Soil temperature and depth of legume germination during early and late dry season fires in a tropical eucalypt savanna of north‐eastern Australia

Abstract Temperatures that significantly increase seed germination of some tropical legumes (i.e. 80–100°C) were documented in the topsoil during the passage of early (May) and late (October) dry season fires in a tropical eucalypt savanna of north‐eastern Australia. Elevated temperatures penetrated at least 30 mm into the soil during the higher‐intensity, late dry season fires, but were only detected at 10 mm during the early dry season fires. The depth from which germination of two native legume forbs Galactia tenuiflora and Indigofera hirsuta occurred was positively related to the temperature elevation in the topsoil and was greater after late compared with early dry season fires. A broader range in germination depth, resulting in higher seedling densities, was recorded for I hirsuta after late dry season fires. These results suggest that seedling emergence of native leguminous forbs is likely to occur at a greater density after late rather than early dry season fires in tropical eucalypt savannas of north‐eastern Australia. Therefore, the season of burning, as a result of its relationship to fire intensity, can influence species composition through its effect on seed germination.     

1996—2005年北京城市生态质量动态

从生态要素、生态过程、生态功能和生态问题4个主题出发,构建了包含16个指标的北京城市生态质量评价指标体系,并分别采用熵权法、最差状态法和最佳状态法对指标进行赋权,通过加权平均法构建了北京城市生态要素指数（EEI）、生态过程指数（EPI）、生态功能指数（EFI）、生态问题指数（EDI）和综合生态质量指数（CEI）,用以评价1996—2005年北京城市生态质量动态变化.结果表明：研究期间,北京城市EEI无明显改善,持续维持在远离理想点的水平;EPI和EFI改善显著,由1996年的远离理想点到2005年接近于理想点的水平;EDI的年度波动较大,普遍远离理想点;CEI得到持续改善,但离理想点依然有一定距离.当人均国内生产总值（GDP）小于3 000美元时,EPI、EFI和CEI随GDP的增长而快速增大,改善显著,当人均GDP超过3 000美元后,EPI、EFI和CEI随GDP增长而增大的速度减慢;EEI和EDI受人均GDP的影响较小,主要受限于自然条件及全球和区域环境的变化.     

Pyrodiversity begets plant–pollinator community diversity

Fire has a major impact on the structure and function of many ecosystems globally. Pyrodiversity, the diversity of fires within a region (where diversity is based on fire characteristics such as extent, severity, and frequency), has been hypothesized to promote biodiversity, but changing climate and land management practices have eroded pyrodiversity. To assess whether changes in pyrodiversity will have impacts on ecological communities, we must first understand the mechanisms that might enable pyrodiversity to sustain biodiversity, and how such changes might interact with other disturbances such as drought. Focusing on plant–pollinator communities in mixed‐conifer forest with frequent fire in Yosemite National Park, California, we examine how pyrodiversity, combined with drought intensity, influences those communities. We find that pyrodiversity is positively related to the richness of the pollinators, flowering plants, and plant–pollinator interactions. On average, a 5% increase in pyrodiversity led to the gain of approximately one pollinator and one flowering plant species and nearly two interactions. We also find that a diversity of fire characteristics contributes to the spatial heterogeneity (β‐diversity) of plant and pollinator communities. Lastly, we find evidence that fire diversity buffers pollinator communities against the effects of drought‐induced floral resource scarcity. Fire diversity is thus important for the maintenance of flowering plant and pollinator diversity and predicted shifts in fire regimes to include less pyrodiversity compounded with increasing drought occurrence will negatively influence the richness of these communities in this and other forested ecosystems. In addition, lower heterogeneity of fire severity may act to reduce spatial turnover of plant–pollinator communities. The heterogeneity of community composition is a primary determinant of the total species diversity present in a landscape, and thus, lower pyrodiversity may negatively affect the richness of plant–pollinator communities across large spatial scales.     

