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1.
Abstract

Monitoring and understanding of land use/forest cover dynamics as well as the factors affecting the changes in land use/forest cover are necessary for the sustainable management of natural resources. This study analyzes the spatial and temporal changes in land use and forest cover patterns in a typical mountain forest area in the Torul State Forest Enterprise area of Northeastern Turkey. The investigation evaluates the temporal changes of the spatial structure of forest conditions through the spatial analysis of forest-cover type maps from 1984 and 2005 using GIS and FRAGSTATS. The evidence presented here showed that there were drastic changes in the temporal and spatial dynamics of land use/forest cover, and between 1984 and 2005 there was a net increase of 19.9% in total forested area. Productive forest area increased by 3161 ha, although degraded forest area increased 9216 ha. In examining the changes of crown closure and development stages of the forest ecosystem during the study period, the forest stand area with low crown closures increased. The regenerated area increased because of regeneration activities while the other development stages were left to grow to older development stages in the period. These results regarding the crown closure and development stage show that forest quality has increased, and this is partly due to emigration of the rural population in Torul. In terms of spatial configuration, the landscape structure in Torul, the State Forest Enterprise area, changed substantially over the 21-year study period, resulting in fragmentation of the landscape as indicated by large patch numbers and smaller mean patch sizes, owing to heavy timber subtraction, illegal cutting, and uncontrolled stand treatments.  相似文献   

2.
The micromammalian fauna from Border Cave is analysed in terms of community composition and structure. Changes in these aspects are interpreted as indicative of changes in vegetation and climate in the vicinity of the cave during the period of deposition. It would appear that vegetation comprised relatively extensive forest or thick bush and dense grass during wetter phases and fairly open savanna woodland, even open grassland, during drier periods. Variation through time in mean mandibular size in two species of Crocidura (musk shrew) was different both in the two species and from what was expected. It now seems likely that the size change constitutes a response to complex phenomena and not simply to changes in temperature. Comparison with the Boomplaas A sequence indicates that the same general pattern of change is reflected at both sites but that there was a greater amplitude of change at Boomplaas A and that 18O stage 4 was dry at this site but wet at Border Cave. Evidence for periodic changes in the distribution of various species, and in some cases the mutually exclusive occurrence of ecologically equivalent species, has implications for the zoogeography of the species involved. In particular, the occurrence of Pelomys fallax (creek rat) in the lower half of the sequence is of interest in view of its present distribution 600 + km north of Border Cave.  相似文献   

3.
A synoptic view and interpretation of archaeological material from the mesolithic to the end of the Iron Age is provided, and this is viewed in the context of available palaeoenvironmental information. The evidence of various settlement forms suggests that mesolithic folk occupied the region for a long period, but their environmental impact appears to have been low although not negligible. In neolithic times a probably higher population density was capable of more thorough changes of vegetation but the total permanent alteration of ecosystems is thought to be small. Evidence for settlement is entirely inferential. By contrast, the Bronze and Iron Ages were periods of considerable clearance of forest and subsequent ecological changes like the leaching of soils increased, and traces of settlement are plentiful. New data on Iron Age settlements shows a downward movement of settlement sites and some Celtic fields are noted, though they are sparse compared with other uplands in Great Britain. A number of unanswered questions are posed, mostly about the nature of the settlement pattern in mesolithic, Bronze Age and Iron Age times. No complete synthesis of archaeological and palaeoenvironmental data is yet possible at this scale but certain parts of the moors have a high potential for reconstructing prehistoric geography.  相似文献   

4.
Numerous anthropogenic stressors have impacted the region surrounding Sudbury, Ontario, leading to pronounced vegetation and landscape change. Few long‐term records exist to understand the nature or timing of this change. We use pollen analysis from radiometrically dated sediments of Clearwater Lake to compare pre‐ and post‐settlement vegetation. Beginning ~1850 CE, the record shows major shifts in forest composition, coincident with settlement and the beginnings of lumbering. These changes are unprecedented for the past ~5000 years, and consist of increases in diversity and abundance of deciduous tree taxa and herbaceous disturbance indicators. While evidence of mining appears as early as 1900 CE, little effect is seen in the pollen record until ~1930 CE, when sedimentation rates increased and acidification of the lake also began. At this time, further increases in palynological disturbance indicators and minimum sediment organic matter levels indicate the period of maximum vegetation loss. As a result of reduced emissions since the 1970s, water quality began to improve in Clearwater Lake and there are some decreases in the abundances of shade‐intolerant disturbance indicators in the pollen record. However, the fact that the pollen assemblages do not resemble those prior to 1850 suggests lasting vegetation changes.  相似文献   

