Effects of fire on forest dynamics in southern Switzerland

Abstract. We analysed the influence of fire on species composition, floristic diversity and indicator values of the vegetation in forests of the Canton Ticino (South Switzerland). Both frequency of fire and time since last fire were taken into account using variance analysis. Results show a strong interaction of these two parameters, i.e. the reaction of the vegetation after a fire depends on the frequency of past fires. A rapid recovery is generally observed after fire, involving both herbaceous and woody species. However, a long-term tendency towards floristic and edaphic impoverishment is observed with increasing frequency of fires. This phenomenon appears to be linked to the progressive dominance of a few fire-tolerant species.     

Long-term forest fire ecology and dynamics in southern Switzerland

1 Pollen and charcoal analysis at two lakes in southern Switzerland revealed that fire has had a prominent role in changing the woodland composition of this area for more than 7000 years.
2 The sediment of Lago di Origlio for the period between 5100 and 3100  bc cal. was sampled continuously with a time interval of about 10 years. Peaks of charcoal particles were significantly correlated with repeated declines in pollen of Abies , Hedera , Tilia , Ulmus , Fraxinus excelsior t., Fagus and Vitis and with increases in Alnus glutinosa t., shrubs (e.g. Corylus , Salix and Sambucus nigra t.) and several herbaceous species. The final disappearance of the lowland Abies alba stands at around 3150  bc cal. may be an example of a fire-caused local extinction of a fire-intolerant species.
3 Forest fires tended to diminish pollen diversity. The charcoal peaks were preceded by pollen types indicating human activity. Charcoal minima occurred during periods of cold humid climate, when fire susceptibility would be reduced.
4 An increase of forest fires at about 2100  bc cal. severely reduced the remaining fire-sensitive plants: the mixed-oak forest was replaced by a fire-tolerant alder–oak forest. The very strong increase of charcoal influx, and the marked presence of anthropogenic indicators, point to principally anthropogenic causes.
5 We suggest that without anthropogenic disturbances Abies alba would still form lowland forests together with various deciduous broadleaved tree taxa.     

Effects of regeneration burning on the properties of forest soils in southern Tasmania: Comments on recent study by Elliset al. (1982)

Summary Important methodological factors which should be considered when attempting to measure and interpret the effects of hot slash fires on the properties of forest surface soils are briefly discussed. Soil properties cannot be assumed to be similar, prior to cutting and burning of forest, on coupes located several kilometres apart in dissected terrain. In order to study the effects of forest treatment on soil properties, sites should either be closely adjacent or preferably measurements should be taken before and after treatment on the same experimental area.It is argued that the conclusions reached by Elliset al. regarding the effects of regeneration burning on soil properties in southern Tasmania are unjustified because of the use of inappropriate experimental methods.     

Borrelia burgdorferi in ticks of the Canton Tessin (Switzerland)

In the northern Alps it is hard to find an Ixodes ricinus population which does not harbour Borrelia burgdorferi. The infection rates range from 5 to 34% for adults and nymphs to 3.1% for larvae. This study shows that the infection rates on the southern side of the Alps are similar, at 25% for adults, 36.2% for nymphs and 3.2% for larvae. With respect to tick species other than I. ricinus, we did not succeed in finding any spirochetes in Dermacentor marginatus, Haemaphysalis punctata, Ixodes hexagonus, Rhipicephalus sanguineus.     