多气候情景下中国森林火灾风险评估

森林火灾风险主要取决于致灾因子、承灾体以及防灾减灾能力,综合评估和预测森林火灾风险是制定科学的林火管理政策的基础.本文基于经典自然灾害风险模型和可获取数据构建森林火灾风险评估模型与指标体系,评估过去和未来的森林火灾风险.未来气候情景数据包括RCP 2.6、RCP 4.5、RCP 6.0和RCP 8.5下5个全球气候模式(GFDL-ESM2M、HadGEM2-ES、IPSL-CM5A-LR、 MIROC-ESM-CHEM和NorESM1-M)日值数据.根据最高温度、最小相对湿度、平均风速和每日降水量分别计算1987—2050年历史观测数据和未来气候情景下各格点每日火险天气指数系统中各个指数.结果表明: 1987—2010年,森林火灾风险高和很高的区域分别占21.2%和6.2%,主要分布在大兴安岭和长白山地区、云南大部分区域和南方零散分布的区域.森林火灾可能性高和很高的区域主要分布在东北和西南地区,分别占森林面积的13.1%和4.0%.与观测时段相比,2021—2050年RCP 2.6、RCP 4.5、RCP 6.0和RCP 8.5情景下森林火灾可能性高和很高的区域分别增加0.6%、5.5%、2.3%和3.5%,华北地区增幅明显.气候变化引起的森林火灾高风险区域有些增加,RCP 8.5情景下增幅最明显(+1.6%).     

A Burning Issue: Rethinking the Transition from Hunter‐Gatherer to Industrial Sociometabolic Regimes

Hunter‐gatherers are commonly seen as having a fundamentally different sociometabolic regime from agrarian and industrial societies because they are thought to directly appropriate the products of natural ecosystems without modifying those systems in order to enhance their productivity. However, ethnographic and archeological evidence reveals that many hunter‐gatherers extensively employed fire to manage their ecosystems so as to increase production of desirable wild resources, thus engaging in “colonization of nature” that is not qualitatively different from that practiced by other types of society. They systematically burned wild vegetation in order to increase populations of edible wild plants consumed by humans and promote growth of forage for game animals. Deliberate ecosystem burning by Australian Aborigines represented an energy expenditure of 1,512 gigajoules per capita per year (GJ/capita/yr), a level of energy use that is more than three times higher than the United States (445 GJ/capita/yr). It is their profligate consumption of biomass energy that explains why the quality of life of many hunter‐gatherers was often better than that of traditional settled peasant farmers. Hence, the extent to which hunter‐gatherers have a distinct type of sociometabiolic regime is called into question. It can be argued that in the course of social evolution, there have been only two sociometabolic regimes. In one type, which includes hunter‐gatherers, swidden agriculturalists, and industrial societies, extrasomatic energy does most of the productive work, whereas in the other type, that of premodern settled agriculturalists, production is largely dependent on human muscle power.     

Fire history influences on the spatial heterogeneity of soil nitrogen transformations in three adjacent stands in a dry tropical forest in Thailand

Spatial patterns of soil nitrogen (N) transformations were examined using geostatistical analysis in three adjacent stands with different fire history (0, 10 and 35 years since the latest fire, respectively) in a dry tropical forest in Thailand. A larger pool of total inorganic N and a faster rate of N mineralization were recorded in the stand with longer fire prevention. At the spatial scale analyzed, the proportion of spatially dependent variance to the total variance of N mineralization and nitrification increased from 0.39 to 0.73, and from 0.40 to 0.77, respectively, with the time since the latest fire. The spatial autocorrelation ranges of N mineralization and nitrification decreased from 9.0 to 3.28 m, and 9.0 to 2.77 m, respectively, with the time since the latest fire. These results suggested that fire history affected not only the level of available soil N, but also the spatial heterogeneity of soil N transformations, presumably due to the difference in plant influences on soil.     

