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1.
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. 相似文献
2.
Lesley Head 《The Australian geographer》1989,20(1):37-46
To what extent were Australian vegetation patterns in 1788 a product of human activity? Pollen and charcoal evidence which addresses this question is reviewed. I discuss the nature of the evidence, particularly the difficulties involved in establishing relationships between charcoal and fire history, and between fire history and human activity. I then address the broader question from the perspectives of both time and space by examining three key periods which might be expected to provide relevant evidence: (i) the time of initial human colonisation of the continent; (ii) the late Holocene, when Aboriginal population densities are thought to have increased substantially; and (iii) the last 200 years, when Aboriginal influences on the landscape have been mostly removed. Impacts are likely to have been different in different environments, with vegetation types vulnerable to fire showing the most marked changes. I conclude with a discussion of ways alternative interpretations have been utilised by competing groups in land management debates. 相似文献
3.
羊啃食动力学模拟与内蒙古西部气候变化适应 总被引：1，自引：0，他引：1
将定性分析、民主参与式评估和定量数值模拟方法结合起来,对阿拉善气候变化适应问题进行了简要评估并重点分析了土地退化、放牧和草原管理策略之间的关系。阿拉善主要的适应政策是禁牧和生态移民。禁牧后荒漠草原植被得到恢复,但移民增加了绿洲压力,过度开垦又造成周边土地沙化;过度抽取地下水致使水位下降并伴随咸水入侵和地表盐碱化。禁牧的另一个副作用是造成草原鼠害加重及火灾风险增加,生物多样性也呈现先升后降趋势。一些灌木因缺乏啃食出现退化迹象等,说明一定程度的啃食有利于维持草原生态平衡。因此,动物是草原生态系统不可或缺的成员之一。我们用一个包含动物啃食等的森林生态动力模式模拟了啃食动力学,结果表明,有限的放牧有利于草场更新并能充分利用草原资源;过度放牧导致草场退化并伴随羊群死亡。因此,需要将圈养和限制性放牧结合起来,制定可持续性适应政策。 相似文献
4.
Loss of species richness and reduced abundance have been the main responses to perturbations of small- and medium-sized mammals in arid and semi-arid areas. Nonetheless, some mammal species whose habitat requirements are met in disturbed patches may benefit from structural changes in the environment brought about by perturbations.In desert areas of Argentina different mammal responses are attributable to both a lower complexity of disturbed patches and a decrease in sheltered places. Therefore, species associated with high plant cover either decrease in number or become locally extinct at sites affected by fire or grazing, whereas species using open areas are favored by these events.The negative effects historically assigned to different disturbances may be mitigated by adopting a hierarchical approach that considers patch diversity in different successional stages as well as the multiple opportunities of patch occupation by mammal species. 相似文献
5.
The “perfect landscape” concept is based on the notion that any specific geomorphic system represents the combined, interacting effects of a set of generally applicable global laws and a set of geographically and historically contingent local controls. Because the joint probability of any specific combination of local and global controls is low, and the local controls are inherently idiosyncratic, the probability of existence of any given landscape is vanishingly small. A perfect landscape approach to geomorphic complexity views landscapes as circumstantial, contingent outcomes of deterministic laws operating in a specific environmental and historical context. Thus, explaining evolution of complex landscapes requires the integration of global and local approaches. Because perfection in this sense is the most important and pervasive form of complexity, the study of geomorphic complexity is not restricted to nonlinear dynamics, self-organization, or any other aspects of complexity theory. Beyond what can be achieved via complexity theory, the details of historical and geographic contexts must be addressed. One way to approach this is via synoptic analyses, where the relevant global laws are applied in specific situational contexts. A study of non-acute tributary junctions in the lower Brazos River, Texas illustrates this strategy. The application of generalizations about tributary junction angles, and of relevant theories, does not explain the unexpectedly high occurrence or the specific instances of barbed or straight junctions in the study area. At least five different causes for the development of straight or obtuse junction angles are evident in the lower Brazos. The dominant mechanism, however, is associated with river bank erosion and lateral channel migration which encroaches on upstream-oriented reaches of meandering tributaries. Because the tributaries are generally strongly incised in response to Holocene incision of the Brazos, the junctions are not readily reoriented to the expected acute angle. The findings are interpreted in the context of nonlinear divergent evolution, geographical and historical contingency, synoptic frameworks for generalizing results, and applicability of the dominant processes concept in geomorphology. 相似文献
6.
