO2 concentrationsin the air under selected climatic conditions, and the effects of air pollution on forest trees in Balikesir. Samples of leaves were collected from the City Parks in Balikesir, Deirmenboaz forested area located 10 km far fromBalikesiron the Balikesir-Bursa highway, and from the forestation areas near the Balikesir-Edremit highway. Sulfur contents of the leaves were very high especially in the city (2650–5300 g m-3).Samples from other areas had values lower than this range but above the usual values (850–3612 g m-3). The diameter increments of the trees were found to be lower and these results clearly showed the adverse impacts. Negative correlations were found between these sulfur concentrations and the daily mean temperatures and wind speeds. Positive correlation was seen between these concentrations and pressures, humidities. Emission sources must be controlled in order to safeguard the forests which protects the soil, facilitate water production, assimilate carbon dioxide in air and produce oxygen. It must be considered that the problems are not only regional but have a global identity. 相似文献
142.
Clow David W. Striegl Robert G. Nanus Leora Mast M. Alisa Campbell Donald H. Krabbenhoft David P. 《Water, Air, & Soil Pollution: Focus》2002,2(2):139-164
A chemical survey of 69 high-altitude lakes in seven national parks in the western United States was conducted during the fallof 1999; the lakes were previously sampled during the fall of 1985, as part of the Western Lake Survey. Lakes in parks in the Sierra/southern Cascades (Lassen Volcanic, Yosemite, Sequoia/Kings Canyon National Parks) and in the southern RockyMountains (Rocky Mountain National Park) were very dilute; medianspecific conductance ranged from 4.4 to 12.2 S cm-1 andmedian alkalinity concentrations ranged from 32.2 to 72.9 eqL-1. Specific conductances and alkalinity concentrations were substantially higher in lakes in the central and northernRocky Mountains parks (Grand Teton, Yellowstone, and GlacierNational Parks), probably due to the prevalence of more reactivebedrock types. Regional patterns in lake concentrations of NO3 and SO4 were similar to regional patterns in NO3 and SO4 concentrations in precipitation, suggestingthat the lakes are showing a response to atmospheric deposition.Concentrations of NO3 were particularly high in Rocky Mountain National Park, where some ecosystems appear to be undergoing nitrogen saturation. 相似文献
143.
Only a few empirical studies on forest aesthetics have adopted a water-based perspective for observers and have investigated
the perceived visual quality of forested shorelines. In forested environments with many lakes, such as the boreal forest in
the Canadian Shield, individuals have greater exposure to forests from water-based rather than in-stand vantage points. This
study employed the psychophysical research direction to explore the relationships between scenic beauty and biophysical characteristics
of the forested shorelines in the boreal forests. Two model forms were tested. One model related the variation of shoreline
forest aesthetic evaluations of near-vista views (140 m offshore) to a set of forest mensuration data. Tree size, tree mortality,
conifer shrubs, tree density, amount of hardwood, and slope explained 60.2% of the variance in scenic beauty between the study
sites. A second model was calibrated to test the relationship between an already existing ecosystem vegetation classification
system and the aesthetic evaluations of the same forested shorelines. When the ecosystem classification was simplified to
eight groups, the model explained 48.5% of variance. These models suggest that the psychophysical approach to studying aesthetics
can be applied successfully to near-vista evaluations of scenic beauty. The finding that a forest ecosystem classification
system is highly related to scenic beauty suggests that, at least in the boreal forest, managers can reasonably estimate the
scenic beauty of forested shoreline environments from an ecosystem classification, with little need for intensive data on
these sites. 相似文献
144.
We examined the impact of single-tree selective logging and fuel reduction burns on the abundance of hollow-nesting bird species
at a regional scale in southeastern Queensland, Australia. Data were collected on species abundance and habitat structure
of dry sclerophyll production forest at 36 sites with known logging and fire histories. Sixteen bird species were recorded
with most being resident, territorial, obligate hollow nesters that used hollows that were either small (<10 cm diameter)
or very large (>18 cm diameter). Species densities were typically low, but combinations of two forest management and three
habitat structural variables influenced the abundances of eight bird species in different and sometimes conflicting ways.
The results suggest that habitat tree management for biodiversity in production forests cannot depend upon habitat structural
characteristics alone. Management histories appear to have independent influence (on some bird species) that are distinguishable
from their impacts on habitat structure per se. Rather than managing to maximize species abundances to maintain biodiversity, we may be better off managing to avoid extinctions
of populations by identifying thresholds of acceptable fluctuations in populations of not only hollow-nesting birds but other
forest dependent wildlife relative to scientifically valid forest management and habitat structural surrogates. 相似文献
145.
大兴安岭林区地下火形成火环境研究 总被引:6,自引:0,他引:6
地下火作为森林中一种难以控制的燃烧现象,其形成机理极为复杂。我国大兴安岭林区是森林地下火的多发地区。对该地区2002年发生的地下火研究表明:丰富的近土壤层和地下可燃物是森林地下火发生的物质条件,气象条件促进了森林地下火的发生,特别是在遇到降水少、长期干旱、地面温度增加、相对湿度降低和可燃物干燥的情况下,就很容易引起地下火灾。地下火有地理和时间分布特征。地表火主要发生在原始森林区域,如针叶林、阔叶林或针阔混交林,都有可能发生地下火。地下火一般燃烧速度慢,持续时间长,燃烧充分,具有隐蔽性强、燃烧不连续、方向易变等特点,地下火在所有火灾中对森林危害最大,特别是对落叶松、樟子松、云杉等的破坏更为严重。 相似文献
146.
