Pollination,reproduction, and fire in California Arctostaphylos

Summary The pollination biology as related to divergent post-fire reestablishment strategies was examined during flowering sequences for two years in sympatric populations of Arctostaphylos pringlei and A. glandulosa var. mollis. Arctostaphylos pringlei reestablishes post-fire populations by means of fire-stimulated germination of previously dormant seeds, while A. glandulosa var. mollis resprouts from large subsurface burls. Arctostaphylos pringlei produced more flowers per unit plant size, exhibited faster nectar production and higher nectar concentration, attracted nearly twice the number of pollinator visitations, and set more seed when self-pollinated. This substantiated the hypothesis that in these two species the amount of reproductive energy allocated to flower, nectar, and seed production reflected the relative significance of seeding compared to a resprouting post-fire establishment strategy.     

The influence of dominant shrubs,fire, and time since fire on soil seed banks in mixed chaparral

The composition and density of soil seed banks beneath co-occurring Adenostoma fasciculatum and Ceanothus greggii shrubs from three chaparral stands last burned 9, 35 and 85 years before 1986 were investigated. The overall density of seeds in the soil, as estimated by germinations under greenhouse conditions, increased with time since fire (ca. 8000 to 25000/m²). However, this increase was due entirely to the accumulation of A. fasciculatum seed in the soil (ca. 2000 to 21000/m²). In contrast, the density of C. greggii seed was different in each of the three stands, but was not correlated with time since fire: maximum densities were recorded from the 35 year old stand (ca. 2000/m²).A total of 31 taxa germinated and 17 occurred in sufficient numbers to be analyzed statistically. Germinable seed densities of three herb species were not influenced by soil source (beneath A. fasciculatum or C. greggii), time since fire, or the direct effects of a controlled fire treatment. Germinable seed densities of a further nine species were significantly influenced by the elapsed time since stands last burned. The densities of four decreased and five increased. Four of the species that increased in seed density over the three stands were annuals, suggesting that the chaparral sub-canopy habitat is not as unfavorable for annuals as is often assumed. The fire treatment decreased germinable seed densities of four annual species by 40–70%, but increased the germinable seed densities of the shrubs A. fasciculatum and C. greggii, and the annual Phacelia brachyloba. Our results indicate that seeds of A. fasciculatum will increase in the soil bank for at least 85 years after fire in chaparral where it is dominant. In contrast, seed reserves of C. greggii appear to be influenced primarily by site-specific patterns of seed production and by the intensity of post-dispersal seed predation.     

澳大利亚森林火灾的管理与火生态的研究

澳大利亚是火灾频发的地区．每年因森林火灾的危害都要造成相当的社会、经济损失及生态环境的破坏,故火生态的研究及火的管理在澳大利亚的生态学研究中一直占有重要地位．本文主要讨论了澳洲森林大火起燃的物理过程和机制、可燃物的特征、林火的特点、习性及对生态环境的影响和如何控制和减少火灾的危害性,达到对火进行利用、控制和管理的目的．     

火控制政策对大兴安岭森林景观、可燃物动态及火险的长期影响

大兴安岭50年来严格的火控制政策已经极大地改变了自然火格局,同时也改变了森林的物种组成和年龄结构。理解大兴安岭森林对长期火控制的响应是制定森林可持续发展的依据之一。本文应用LANDIS模型模拟了大兴安岭森林景观对自然火(1950年以前)和灭火(1950年以后)的长期响应(300年)。结果表明：灭火显著增加了落叶松面积,增加其过熟林面积,减少其幼龄林面积;同时也显著减少白桦面积,减少其幼龄林面积;灭火延长火烧轮回期,火烧次数减少,灾难性火灾发生的机率增加,火险在模拟的50年内迅速上升到高火险等级。在自然火格局下,火险在整个模拟过程中保持较低的等级。所以如果现行的高强度灭火政策继续实施的话,必须要制定大范围的可燃物管理措施(计划火烧、粗可燃物处理等),以降低灾难性火灾发生的机率。计划火烧加粗可燃物去除将成为可燃物管理和森林可持续经营的首选措施。如何评价大兴安岭地区可燃物处理措施的效果,在保持木材生产和生态作用稳定的条件下,最大程度地降低火险也是亟待解决的问题。     

