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1.
Forests cover 29% of the continents. Their importance for mankind is not only due to wood production but also by their manyfold influences on the biosphere. The properties of forest stands influence climate, water balance, air constituents and the dynamic of atmosphere. The welfare functions of forests can be observed in the global as well as in the local or microscale. Anthropogenic measures, as deforestation and air pollution, endanger the forests and by that one of the main pillars of nature on earth.  相似文献   

2.
E. J. Gärtner 《GeoJournal》1988,17(2):165-171
Present forest damage phenomena are observed for many tree species, on all soils and sites as well as in areas with considerable climatic variation. They cannot be explained without assuming a significant contribution of air pollution in particular as consequence of the two- to fourfold higher deposition under forest stands than on adjacent open areas. So far only loss and yellowing of needles or leaves are suitable operational symptoms for forest damage surveys. These indicate that in the Federal Republic of Germany for the period 1984–1987 in the important stands over 60 years of age a reduction of trees without damage symptoms from 31% to 24% occurred in spite of prevailing growth promoeing weather. This points to a considerable destabilization of forest ecosystems. As forests are complex ecosystems rather than just an assemblage of leaves, rootes or trees any interpretation of phenomena has to consider the complex and permanently changing interaction between the elements of the ecosystem themselves as well as its basic changing interaction between the elements of the ecosystem themselves as well as its basic environmental factors in atmosphere and soils. Field experience shows that for a given situation mostly several of the cause explaining hypotheses appear to we valid. Thus the phenomena are reflecting the influence of an array of stress factors acting directly on the foliage of the tree or indirectly through the soil and often in a synergic pattern. The model of considering anthropogene increased acid deposition with subsequent acidification of soils, damage of fine roots and impediment of water and nutrient supply of the tree is conclusive and isoprogressively being verified by experiments. For counteracting the observed destabilization and deterioration of forests a consequent policy of reduction of air pollution in its various forms and avoidance of forest management measures increasing system related acidification of forests are urgently required.  相似文献   

3.
Four pollen sequences along a transect from north-central Iowa to southeast Wisconsin reveal the distribution of prairie and forest during the Holocene and test the use of pollen isopolls in locating the Holocene prairie-forest border. Prairie was dominant in central Iowa and climate was drier than present from about 8000 to 3000 yr B.P. During the driest part of this period in central Iowa (6500-5500 yr B.P.), mesic forest prevailed in eastern Iowa and Wisconsin, suggesting conditions wetter than at present. Prairie replaced the mesic forest about 5400 yr B.P. in eastern Iowa but did not extend much farther east; mesic forests were replaced in southern Wisconsin and northern Illinois about 5400 yr B.P. by xeric oak forests. This change from mesic to xeric conditions at 5400 yr B.P. was widespread and suggests that the intrusion of drier Pacific air was blocked by maritime tropical air from the Gulf of Mexico until the late Holocene in this area.  相似文献   

4.
In many metropolitan regions, natural sources contribute a substantial fraction of volatile organic compound (VOC) emissions. These biogenic VOC emissions are precursors to tropospheric Ozone (O3) formation. Because forests make up 59% of the land area in Taiwan Province, China, the biogenic VOC emissions from forests and farmland could play an important role in photochemical reactions. On the other hand, anthropogenic emissions might also be one of the major inputs for ground level O3 concentrations. Hence, emission inventory data, grouped as point, area, mobile and biogenic VOC sources, are a composite of reported and estimated pollutant emission information and are used by many air quality models to simulate ground level O3 concentrations. Before using relevant air quality models, the emission inventory data generally require huge amounts of processing for spatial, temporal, and species congruence with respect to the associated air quality modeling work. The fist part of this research applied satellite remote sensing and geographic information system (GIS) analyses to characterize land use/land cover (LULC) patterns, integrating various sources of anthropogenic emissions and biogenic emissions associated with a variety of plant species. To investigate the significance of biogenic VOC emissions on ozone formation, meteorological and air quality modeling were then employed to generate hourly ozone estimates for a case study of a high ozone episode in southern Taiwan, which is the leading industrial hub on the island. To enhance the modeling accuracy, a unique software module, SMOKE, was set up for emission processing to prepare emission inputs for the U.S. EPA’s Models-3/CMAQ. An emission inventory of Taiwan, TEDS 4.2, was used as the anthropogenic emission inventory. Biogenic emission modeling was accomplished by BEIS-2 in SMOKE, with improvement of local LULC data and revised emission factors. Research findings show that the majority of biogenic VOC emissions occur in the mountainous areas and farmlands. However, the modeling outputs show that downwind of the most heavily populated and industrialized areas, these biogenic VOC emissions have less impact on air quality than do anthropogenic emissions.  相似文献   