5.
Pollen analysis in relation to archaeological excavations has been carried out by the coast of central Norway to investigate for the first time long-term human impact on the vegetation in this region. A total of 297 samples from eleven archaeological sites and connected bogs/peat profiles reveal the vegetation development from the Mesolithic until today. Principal Component Analysis (PCA) is used to identify and elucidate the development through time and space, and the results of pollen diagrams from bogs are compared to the results of on-site pollen data. Human impact has transformed the vegetation to a varying degree in different time periods. A dense population connected to the shoreline is slightly visible as opening-up of the forest in the Mesolithic, whereas re-use of Mesolithic settlement sites for cultivation and grazing in the Late Neolithic and Early Bronze Age (from c. 2300 cal BC) is clearly documented by palaeobotany but weakly recorded in the archaeological record. Areas for settlement and cultivation are found from the Late Bronze and Iron Ages and pollen analysis contributes to a detailed picture of utilization of the landscape. The investigation shows the potential of combining archaeological and botanical data and analysing several small pollen sequences within an excavation area to reveal spatial patterns in vegetation development and human impact through time.  相似文献   

6.
Simplistic interpretations of the impact of newcomers on South American ecosystems retain currency in the environmental history of the subcontinent. European settlement is almost invariably seen to produce a continuous and linear destruction of the environment. On the basis of several crisis narratives contained in historical documents, it is widely accepted that there was a severe decrease in the extent of woody vegetal formations in the Río de la Plata area during the 19th and 20th centuries. To test this perception, and to develop a more accurate and more complex analysis of the environmental consequences of European occupation, this article focuses on Uruguayan territory from c. 1800 to 2000. Changes in the shape and extent of forest lands in this broad area were assessed by comparing 251 land-survey charts, drawn between 1830 and 1860, with modern-day forest maps. Changes in shrubland abundance were assessed by comparing current distributions with those inferred from the accounts of five travellers who passed through this territory in the first half of the 19th century. Over 200 years, there is no evidence of major changes in forest distribution, extent or shape, and shrublands appear to be much more abundant today than in the early 19th century. These observations, although based on limited data, contradict the most common interpretation of regional environmental evolution. They confirm other claims that the idea of forest destruction in the early 19th century was created and manipulated by actors involved in land conflicts. Close examination of such socially-constructed crisis narratives, through the use of new archives, leads to a better understanding of recent changes in the South American environment.  相似文献   

7.
A palaeoecological approach was undertaken to investigate the last 400 years of change in vegetation, fire, nutrient mobility, lake productivity and erosion associated with Aboriginal and European land-use practices in a forested environment in eastern Victoria. Melaleuca ericifolia scrub, although present prior to European settlement, has expanded around Lake Curlip in the last 200 years, primarily due to the action of fire on a forest already weakened by drought. A fern understorey has declined in extent and a more open aspect has developed in the forest. Fire has been a major component of vegetation dynamics in the historical period. Erosion rates were comparatively low and associated with fire during prehistoric times, but after European settlement its increase is more closely related to land clearance and flooding than fire. The response of vegetation to both anthropogenic and natural influences changed during the historical period. Although fire is an integral part of vegetation change, it is not an over-riding effect at Lake Curlip. Drain construction in the swamp has reduced the impact that any accumulation of pasture improvement chemicals may have had on eutrophication of the lake.  相似文献   

8.
Palaeoecological analyses from a small fen deposit, combined with pollen analysis from buried soil profiles under prehistoric burial mounds, have been used to investigate the timing and vegetation change associated with the Holocene development of a cultural landscape in southern Sweden. Traditional pollen analysis is complemented with plant macrofossil analysis and soil pollen analysis from within and in close proximity to the burial mounds in the coastal Bjäre peninsula, well known for its high density of well-preserved Bronze Age monuments. The vegetation development is linked to the construction of the burial mounds. A marked increase of cultural impact on the landscape is recorded during the Neolithic–Bronze Age transition and estimates of landscape openness suggest that by the onset of the Bronze Age, forest cover was only 20–40%, falling to 10% in the immediate vicinity of the burial mounds themselves. The coastal strip appears to have been affected by human activity to a greater extent and at an earlier date than sites from further inland in southern Sweden and the Bronze Age burial mounds were most likely designed to be visible in a largely deforested landscape.  相似文献   