Vegetation trends following fire in the Roggeveld, Mountain Renosterveld, South Africa

The Mountain Renosterveld vegetation of the Roggeveld is an escarpment type renosterveld showing strong karroid affinities. Fire plays an important role as a landscape scale disturbance that shapes plant communities in this vegetation type, however, post-fire succession has never before been documented for renosterveld vegetation. A study was therefore conducted in the northern Roggeveld to improve our understanding of the recovery of the vegetation following fire. The natural vegetation recovery was analysed using line transect data accumulated at five different sites over a ten year period. This paper reports on the post-fire vegetation trends with respect to changes in species composition, species richness, life form composition and life form richness. Vegetation cover began to re-establish within the first nine months following the fire, and remained at a high level from years 3 to 10. At the first survey the species richness varied from 13 to 17 species, with the highest species richness (14 to 31 species) generally encountered at each transect after three years. The highest Shannon index values were generally found within the first three years and the lowest Shannon index values were found in years 9 and 10. In all cases the Principal Co-ordinate Analysis ordinations of the species composition data indicated a clear separation in the species composition between the first two years (years 1 and 2) following the fire and the remaining years (year 3 to 10). This study also supports the ‘initial floristic composition’ model of Egler (1954) in that all or the majority of species encountered during the succession were already present at the beginning of the recovery phase and there was a rapid re-establishment of the initial plant community.     

Different effects of fire age and fire recurrence on grass and woody plant chemistry in Kafue National Park,Zambia

In savannas, fire and herbivores are important drivers of natural ecosystem processes. Fire is also used intensively for management purposes. However, reported fire effects differ between studies. Reasons for these differences are still poorly understood. Here, we investigated the effects of fire on leaf chemistry of grasses and woody plants in the savanna of the Busanga Flood Plain, Zambia, in relation to the time elapsed between plant sampling and the last fire (fire age) and the frequency of fires during the last 16 years (fire recurrence). We analyzed leaves for their nitrogen, carbon, and fiber concentrations, and estimated their metabolizable energy content, reflecting feed quality for browsers and grazers. Grasses and woody plants differed in all chemical components and showed different responses to fire. Grass quality was higher at sites burnt in the year of sample collection than at sites burnt only in previous years, but did not change under different fire recurrences. Leaves of woody plants did not differ in relation to fire age but their quality increased with increasing fire recurrence. In woody plants, the carbon content responded to the interaction between fire age and fire recurrence, indicating changes in carbon allocation in response to fire. Thus, burning increased feed quality for grazers and browsers but on different temporal scales. The scale effects may contribute to the differences in resource allocation described by different studies. They merit more attention in management decisions as well as in future studies on fire effects in savanna systems.     

Climate change,fuel and fire behaviour in a eucalypt forest

A suite of models was used to examine the links between climate, fuels and fire behaviour in dry eucalypt forests in south‐eastern Australia. Predictions from a downscaled climate model were used to drive models of fuel amount, the moisture content of fuels and two models of forest fire behaviour at a location in western Sydney in New South Wales, Australia. We found that a warming and drying climate produced lower fine fuel amounts, but greater availability of this fuel to burn due to lower moisture contents. Changing fuel load had only a small effect on fuel moisture. A warmer, drier climate increased rate of spread, an important measure of fire behaviour. Reduced fuel loads ameliorated climate‐induced changes in fire behaviour for one model. Sensitivity analysis of the other fire model showed that changes in fuel amount induced changes in fire behaviour of a similar magnitude to that caused directly by sensitivity to climate. Projection of changes in fire risk requires modelling of changes in vegetation as well as changes in climate. Better understanding of climate change effects on vegetation structure is required.     