5.
It is shown that the usage of forests and their working takes very distinctive forms. These depend in particular on human societies with their distinctive demand on the forest. The range of the contribution by the forests is shown by considering on one hand the slight usage by gathering and hunting people, on the other the protective forests of industrial states. This must be considered in any treatment of forests from the geographical view-point if a correct regional ordering of man's forestry activities is to be presented. The system of usage and working here presented can serve as a basis. Regional investigations are needed to refine the division, and here opens up a wide field of research. It is nevertheless accepted that the multi-functional character of forests, expressing the wishes and needs of the community, remains in the foreground of forest goegraphy.  相似文献   

6.
The tsunami that deeply impacted the North Indian Ocean shores on 26 December 2004, called for urgent rehabilitation of coastal infrastructures to restore the livelihood of local populations. A spatial and statistical analysis was performed to identify what geomorphological and biological configurations (mangroves forests, coral and other coastal vegetation) are susceptible to decrease or increase coastal vulnerability to tsunami. The results indicate that the width of flooded land strip was, in vast majority, influenced by the distance to fault lines as well as inclination and length of proximal slope. Areas covered by seagrass beds were less impacted, whereas areas behind coral reefs were more affected. The mangroves forests identified in the study were all located in sheltered areas, thus preventing to address the potential protecting role of mangroves forests.  相似文献   

7.
Numerical techniques were used to study chironomid distribution and abundance in lakes from a 1000 km transect in Finland, with special interest on the effect of local summer air temperatures on chironomid assemblages. The final aim of the study was to develop a chironomid‐based palaeotemperature inference model. The dataset consisted of 82 lakes (of which 77 were used in the model after deletion of outliers), with catchments spanning from boreal coniferous forests to mountain birch woodland and tundra vegetation. Numerical analysis showed that the mean July air temperature was the most significant variable explaining the distribution and abundance of chironomids in Finnish lakes. Weighted‐averaging partial least squares techniques were used to develop a palaeotemperature inference model for mean July air temperature reconstructions. The model performance statistics were favourable, with cross‐validated coefficient of determination (r2) of 0.78, root mean squared error of prediction of 0.721°C and maximum bias of 0.794°C. Based on these values, the transfer function is a valid means of performing quantitative palaeotemperature estimates in downcore studies. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

8.
This paper integrates studies on the natural subtropical montane evergreen broad-leaved forests (EBLFs) and secondary succession of the forests and plantations in Yunnan, to provide a basis for evaluating the sustainability of the forests in the mountain ecosystems of Yunnan, China. The EBLFs include mid-montane moist, monsoon, and semi-humid categories. The monsoon EBLF yielded the highest indices of the Shannon-Wiener H, Equitability J, Simpson D and Fisher’s alpha, followed by the mid-montane moist EBLF, then by the semi-humid forest. Since human uses have varied widely, the plant communities ranged from pioneer deciduous broad-leaved and/or pioneer coniferous stands to late-successional evergreen broad-leaved stands. The secondary succession pathways were from pioneer deciduous stands of Alnus accompanied by stands of pioneer coniferous Pinus and Keteleeria, through broad-leaved and coniferous mixed stands, to late-successional evergreen broad-leaved forests of Cyclobalanopsis and Castanopsis. In Yunnan, the EBLF is commonly replaced by plantations of exotic fast-growing Eucalyptus to produce industrial wood, oil, pulp and fuel. The result has been reduced plant diversity, and great loss of soil nutrients by erosion and runoff, as compared to the EBLF. Seventy-six plant species in the area have been ranked as critically endangered, endangered, or vulnerable. Their condition is seen as largely attributable to habitat loss or degradation. A clear understanding of ecological features and succession pathways of the EBLF can lead to more effective conservation and management of these fragile forests and the mountain ecosystems.  相似文献   