CHRISTINE ERIKSEN 《The Geographical journal》2007,173(3):242-256
Despite the historical importance of fire as a savanna land management tool, much controversy still surrounds discussions on anthropogenic fire utilization and the sustainability of indigenous land management practices in African savannas. This controversy is arguably a result of a discord between official fire policies and actual indigenous fire practices – a discord based on a gap in existing knowledge of, and a lack of informed literature on, the importance of fire for socio-economic and environmental survival in savanna environments. Addressing a continuing lack of research on the political ecology of fire, this study investigates the historical and present day socio-economic, environmental and political frameworks that affect anthropogenic burning regimes and land management in the Kafinda Game Management Area and Kasanka National Park in Zambia. A series of participatory research activities revealed the continuing importance of fire to rural livelihoods, but that a mismatch in desired burning regimes exists between local stakeholders. The paper argues that local power relations are preventing the local communities from adopting burning regimes that would be more environmentally sustainable and more in line with present day farming systems. 相似文献
7.
《Journal of Arid Environments》1999,41(1):27-35
The effect of both a non-prescribed summer fire and grazing at high stocking rate following fire on plant community composition, the frequency of occurrence of bare soil, grasses and shrubs, species diversity and biomass of herbaceous forage were evaluated for three growing seasons after fire. Changes in community composition occurred as a consequence of both fire and grazing. Communities were dominated by unpalatable shrubs and grasses in unburned sites as a result of a long history of overgrazing. Fire contributed to a conversion of those shrublands to communities with a more favourable balance between woody and herbaceous species. The frequency of palatable grasses and herbaceous forage biomass increased by a factor ofc. 3 at the expense of woody vegetation. Grazing after fire had significant positive (i.e. decrease in undesirable grasses) and negative (i.e. increase in bare soil) effects. 相似文献
8.
Research on grazing effects usually compares the same sites through time or grazed and ungrazed sites over the same time period. Both approaches are complicated in arid environments where grazing can have a long undocumented history and landscapes can be spatially heterogenous. This work employs both approaches simultaneously by comparing grazed and ungrazed samples through both time and space using fossil plant macrofossils and pollen from packrat middens. A series of 27 middens, spanning from 995 yr BP to the present, were collected from Glen Canyon in southeastern Utah, USA. These middens detail vegetation change just prior to, and following, the historical introduction of domesticated grazers and also compares assemblages from nearby ungrazable mesas. Pre-grazing middens, and modern middens from ungrazed areas, record more native grasses, native herbs, and native shrubs such as Rhus trilobata, Amelanchier utahensis, and Shepherdia rotundifolia than modern middens from grazed areas. Ordinations demonstrate that site-to-site variability is more important than any temporal changes, making selection of comparable grazed versus ungrazed study treatments difficult. But within similar sites, the changes through time show that grazing lowered the number of taxa recorded, and lessened the pre-existing site differences, homogenizing the resultant plant associations in this desert grassland. 相似文献
9.
Impact of rainfall variability and grazing pressure on plant diversity in Mongolian grasslands 总被引：1，自引：0，他引：1
Climate and grazing are the main drivers of plant community composition and species richness in arid environments. This study aimed to examine the vegetation response to a spatial precipitation gradient, interannual rainfall variability, and grazing pressure in Mongolia. To examine the effect of a spatial precipitation gradient, we compared species richness among six sites. To investigate the effects of interannual rainfall variability and grazing pressure, we compared species richness for 2 years at two sites, in desert-steppe and steppe areas. The regional gradient in annual precipitation showed positive and negative relationships with grass richness and shrub richness, respectively, although total species richness did not vary significantly. The proportions of the different functional groups were affected by grazing pressure and rainfall variability in both zones. In the desert-steppe zone, species richness was lower in the drier year but did not vary with grazing pressure. In the steppe zone, species richness varied significantly with grazing pressure but did not vary between years. Precipitation would be more important than grazing pressure on vegetation changes in drier areas with high rainfall variability. 相似文献
10.