9.
A major advantage of satellite remote sensing is that the imagery acquired provides a synoptic view of the landscape. Thus, repeat coverage by the satellite on a regular basis permits the detection of changes in land‐cover over time. This study demonstrates the application of remote sensing technology to the monitoring of mining activities at the Athabasca Oil Sands region of Alberta, Canada. First, we describe the techniques used to match a time sequence of Landsat imagery, both spatially and spectrally, to ensure that the spectral changes through time are due to land‐cover variations. A series of spectral trajectories were then extracted to assess changes in land‐cover through time. Secondly, a land‐cover classification was produced from the baseline 1984 imagery and, using historic and future mine extents, the classification was analyzed to determine the proportion of each land‐cover type affected through development. Results of the analysis indicate that since 1984 there has been a larger reduction in mixedwood dense and broadleaf vegetation classes than mixedwood sparse or dense conifer stands in the area. Based on the delineations of mine‐site activity, the area of woodland and wetland habitat subject to development has increased from approximately 2,520 hectare (ha) in 1984 to 32,930 ha in 2005.  相似文献   

10.
A sequence of samples of micromammalian remains from Klasies River Mouth on the south coast of South Africa provides evidence of vegetational and climatic change during the Late Pleistocene. The evidence suggests the presence of a vegetational mosaic similar to that of the present but with relatively more open vegetation at the time the central part of the sequence was being deposited than was the case at the beginning or the end. Fluctuations occurred in general climatic conditions, as indicated by the Shannon—Wiener index of diversity, but conditions appear to have remained relatively moderate throughout with no evidence of glacial or interglacial maxima. Changes in sea level are probably also reflected in changed proportions of various species of small mammal. The site has yet to be dated conclusively but the micro-mammalian data tend to support other lines of evidence which suggest that this sequence of deposits was laid down during isotope stage 5, probably substages 5d—a. Human response to the challenge of changing conditions can be shown to lag behind those changes as recorded by micromammals.  相似文献   

11.
The Early Medieval period in Ireland (c. A.D. 400–1150) has been the subject of much archaeological and historical study. The recent application of various forms of archaeological sciences, as well as palaeoenvironmental studies, to the archaeological record have, however, added fresh impetus to this study area. It seems increasingly evident that significant changes to economy and society occurred during this period and were not recorded in detail in the contemporary documentary sources. This paper will attempt to outline those changes and to assess whether, or to what extent, they were influenced by climate change.  相似文献   

12.
The normalised difference vegetation index (NDVI) has evolved as a primary tool for monitoring continental‐scale vegetation changes and interpreting the impact of short to long‐term climatic events on the biosphere. The objective of this research was to assess the nature of relationships between precipitation and vegetation condition, as measured by the satellite‐derived NDVI within South Australia. The correlation, timing and magnitude of the NDVI response to precipitation were examined for different vegetation formations within the State (forest, scrubland, shrubland, woodland and grassland). Results from this study indicate that there are strong relationships between precipitation and NDVI both spatially and temporally within South Australia. Differences in the timing of the NDVI response to precipitation were evident among the five vegetation formations. The most significant relationship between rainfall and NDVI was within the forest formation. Negative correlations between NDVI and precipitation events indicated that vegetation green‐up is a result of seasonal patterns in precipitation. Spatial patterns in the average NDVI over the study period closely resembled the boundaries of the five classified vegetation formations within South Australia. Spatial variability within the NDVI data set over the study period differed greatly between and within the vegetation formations examined depending on the location within the state. ACRONYMS AVHRR Advanced Very High Resolution Radiometer ENVSAEnvironments of South Australia EOS Terra‐Earth Observing System EVIEnhanced Vegetation Index MODIS Moderate Resolution Imaging Spectro‐radiometer MVC Maximum Value Composite NDVINormalised Difference Vegetation Index NIRNear Infra‐Red NOAANational Oceanic and Atmospheric Administration SPOT Systeme Pour l’Observation de la Terre  相似文献   

