A thousand years of environmental change and human impact in the alpine zone at Mt Kosciusko,New South Wales

This study reconstructs erosion, productivity, fire and vegetation records at Club Lake, in the alpine zone of Kosciusko National Park (the highest mountain region in Australia), and uses them to compare the prehistoric and historic periods. While disturbance in the prehistoric period was found to be minimal and mainly activated by fire, the impact of land uses after European arrival initiated a change in the erosion and fire regime and brought new grazing animals and exotic plant species. These triggered temporal changes in eutrophication and the nature of erosion, and significant vegetation changes. There was a reduction in the stability and persistence of species representation, especially in herbfield vegetation, and little recovery is evident despite the cessation of summer grazing. It is apparent that the area is very sensitive to disturbance by human impact and large fires.     

岩溶地区人类活动的水文效应研究现状及展望

在全球气候变化背景下,加之岩溶生态系统的脆弱性及敏感性,地表水与地下水交换迅速,岩溶水动力系统对人类活动及其造成的生态环境变化反馈敏感。岩溶地区人类活动导致的植被退化、石漠化等环境问题已对岩溶地区的水文水循环过程造成了严重影响,水资源问题已成为岩溶地区发展的重要限制因素。本文在对岩溶生态系统及水文环境特性分析的基础上,从土地利用变化的水文效应,人类活动对降水—径流的影响、岩溶水资源的开发利用、岩溶地下水污染及水文模型在岩溶地区的应用等方面,概述了岩溶地区人类活动水文效应的相关研究现状与不足,总结了未来岩溶地区人类活动水文效应的5个研究趋势,并探讨了研究中的重点及难点问题。     

Climate‐induced migration: Exploring local perspectives in Kiribati

A number of studies have indicated that the long term habitability of Kiribati, a low‐lying country in the central tropical Pacific Ocean, is tenuous given the impacts of climate change, particularly sea level rise. In an effort to plan for the resultant challenges ahead, a number of national policies and programs have surfaced to reduce the impact of localized changes on people's livelihoods. This study explores how local community members (n = 60) have taken it upon themselves to respond to the impacts of climate change by utilizing a number of different strategies. The results highlight that: first, respondents consider climate change to be the most concerning issue for sustaining their livelihoods; second, respondents have built physical defences, relocated temporarily or permanently, and sought government assistance to adapt to localized climate‐related impacts; and third, the majority of respondents indicated that they would migrate as a long term strategy to respond to the future impacts of climate change.     

A Late Holocene Vegetation and Environment Record from Byenup Lagoon,South-western Australia

South-western Australia has a Mediterranean-type climate and its infertile soils support a highly diverse angiosperm flora. Little is known of the vegetation history of this region, and this means that little can be said of the roles of environmental stability, climate change, or human impact on the maintenance or development of the high biodiversity of the region. This study presents a pollen and fossil charcoal record from two peat profiles from a freshwater lagoon region near Lake Muir, east of Manjimup, in south-western Australia. The record shows a glimpse of an early Holocene where a mix of Casuarina and eucalypts with an understorey of heath and some open herbaceous vegetation, including chenopods, occurred. Fire was not an important factor at this time. The main record begins from about 4800 BP, and shows a vegetation mix of Corymbia calophylla and Eucalyptus marginata, with the latter becoming dominant by about 3500 BP. Corymbia calophylla again becomes prominent in the last few centuries. A heathy understorey is present throughout the last 4800 years, but was apparently less dense during phases when C. calophylla was more prominent. Melaleuca woodland has been the main vegetation type around the wetland areas and areas of inundation since the mid-Holocene. Major fire periods at Byenup, around 4200 BP and between about 3000 and 2000 BP, did not result in major vegetation changes. An analysis of cation content in the sediments suggests that weathering and erosion rates have been relatively stable throughout the record, but an increase in phosphorus and possibly organic matter in the surface layers suggests that agricultural practices have led to changes in the chemistry of sediments. It is hypothesised that an increase in effective precipitation about 4800 BP led to the initiation of the continuous part of the sediment record at Byenup. This increase most likely resulted from a more effective westerly wind stream. Changes since this time are more likely a result of changing fire regime and the interaction of species, rather than climate shifts.     

