Stand structure, fuel loads, and fire behavior in riparian and upland forests, Sierra Nevada Mountains, USA; a comparison of current and reconstructed conditions

Fire plays an important role in shaping many Sierran coniferous forests, but longer fire return intervals and reductions in area burned have altered forest conditions. Productive, mesic riparian forests can accumulate high stem densities and fuel loads, making them susceptible to high-severity fire. Fuels treatments applied to upland forests, however, are often excluded from riparian areas due to concerns about degrading streamside and aquatic habitat and water quality. Objectives of this study were to compare stand structure, fuel loads, and potential fire behavior between adjacent riparian and upland forests under current and reconstructed active-fire regime conditions. Current fuel loads, tree diameters, heights, and height to live crown were measured in 36 paired riparian and upland plots. Historic estimates of these metrics were reconstructed using equations derived from fuel accumulation rates, current tree data, and increment cores. Fire behavior variables were modeled using Forest Vegetation Simulator Fire/Fuels Extension.Riparian forests were significantly more fire prone under current than reconstructed conditions, with greater basal area (BA) (means are 87 vs. 29 m²/ha), stand density (635 vs. 208 stems/ha), snag volume (37 vs. 2 m³/ha), duff loads (69 vs. 3 Mg/ha), total fuel loads (93 vs. 28 Mg/ha), canopy bulk density (CBD) (0.12 vs. 0.04 kg/m³), surface flame length (0.6 vs. 0.4 m), crown flame length (0.9 vs. 0.4 m), probability of torching (0.45 vs. 0.03), predicted mortality (31% vs. 17% BA), and lower torching (20 vs. 176 km/h) and crowning indices (28 vs. 62 km/h). Upland forests were also significantly more fire prone under current than reconstructed conditions, yet changes in fuels and potential fire behavior were not as large. Under current conditions, riparian forests were significantly more fire prone than upland forests, with greater stand density (635 vs. 401 stems/ha), probability of torching (0.45 vs. 0.22), predicted mortality (31% vs. 16% BA), and lower quadratic mean diameter (46 vs. 55 cm), canopy base height (6.7 vs. 9.4 m), and frequency of fire tolerant species (13% vs. 36% BA). Reconstructed riparian and upland forests were not significantly different. Our reconstruction results suggest that historic fuels and forest structure may not have differed significantly between many riparian and upland forests, consistent with earlier research suggesting similar historic fire return intervals. Under current conditions, however, modeled severity is much greater in riparian forests, suggesting forest habitat and ecosystem function may be more severely impacted by wildfire than in upland forests.     

Effect of season, location and fire on Collembola communities in buttongrass moorlands, Tasmania

Collembola of buttongrass moorlands in Tasmania were surveyed monthly over a 12 month period, using sweep nets and pitfall traps, at two locations, one at 760 m and the other at 325 m altitude. At each location, there were two pairs of sites with each pair straddling a fire boundary. The younger regrowth sites had been burnt less than 12 years previously and the older regrowth sites burnt more than 24 years previously. Nearly 30,000 individuals were collected belonging to 42 taxa. Most Collembola were identified to morphospecies with virtually all mature specimens identified to genus level and immature specimens recognised to family level. Three named species were recorded. Genera with Gondwanan (41%) and cosmopolitan (33%) distributions dominated the Collembola of buttongrass moorlands. The Collembola communities differed significantly between locations and this, in part, reflected differences in vegetation. Brachystomellidae, Odontellidae, Paronellidae, Katiannidae n. gen. and Sminthurididae were more common at the high altitude sites where the vegetation contained more grasses and sedges and occurred on relatively fertile soils. Parakatianna spp., cf. Tomocerura spp., cf. Drepanura sp., Sminthurinus spp. and Rastriopes sp. were more common at the low altitude sites where the vegetation contained more shrubs and occurred on relatively infertile soils. The Collembola community differed significantly between seasons with one group of taxa being more common in autumn and/or winter (Acanthomurus spp., cf. Tomocerura spp., Paronellidae, Lasofinius spp., Polykatianna cf. aurea, Parakatianna spp., Sminthurinus spp. and Katianna spp.) and another group of taxa more common in summer or summer and autumn (Odontellidae, cf. Drepanura sp., Rastriopes sp., Corynephoria sp. and Dicyrtomidae). We found some evidence of a difference between Collembola communities in the two ages of regrowth we compared but only for the low altitude sites. Polykatianna cf. aurea, Parakatianna spp., Sminthurinus spp., cf. Tomocerura spp. and Rastriopes sp. were caught in lower numbers on young regrowth sites compared with old regrowth sites. We also present data from another low altitude site where we used a space-for-time design to further investigate the impact of fire on Collembola. We found a significant positive relationship between age of buttongrass regrowth and the number of Rastriopes sp. caught and this was correlated with the ground cover of plant species within the family Myrtaceae.     