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．     

Population age structure of Pinus banksiana at the southern edge of the Canadian boreal forest

Abstract. To assess the effects of site type, forest initiation periods and fire regimes on the dynamics of Pinus banksiana (Jack pine), the age structure of 69 populations of the species was analyzed. Two landscapes with different fire regimes were selected in the southern part of the Canadian boreal forest in Québec: the ‘mainland landscape’ is characterized by a fire regime of large lethal fires, the ‘island landscape’ is affected by a complex fire regime including lethal and non-lethal fires. Age structure was compared between forest initiation periods and site types (mesic mainland, xeric mainland and xeric island) using the Shannon regularity index. An even-aged population structure was found within the first 100 yr following a lethal fire, while after that period the population structure becomes more uneven-aged. Under mesic conditions, populations tend to have an even-aged structure, under xeric conditions an uneven-aged structure. Natural openings present in xeric sites allow for recruitment in the absence of fire. This permits the self-maintenance of Pinus banksiana. Xeric island populations show more uneven-aged structures than xeric mainland populations. The occurrence of non-lethal fires on the islands creates uneven-aged structures. Further, the results suggest that the selection pressure of the island fire regime, favouring non-serotinous and mixed P. banksiana individuals, is one of the factors responsible for a higher recruitment in the absence of fire on islands than on the mainland.     

The effect of long‐term repeated burning and fire exclusion on above‐ and below‐ground Blackbutt (Eucalyptus pilularis) forest vegetation assemblages

We used a long‐term fire experiment in south‐east Queensland, Australia, to determine the effects of frequent prescribed burning and fire exclusion on understorey vegetation (<7.5 m) richness and density in Eucalyptus pilularis forest. Our study provided a point in time assessment of the standing vegetation and soil‐stored vegetation at two experimental sites with treatments of biennial burning, quadrennial burning since 1971–1972 and no burning since 1969. Vegetation composition, density and richness of certain plant groups in the standing and soil‐stored vegetation were influenced by fire treatments. The density of resprouting plants <3 m in height was higher in the biennially burnt treatment than in the unburnt treatment, but resprouters 3–7.5 m in height were absent from the biennial burning treatment. Obligate seeder richness and density in the standing vegetation was not significantly influenced by the fire treatments, but richness of this plant group in the seed bank was higher in the quadrennial treatment at one site and in the long unburnt treatment at the other site. Long unburnt treatments had an understorey of rainforest species, while biennial burning at one site and quadrennial burning at the other site were associated with greater standing grass density relative to the unburnt treatment. This difference in vegetation composition due to fire regime potentially influences the flammability of the standing understorey vegetation. Significant interactions between fire regime and site, apparent in the standing and soil‐stored vegetation, demonstrate the high degree of natural variability in vegetation community responses to fire regimes.     

森林林下植被生物量收获的样方选择和模型

在控制误差内寻求样方的最小面积和最少样方数量是植被生态学野外研究的重要问题。在综合考虑取样的边界效应和时间、劳力消耗的基础上,研究了在控制误差内测定森林林下植被生物量时应选择的最佳样方大小和数量,并找出最佳的自变量拟合了估算林下植被生物量的预测方程。结果表明,利用Wiegert的方法测定研究区林下植被生物量取样方案,得出0．25m。的小样方为最佳取样面积。但小样方受边界效应的影响很大,会产生过高的生物量估计。通过分析了边界效应的影响和生物量相对平均值的变化,得出2m×1m是本研究的最佳样方面积,而10个2m×1m的样方能把标准误差控制在生物量平均值的10％以内。灌木生物量回归方程所选取的3个自变量D^2H、CH和P日中,CH与灌木生物量的相关性和以CH为自变量的线性回归方程的拟合度较其他2个变量好。而以PH为自变量的灌木生物量预测方程在实际操作中能提高研究的简便性和效率。以PH为自变量的林下草本层单位面积生物量的预测方程分别为Wv=11．65＋4．25（PH）和wD=24．23＋6．85（PH）。     

Long-term dynamics of vegetation and disturbance of a southern boreal spruce swamp forest