To understand the effects of grazing activities and climate change on sandy grassland ecosystems in northern China, a livestock field grazing and enclosure experiment was conducted from 1992 to 2006 in Horqin Sand Land, Inner Mongolia. The results showed that sustained heavy grazing resulted in serious degradation of the vegetation; moderate grazing can maintain vegetation stabilization; and light grazing can promote rapid restoration of degraded vegetation. The livestock productivity was the highest in the moderate grazing grassland, and sustained heavy grazing resulted in rapid decrease of the livestock productivity. Heavy grazing can cause a retrogressive succession of grassland vegetation, whereas moderate and light grazing may promote progressive succession of plant species. The effects of changing climate on succession processes were not significant in the short term; a warm-humid climate is favorable to restoration of degraded vegetation, whereas a sustained warm-drought climate may result in degradation of grassland vegetation. Heavy livestock grazing should be stopped for the sustainable use of grassland; the proper grazing intensity for sandy grassland is two to three sheep or sheep equivalents per hectare in Inner Mongolia. 相似文献
11.
中国泥石流形成环境剖析 总被引：2，自引：0，他引：2
丰富的松散固体物质、充沛的水源和陡峻的地形,作为泥石流形成的三个基本条件,已得到学者们的认同。就本质而言,这三者可归纳为能量和物质两大因素。本文从中国泥石流区域分布着眼,从不同尺度的自然环境因素和人为活动,探讨中国泥石流形成发展的基本规律。研究结果表明,大尺度的区域地质背景、大地貌单元和犬气候系统是控制泥石流形成发育的主导因素;不稳定斜坡因子、小尺度水文气象因子、流域形态因子、森林植被因子等,在大尺度因素的基础上,对泥石流的形成有重要影响;历史上,特别是近期人类经济活动对环境的不良影响,加剧了泥石流的发展。泥石流灾害非单一因子所致,而是诸多因子综合作用的结果,是山地环境退化的产物。泥石流活动具有开放性、内外营力作用的共同性以及自然因素和人为因素的复合性这三大特点。 相似文献
12.
Marianne C. Edwards Jane Wellens Dawud Al-Eisawi 《Applied geography (Sevenoaks, England)》1999,19(4):3953
In this paper we discuss how low spatial resolution (1 km) ERS ATSR-2 and NOAA AVHRR satellite data were used to map and monitor changes in the grazing vegetation of the Badia region of Jordan. This area is typical of many arid zone grazing areas, comprising sparse vegetation and highly reflective soils. These two factors were found to severely limit the usefulness of satellite-derived vegetation indices that are frequently used to map and monitor vegetation in more temperate areas. Furthermore, the relationship between vegetation indices and percentage vegetation cover was found to be site-specific, thus reducing their application for large-scale vegetation monitoring. As an alternative, a hybrid geometric optical/empirically based model was developed for the area. This was based on the illumination geometry and reflectance values from the red and near-infrared scattergram of the satellite images. The output of the model was a series of maps indicating percentage vegetation cover for different dates and these were used to construct maps showing areas of vegetation change. Strong correlations (r2=0.837) were found between estimates of percentage vegetation cover derived from the model, and measurements made at a series of 16 field sites in the area. The use of geometric optical models based on satellite imagery improves the ability to map areas of grazing vegetation in arid areas such as the Badia and provides a good alternative to the use of vegetation indices. 相似文献
13.
基于国内现行的森林火险气象指数和单因子火险贡献度模型,以及逻辑回归模型和随机森林模型,在林火预报中引入微波遥感土壤水分信息,使用MCD14DL火点数据集和地面气象观测资料对广东省不同时间尺度的林火发生概率进行预测。结果表明：逻辑回归模型和随机森林模型构建的林火预测模型显著优于现行的森林火险气象指数和单因子火险贡献度模型,预测精度提升约20%。其中,随机森林模型对林火频数的解释程度最高（两者相关系数为0.476）。此外,加入微波土壤水分信息后,相较原有的基于气象要素的林火预测模型,2种机器学习模型的预测精度均略有提升,体现了表层土壤水分信息在林火预报中的重要性。研究可为高效提取对地观测信息,以改进华南地区不同时间尺度的林火预报工作提供参考。 相似文献
14.