Activated carbon amendments to soil alters nitrification rates in Scots pine forests

The influence of charcoal on biotic processes in soils remains poorly understood. Charcoal is a natural product of wildfires that burned on a historic return interval of ∼100 years in Scots pine (Pinus sylvestris L.) forests of northern Sweden. Fire suppression and changes in forest stand management have resulted in a lack of charcoal production in these ecosystems. It is thought that charcoal may alter N mineralization and nitrification rates, however, previous studies have not been conclusive. Replicated field studies were conducted at three late-succession field sites in northern Sweden and supporting laboratory incubations were conducted using soil humus collected from these sites. We used activated carbon (AC), as a surrogate for natural-occurring fire-produced charcoal. Two rates of AC (0 and 2000 kg ha⁻¹), and glycine (0 and 100 kg N as glycine ha⁻¹) were applied in factorial combination to field microplots in a randomized complete block pattern. Net nitrification, N mineralization, and free phenol concentrations were measured using ionic and non-ionic resin capsules, respectively. These same treatments and also two rates of birch leaf litter (0 and 1000 kg ha⁻¹) were applied in a laboratory incubation and soils from this incubation were extracted with KCl and analyzed for NH₄⁺ and NO₃⁻. Nitrification rates increased with AC amendments in laboratory incubations, but this was not supported by field studies. Ammonification rates, as measured by NH₄⁺ accumulation on ionic resins, were increased considerably by glycine applications, but some NH₄⁺ was apparently lost to surface sorption to the AC. Phenolic accumulation on non-ionic resin capsules was significantly reduced by AC amendments. We conclude that charcoal exhibits important characteristics that affect regulating steps in the transformation and cycling of N.     

梨火疫细菌实时荧光PCR和诱捕PCR-ELISA检测方法的建立

根据梨火疫细菌中独特而保守存在的质粒pEA29，设计了1对引物和3条探针，建立了实时荧光PCR检测方法和诱捕PCR-ELISA检测方法。实时荧光PCR采用带荧光标记的核酸杂交探针，边扩增边检测，步骤简单，不需PCR后处理，可避免假阳性和交叉污染；诱捕PCR-ELISA检测方法只需简单处理的样品就能检测，减少了核酸不纯出现的漏检，由于增加了核酸杂交探针，可不需凝胶电泳EB染色检测，不会出现假阳性问题。     

火生态因子对草原的效应及有计划用火的研究

火烧可以提高禾草类的生物量25—30%,可以快速地(当年)大幅度提高羊草种群的生物量达100%以上。火烧提高羊草的抽穗率,促进草群更新复壮。火烧可以有效地抑制针茅种群的增长,并改变群落中的种群分布格局,促进羊草种群形成均匀分布格局,扩大羊草种群在群落中的生态位。火烧对草原的总生产力不发生负效应,一次火烧的正效应可持续2—3年。基于以上的结果,我们认为锡林郭勒草原区中,东部含有羊草的草原群落,可在春季四月下旬进行火烧,将会取得良好的效果。     

Inhibitory activities of venom alkaloids of Red Imported Fire Ant against Clavibacter michiganensis subsp. michiganensis in vitro and the application of piperidine alkaloids to manage symptom development of bacterial canker on tomato in the greenhouse

Tomato bacterial canker caused by Clavibacter michiganensis subsp. michiganensis (CMM) is a highly destructive disease that has caused major economic losses in tomato production worldwide. In seeking disease management alternatives, the inhibitory activity of alkaloids extracted from the Red Imported Fire Ant was studied in the laboratory and the greenhouse. Piperidine and piperideine alkaloids each significantly inhibited CMM growth on nutrient agar plates. The inhibitory activity of piperidine alkaloids was stable at 4 ^° C and 22 ^° C for 12 weeks and at 54 ^° C for 4 weeks. The growth of CMM was negatively correlated with the concentration of piperidine alkaloids in nutrient broth. In the greenhouse, piperidine alkaloids also significantly reduced the symptom development on two tomato cultivars, Better Boy and DRK7018F1. This is the first demonstration that piperidine and piperideine alkaloids from the Red Imported Fire Ant are highly inhibitory against a plant-pathogenic bacterium, viz. CMM. Piperidine alkaloids could provide satisfactory management of CMM bacterial canker on tomato seedlings in the greenhouse. Our findings may lead to the development of a new group of bactericides.     