Use of guilds for modelling avian responses to vegetation in the Intermountain West (USA)

Aim Individually focused conservation management of many species is expensive and logistically impractical. Mesofilter conservation methods may facilitate the simultaneous management of multiple species. We used data on distributions of two sets of avian guilds, based on dependence on riparian vegetation and on nest location, to relate occurrence rates to environmental variables. Variables were selected by expert opinion and are likely to be affected by changes in climate and land use. Location Data were collected from 2001–06 in four adjacent mountain ranges in the central Great Basin (Lander, Nye and Eureka counties, Nevada, USA): the Shoshone Mountains and the Toiyabe, Toquima and Monitor ranges. Methods Data on occurrence of birds, vegetation composition and vegetation structure were obtained in the field. Geographical coordinates and the normalized difference vegetation index were derived from a digital elevation model and a satellite image. To construct a general model for guilds as a whole, while allowing flexibility for variation in the functional responses of individual species, we applied multivariate adaptive regression splines. Results The predictive capacity of expert knowledge of relationships between birds and vegetation was inconsistent. Latitude, longitude and elevation may constrain the response of some guilds to changes in vegetation structure and composition. Guild‐based models were useful for modelling species with sparse distributions, which are difficult to model individually. In essence, this method supplements models for the individual species with patterns for the guild to which they belong. Main conclusions Guilds of birds appeared to have predictable associations with selected attributes of vegetation structure and composition. The criteria by which species are grouped into guilds may affect the success of predictions and management interventions. Our derived models offer the potential to predict effects on the avifauna of management or climate‐driven change in vegetation.     

Tree–grass coexistence in the Brazilian cerrado: demographic consequences of environmental instability

Aim Tropical savanna ecosystems are uniquely characterized by the co‐dominance of both trees and grasses. An operational understanding of the ecological processes involved in maintaining this condition is essential for understanding both the functioning of savanna systems as well as their potential response to environmental change. A simple model is presented to explore the potential for a demographic mechanism of long‐term tree persistence and temporal physiognomic stability in the Brazilian cerrado. Location The model is developed based on data from the humid cerrado of Brazil. Methods In contrast to many existing models of tree–grass dynamics a model is presented which is based on data from the humid cerrado of Brazil, which is both qualitatively and quantitatively different from many of the more arid savannas of the palaeotropics. The model focuses on the dynamics of a synthetic tree population, with particular attention given to reproduction, seedling establishment and fire effects; with separate sub‐models for grass production, fire and rainfall. Results The model successfully predicts coexistence across the full range of observed vegetation physiognomies, but only under limited conditions. Under coexistence conditions, the dynamics of the tree population are characterized by long periods of gradual decline, punctuated by occasional bursts of growth. However, in agreement with earlier studies, the model consistently over‐predicts domination by the tree component. Fire is identified as an overriding factor in determining model behaviour, and the response of reproduction and sapling recruitment to variance in the frequency of fire ignition is identified to be of potential importance in the functioning of the Brazilian cerrado. The key dynamics of the model which promote tree–grass coexistence are consistent with a number of established determinants of ecological resilience in savanna systems. Main conclusions The model identifies the importance of the effective exploitation of rare opportunities for favourable recruitment (e.g. exclusion from fire) by the tree population, in promoting coexistence within a predominantly adverse environment. Support is provided for an alternative demographic mechanism of tree–grass coexistence in the cerrado (the storage effect), which is not based on the limiting assumption of niche partitioning through differences in rooting depth. The results are consistent with those presented by recent modelling work based on the more arid savannas of southern Africa. The model presented here differs in the emphasis given to particular environmental and life‐history attributes which are critical in determining the tree–grass balance, but provides further general support for the potential role of demographic mechanisms (such as the storage effect) in determining the structure of tropical savannas. Despite having clear limitations, models can serve as valuable heuristic tools to aid the integration and exploration of existing data sets as well as our present understanding of key ecological processes.