Abstract. Analysis of pollen, charcoal and loss-on-ignition in peat cores from a Picea aèies-dominated swamp forest in central Sweden show the vegetation changes and disturbance patterns over 9500 yr. Six major sequences of local vegetation development are identified: (A) Pinus period, ca. 9500–7000 cal. BP; (B) Open mire period (ca. 7000–4500 cal. BP; (C) Betula period, ca. 4500–2300 cal. BP; (D) Picea period (ca. 2300–1000 cal. BP; (E) Human impact period (ca. 1000–100 cal. BP); and (F) Period of human abandonment during the last ca. 100 yr. The swamp forest has been highly dynamic in response to various natural and anthropogenic disturbance agencies. Several fires have heavily influenced the vegetation development. During the last ca. 900 yr human influence has been important, initially from grazing and trampling by domesticated animals (ca. 1000–500 cal. BP), and subsequently small-scale cereal growing (ca. 400–100 BP). Cutting, burning and animal browsing influenced the structure and dynamics of the swamp forest by creating a more open stand and suppressing tree regeneration. Recent cessation of human impact has led to increased tree regeneration and a denser swamp forest stand. The present high biodiversity, and subsequent conservation interest does not result from long-term stability or absence of fire and human impact. However, in spite of repeated disturbances, a continuity of old and senescent trees produced a forest type with abundant dead wood. With the relatively minor importance of fire over long periods of time, the swamp forest developed a structure maintaining a high biological diversity. An important issue for maintaining long-term biodiversity in the boreal landscape must be to create a mosaic where different forest types are present, with a variety of structures, substrates and processes, to provide a certain degree of freedom for species to move around in the landscape.     

Potential role of ignition management in reducing unplanned burning in Arnhem Land,Australia

Fire management attempts to coerce fire into a desired regime using three primary strategies: prescribed burning, fire suppression and ignition management. The West Arnhem Land Fire Abatement project (WALFA), where prescribed Early Dry Season burning is used to reduce unplanned Late Dry Season burning, is heralded as model for prescribed burning. However, a previous analysis found that Late Dry Season area burnt in WALFA had been reduced further than would be expected based purely on the Early Dry Season treatment area. This study investigated whether treatment has reduced the number and size of unplanned fires. Daily burnt area mapping from MODIS satellite sensors was used to identify individual fires to compare fire activity before and after management was introduced in WALFA (2005) and in a control region in East Arnhem Land. Late Dry Season area burnt reduced after treatment in WALFA but also in the control region. The number of fires in August–October increased after treatment. There is a period from early August until late September when human ignitions can cause huge fires. Late Dry Season area burnt was strongly influenced by the size of the largest single fire and only weakly by the number of ignitions. Early Dry Season area burnt had modest effects on both the number and maximum size of Late Dry Season fires. Eliminating the largest fire in each 1600 km² sample block would have halved the total Late Dry Season area burnt. A similar reduction could be obtained from a 14% annual treatment with Early Dry Season fire, but this may not reduce the overall area burnt. If overall fire frequency is the main threat to biodiversity in the savannas, then the best solution will be to prevent the small subset of fires that have the potential to become very large.     

Assessing the relative fire proneness of different forest types in Portugal

Abstract

We have assessed the fire proneness of the main forest types in Portugal classified according to the main species, using three different approaches: the use of resource selection ratios applied to burned patches, the proportion of randomly located plots that were burned and the proportion of burned National Forest Inventory plots. The results allowed ranking fire proneness according to the following decreasing order: maritime pine forests, eucalyptus forests, unspecified broadleaf forests, unspecified conifer forests, cork oak forests, chestnut forests, holm oak forests and stone pine forests. In order to understand the obtained results we have assessed the structure of the different forest types using the percent cover of seven vegetation layers (C1–C7), a Tree Dominance Index, a Height Index and a Cover Index (IC). Structural variables and stand composition were used to predict fire probability according to binary logistic modelling. Only four structural variables and stand composition provided significant results, the latter being the most important variable for explaining fire probability. These models were used to predict fire probability for different stand types as a function of IC.     