Climatic change and fire potential in South-Central British Columbia, Canada

The incidence and severity of forest fires are linked to the interaction between climate, fuel and topography. Increased warming and drying in the future is expected to have a significant impact on the risk of forest fire occurrence. An increase in fire risk is linked to the synchronous relationship between climate and fuel moisture conditions. A warmer, drier climate will lead to drier forest fuels that will in turn increase the chance of successful fire ignition and propagation. This interaction will increase the severity of fire weather, which, in turn, will increase the risk of extreme fire behaviour. A warmer climate will also extend fire season length, which will increase the likelihood of fires occurring over a greater proportion of the year. In this study of the North Okanagan area of British Columbia, Canada, the impacts of climate change of fire potential were evaluated using the Canadian Forest Fire Danger Rating System and multiple climate scenario analysis. Utilizing this approach, a 30% increase in fire season length was modelled to occur by 2070. In addition, statistically significant increases in fire severity and fire behaviour were also modelled. Fire weather severity was predicted to increase by 95% during the summer months by 2070 while fire behaviour was predicted to shift from surface fire‐intermittent crown fire regimes to a predominantly intermittent‐full crown fire regime by 2070 onwards. An increase in fire season length, fire weather severity and fire behaviour will increase the costs of fire suppression and the risk of property and resource loss while limiting human‐use within vulnerable forest landscapes. An increase in fire weather severity and fire behaviour over a greater proportion of the season will increase the risks faced by ecosystems and biodiversity to climatic change and increase the costs and difficulty of achieving sustainable forest management.     

Behavioral and developmental homeostasis in the fire ant, Solenopsis invicta

The von Bertalanffy rule (1960) predicts that low incubation temperature during larval development will result in larger adult body size. If larval development in social insects followed this rule, then low incubation temperature would induce the development of larger workers and possibly even sexuals. To test this prediction, the effect of incubation temperature on larval development, larval meal size, larval tending and worker recruitment to food in the fire ant, Solenopsis invicta was investigated. Temperatures tested where within the range at which brood remains viable.Contrary to the predictions of the von Bertalanffy rule, worker size was unaffected by incubation temperature, and sexuals were reared at the high rather than the low incubation temperature. Moreover, larval meal size, the rate of larval tending by workers and the total number of workers recruited to food were unaffected by temperature.Mechanisms regulating developmental and behavioral homeostasis were as follows: the duration of larval development and the rate of larval growth changed proportionately with temperature such that the mean and variation of pupal size was unaffected by incubation temperature. Larvae solicited at the same rate, swallowed at the same rate and swallowed for the same duration such that meal size was unaffected by incubation temperature. On the brood pile, fewer workers tended brood at higher incubation temperatures, but worker tempo increased; as a result, brood tending was not adversely affected by incubation temperature. The rate of worker recruitment to food sites outside the nest increased with temperature, but the duration of the recruitment effort decreased such that, over time, the same total number of workers was employed to retrieve food.Incubation humidity was also investigated. When brood chambers were less than 100% humid, workers recruited to food and tended larvae (retrieved, sorted and groomed them), but did not feed larvae. Eventually, larvae died of starvation and were cannibalized.     

Mixed-conifer understory response to climate change, nitrogen, and fire

California's Sierra Nevada mountains are predicted to experience greater variation in annual precipitation according to climate change models, while nitrogen deposition from pollution continues to increase. These changes may significantly affect understory communities and fuels in forests where managers are attempting to restore historic conditions after a century of altered fire regimes. The objective of this research was to experimentally test the effects of increasing and decreasing snowpack depth, increasing nitrogen, and applying prescribed fire to mixed-conifer forest understories at two sites in the central and southern Sierra Nevada. Understory response to treatments significantly differed between sites with herb biomass increasing in shrub-dominated communities when snowpack was reduced. Fire was a more important factor in post-treatment species richness and cover than either snowpack addition or reduction. Nitrogen additions unexpectedly increased herbaceous species richness. These varied findings indicate that modeling future climatic influences on biodiversity may be more difficult than additive prediction based on increasing the ecosystem's two limiting growth resources. Increasing snowpack and nitrogen resulted in increased shrub biomass production at both sites and increased herb production at the southern site. This additional understory biomass has the potential to increase fuel connectivity in patchy Sierran mixed-conifer forests, increasing fire severity and size.     