Integrating climate change into forest management in South-Central British Columbia: An assessment of landscape vulnerability and development of a climate-smart framework

The achievement of sustainable forest management requires the incorporation of risk and uncertainty into long-term planning. Climatic change will have significant impacts on natural disturbances, species and ecosystems, particularly on landscapes influenced by forest management. Understanding where vulnerabilities lie is important in managing the risks associated directly or indirectly with climatic change. The vulnerability of landscapes to natural disturbances, the resilience of ecosystems and distribution of species are all important components that need to be considered when undertaking forest planning, but climatic change is rarely factored into such planning. In this study, the vulnerability of fire potential, fire regimes, ecosystems and species to climatic change was modelled for a 145,000 ha landscape in the south-central interior of British Columbia, Canada. The results from these analyses were used to guide forest zoning, using the triad zoning framework, and for the development of a “climate-smart” management framework. The use of climate-smart management is advocated as a decision-making framework for managing forested landscapes based on an understanding of landscape vulnerability to future climatic change. From this understanding, the maintenance of ecosystem health and vitality could be achieved.     

Historical change in coastal sage scrub in southern California,USA in relation to fire frequency and air pollution

Invasions resulting in the transformation of one ecosystem to another are an increasingly widespread phenomenon. While it is clear that these conversions, particularly between grassland and shrubland systems, have severe consequences, it is often less clear which factors are associated with these conversions. We resampled plots from the 1930s (Weislander VTMs) to test whether two widely assumed factors, changes in fire frequency and nitrogen deposition, are associated with the conversion of coastal sage scrublands to exotic grasslands in southern California. Over the 76-year period, coastal sage scrub cover declined by 49%, being replaced predominantly by exotic grassland species. Grassland encroachment was positively correlated with increased fire frequency and, in areas with low fire frequencies, air pollution (percent fossil carbon as indicated by ∂¹⁴C, likely correlated with nitrogen deposition). We conclude that increases in fire frequency and air pollution over the last several decades in southern California may have facilitated the conversion of coastal sage shrubland to exotic grassland systems.     

Historical range of variability in eastern Cascades forests,Washington, USA

The historical range of variability (HRV) has been suggested as a coarse filter approach to maintain ecosystem sustainability and resiliency. The historical range of variability in forest age structure for the central eastern Cascade Range in Washington State, USA was developed from historical fire return intervals and the manner in which fire acted as both cyclic and stochastic processes. The proportions of seven forest structural stages calculated through these processes were applied to the area of each forest series within the central eastern Cascades landscape. Early successional forest stages were more common in high elevation forest than low elevation forest. The historical proportion of old growth and late successional forest varied from 38 to 63 percent of the forested landscape. These process-based estimates are consistent with those developed from forest structural information. HRV is a valuable planning tool for ecosystem conservation purposes, but must be applied to real landscapes with consideration of both temporal and spatial scale. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evidence of selective burning in Sardinia (Italy): which land-cover classes do wildfires prefer?

The objective of this paper is to identify land-cover types where fire incidence is higher (preferred) or lower (avoided) than expected from a random null model. Fire selectivity may be characterized by the number of fires expected in a given land-cover class and by the mean surface area each fire will burn. These two components of fire pattern are usually independent of each other. For instance, fire number is usually connected with socioeconomic causes whereas fire size is largely controlled by fuel continuity. Therefore, on the basis of available fire history data for Sardinia (Italy) for the period 2000–2004 we analyzed fire selectivity of given land-cover classes keeping both variables separate from each other. The results obtained from analysis of 13,377 fires show that for most land-cover classes fire behaves selectively, with marked preference (or avoidance) in terms of both fire number and fire size. Fire number is higher than expected by chance alone in urban and agricultural areas. In contrast, in forests, grasslands, and shrublands, fire number is lower than expected. In grasslands and shrublands mean fire size is significantly larger than expected from a random null model whereas in urban areas, permanent crops, and heterogeneous agricultural areas there is significant resistance to fire spread. Finally, as concerns mean fire size, in our study area forests and arable land burn in proportion to their availability without any significant tendency toward fire preference or avoidance. The results obtained in this study contribute to fire risk assessment on the landscape scale, indicating that risk of wildfire is closely related to land cover.