Impacts of grazing on lowland heathland in north-west Europe

Lowland heathland habitats are recognized to be of high conservation value throughout north-west Europe. Current management approaches focus on arresting natural succession to woodland, and include the use of vegetation cutting, burning and grazing by livestock. However, the introduction of grazing has proved controversial, highlighting the need for evidence regarding its effectiveness. A systematic review of the scientific literature was therefore performed, which identified 13 studies with appropriate comparators (such as untreated controls). Meta-analysis of these data indicated that grazing can result in an increase in the ratio of grassland to ericoid shrub cover, but insufficient experimental evidence was available to assess the effectiveness of any other intervention, indicating a lack of replicated studies with controls. Two forms of expert knowledge were also compiled, based on information in the scientific literature excluded from the meta-analysis, and questionnaire responses of heathland managers. While these two evidence sources were generally in close correspondence, beliefs of heathland managers contradicted the scientific literature with respect to the impact of grazing on the ratio of grassland to ericoid shrubs. Incorporating a range of evidence sources in systematic reviews can therefore provide insights into contradictions in the evidence base. While a large majority of practitioners (94%) believe that grazing is an effective management option for lowland heath, evidence for a number of negative impacts on habitat attributes was recorded, highlighting the need for improved monitoring and experimental analysis of the effectiveness of management interventions.     

Burning season influences the response of bird assemblages to fire in tropical savannas

Fire plays a pivotal role in structuring ecosystems and often occurs as a human-mediated disturbance for land management purposes. An important component of fire regime is the season of burn. In tropical savannas, most fire management occurs during the dry season; however, wet season burning is often used for pastoral management and may be useful for controlling introduced plant species. We used replicated, experimental fire treatments (unburnt, dry season burnt and wet season burnt), spanning two habitats (riparian and adjacent open woodland), to examine the short- (within 12 months of fire) and longer-term (within four years of fire) changes of bird assemblages in response to wet and dry season burning in tropical savannas of northern Australia. Within 12 months of fire, we observed higher abundances of birds in the burnt treatments, although some species (e.g., red-backed fairy-wren, Malurus melanocephalus) were rarely observed in burnt sites. Dry season burnt sites contained higher abundances of insectivores and granivores, while wet season burnt sites had more carnivores. Four years following burning, dry season burnt sites were characterized by lower abundances, especially of nectarivores and granivores. Dry season burnt sites also contained a different assemblage than wet season burnt sites, but few differences were observed between wet season burnt and unburnt sites. Our results confirm that differences in fire regimes can substantially alter bird assemblages, especially in riparian zones, and emphasize the importance of incorporating burning season in fire management strategies.     

林火预测预报研究综述

在危害森林的诸因子中,火灾是一种最具破坏性的灾害,各林业先进国家都非常重视林火研究工作。在世界范围内,林火预测预报的应用已成为越来越多的有林国家林火管理的有力工具。林火预测预报从二十世纪20年代迄今,已有80余年的历史,在世界各国发展很快。林火预测预报分为火险天气预报、林火发生预报和林火行为预报。林火预报研究中的关键问题是选择主要的林火因子和合适的林火预测预报方法。     

Population viability of Cape mountain zebra in Gamka Mountain Nature Reserve, South Africa: the influence of habitat and fire

The small Cape mountain zebra population in Gamka Mountain Nature Reserve represents a third of the entire gene pool of this endangered species and is thus vital for it’s conservation. Presently, management of this population is largely hands off, with the belief that it will grow to levels which will allow it to form a source for the mixing of mountain zebra stocks in the future. The growth of this population however, has been slow and we investigated the influence of habitat and fire on this growth. Firstly, we used a diffusion model to perform a population viability analysis. This analysis indicated that the population had a low probability of attaining quasi-extinction in the next 50 years (G = 0.0032). However, our findings indicated that less than 30% of the reserve was suitable for mountain zebra and that the preferred habitat would have to be burnt at unnaturally short intervals to sustain the present growth. We therefore argue that the risk of quasi-extinction to this population is greater than predicted and suggest that management options need to be implemented to reduce this risk. These options include; translocation to another protected area; acquisition of adjacent land; burning preferred habitat at unnaturally short intervals; forming a conservancy with adjacent landowners; leasing cultivated land for pasture. We suggest that only the latter two options are likely to stimulate mountain zebra population growth in the short term and that these should receive immediate attention.     