Early fire and forest change in the Baliem Valley, Irian Jaya, Indonesia

Abstract. A 3.5 m section of organic sediment was obtained from a karstic pond on a hill in the centre of the Baliem Valley, one of the major settled intermontane highland areas of New Guinea. The material spans two time periods each of approximately 2 millennia, one from about 2000 BP to the present and the other from 33,500 to 31,500 BP. The pollen analysis of the earlier section showed that it formed when the valley was forested by Nothofagus forest, but a carbonized particle input was consistently present after about 32,500 years ago. The recent section covers a period when the hill was totally cleared except for grassland and some open shrubby regrowth. The early burning and associated clearances are tentatively ascribed to a human origin. Fire is associated with slope erosion on the hill at 28,000 BP which supports the hypothesis of long term human settlement in the area.     

Fire incidence,but not fire size,affects macropod densities

The regeneration of plants post‐fire has widely been shown to be attractive to vertebrate herbivores. However, there are few data relevant to the effect of fire size on herbivore densities. In dry eucalypt forest in one region and hummock sedgeland in another region, we used timed scat counts to test the effect of fire and fire size on Tasmanian macropod densities 6 months after burning. We also tested whether soil characteristics and the nature of ground cover related to the degree of attractiveness of post‐burn regeneration. Soil nutrients and higher covers of grasses and herbs in ground layer vegetation were associated with higher macropod densities. In dry eucalypt forest, fire incidence and fire size did not affect macropod density, while in hummock sedgeland, fire had a positive effect on macropod density, but fire size had no effect.     

Burning phylogenies: fire, molecular evolutionary rates, and diversification

Mediterranean-type ecosystems are among the most remarkable plant biodiversity "hot spots" on the earth, and fire has traditionally been invoked as one of the evolutionary forces explaining this exceptional diversity. In these ecosystems, adult plants of some species are able to survive after fire (resprouters), whereas in other species fire kills the adults and populations are only maintained by an effective post-fire recruitment (seeders). Seeders tend to have shorter generation times than resprouters, particularly under short fire return intervals, thus potentially increasing their molecular evolutionary rates and, ultimately, their diversification. We explored whether seeder lineages actually have higher rates of molecular evolution and diversification than resprouters. Molecular evolutionary rates in different DNA regions were compared in 45 phylogenetically paired congeneric taxa from fire-prone Mediterranean-type ecosystems with contrasting seeder and resprouter life histories. Differential diversification was analyzed with both topological and chronological approaches in five genera (Banksia, Daviesia, Lachnaea, Leucadendron, and Thamnochortus) from two fire-prone regions (Australia and South Africa). We found that seeders had neither higher molecular rates nor higher diversification than resprouters. Such lack of differences in molecular rates between seeders and resprouters-which did not agree with theoretical predictions-may occur if (1) the timing of the switch from seeding to resprouting (or vice versa) occurs near the branch tip, so that most of the branch length evolves under the opposite life-history form; (2) resprouters suffer more somatic mutations and therefore counterbalancing the replication-induced mutations of seeders; and (3) the rate of mutations is not related to shorter generation times because plants do not undergo determinate germ-line replication. The absence of differential diversification is to be expected if seeders and resprouters do not differ from each other in their molecular evolutionary rate, which is the fuel for speciation. Although other factors such as the formation of isolated populations may trigger diversification, we can conclude that fire acting as a throttle for diversification is by no means the rule in fire-prone ecosystems.     

FARSITE火行为模型的原理、结构及其应用

应用空间直观火行为模型模拟大的时空尺度上的林火蔓延过程成为林火管理、规划和科学分析的有效工具。FARSITE(Fire Area Simulator)是一个基于热物理、燃烧学和试验理论为一体的空间直观火行为模型,它集成了现有的地表火、树冠火、飞火和火加速等子模型。FARSITE能够利用GIS和RS提供的空间数据,模拟大时空尺度的林火蔓延,模拟结果能够以地图形式输出,反映林火行为的瞬时状态。本文介绍了FARSITE模型的基本原理、结构和运行机制,并将其应用到丰林自然保护区林火蔓延模拟,以期为国内林火管理和火行为模型的开发提供参考。