风电场对草地植被生长影响分析——以内蒙古灰腾梁风电场为例

利用2000~2014年的MOD13Q1-NDVI数据,对内蒙古灰腾梁风电场及该电厂50 km缓冲区内的植被生长情况进行了分析。结合气象数据,重点探讨了风向对植被生长的影响。与2000~2008年风电场建设完成前植被生长相比,2008年后风电场运行对植被的生长产生了明显的影响,但影响范围和强度是不均匀的,结果表明：① 风电场运行对风电场区域内/外植被的影响机制是不同的,风电场区域内不利于植被的生长,而上/下风区域却有利于植被的生长;② 相对于风电场建成前,风电场建成后的2008 ~2014年缓冲区和风电场区域植被恢复比例分别上升了26.66%和13.14%,但上风区域却上升了51.83%,下风区域上升了41.07%。可见风电场上/下风区植被恢复比例,尤其是上风区植被的恢复比例要远高于其它区域;③ 距离风电场中心30~40 km的上风区很可能是受风电场影响最为明显的区域。     

Vulnerability and adaptation to climate-related fire impacts in rural and urban interior Alaska

This paper explores whether fundamental differences exist between urban and rural vulnerability to climate-induced changes in the fire regime of interior Alaska. We further examine how communities and fire managers have responded to these changes and what additional adaptations could be put in place. We engage a variety of social science methods, including demographic analysis, semi-structured interviews, surveys, workshops and observations of public meetings. This work is part of an interdisciplinary study of feedback and interactions between climate, vegetation, fire and human components of the Boreal forest social–ecological system of interior Alaska. We have learned that although urban and rural communities in interior Alaska face similar increased exposure to wildfire as a result of climate change, important differences exist in their sensitivity to these biophysical, climate-induced changes. In particular, reliance on wild foods, delayed suppression response, financial resources and institutional connections vary between urban and rural communities. These differences depend largely on social, economic and institutional factors, and are not necessarily related to biophysical climate impacts per se. Fire management and suppression action motivated by political, economic or other pressures can serve as unintentional or indirect adaptation to climate change. However, this indirect response alone may not sufficiently reduce vulnerability to a changing fire regime. More deliberate and strategic responses may be required, given the magnitude of the expected climate change and the likelihood of an intensification of the fire regime in interior Alaska.     

Late holocene environmental change in an upper Montane area of the snowy mountains,New South Wales

This study examines environmental change in the upper montane zone of the Australian Eastern Highlands during the late Holocene, by analysing vegetation, fire and erosion records contained within a small fen located in a frost hollow. Differences in environmental parameters across the prehistoric—historic boundary were particularly investigated in an attempt to characterise better the changes associated with the imposition of European land‐use practices. Decreases in arboreal pollen and an increased charcoal concentration near the base of the analysed sequence, interpreted to be about 1600 y BP until about 1300 y BP, are suggestive of reduced moisture availability. After this, a period of relative stability continued to the close of the prehistoric period. The arrival of Europeans in the region triggered changes in the sediment record, including an increase in the accumulation of sediment by an order of magnitude, and changes in the surrounding vegetation. Saturated isothermal remnant magnetism (SIRM) was found to be significantly higher in the historic period compared to the analysed prehistoric period, suggesting an alteration in the erosional processes within the catchment. The concentration of charcoal was comparable between the prehistoric and historic periods; however, the increased sedimentation rate of the historic period infers an increased accumulation of charcoal. Fire did not appear to be related to the vegetation changes evident in the historic period, perhaps due to the use of cool fires by the pastoralists.     