Multivariate analysis of landscape wildfire dynamics in a Mediterranean ecosystem of Greece 总被引：5，自引：0，他引：5
Kostas D Kalabokidis Nikos Koutsias Pavlos Konstantinidis† Christos Vasilakos‡ 《Area》2007,39(3):392-402
This paper focuses on spatial distribution of long-term fire patterns versus physical and anthropogenic elements of the environment that determine wildfire dynamics in Greece. Logistic regression and correspondence analysis were applied in a spatial database that had been developed and managed within a Geographic Information System. Cartographic fire data were statistically correlated with basic physical and human geography factors (geomorphology, climate, land use and human activities) to estimate the degree of their influence at landscape scale. Land cover types of natural and agricultural vegetation were the most influential factors for explaining landscape wildfire dynamics in conjunction with topography and grazing. 相似文献
15.
Palaeoecological studies have identified the broad patterns of environmental and climate change in highland south‐eastern Australia, but the detail of human impact on a variety of parameters and their interlinkages is largely missing. This study compares the erosion, productivity, fire and vegetation history in prehistoric and historical times at Burraga Swamp in montane rainforest in New South Wales. The known human impact is meagre; the major presently sustained impacts involve forestry in the surrounding sclerophyll forests and a low level of visits to the swamp by day‐walkers. While no significant changes in the largely oligotrophic conditions or in fire frequency were detected, changes in erosion rates and some vegetation change can be attributed to impacts since European settlement. There has been a small decline in eucalypts and a loss of fern cover, while grasses, Urtica and exotic species have expanded. It is clear that upland sites are sensitive to environmental change including low‐level human impact. 相似文献
16.
森林净初级生产力(NPP)反映了森林植被固定和转换光合产物的能力,表示了森林碳汇功能强度,也是评价森林植被的演替状况以及陆地生态系统承载力的主要指标。基于遥感、清查资料等方法估算NPP已经取得了一些进展,但传统的研究方法受限于观测(调查)年份,难以有效获取长时间尺度的区域森林种群或群落年际NPP。树轮资料较为有效地反映了历史时期森林植被的逐年生长状况,从而在估算高精度且长时间尺度区域森林种群及群落NPP中具有较大的优势。本文对利用树轮资料重建区域森林NPP的两种主要方法进行了总结,第一种方法主要是依据树轮资料提供的立木逐年生长量进行生物量以及NPP的估算;第二种方法则是利用树轮指数与其他植被指数的相关性间接反演过去时间段区域森林群落NPP的变化。上述两种估算NPP的方法均存在较多的限制性,未来利用树轮资料估算NPP的时空精度仍有待提高。 相似文献
17.
African Fire Cultures,Cattle Ranching,and Colonial Landscape Transformations in the Neotropics 
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下载免费PDF全文 Fire regimes emerge partly from human activities that reflect cultural‐ecological knowledge of the relationships among fire, vegetation, grazing, climate, and other variables, as well as social relations. More knowledge of such “fire cultures,” past and present, therefore remains necessary to better understand the causes and persistent consequences of landscape burning. In the neotropics, people have used fire for centuries to manage livestock pastures. Conventional wisdom has long posited that such practices derived solely from antecedent European and indigenous, Native American fire cultures. Analysis of accounts of rangeland burning from throughout the neotropics during colonial times, however, demonstrates that ranchers incorporated African fire cultures and that the timing of burning shifted from early during the dry season in the sixteenth century to late during the dry season by the nineteenth century. 相似文献
18.