The effects of fire and predators on the long-term persistence of an endangered shrub, Grevillea caleyi

Grevillea caleyi is an endangered plant species with a restricted range lying partly within Ku-ring-gai Chase and Garigal National Parks in NSW, Australia. The principle threatening processes affecting G. caleyi are habitat destruction and adverse fire regimes combined with high levels of seed predation. A stochastic, spatially explicit, individual-based model was constructed to investigate the population dynamics of small populations of the species and to determine the impact of a variety of management strategies. Results of model simulations indicate there is a high risk of population decline and local extinction in remnant sites with small populations under current management regimes. The most effective fire management strategy is to schedule fires that burn 20-100% of sub-populations every 5-15 years, in combination with reduced predation rates. When predation management strategies are employed in conjunction with a structured fire regime, then a 20-30% reduction in predation rates can improve the chance of long-term persistence substantially.     

GIS技术在划分巴西陆稻"IAPAR9"适宜种植区域中的应用

用贵州多年引种巴西陆稻 (IAPAR9)的试验资料与当地的气候资源进行对比分析 ,找出影响生育的关键气象因子和指标 ,并采用GIS技术推算出贵州不同地理背景下 1km× 1km网格点上的有关气候要素值 ,对巴西陆稻的适宜种植区域进行划分     

华中丘陵红壤的水分问题 Ⅱ.旱地红壤的水分状况

本文研究表明,与荒地红壤相比,旱地红壤表土的物理性质已有明显不同,土壤容重和土壤阻力较低,而土壤孔隙度较高。但心土和底土层的物理性质仍类似荒地红壤,然而,这些土层中高水势段的释水性却比荒地红壤相应土层中的更低。年内不同时期内的贮水量,旱地红壤比地红壤高,因而伏秋旱期间土体中出现代于萎蔫含水量值的时间较迟,干旱深度较浅。     

Forty years of lowland monsoon rainforest expansion in Kakadu National Park, Northern Australia

Monsoon rainforest is a key habitat in sustaining the natural and cultural values for which Kakadu National Park is World Heritage listed. The integrity of monsoon rainforest boundaries was thought to have been threatened by an increase in fire and feral animal disturbance over the last few decades. However, as no broad-scale assessment of rainforest boundary change had been undertaken, the rate and even direction of boundary change remained uncertain. In this study changes to the boundaries of 50 monsoon rainforest patches were assessed using temporal sequences of digitised aerial photography, with a view to understanding the relative importance of the drivers of change. Boundaries were compared for each of the years 1964, 1984, 1991 and 2004. Vegetation types were manually classified for each year with a 20 × 20 m point lattice, based primarily on the distance between tree crowns. Transition matrices, size-class distributions and fragmentation indices were calculated. Field samples of a subset of 30 rainforest patches supported the accuracy of the GIS-based mapping of rainforest boundaries. Rainforest patches increased in size between 1964 and 2004 by an average of 28.8%, with an average area increase of 4.0 ha. The expansion is likely to have been primarily driven by increases in variables such as rainfall and atmospheric CO₂, but has been strongly mediated by fire regime. This project has provided land managers with an appreciation of the extent and causes of landscape-scale changes to rainforest boundaries. This will contribute to ‘adaptive management’ programs, especially with respect to fire management.     

营林措施对森林土壤N2O排放影响的研究进展

森林土壤是大气N_2O重要的排放源。施肥、采伐、火烧、林下植被管理等营林措施和土地利用变化改变了土壤理化性质和土壤微气候,显著影响森林土壤N_2O的产生与排放。综述了森林土壤N_2O排放对不同营林措施的响应,探讨了营林措施影响土壤N_2O排放的主要机理,并提出目前研究的不足和未来研究的重点。总体而言,森林转变为农田、草地后增加了土壤N_2O排放,而农田和草地恢复成人工林后减弱了土壤N_2O排放;天然林转换为人工林或次生林后土壤N_2O排放没有明确结论;森林生态系统\"氮饱和\"程度使得森林土壤N_2O排放对施肥呈非线性响应,即初期无明显响应、中期缓慢增加和后期急剧增加;火烧一般增加土壤N_2O排放;采伐改变土壤温度、含水量、有机碳的分解和利用等,从而增强森林土壤N_2O排放能力;剔除林下植被提高土壤温度,加快了表层土壤有机碳的分解矿化,促进土壤N_2O排放;种植固氮植物增加了土壤有机碳和土壤氮含量,土壤N_2O排放增强。今后的研究应更多地关注多种因素和气候变化对林地土壤N_2O排放影响的内在机理以及氨氧化细菌、硝化细菌和反硝化细菌等微生物对各种干扰因素的响应机制。     