Temporal change in the landscape erosion pattern in the Yellow River Basin,China

Using Landsat TM data from 1995 and 2000, changes in the landscape erosion pattern of the Yellow River Basin, China were analysed. The aim was to improve our understanding of soil‐erosion change so that sustainable land use could be established. First, a soil‐erosion intensity index model was developed to study soil‐erosion intensity change in the study area. Over the 5 years, the areas of weak erosion, moderate erosion, severe erosion, and very severe erosion all increased. The area of weak erosion increased dramatically by 7.94×10⁵ ha, and areas of slight erosion and acute erosion decreased by 1.93×10⁶ ha and 4.50×10⁴ ha, respectively. The results show that while the intensity of soil erosion has gradually been decreasing as a whole, in some regions the soil erosion is becoming more severe. Based on landscape indices, the pattern of changes in soil erosion over the past 5 years was analysed. The changes in landscape pattern of soil erosion resulted from human activities. Analysis showed that human impact increases fragmentation, having three major effects on landscape pattern, reduction in patch area, variations in patch shape, and changes in spatial pattern. In the study area, population growth, farming, governmental policy and forest degradation are the major factors causing soil erosion change over a 5‐year period.     

An assessment of land use and other factors affecting sediment loads in the Rio Puerco watershed, New Mexico

Rapid channel erosion in the Rio Puerco watershed of northwest New Mexico has been attributed to land use, climate changes, and internal channel adjustments. The objectives of this study were to assess (1) the impacts of land uses on sediment load, (2) the quantitative relationships between land use and sediment load, and (3) the effectiveness of different erosion control methods. The impacts of land uses on sediment load were assessed via hypotheses that, holding other erosion-related variables constant, sediment load correlates positively with grazing intensity and with density of unpaved roads, and correlates negatively with the number of erosion control treatments. We calculated the average annual sediment load for 17 subbasins of 0.67–17.97 km² by comparing sediment accumulation at two points in time (mid-1960s and 1999) behind intact sediment retention structures. We assessed land use via grazing records and measurements of unpaved roads generated from aerial photographs. Soil characteristics, vegetation, and physical factors were quantified for each subbasin. Using 18 variables for each subbasin, we employed Mallow's C_p as a selection criterion. We used six statistical models, including multiple regression and principal components analysis, to determine inherent mathematical relationships between significant independent variables and sediment load. The results indicate that sediment load does not correlate with grazing intensity except in small, relatively low-relief basins with fewer bedrock exposures. However, this interpretation may be compromised by the low quality of data available to quantify grazing. Sediment load is highly sensitive to the presence of unpaved roads, which serve as high gradient, channelized conduits of water and sediment during storms. Sediment load does not correlate with erosion control except in the subset of small, relatively low-relief subbasins that also proved sensitive to grazing intensity. Overall, the statistical analyses suggest that the impact of land uses on sediment load can be assessed using the data available although physical factors appear more significant than land use in producing high sediment loads in the Rio Puerco subbasins. Historical erosion control techniques, as implemented in the Rio Puerco watershed, prove largely ineffective against accelerated sediment loads because they have not been appropriately implemented or maintained.     

Fire Severity,Water Repellency Characteristics and Hydrogeomorphological Changes Following the Christmas 2001 Sydney Forest Fires

Soil water repellency can enhance overland flow and erosion and may be altered by fire. The Christmas 2001 bushfires near Sydney allowed investigation of the relationship between fire severity, water repellency and hydrogeomorphological changes. For two sub-catchments with differences in fire severities in Nattai National Park, south-west of Sydney, this paper considers: (1) the links between fire severity based on SPOT image analysis and ground observation of fire severity and repellency; (2) the textural and organic/minerogenic characteristics of eroded sediment; and (3) erodibility, erosion and deposition of soils in both catchments. Ground surveys show that image analysis reflects well the degree of vegetation consumption by fire, but cannot adequately predict the degree of ground litter consumption, associated soil heating and repellency effects. Fire had varying effects on repellency, leaving it unchanged, destroying it or enhancing it, depending on the soil temperature reached. The main post-fire hydrogeomorphological changes have been widespread erosion and colluvial and alluvial deposition of topsoil in foot-slope locations and river systems, but only localised redistribution of the highly erodible, repellent sandy subsurface layer. The fire did not trigger major geomorphological change in the study area, but fires probably cause important topsoil and nutrient depletion and may also affect water quality.     

