加拿大北方森林过去、当前和未来的火灾频率:对于森林可持续经营的意义

在过去的几十年里,对基于对历史上自然干预动力的理解的森林经营方法的开发兴趣日益增加.这一方法的理由是,有利于景观组成和林分结构及自然生态系统的经营活动也应当保持生物多样性和基本的生态功能.在火灾居支配地位的景观,用森林经营替代火灾这一方法只在当前火频率和未来火频率比工业化以前的火频率低得多的情况下才有可能.通过将当前火频率、未来火频率与在加拿大北方森林中再现的森林火灾历史的比较,我们讨论了这一问题.对于多块研究地而言,当前火频率和2倍CO.及3倍CO2情形下模拟的未来火频率都低于过去火频率,这暗示着森林经营可以被用于重建受控于火灾的、工业化以前景观的林木年龄结构.但对目前的同龄林经营来说,还有一些重要的限制因子.     

Past, current and future fire frequency in the Canadian boreal forest: implications for sustainable forest management

Over the past decades, there has been an increasing interest in the development of forest management approaches that are based on an understanding of historical natural disturbance dynamics. The rationale for such an approach is that management to favor landscape compositions and stand structures similar to those of natural ecosystems should also maintain biological diversity and essential ecological functions. In fire-dominated landscapes, this approach is possible only if current and future fire frequencies are sufficiently low, comparing to pre-industrial fire frequency, that we can substitute fire by forest management. We address this question by comparing current and future fire frequency to historical reconstruction of fire frequency from studies realized in the Canadian boreal forest. Current and simulated future fire frequencies using 2 and 3 x CO2 scenarios are lower than the historical fire frequency for many sites, suggesting that forest management could potentially be used to recreate the forest age structure of fire-controlled pre-industrial landscapes. There are however, important limitations to the current even-age management.     

Control of Organic Emissions from Surface Coating Operations

ABSTRACT

Step tracer tests were carried out on lab-scale biofilters to determine the residence time distributions (RTDs) of gases passing through two types of biofilters: a standard biofilter with vertical gas flow and a modified biofilter with horizontal gas flow. Results were used to define the flow patterns in the reactors. “Non-ideal flow” indicates that the flow reactors did not behave like either type of ideal reactor: the perfectly stirred reactor [often called a "continuously stirred tank reactor" (CSTR)] or the plug-flow reactor.

The horizontal biofilter with back-mixing was able to accommodate a shorter residence time without the usual requirement of greater biofilter surface area for increased biofiltration efficiency. Experimental results indicated that the first bed of the modified biofilter behaved like two CSTRs in series, while the second bed may be represented by two or three CSTRs in series. Because of the flow baffles used in the horizontal biofilter system, its performance was more similar to completely mixed systems, and hence, it could not be modeled as a plug-flow reactor. For the standard biofilter, the number of CSTRs was found to be between 2 and 9 depending on the airflow rate. In terms of NH₃ removal efficiency and elimination capacity, the standard biofilter was not as good as the modified system; moreover, the second bed of the modified biofilter exhibited greater removal efficiency than the first bed. The elimination rate increased as biofilter load increased. An opposite trend was exhibited with respect to removal efficiency.     

Learning to recognize novel predators under weakly acidic conditions: the effects of reduced pH on acquired predator recognition by juvenile rainbow trout

Summary. Recent studies have demonstrated that under weakly acidic conditions (pH 6.0), many prey fishes, including juvenile rainbow trout (Onchorhynchus mykiss), do not exhibit overt antipredator responses to conspecific chemical alarm cues. In laboratory trials, we investigated the potential effects of reduced pH on the ability of hatchery reared, predator naïve juvenile rainbow trout to acquire the recognition of a novel predator (yellow perch, Perca flavenscens). Initially, we exposed trout to the odour of a predatory yellow perch, buffered to pH 6.0 (weakly acidic) or pH 7.0 (neutral) paired with conspecific skin extracts (also buffered to pH 6.0 or 7.0) or a distilled water control. Juvenile trout exhibited significant increase in antipredator behaviour when exposed to neutral skin extract (pH 7.0). When retested 48 hours later to perch odour alone (pH 7.0), only trout initially conditioned with neutral skin extracts (pairs with either neutral or acidic perch odour) exhibited a learned recognition of perch odour as a predator risk. Those initially exposed to weakly acidic skin extract or the distilled water control did not show a learned response to predator odour. These results demonstrate that the ability to acquire the recognition of novel predators is impaired under weakly acidic conditions, as would occur in natural waterways affected by acidic precipitation.     

Evaluation of pay-for-release conservation incentives for unintentionally caught threatened species

In the developing world, the exploitation of threatened species jeopardizes their permanence in the wild. Because not all captures are intentional, for instance when capture methods have low selectivity, pressure on these species may be lessened by releasing living incidentally caught animals. However, it is often unrealistic to expect people to voluntarily do so because it means foregoing the benefits of resource extraction. Financial incentives for such animal release may foster conservation objectives. Reducing human–animal conflicts, protecting natural habitat, and conserving nests of threatened species are examples of conservation benefits that can be built on financial reward systems. However, incentives aiming to protect unintentionally captured threatened species are scarce. We considered pay for release, a type of ecosystem-service payment designed to foster the release of incidentally captured threatened species. We aimed to determine the best conditions to implement this scheme, its potential benefits (e.g., incentivizing the release of threatened species), and pitfalls and priority research needs (e.g., required conditions for pay for release to work) to show that its global applicability is possible. Given that approaches solely based on education and law enforcement may be ineffective under some circumstances, we argue that pay for release can protect incidentally captured endangered species if used under conditions conducive for its success. When local participants’ intrinsic motivation for conservation is weak, but the release of incidentally live-caught animals into their habitats is readily achievable, pay-for-release schemes could jump start urgently needed conservation efforts against indiscriminate animal harvesting.