Immediate effects of wildfires on water repellency and aggregate stability in Mediterranean calcareous soils

Alkaline soils are considered much less prone to developing water repellency induced by fire than acidic soils. Here we report on the persistence of water repellency present in calcareous soils immediately after wildfires in 10 burned areas in SE Spain, its distribution in different aggregate size fractions (< 2, 2–1, 1–0.5, 0.5–0.25 and < 0.25 mm) and on results from aggregate stability tests. We also distinguished between soil samples taken beneath pine (Pinus halepensis) and beneath understory vegetation.     

山地农业生态系统持续发展的有效途径——坡地农业技术

本文简述了坡地农业技术(SALT)的原理和内容,分析了该技术在治理水土流失和大强度就地解决有机质投入,提高生物生产力和改善生态环境中的作用,指出坡地农业技术是山地农业生态系统持续发展的一个有效途径。     

不同灌溉处理对旱稻根系生长及水分利用效率的影响

通过对不同灌溉处理下旱稻根系生长及水分利用效率的试验研究,结果表明：早稻根系大部分根干重都集中在地表以下30cm内;不同灌水处理对根量及其分布有着显著不同的影响,灌水量越少,水分胁迫处理下的根系系统在30cm以下分布相对越多,中下层土壤中根系占的百分率越高;其中限量灌溉Ⅱ产量较充分灌溉处理减幅最小,穗粒数减幅也最小,农业水分利用效率最高,根冠比次高,增加了对土壤深层水的利用,减少了灌溉水的投入。在水资源缺乏的北京地区,是一种较为合理的灌溉方式。     

Fire regimes and the conservation of sandstone heath in monsoonal northern Australia: frequency, interval, patchiness

Heathlands are scattered across fire-prone monsoonal northern Australia mostly in dissected sandstone terrain. Such communities, although floristically depauperate by comparison with heathlands in southern Australia and southern Africa especially, share in common a relatively high proportion of fire-sensitive, obligate-seeder shrub species. The paper explores the implications of frequent fires, and associated short inter-fire intervals, on populations of obligate-seeder shrub species occurring in extensive heathlands occupying the western rim of the Arnhem Plateau, in the Northern Territory. Two studies are presented. With reference to published data concerning the maturation times of regional obligate-seeder shrubs, the first study reports on minimum and maximum intervals between fires determined from a 16-year fire history, 1980-1995, for the Plateau landform unit in Kakadu National Park, interpreted from LANDSAT MSS imagery. While species with maturation times of 5 or more years are common in the regional heath flora, minimum fire interval data for each 1 ha pixel indicate that 69% of heath habitats had been burnt at least once by fires recurring within 3 years, and 64% had a maximum fire interval of 5 years; 11% burnt only once or remained unburnt. The second study reports on the effects of an unreplicated experimental fire, involving observations on ca. 4000 individual shrubs, on ensuing heath floristic composition and abundance, undertaken 3 years after a wildfire had burnt the same site. Despite the experimental fire being highly patchy, substantial declines in the occurrence and density of many obligate-seeder shrub species were attended by increases in many herbs, including flammable grasses. Three years after the experimental fire the number of obligate-seeder shrubs was still less than half that pre-fire despite significant recruitment of some species in latter years. Collectively, these and other published data indicate that minimum fire return intervals of at least 4-5 years are required for conserving rapidly maturing tropical sandstone heath obligate-seeder shrubs, and longer still on sites comprising species with longer maturation times. For conservation management purposes individual fires should be small (especially in relation to the extent of any one tract of heath), patchy, and recurring intervals between fires should be varied as far as practicable.     

旱地土壤中的硝化-反硝化作用

本文综述了国内外旱地土壤硝化 -反硝化作用的过程及其影响因数和硝化 -反硝化作用产生的N2 O量及其影响因素以及旱地土壤上氮肥硝化 -反硝化损失量等方面的研究进展