RELATIONSHIP OF ECO-ENVIONMENTAL CHANGE WITH NATURAL EROSION AND ARTIFICIALLY ACCELERATED EROSION

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Lake sediment evidence for late Holocene climate change and landscape erosion in western Iceland

Ecosystem variability must be assessed over a range of timescales in order to fully understand natural ecosystem processes. Long-term climate change, at millennial and centennial scales, is a major driver of natural ecosystem variability, but identifying evidence of past climate change is frequently confounded by human-induced impacts on the ecosystem. Iceland is a location where it is possible to separate natural from anthropogenic change in environmental archives, as the date of settlement is accepted to be around AD 874, prior to which the island was free from proven human impacts. We used a lake sediment core from Breieavatn, near Reykholt, a major farm of the Norse period in western Iceland, to examine landscape development. A change in pollen concentration in the sediments, especially the decline in Betula, indicated initial landscape degradation immediately post-settlement, whereas the chironomid fauna and reconstructed temperatures were relatively complacent during this period. The pollen evidence is corroborated by ¹⁴C analyses, which indicate an increase in older carbon entering the lake, inferred to have been caused by increased erosion following settlement. Further decreases in Betula pollen occurred around AD 1300, pre-dating a drop in chironomid-inferred temperatures (CI-T) of ~1°C over 100–200 years. The CI-T reconstruction also shows a significant cooling after ~AD 1800, likely indicative of the coldest phase of the Little Ice Age. The evidence suggests that the chironomid record was relatively unaffected by the increased landscape degradation and hence reveals a temperature reconstruction independent of human impact.     

A field study of wind erosion following a grass fire on the Llano Estacado of North America

Interactions between earth, wind, and fire have always played an important role in the formation and evolution of the level plains of the Llano Estacado of North America. The uppermost sediments of this vast region are aeolian deposits, formed by aeolian deposition into grassland vegetation. Grass cover enhances aeolian deposition by slowing near-surface winds and vegetation secures sediments once they are deposited. The benefits of grass cover, however, are lost when occasional fires remove protective vegetation from fields. After a fire, the underlying soil surface becomes exposed and susceptible to wind erosion until the vegetative cover is re-established. The purpose of this study was to explore the post-fire recovery process by monitoring temporal variations in aeolian transport and changes in the threshold velocity of a burned grass field located in Lubbock County, Texas. A continuous record of wind erosion activity was obtained during a six-month period as the surface recovered from a highly erodible state to a more vegetated and stable surface. Results suggest that the threshold wind speed of the field increased from less than 10 m/s immediately following the fire to above 19 m/s in a three-month period as vegetation naturally recovered.     

黄土高原祖厉河流域潜在植被分布模拟研究

植被空间分布格局深受环境影响, 分析植被与环境之间的关系一直是植物生态学的中心问题。论文从黄土高原自然植被恢复问题出发, 引出植被恢复的参照标准- 潜在自然植被。 依据气象站和雨量站观测资料, 建立气温降水与海拔高度和地理位置的统计方程, 以GIS 为技术支撑, 对两大环境变量进行空间化。通过野外观测取样, 结合气温降水的空间分布, 界定祖厉河流域不同草地覆盖度的生境空间。根据生境空间边界函数, 对整个流域内的潜在草地植被分布进行模拟。草地分布现状与潜在草地分布对比发现, 低覆盖草地由北向南扩展, 占潜在中覆盖草地面积的37.39%, 占潜在高覆盖草地面积的34.98%。中覆盖草地也在此向南部区域和北部山地扩展, 占潜在高覆盖草面积的11.51%。高覆盖草地收缩到南部和北部山地狭小地带, 仅占其应有区域的4.84%。     