Changes in the forest floor of Canadian southern boreal forest after disturbance

Abstract. The concentrations and contents of organic matter and nutrients in organic deposits on the forest floor were estimated along a 231-yr chronosequence following fire at the southern limit of the boreal forest in eastern Canada. The sampling design was stratified to take into account the variability related to the presence of the principal tree species as well as to the presence of large gaps created by a recent spruce budworm (Choristoneura fumiferana) outbreak. The forest floor showed a steady accumulation of organic matter and total nutrients with time-since-fire and a 50 % decrease in the concentrations of available P and K, but not N (as determined by aerobic incubation). The increase in forest-floor weight was accompanied by an increased storage of available N, Ca and Mg. The availability of N and Ca was more strongly affected by tree species and gaps than by time-since-fire. A high N-availability was observed under Betula papyrifera and in gaps, while high a Ca-availability was found near Populus tremuloides and Thuja occidentalis. In old sites, the forest floor of gaps, created by a recent spruce budworm outbreak, had a necromass similar to that of a young forest, but the low concentrations of available P and K of an old forest.     

Classification and gradient analysis of the beech forest vegetation of the southern Rodopi (northeast Greece)

Pure and mixed beech forest vegetation of the southern Rodopi range (northeast Greece) was studied using 614 relevés and multivariate analyses (TWINSPAN and DCA). Classification of the relevés resulted in 12 vegetation units, 8 of which were ranked as associations or communities and the rest as subcommunities and variants. DCA diagrams of relevés and taxa indicated that floristic differentiation was attributed mainly to factors such as altitude (affecting temperature and humidity), soil nutrient content and substrate type (affecting physical and chemical soil properties). Differential taxa of vegetation units were chosen based on their phi coefficient values, which were calculated from three different percentage synoptic tables that corresponded to three ranks (ecological groups, associations and communities, and subcommunities and variants) of floristic differentiation. The calculation of phi coefficient on the basis of relative constancy of taxa helps to overcome the problem of the dependence of fidelity values on the number of relevés per vegetation unit and to facilitate the better investigation of the floristic differentiation even of rare vegetation units represented by a small number of relevés. Furthermore, the calculation of fidelity values for different hierarchical levels enables a more detailed and thorough investigation of the floristic differentiation of the vegetation units.     

The effect of burning on soil enzyme activities in natural grasslands in southern India

Soil amylase, cellulase, invertase and phosphatase activities were determined following wildfire in a savanna type grassland in southern India. Activities of these enzymes increased substanially in burned soils compared to those in adjacent unburned soils. Surface soil (0–10 cm) exhibited a greater increase in enzyme activities than subsurface soil (10–20 cm). Amylase activity was more pronounced following fire than the other enzyme activities.     

Human Impacts on the Fire Regime of Interior Alaska: Interactions among Fuels, Ignition Sources, and Fire Suppression

Wildfire is the major natural agent of disturbance in interior Alaska. We examined the magnitude of human impact on fire by comparing fire regime between individual 1-km² grid cells designated for fire suppression with lands where fires are allowed to burn naturally. Two-thirds of interior Alaska has an essentially natural fire regime, with few human ignitions, negligible suppression activity, and many large lightning-caused fires. In the 17% of land that is designated for fire suppression due to its proximity to communities and roads, there was a 50% reduction in the proportion of area burned from 1992–2001, relative to areas without suppression. The remaining 16% of land serves as a buffer, receives some suppression, and has an intermediate fire regime. Even though there were 50 times more fires and the fire season began two months earlier in lands designated for suppression, most of these fires were lit by people and remained small because fires tended to occur at times and places less favorable for fire spread and were more accessible to fire fighters compared to lands not designated for suppression. Even in the absence of fire suppression, human-caused fires were less likely to exceed 400 ha compared to lightning-caused fires. Fire suppression reduced area burned in all fuel types but was somewhat more effective in less flammable (non-forest) vegetation. Alaska’s fire policy of focusing suppression efforts on a small proportion of the fire-prone region maximizes the ecological and social benefits associated with fire-dependent ecosystem services, while minimizing the social and ecological costs of suppression. Application of this policy to other areas would require well-informed managers and stakeholders to make difficult decisions about the relative costs and benefits of fire across ecologically and culturally variable landscapes.     