Lowest Effect Levels of Lead and Mercury on Decomposition of Mor Layer Samples in a Long-Term Experiment 总被引:2,自引:0,他引:2
Indications of possible negative effects of lead (Pb) and mercury(Hg) on microbial respiration in Southern Swedish forest humus layers led to experiments on dose-response relationships by additions of metal salts in the laboratory. Respiration rates andweight loss due to decomposition of organic material were measured. For relevance to field situations metal doses were low,the time span was long, 550 days including freeze storage, and microbial activity was kept up by plant litter additions. We looked for effects of Pb and Hg at levels moderately elevated above the Southern Swedish reference, as well as combined effectsof Pb + Hg. A reduction in respiration and decomposition of10% was found at about 225–245 g g-1 of total Pb, i.e. ata Pb level elevated 3.5 times. Although small effects of Hg werefound even at the lowest dose level, 10% inhibition of microbialactivity appeared temporarily at about 2–3 g g-1 of total Hg, i. e. at 6–8 times the reference level. There were nolong-term additive effects of Pb and Hg on decomposition. Type of anion had a strong influence on the test, chlorides of Pbbeing more toxic than nitrates. Long-term monitoring and maintenance of microbial activity during the experiment were prerequisites for the occurrence of effects at low metal levels. 相似文献
147.
Traditional Land-Use Systems and Patterns of Forest Fragmentation in the Highlands of Chiapas, Mexico 总被引:1,自引:0,他引:1
Ochoa-Gaona S 《Environmental management》2001,27(4):571-586
The influence of slash-and-burn agriculture and tree extraction on the spatial and temporal pattern of forest fragmentation
in two municipalities in the highlands of Chiapas, Mexico was analyzed. The data series were derived from two subsets of satellite
images taken in 1974 and 1996. The analysis was based on area, edge, shape, core area, and neighbor indices. During the 22
years, the dense forest decreased by 8.9%/yr in Huistán and by 8.6%/yr in Chanal, while open/disturbed forest, secondary vegetation,
and developed area increased in both municipalities. The total number of fragments increased by 1.4%/yr and 2.3%/yr in Huistán
and Chanal, respectively. Dense forest showed the highest increase in the number of fragments (6%/yr in Huistán and 12%/yr
in Chanal), while edge length, core area, and number of dense forest core areas decreased. The larger fragments of dense forest
present in 1974 were divided into smaller fragments in 1996; at the same time, they experienced a process of degradation toward
open/disturbed forest and secondary vegetation. Two different fragmentation patterns could be distinguished based on agricultural
or forestry activities. Forest fragmentation did not occur as a continuous process; the pattern and degree of fragmentation
were functions of land tenure, environmental conditions, and productive activities. The prevalence of rather poor soil conditions,
small-holdings, growing human population densities, increasing poverty, and the absence of alternative economic options will
maintain a high rate of deforestation and forest fragmentation in the studied region. 相似文献
148.
A simple method for the quantitative gradient analysis of a xerotermic forest-margin ecotone is described. In this method, the mean value of the coefficient of similarity between all plots of the transect is used for estimating the rate of changes in species composition. Changes in the phytosociological spectrum are analyzed. The method adequately reflects trends in the displacement of forest species by forest-margin, steppe, and meadow species. 相似文献
149.
This paper describes an application of multiple criteria analysis (MCA) in assessing criteria and indicators adapted for a
particular forest management unit. The methods include: ranking, rating, and pairwise comparisons. These methods were used
in a participatory decision-making environment where a team representing various stakeholders and professionals used their
expert opinions and judgements in assessing different criteria and indicators (C&I) on the one hand, and how suitable and
applicable they are to a forest management unit on the other. A forest concession located in Kalimantan, Indonesia, was used
as the site for the case study. Results from the study show that the multicriteria methods are effective tools that can be
used as structured decision aids to evaluate, prioritize, and select sets of C&I for a particular forest management unit.
Ranking and rating approaches can be used as a screening tool to develop an initial list of C&I. Pairwise comparison, on the
other hand, can be used as a finer filter to further reduce the list. In addition to using these three MCA methods, the study
also examines two commonly used group decision-making techniques, the Delphi method and the nominal group technique. Feedback
received from the participants indicates that the methods are transparent, easy to implement, and provide a convenient environment
for participatory decision-making. 相似文献
150.
森林资源在生态系统的保护中有着多方面的功能,保护森林资源对于环境保护、经济发展和科学研究有着重要意义。我国森林资源破坏严重,其中重要原因之一就是有关森林资源保护法律中存在着许多不完善之处。本文指出我国《森林法》关于法律责任规定存在的问题,提出了违法砍伐林木者应当承担远期保护责任的立法建议。 相似文献