Recent environmental changes inferred from the sediments of small lakes in Yellowstone's northern range

Recent sediments of eight small lakes in the northern winter range of Yellowstone National Park were cored to examine stratigraphic records of past changes in limnology and local environment that might be attributed to grazing and other activities of elk, bison, and other large ungulates. Cores of undisturbed sediment were analyzed at close intervals to depths covering the last 100–150 years according to chronologies established by lead-210 dating. Pollen analyses were made to show change in regional vegetation, and diatom and geochemical analyses were made to reveal possible limnological changes resulting from soil erosion and nutrient input from the lake catchments.Variations in sedimentary components prior to establishment of the Park in 1872 indicate some natural variability in environmental factors e.g., erosional inputs in landslide areas west of Gardiner. All lakes had abundant nutrient inputs.After the Park was founded, fire suppression may have been responsible for small increases in pollen percentages of various conifers and Artemisia tridentata (big sagebrush) at different times in different lakes. Perceptible decreases in pollen of willow, aspen, alder, and birch at different times may reflect local ungulate browsing, although drier climatic conditions may have been a factor as well.The most striking manifestation of accelerated erosion in a catchment was found at a lake located beside a road constructed in the 1930s. In contrast to changes at this site, the record of erosion at other lakes is hardly perceptible. Changes in sediment-accumulation rates seen at most sites result from redistribution of sediment within the lake after initial deposition.In the century following Park establishment, the abundance of planktonic diatoms relative to benthic taxa varies among lakes and may reflect differential nutrient inputs or changes in lake level. Four of the five lakes analyzed for diatoms show in the last few decades an increase in planktonic relative to benthic species, implying elevated nutrient inputs. The recent flora, however, is similar to that in pre-Park levels which suggests that these lakes have not been perturbed outside their normal range. Increased nutrient supply in recent decades for at least two of the lakes is supported by the geochemical data, which show an increase in biogenic silica and in organic matter.As a whole, our investigation of the sedimentary record does not support the hypothesis that ungulate grazing has had a strong direct or indirect effect on the vegetation and soil stability in the lake catchments or on the water quality of the lakes.     

Interactions between onshore bedrock-channel incision and nearshore wave-base erosion forced by eustasy and tectonics

We explore the response of bedrock streams to eustatic and tectonically induced fluctuations in base level. A numerical model coupling onshore fluvial erosion with offshore wave‐base erosion is developed. The results of a series of simulations for simple transgressions with constant rate of sea‐level change (SLR) show that response depends on the relative rates of rock uplift (U) and wave‐base erosion (?_w). Simple regression runs highlight the importance of nearshore bathymetry. Shoreline position during sea‐level fall is set by the relative rate of base‐level fall (U‐SLR) and ?_w, and is constant horizontally when these two quantities are equal. The results of models forced by a realistic Late Quaternary sea‐level curve are presented. These runs show that a stable shoreline position cannot be obtained if offshore uplift rates exceed ?_w. Only in the presence of a relatively stable shoreline position, fluvial profiles can begin to approximate a steady‐state condition, with U balanced by fluvial erosion rate (?_f). In the presence of a rapid offshore decrease in rock‐uplift rate (U), short (～5 km) fluvial channels respond to significant changes in rock‐uplift rate in just a few eustatic cycles. The results of the model are compared to real stream‐profile data from the Mendocino triple junction region of northern California. The late Holocene sea‐level stillstand response exhibited by the simulated channels is similar to the low‐gradient mouths seen in the California streams.     