13.
《Political Geography》1999,18(4):437-476
The major issue of pollution control in water quality management is too often postponed or neglected in treaties concerning international river basins. Deterioration of transboundary waters cannot be dealt with unilaterally, and is often treated by the affected parties as secondary to the primary goal of economic development, even in settings conducive to high levels of pollution. This frequently results in environmental crises.This paper focuses on the way in which water quality is addressed in seven selected international basin accords. A framework for the structured comparisons of these basins is presented, based on the following four major forces that were found to influence the extent to which pollution issues were encompassed within the accords: flash-points, financial capacities, globalization/regionalization, and political windows of opportunity.The extent to which the above forces were mobilized to influence the water quality aspects of the treaties that have been studied, varies in accordance with: the severity of the water quality problem in relation to the basins' physical and human settings; the level of competitive uses of basin waters; the level of economic development of each riparian and the co-basin states as a whole; the locational setting and political power asymmetry among riparian states; and whether or not the institutions or agreements are basin-wide. The forces identified in this study are meant to provide some guidance to the factors conducive to failure or success.  相似文献   

14.
The analysis investigates the base heights of the ionosphere (hF) when spread-F is recorded at Brisbane, Australia, for 2 separate periods, namely July and August 1966 when spread-F occurs frequently and September and October 1966 when the activity is much lower. It is found that for July and August there is little tendency for spread-F to occur preferentially when the base height is above the average for the period. However, for the September–October period, spread-F occurs more often (by a factor of 2 or 3 depending on the geomagnetic activity) when the base height is above rather than below the average height. Also, this analysis shows that the overall spread-F occurrence (for both periods investigated) decreased to some extent following increased geomagnetic activity. This suppressed activity in the hours following geomagnetic activity is confirmed by superposed-epoch analyses using K indices (for Macquarie Island) as controls. It is suggested that the results of all the analyses might be explained by invoking a transition height in the ionosphere (controlled by the neutral-particle density of the upper atmosphere). Ionospheric off-vertical reflections from above this height would be recorded as spread-F traces in this model. This transition height would be low in July and August when the neutral-particle density is low and higher in September and October. It is further proposed that changes in the neutral-particle density could also be associated with reduced spread-F activity following increased geomagnetic activity, as well as influencing the diurnal, annual and sunspot-cycle variations of spread-F occurrence in mid-latitudes.  相似文献   

15.
Palaeo-environmental data from accumulated lake sediments at Phayao, northwest Thailand, provide a record of vegetation and environmental change from approximately 20,000 years Before Present. This is an important region archaeologically, with claims in the 1970s for an ‘early’ transition to domestication having arisen from a number of cave sites. Multiple indices are used to determine if people had an observable impact on the natural environment, and to determine the timing and magnitude of impacts associated with the development of agricultural land use in the region. An initial increase in sedimentation rate is apparent from ca. mid-2nd C AD. Changes in phytoplankton concentrations are apparent from the late 3rd C AD, and evidence for initial forest disturbance is apparent from the 5th or 6th C AD, with impacts becoming more severe over time to reach a pre-modern maximum in the 11th to the 13th C AD. Changes in agricultural practices are apparent during the 14th C AD, with an increased emphasis on rice agriculture and incipient management of the regenerating forests. Based on these data we suggest that agricultural intensification in the early part of the 1st millennium AD destabilised catchment slopes, through clearance of dryland vegetation and swidden agriculture. There is no direct evidence for the impacts of earlier peoples on the vegetation of the area, which we take to indicate that agricultural intensification was later here than in the lowlands to the east and south.  相似文献   

16.
In the context of global warming, changes in extreme weather and climate events are expected, particularly those associated with changes in temperature and precipitation regimes and those that will affect coastal areas. The main objectives of this study were to establish the number of extreme events that have occurred in northeastern New Brunswick, Canada in recent history, and to determine whether their occurrence has increased. By using archived regional newspapers and data from three meteorological stations in a national network, the frequency of extreme events in the study area was established for the time period 1950–2012. Of the 282 extreme weather events recorded in the newspaper archives, 70% were also identified in the meteorological time series analysis. The discrepancy might be explained by the synergistic effect of co‐occurring non‐extreme events, and increased vulnerability over time, resulting from more people and infrastructure being located in coastal hazard zones. The Mann Kendall and Pettitt statistical tests were used to identify trends and the presence of break points in the weather data time series. Results indicate a statistically significant increase in average temperatures and in the number of extreme events, such as extreme hot days, as well as an increase in total annual and extreme precipitation. A significant decrease in the number of frost‐free days and extreme cold days was also found, in addition to a decline in the number of dry days.  相似文献   