9.
At a time when the concept of ‘human and environmental symbiosis’ has taken on much significance, protection of suburban forests (i.e. forests adjacent to or near developed areas) is a topic that has drawn much attention. Suburban forests have, since ancient times, been places where people have gathered firewood and cultured trees. As a result, the vegetation of suburban forests is only partially natural and continues to change as the forms of human activity in and around them changes. Accurate forecasts of how suburban forests will change are, therefore, an important element in the debate over how to protect them. In this study, a suburban forest was analyzed with laser radar sensing, multi-spectrum scanning, digital photogrammetry analysis, aerial photograph interpretation, and a field survey. Data gathered using these techniques were compiled on a GIS to forecast future changes in the forest. Aerial photographs taken over the past 50 years were analyzed to illuminate changes in the forest over that period. Specifically, comparisons of precise Digital Elevation Models (DEMs) measured by using digital photogrammetry workstations made it possible to estimate growth in forest height. The possible future conversion of such results to estimates of amounts of carbon dioxide consolidated by forests should be very significant for discussions of global environmental problems. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

10.
Meta-analysis and other statistical methods were used to evaluate how changes in soil organic carbon (SOC) content in post-mining soils are related to different factors; the data were obtained from 17 studies covering 93 temperate post-mining sites in the Northern Hemisphere that had been revegetated by forest or grassland either by reclamation or natural succession. Because many studies have failed to report any measures of variance, only part of the data were used for meta-analysis. According to the meta-analysis, the rate of SOC accumulation was unrelated to vegetation type. In a separate analysis that included all available data and in which rates of SOC accumulation at each site were used as individual entries, the rate of SOC accumulation differed depending on the age of the site and vegetation type. Under deciduous forests, the rate reached a maximum after 5–10 years and then decreased. Under coniferous forests, the initial SOC values were lower than under deciduous forests, but slowly increased with age and reached a maximum after 30–40 years. No significant temporal trend was found in grasslands, probably because the data set included only relatively young grassland sites. Based on data from sites younger than 30 years, sites with grasslands and deciduous forests accumulated SOC faster than sites with coniferous forests. The rate of accumulation was negatively correlated with temperature under coniferous forests, but positively correlated with temperature in grasslands. This suggests that carbon sequestration is favored by cold climates in coniferous forests, but by warm climates in grasslands. Deciduous forests were intermediate. Compared to conifers, deciduous trees may support SOC sequestration deeper in the soil profile, which may enhance SOC stability. A large proportion of post-mining sites reach the pre-mining SOC stock within 20 years or less after reclamation.  相似文献   

11.
以新疆喀纳斯自然保护区为研究区, 评价了HJ-CCD影像数据估算植被叶面积指数(LAI)的能力及其对大气订正方法的敏感性.分别利用6S和FLAASH两种大气订正模型对HJ1B-CCD2影像进行大气订正, 比较了大气订正前后不同植被(针叶林、阔叶林、针阔混交林和草地)反射率及5种植被指数(NDVI、SR、SAVI、MSR、ARVI)的变化, 进而建立了4种植被类型LAI的遥感估算模型, 分析了LAI的空间分布格局.结果表明: 大气订正后可见光波段的反射率降低, 6S模型订正后近红外波段的反射率上升, 而FLAASH模型订正后近红外波段的反射率下降.大气订正后NDVI、SR、SAVI(除针叶林)和MSR上升, 6S模型订正后所有植被类型的ARVI下降, FLAASH模型订正后针叶林和阔叶林的ARVI上升, 而针阔混交林和草地的ARVI下降.大气订正提高了植被指数与LAI之间的相关性, 对于针叶林、阔叶林、针阔混交林而言, 利用6S模型订正后的反射率建立的模型优于FLAASH模型订正后的反射率建立的模型, 而草地却相反.经过大气订正, HJ-CCD影像数据可应用于研究区植被LAI的估算.研究区LAI的高值集中在湖泊和河流附近, 低值分布在海拔较高处.山地森林草原带、亚高山森林带、高山灌丛草甸带、高山冻原、高山冰川带植被LAI的平均值分别为2.6、3.9、2.5、1.7和1.0.  相似文献   

12.
The performances of regular support vector machines and random forests are experimentally compared for hyperspectral imaging land cover classification. Special characteristics of hyperspectral imaging dataset present diverse processing problems to be resolved under robust mathematical formalisms such as image classification. As a result, pixel purity index algorithm is used to obtain endmember spectral responses from Indiana pine hyperspectral image dataset. The generalized reduced gradient optimization algorithm is thereafter executed on the research data to estimate fractional abundances in the hyperspectral image and thereby obtain the numeric values for land cover classification. The Waikato environment for knowledge analysis (WEKA) data mining framework is selected as a tool to carry out the classification process by using support vector machines and random forests classifiers. Results show that performance of support vector machines is comparable to that of random forests. This study makes a positive contribution to the problem of land cover classification by exploring generalized reduced gradient method, support vector machines, and random forests to improve producer accuracy and overall classification accuracy. The performance comparison of these classifiers is valuable for a decision maker to consider tradeoffs in method accuracy versus method complexity.  相似文献   