多尺度土地利用与土壤侵蚀

土地利用能够通过改变一系列的自然现象和生态过程影响土壤侵蚀,尺度不同,土地利用与土壤侵蚀的作用机制也会发生变化。本文针对坡面尺度、小流域／流域尺度和区域尺度,综述了不同尺度上土地利用对土壤侵蚀的影响研究。其中,在坡面尺度上,土地利用与土壤侵蚀的研究主要包括土地利用方式和土地管理措施对土壤侵蚀的影响,相应尺度上的模型有USLE／RUSLE、WEPP等;在小流域／流域尺度上,土地利用与土壤侵蚀的研究主要涉及土地利用结构和土地利用格局对土壤侵蚀的影响,相关的模型有LISEM、AGNPS、EUROSEM和SEDEM等;在区域尺度上土壤侵蚀评价研究主要是通过尺度上推和宏观因子评价的方法进行。多尺度土地利用与土壤侵蚀研究作为自然地理学研究中的热点问题,在进一步的研究中需要关注多尺度综合与尺度转换、土地利用政策效应、土地利用格局与土壤流失过程等方面的研究内容。     

RELATION BETWEEN VEGETATION CHANGES, CLIMATE VARIABLES AND LAND-USE POLICY IN SHAANXI PROVINCE, CHINA

Shaanxi Province in China has been exposed to climate variability and dramatic land‐use policies. The aim here is to examine vegetation changes in this area on a regional scale from 2000 to 2004 in relation to land‐use changes and climate traits. The data in this assessment include remote sensing information from moderate‐resolution imaging spectro‐radiometer normalized difference vegetation index from 2000 to 2004, and climate data (precipitation and temperature) from 1956 to 2000. The results show an increase in vegetation production from 2000 to 2004, particularly in the north, which cannot be explained solely by climate impacts. Since the vegetation in the north is more dependent on climate variation than the other parts of Shaanxi due to more serious water limitation, the results suggest that the large‐scale land‐use policy implemented over the last decade, with a focus on northern Shaanxi, is possibly having an impact on the overall vegetation.     

A diatom-based Holocene record of human impact from a coastal environment: Tuckean Swamp, eastern Australia

Diatom-based paleolimnological studies are being increasingly used to track anthropogenic change in estuaries. Little is known, however, about the direction and nature of long-term environmental changes in Australian estuaries. In this study, shifts in diatom assemblages preserved in a ²¹⁰Pb and C¹⁴ AMS dated sediment core from Tuckean Swamp were analysed to determine environmental changes that had taken place as a result of changing land-use practices. Prior to European impact, the diatom assemblage remained relatively stable and was dominated by Actinocyclus normanii and Diploneis smithii. An increasing dominance of Cyclotella meneghiniana correlates well with changed land use activities in the catchment area and indicates an increase of freshwater influence in the swamp’s environment. A major shift in species composition began ∼1970, Eunotia flexuosa becoming dominant. The assemblage shifts recorded at this site appear to be consistent with environmental changes triggered by human activities such as vegetation clearance, drainage and the construction of a barrage. This study demonstrates the use of paleolimnoology in an estuarine environment to provide pre-impact data necessary for management of the aquatic environment.     

A Comparison of the Environmental Changes of the Post-European Period with those of the Preceding 2000 Years at Lake Keilambete,South-western Victoria

Several parameters representing aspects of vegetation, fire, erosion and lacustrine productivity are investigated to compare the environmental changes of the historic period against those of the last 2000 years at Lake Keilambete in south-western Victoria. The average sedimentation rate post-dating European settlement was found to be c .2.5 times that of the analysed pre-European period and the nature of this sediment is distinctly different. Pollen representation was generally stable prior to the European period, but instability increased subsequently, reflecting the influence of pastoralism and the increase in exotic plant species. An increased concentration (and variability) of carbonised particles in the historic period, despite the faster rate of sedimentation, suggests a complex change in the fire regime of the region. The productivity of Lake Keilambete has varied in the past (e.g. it was elevated between c .1750 and 1250 years BP) but the response to European land use was diminutive. The expression of the quantified sedimentary parameters as average accumulation rates suggests a marked difference in the rate of landscape processes between the pre- and post-contact periods. The environmental change of the post-European period suggests that this landscape was particularly susceptible to the land-use strategies of the European settlers.