吉林省主要林型森林火灾的碳量释放

火是森林生态系统主要的干扰因子,森林火灾的频繁发生不仅使森林生态系统遭到破坏,同时也造成了含碳温室气体的大量释放。国际上对森林火灾释放温室气体的研究越来越多,中国学者也对我国森林火灾释放的温室气体进行了研究。当前,对森林火灾释放碳量的估算主要应用平均生物量数据,而不是应用每次森林火灾实际燃烧的生物量,另外对林型森林火灾碳释放的差异研究不够深入。根据每次森林火灾实际燃烧的生物量来研究吉林省主要林型森林火灾碳释放。根据吉林省1969—2004年的森林火灾统计数据,计算出了吉林省主要林型森林火灾释放碳量。其中,白桦林、阔叶混交林、针阔混交林、落叶松林、柞树林、杨树林和红松林森林火灾直接释放的碳量占1969—2004年吉林省森林火灾碳释放总量的99.7%。白桦林、阔叶混交林、针阔混交林、落叶松林、柞树林、杨树林和红松林森林火灾年均释放的碳量分别为6593.75-8791.66、5650.28-7533.71、3906.57-5208.76、2110.75-2814.33、1613.71-2151.61、295.49-393.98、234.37-312.50 t。用排放比法得出了吉林省主要林型森林火灾释放的CO2、CO、CH4量。白桦林、阔叶混交林、针阔混交林、落叶松林、柞树林、杨树林和红松林森林火灾年均释放的CO2量分别为21759.36-29012.48、18645.93-24861.24、12891.69-17188.92、6965.46-9287.29、5325.25-7100.33、975.11-1300.14、773.43-1031.24 t,年均释放的CO量分别为1583.09-2110.78、1356.57-1808.76、937.93-1250.57、506.77-675.69、387.43-516.58、70.94-94.59、56.27-75.03 t,年均释放的CH4量分别为534.71-712.94、458.20-610.93、316.80-422.39、171.17-228.22、130.86-174.48、23.96-31.95、19.01-25.34 t。通过时间系列分析,白桦林自1980年以后、针阔混交林自1984年以后和红松林自1983年以后已经不是主要森林火灾碳释放林型。目前主要森林火灾碳释放林型为阔叶混交林、落叶松林、柞树林和杨树林,特别是柞树林,年均碳释放为237.12-316.16 t。     

Interactive response of herbivores,soils and vegetation to annual burning in a South African savanna

Abstract Despite decades of research, the primary factors determining savanna structure remain elusive – a conundrum termed ‘the savanna problem’. After 47 years of annual burning in Terminalia woodland and Acacia/Combretum savanna on sandy, granite‐derived soils in the southern Kruger National Park, South Africa, a dense cover of trees and shrubs persists on some burnt plots and is largely absent from others. We postulated that intense browsing pressure by antelope and other herbivores prevents recruitment of trees in burnt plots and that herbivores concentrate on plots that are richest in nutrients. Herbivore abundance did not show a relationship with soil macronutrients and we consequently investigated micronutrient status. The reduction in tree cover as a result of annual burning was positively correlated with mass of herbivores (15–1500 kg) (r ² = 0.61, n = 8). This index of herbivore abundance was in turn positively correlated with total Zn (r ² = 0.64, n = 8). Other indices of herbivore abundance showed significant relationships with total clay content and total Mn. We suggest that herbivores concentrate on sites with greater clay content (possibly due to a greater availability of micronutrients), and that tree cover can remain relatively dense under a regime of annual burning if browsing pressure is not intense. The long‐term burn experiments in the Kruger National Park savanna provide a platform for unravelling the savanna problem. Determining possible interactions between soil properties, herbivory and fire is a step in this direction.