17.
A holistic landscape approach to cultural resource analysis of a set of archaeological sites in the central Penobscot Valley led to inferences regarding the Holocene physical and biological environmental context. Targeted environmental studies include (1) examination of forest and wetland changes through time and (2) lake-level studies as a key to paleohydrology. These studies were combined with broad-scale geomorphic investigations and detailed stratigraphic analyses, and studies of archaeological sites and their artifact assemblages. Together, these studies provide a picture of dramatic changes to the physical and vegetational landscape. These included reestablishment of a major river following deglaciation, evolution of extensive lakes to uplands and peatlands, and a shifting mosaic of open and closed forest composed of a variety of hardwood and softwood species. Inferences based on buried soils exposed in archaeological excavations supported climatic interpretations based on vegetation and paleohydrology. As a result, this work allowed evaluation of (1) site formation and preservation processes and (2) occupational patterns. Site formation and preservation of Early Holocene sites can be linked to sedimentation by hydraulic damming upstream of rapids at the mouths of tributary streams. Shifting human land use reflected by changes in occupation patterns appears to correspond to changes in forest composition as well as wetland and stream evolution through time.  相似文献   

18.
The period corresponding to the initial phase of cultural evolution in the Late Neolithic of SE Hungary (turn of the 6th and 5th millennia) is characterized by a major transformation recorded both in settlement structure and strategy, as well as material culture of the agrarian societies settled in the SE part of the Great Hungarian Plains. According to the available chronological data and archeology from the sites of multi-layered settlement complexes (tells) located on natural highs of the floodplain of the River Tisza, during the initial phase of its evolution representatives of the Tisza Culture were mainly confined to the SE part of the Great Hungarian Plains south of the Körös River. This period was followed by a relatively stable phase lasting about 150 years which hallmarked the greatest northward expansion of the culture. Some studies noticed strange features in connection with the first settlement complexes dated to the first period especially along the northern borderline of the culture’s distribution; i.e. a loose cluster of distinct settlement nuclei instead of concentration of settlements to a confined area characteristic of tells. Furthermore, by the end of the first phase, in the evolution of some settlements a northward shift of the houses away from the water was recorded. Most likely these reflect a socioeconomic response to some transformation in the local and/or regional riparian environment. As shown by our data gained from the paleoecological analysis of freshwater mollusks from a tell site, the referred pre-transitional period was characterized by pronounced floods causing major perturbations in the regional riparian environment. At the same time, the introduction of new subsistence strategies including shellfishing and fishing and the reordering of settlement structure was also recorded at several sites implying a successful adaptation to such most likely climate-induced perturbation, which is contemporary with the 5.1 ky event known in the literature.  相似文献   

19.
The timing of the introduction, proliferation and decline of backed artefacts in Australia has been much debated. In south-eastern Australia, after initially appearing at least 8500 years ago, backed artefacts greatly increased in number between 4000 and 3500 years ago to the extent that they are found in numerous sites and are recorded in large numbers in individual sites from that time. From about 1500 years ago they declined markedly in number and had seemingly disappeared by the time of British colonization. Models explaining their proliferation advance the proposition that increased backed artefact production was triggered by heightened foraging risk and/or social re-organisation brought about by a change in climate to a regime which was cooler and drier than any other time during the Holocene combined with intensified ENSO climatic conditions. Our study develops this hypothesis by inferring the use of backed artefacts at Mussel Shelter in the Sydney Basin through an integrated use-wear and residue analysis. These inferences provide new insights into the nature of the evolutionary changes in tool production and use in response to the period of altered climatic conditions.  相似文献   

20.
清至民国陇东森林分布的变迁及林业发展概况   总被引:3,自引:0,他引:3  
本文主要利用地方志文献 ,力图恢复清代至民国时期陇东地区森林分布和覆盖状况 ,反映这一时期该地区森林分布面积和分布空间的变化 ,并探求森林覆盖变化的内在原因。在这一时期内 ,陇东地区森林分布面积和空间均呈缩减的态势 ,天然森林进一步遭到破坏。清政府和民国政府虽然意识到森林破坏的严重性 ,并且采取了一些措施 ,如实行对森林开采的不同程度的封禁、制定法令制度来保护以及进行规模不等的植树造林活动等。但收效甚微 ,人工次生林没有发展起来 ,天然森林也继续不断减少  相似文献   

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