13.
全球气候变化对红树林生态系统的影响与研究对策   总被引：10，自引：1，他引：10  
红树林生态系统出现于热带和亚热带的潮间带，是一个脆弱或敏感的生态系统，受到陆相和海相的双重影响，可能是全球气候变化影响的早期指示者。气候变化引起海平面升高的速率在９－１２ｃｍ／１００ａ时或超过红树林底质的沉积速率时，红树林就受到胁迫甚至消亡。平均气温上升可能造成红树林种类组成的变化。一定限度的升温有利红树植物的生长发育，但太高温度不利其叶的形成和光合作用，温度的累积作用会有相当大的影响，并通过土壤  相似文献   

14.
The present study was conducted in two forests in Abha (Capital of Asir Region) and two forests in Al Namas (130 km north of Abha), south western Saudi Arabia (Asir region) to investigate the effect of terraces on rainwater harvesting and growth of Juniperus procera Hochst. ex Endlicher. Farmers grow their crops within Juniper forests and woodlots by constructing terraces from soil and stones to harvest rainwater. Juniper forests and woodlots present important watersheds and sources for water. Study plots were established in four forests, two of which contained maintained terraces and the other two have been covered by abandoned and damaged terraces. The results showed that maintained terraces served as important means for rainwater harvesting, whereas abandoning of terraces resulted in increased soil loss, surface runoff, bulk density and reduced infiltration rates. Significant correlations and regression between soil loss, total runoff, soil bulk density and infiltration rate were provided. Diameter at breast height, total height, basal area, volume, number of trees, crown coverage and regeneration/ha of J. procera were significantly (P < 0.0001) higher in forests with maintained terraces compared with abandoned terraces. Finally, maintained terraces improved rainwater harvesting and growth performance of J. procera.  相似文献   

15.
额尔齐斯河源区森林对春季融雪过程的影响评估   总被引：2，自引：0，他引：2  
春季积雪融水是额尔齐斯河河源区最重要的水资源. 为探索森林对春季融雪过程的影响, 于2014年融雪期在额尔齐斯河河源区的卡依尔特斯河流域, 选择草地、林中空地和林下三种不同地貌条件, 分别观测积雪消融过程. 结果显示: 积雪消融过程中, 积雪深度和雪水当量的变化并不是同步的; 积雪深度的减小是持续发生的, 是新雪密实化作用的结果; 而雪水当量仅在日均空气温度高于 0 ℃ 时才出现快速的下降. 森林具有显著调节空气温度的功能, 三种类型观测点1.5 m处的日平均空气温度表现为草地>林下>林中空地, 其中, 消融期内草地的平均空气温度(-2.5 ℃)远高于林下(-5.4 ℃)和林中空地(-6.1 ℃); 森林的存在显著减小了空气温度的日较差. 草地、林中空地和林下积雪消融持续期分别为20 d、43 d和35 d, 消融期平均积雪消融速率分别为2.1 mm·d-1、1.5 mm·d-1和 1.2 mm·d-1, 即: 草地>林中空地>林下. 另外, 单棵树对积雪的消融速率有极其重要的影响: 树冠外一定距离内积雪的消融速率约为树冠下积雪消融速率的2倍以上; 但由于树冠超过70%的降雪截留效应, 树冠正下方的积雪消融结束时间仍提前树冠外侧约10 d. 积雪的消融由空气温度和辐射强度共同决定: 当日平均空气温度<0 ℃时, 辐射强度对积雪消融影响较大, 消融过程可由空气温度和辐射强度共同描述; 当温度>0 ℃时, 单独的空气温度可直接反映消融速率的变化. 研究还发现, 该流域内积雪的消融主要发生在每天的14:00-19:00, 该时段内积雪消融量约占全天消融总量的50%以上, 这对流域内积雪洪水预报和水资源利用及管理具有重要的指导意义.  相似文献   

