S. 2002. Natural fi re regime: a guide for sustainable management of the Canadian boreal forest. Silva Fennica 36(1): 81-95.The combination of certain features of fi re disturbance, notably fi re frequency, size and severity, may be used to characterize the disturbance regime in any region of the boreal forest. As some consequences of fi re resemble the effects of industrial forest harvesting, conventional forest management is often considered as a disturbance that has effects similar to those of natural disturbances. Although the analogy between forest management and fi re disturbance in boreal ecosystems has some merit, it is important to recognise that it also has its limitations. Short fi re cycles generally described for boreal ecosystems do not appear to be universal; rather, important spatial and temporal variations have been observed in Canada. These variations in the fi re cycle have an important infl uence on forest composition and structure at the landscape and regional levels. Size and severity of fi res also show a large range of variability. In regions where the natural matrix of the boreal forest remains relatively intact, maintenance of this natural variability should be targeted by forest managers concerned with biodiversity conservation. Current forest management tends to reduce this variability: for example, fully regulated, even-aged management will tend to truncate the natural forest age distribution and eliminate over-mature and old-growth forests from the landscape. We suggest that the development of strategic-level forest management planning approaches and silvicultural techniques designed to maintain a spectrum of forest compositions and structures at different scales in the landscape is one avenue to maintain this variability. Although we use the boreal forest of Quebec for our examples, it is possible to apply the approach to those portions of the boreal forest where the fi re regime favours the development of even-aged stands in burns.

Background: The development of forestry as a scientific and management discipline over the last two centuries has mainly emphasized intensive management operations focused on increased commodity production, mostly wood. This "conventional" forest management approach has typically favored production of even-aged, single-species stands. While alternative management regimes have generally received less attention, this has been changing over the last three decades, especially in countries with developed economies. Reasons for this change include a combination of new information and concerns about the ecological consequences of intensive forestry practices and a willingness on the part of many forest owners and society to embrace a wider set of management objectives. Alternative silvicultural approaches are characterized by a set of fundamental principles, including avoidance of clearcutting, an emphasis on structural diversity and small-scale variability, deployment of mixed species with natural regeneration, and avoidance of intensive site-preparation methods. Methods: Our compilation of the authors' experiences and perspectives from various parts of the world aims to initiate a larger discussion concerning the constraints to and the potential of adopting alternative silvicultural practices. Results: The results suggest that a wider adoption of alternative silvicultural practices is currently hindered by a suite of ecological, economic, logistical, informational, cultural, and historical constraints. Individual contexts display their own unique combinations and relative significance of these constraints, and accordingly, targeted efforts, such as regulations and incentives, may help to overcome specific challenges. Conclusions: In a broader context, we propose that less emphases on strict applications of principles and on stand structures might provide additional flexibility and facilitate the adoption of alternative silvicultural regimes in a broader set of circumstances. At the same time, the acceptance of alternative silvicultural systems as the "preferred or default mode of management" will necessitate and benefit from the continued development of the scientific basis and valuation of a variety of ecosystem goods and services. This publication is aimed to further the discussion in this context.

The "dormant basket cell" hypothesis suggests that postinjury hippocampal network hyperexcitability results from the loss of vulnerable neurons that normally excite insult-resistant inhibitory basket cells. We have reexamined the experimental basis of this hypothesis in light of reports that excitatory hilar mossy cells are not consistently vulnerable and inhibitory basket cells are not consistently seizure resistant. Prolonged afferent stimulation that reliably evoked granule cell discharges always produced extensive hilar neuron degeneration and immediate granule cell disinhibition. Conversely, kainic acid-induced status epilepticus in chronically implanted animals produced similarly extensive hilar cell loss and immediate granule cell disinhibition, but only when granule cells discharged continuously during status epilepticus. In both preparations, electron microscopy revealed degeneration of presynaptic terminals forming asymmetrical synapses in the mossy cell target zone, including some terminating on gamma-aminobutyric acid-immunoreactive elements, but no evidence of axosomatic or axoaxonic degeneration in the adjacent granule cell layer. Although parvalbumin immunocytochemistry and in situ hybridization revealed decreased staining, this apparently was due to altered parvalbumin expression rather than basket cell death, because substance P receptor-positive interneurons, some of which contained residual parvalbumin immunoreactivity, survived. These results confirm the inherent vulnerability of dendritically projecting hilar mossy cells and interneurons and the relative resistance of dentate inhibitory basket and chandelier cells that target granule cell somata. The variability of hippocampal cell loss after status epilepticus suggests that altered hippocampal structure and function cannot be assumed to cause the spontaneous seizures that develop in these animals and highlights the importance of confirming hippocampal pathology and pathophysiology in vivo in each case.

No abstract

Although the concept of forest ecosystem management based on Le concept d'arnknagement &yst6mique, soit une approche #am& natural disturbance has generated a great deal of interest, few connagement forestier s'inspirant des perturbations naturelles, suscrete examples exist of FEM principles being put into application.cite de plus en plus d'intkret auprks des forestiers mais son Silvicultural practices that emulate natural disturbances are proapplication concrkte en est encore B ses dkbuts. Des pratiques sylviposed with examples from the principal vegetation zones of coles s'apparentant aux perturbations naturelles sont proposkes Quebec. With the exception of the large-scale use of careful en donnant des exemples pour les principales zones de vCg6ta-logging to protect advanced regeneration in ecosystems generally tion du Qukbec. A l'exception de l'utilisation 2i grande Cchelle de controlled by fire, stand-level silvicultural practices currently used la coupe avec protection de la rkg6nkration et des sols dans des are reasonably similar to natural disturbances, although impor6cosystkmes gknkrdement cont18lCs par les incendies, les pratiques tant differences exist. In contrast, at the forest-level, even-aged ~y l v i c~l e s rkalistes couramment B l'kchelle des ~e u~l e m e n t s management, as is currently rarely adequate sont assez similaires aux perturbations naturelles, bien qu'il duction of the variety of age ,-lasses, stand types, and structural existe encore des diffkrences importantes. Par contre, l'amkcomponents d y found in the boreal forest. A model that allows nagement normal des for& kquiennes, tel que pratiquk actuellean even-aged management approach inspired by natural dynamment, Permet rarement de reproduire adkquatement la varikt6 des ics is proposed.classes d'$ges, des types de peuplements et des composantes structurales habituellement rencontrks en for& boreale. Un modkle permettant d'appliquer une approche d'amknagement Cquienne s'inspirant de la nature est proposk.