Good, bad or 'necessary evil'? Reinterpreting the colonial burning experiments in the savanna landscapes of West Africa 总被引：2，自引：0，他引：2
A simple ecological model underlies contemporary fire policy in many West African countries. The model holds that the timing (or seasonality) of annual savanna fires is a principal determinant of vegetation cover. The model's origin can be traced to the ideas held by influential colonial scientists who viewed anthropogenic fire as a prime force of regional environmental degradation. The main evidence in support of the model derives from the results of a series of long-term burning experiments carried out during last century. The experimental results have been repeatedly mapped onto fire policy often taking the form of a three-tiered model in which fire exclusion is considered the ultimate management objective, late dry-season fire is discouraged and early dry-season fire is allowed but only under specific, often state-controlled circumstances. This paper provides a critique of contemporary fire policy in the region and the fire ecology model on which it is based. Through an analysis of burn scars for the 2002–3 fire season generated from ETM+ imagery, the study documents the spatiotemporal pattern of burning for an area in southern Mali. It argues that current policy, which is informed by an a-spatial model, cannot adequately account for the critical pattern of burning that is characteristic of the region. A reinterpretation of the burning experiments is presented in light of four factors: empirical data; recent developments in patch-mosaic theory; historical evidence on the effects of fire suppression; and data on indigenous burning strategies, all of which suggest a need to reconsider current fire policy. 相似文献
19.
Foy Lake in northwestern Montana provides a record of annual-to-decadal-scale landscape change. Sedimentary charcoal and pollen analyses were used to document fire and vegetation changes over the last 3800 years, which were then compared to similar records from AD 1880 to 2000. The long-term record at Foy Lake suggests shifts between forest and steppe as well as changes in fire regime that are likely the result of climate change. Fire activity (inferred from the frequency of charcoal peaks) averaged 18 fire episodes/1000 years from 3800 to 2125 cal year BP, and increased from 16 fire episodes/1000 years at 2125 cal year BP to 22 episodes/1000 years at 750 cal year BP, a period when the pollen data suggest that steppe vegetation yielded to increasing patches of forest cover. Between 2125 and 750 cal year BP, increased forest cover produced more background charcoal than before and after this period, when vegetation was dominated by steppe. Between 750 and 75 cal year BP steppe has expanded and fire episode frequency averaged 33 episodes/1000 years, increasing to a maximum of 40 episodes/1000 years at ca. 300 cal year BP and then decreasing to present levels. Since AD 1880, the pollen record indicates an increase in shrubs and grasses from AD 1895 to 1960 as a result of vegetation changes associated with timber harvesting and livestock grazing. No fires have been documented in the Foy Lake watershed since AD 1880. Charcoal from the extralocal fires of AD 1910, burning over 4,111,249 ha in Idaho, Montana, and Wyoming, however, is present in Foy Lake. Between AD 1970 and 2000, increased arboreal pollen in the record is consistent with observations that the forest has become more closed. The activities of Euro–Americans have led to a decline in forest cover between AD 1880 and 1970, followed by a recent increase as trees are now growing in areas previously occupied by steppe. Euro–Americans are likely the cause of a reduction in fire activity in watershed since AD 1880. 相似文献
20.
Katarina Pavlek Filip Bišćević Petra Furčić Ana Grđan Vesna Gugić Nino Malešić 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2017,117(1):22-35
Wildfires are an important factor of landscape dynamics in fire-prone environments of the world. In the Mediterranean, one of the most fire-susceptible environments globally, between 45,000 and 50,000 wildfires are recorded every year, causing disturbances in forest and grassland ecosystems. As a Mediterranean country, Croatia faces these problems, averaging over 1000 registered wildfires annually, with the coastal areas dominated by forest fires and continental Croatia by fires on agricultural lands. This research combines various landscape and socio-economic factors in the analysis of fire occurrence in Croatia’s southernmost region of Dalmatia. Around 275 of the largest fires (encompassing 98% of the total burnt area) registered in 2013 were investigated using OLS, and different spatial indices were employed to analyse regional variability in fire distribution. The results revealed that areas more prone to fires are the northern inland areas of Dalmatia and its entire coastal zone. Altitude and vegetation type demonstrated a correlation with fire occurrence, but an increase in population in the study area was also correlated with wildfire occurrence. Regarding vegetation, the grasslands and Mediterranean shrubland (maquis) were found to be the most fire-prone vegetation types in the study region, the distribution of which can be linked to different socio-economic and demographic processes occurring in the Eastern Adriatic. 相似文献