16.
The impact of fire on the environment of the various Sierran conifer forests varies with intensity and frequency. Generally, however, fire (1) prepares a seedbed; (2) cycles nutrients within the system; (3) adjusts the successional pattern; (4) modifies conditions affecting wildlife; (5) influences the mosaic of age classes and vegetation types; (6) alters the numbers of trees susceptible to disease and insects; and (7) both reduces and creates fire hazards. Natural fire frequency apparently coincides with levels of fuel accumulation that result in burns of relatively low intensity at frequent intervals. This may average 8 yr in mixed conifer forests, although frequencies from 4 to 20 yr or more are found in particular sites.In all probability, giant sequoia and various pines of the Sierra survive today because of the role fire plays in the various forest types. National Park Service management policies are aimed at restoring fire, as nearly as possible, to its natural role in Sierran conifer forests. This is being accomplished by prescribed burning at lower and middle elevation types and by allowing lightning fires to burn in higher elevation forests.  相似文献   

17.
Impacts of afforestation on groundwater resources and quality   总被引：4，自引：0，他引：4  
Plans to double the proportion of land under forest cover in Ireland by the year 2035 have been initiated. The plan, primarily financially driven, ignores potential environmental impacts of forestry, particularly impacts on groundwater resources and quality. Since groundwater supplies almost 25% of Ireland's total potable water, these impacts are important. Field investigations indicate that afforestation leads to a reduction in runoff by as much as 20%, mainly due to interception of rainfall by forest canopies. Clearfelling has the opposite impact. Implications are that uncoordinated forestry practices can potentially exacerbate flooding. Groundwater recharge is affected by forestry, largely due to greater uptake of soil water by trees and to increased water-holding capacity of forest soils, arising from higher organic contents. Recharge rates under forests can be reduced to one tenth that under grass or heathland. Groundwater quality may be affected by enhanced acidification and nitrification under forests, due partly to scavenging of atmospheric pollutants by forest canopies, and partly to greater deposition of highly acid leaf litter. The slower recharge rates of groundwater under forests lead to significant delays in manifestation of deterioration in groundwater quality. Electronic Publication  相似文献   

18.
Recent legislation for the restitution of ownership rights to, and subsequent management of, formerly privately owned forests in postsocialist Bulgaria has focused largely albeit not exclusively on the restored forests from the perspective of timber production, that is, `forest' equals `harvestable timber resource'. Using ethnographic data collected in rural Rhodope Mountain communities, this paper presents a local-level perspective on forests and forest use, including the meaning that forests hold for local residents as a source of non-timber forest products such as mushrooms and medicinal plants, of animal pasture, and of firewood for household heating and cooking. This local social perspective is then contrasted with the timber-resource focus of the forestry legislation and subsequent planning for forest use. The scale of forest ownership – in part a function of the restitution legislation – is also addressed in relation to the practicalities of resource management. Generally, the paper demonstrates a mismatch between the postsocialist forestry legislation and local practice and conditions with regard to forests and the natural resources therein. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
This paper presents a quantitative reconstruction of the European late Pleistocene paleoclimate based on 72 rodent assemblages of five sequences from France, Germany and Bulgaria, covering the last interglacial-glacial cycle. They show a pattern of severe changes in temperature, with reduced precipitation during the coldest periods. A tentative correlation between the isotopic and palynological records and the paleotemperature changes is shown. These changes are consistent with variations in atmospheric circulation patterns in response to an expanding-retracting Fennoscandian ice-sheet. They can be attributed to the enhancement-weakening of the Scandinavian-Polar anticyclone and its associated dry winds, the south-north shifting of the North Atlantic Polar Front, and the varying supply of moist air from the Atlantic. Qualitative paleoenvironmental analysis shows broadleaved-deciduous forests in France and Bulgaria during most of the studied period. Taiga and tundra appeared in eastern France during the lower Würm. The German sequence indicates the presence of coniferous forests. These results are broadly consistent with other paleobiological records (mammalian, avian and insect faunas, isotopic record in dental tissue, palynology). The main discrepancies with the paleoclimate inferred from the palynological record are found during the coldest periods and are probably due to the interaction between vegetation, climate, and atmospheric CO2 levels.  相似文献   

20.
J. Wilk 《GeoJournal》2000,50(4):339-347
This study was performed to assess how local inhabitants in two tropical watersheds value forests and perceive both forests and their own capacity to influence the hydrological cycle. Both service and productivity functions were strongly valued, particularly forests' rain-bringing capacity. The view that forests are directly responsible for increased precipitation was especially strong in low rainfall areas. Forests were also seen as important for their ability to retain soil water. The human activity most often mentioned as affecting water availability was tree planting while water conservation structures were not seen as detrimentally affecting others. Water was pictured very strongly as being part of a cycle so that which is used by humans or trees is not considered lost but only displaced to return again as rain. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

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