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La famille des modèles de croissance SiWaWa est conçue pour être utilisable facilement à partir d’entrées les plus simples possibles, en fait au minimum le nombre de tiges (N) et la surface terrière (G), ainsi que l’indice de fertilité (SI, soit hdom à 50 ans). Ces modèles génèrent la distribution des tiges avec une très bonne justesse d’estimation (vers 2-3% du volume sur pied) pour six essences différentes : Épicéa, Pin sylvestre, Douglas, Hêtre, Frêne et Chêne. Ils s’apprêtent particulièrement bien à des tâches d’inventaire. Une application sur téléphone mobile, accompagné d’un module de détermination de la surface terrière selon Bitterlich, utilisant les capteurs des portables (notamment l’optique embarquée) les rend facilement applicables au praticien. Ils présentent l’évolution des peuplements observés pendant 30 ans, déterminent la mortalité naturelle et permettent de prévoir n’importe quand des interventions adaptables aux pratiques de l’utilisateur.

Near-to-nature sylviculture in view of the conflict economy-ecology: panacea or illusion?The concept of near-to-nature sylviculture is open to varying ways of interpretation which mainly depend on the emphasis given to the terni of "culture" and "nature" and the values we associate with these two key expressions. It is, however, not a new concept; it dates back to the last century's sylvicultural conception developed by Karl Gayer. This very form of forest management bas been practised for more than a century in Switzerland; the experience gained is presented here. Sylviculture based on the principle of free use of cuttings is a remarkably liberal concept. It differs essentially from other, stricter concepts derived from the ideology of the perpetuating forest according to Môller. Using the principle of free use of cuttings, the aim is to revaluate the position of the sylviculture with regard to forest management, whose role is control and follow up. This liberal form of combining the principles of naturalness and multifunctionality appears to bc remarkably modern if the need to favour diversity is added. The whole is connected to the fact that current economic conditions are becoming less and less favourable.

Small populations are prone to genetic drift as a consequence of random sampling effects. We investigated whether we could detect such random sampling effects in the English yew (Taxus baccata), a dioecious conifer species occurring in scattered populations in Switzerland. Seven pairs of small and large populations were analyzed using random amplified polymorphic DNA (RAPD) marker bands from 20 individuals per population. Several genetic parameters (mean marker band frequency deviation, molecular variance, population differentiation) indicated that small populations experienced genetic drift. These genetic differences between small and large populations of yew were paralleled by an increased sex ratio bias towards a higher number of females in the small populations. Our findings support earlier assumptions that the Swiss occurrences of yew may be described as metapopulation dynamics, characterized by local colonization and extinction events leading to the observed genetic drift. [ABSTRACT FROM AUTHOR]

This paper discusses the dynamic definition of irregularity; it looks at conditions of sustainability and considers under which conditions irregularity could be promoted efficiently. Irregularity is not usually innate in natural forest ecosystems, the exception being in certain developmental stages of old or over‐mature stands. Because of these natural tendencies, it is necessary to differentiate between temporary stand structures and sustainable irregular systems. Therefore, any assessment of irregularity needs to take the rules of demographic regulation into account. Different kinds of irregularity are discussed, as is the reference scale for implementation. This makes it possible to distinguish between genuine irregularity within the crown layer, full (vertical) irregularity on stand level (plenter system) and horizontal irregularity (for greater reference scales), by creating irregular patches (as under the irregular shelterwood system). The paper presents the differences between broadleaved species and conifers in a full irregular plenter system with a developed vertical structure. These differences are due to the degree to which tree species can support shade, without losing the ability to recover qualitative capacity and, for older stages, to use crown space efficiently. Other factors are also important: the reaction of tree species to openings, the production of epicormic branches, topology and crown expansion. Therefore, broadleaved plenter forests need much lower equilibrium standing volumes than classical conifer plenter forests and there are also losses in volume increment and stem quality. The silvicultural results produced by the different models for differentiating stands and promoting irregularity are also discussed. It is assumed that for broadleaved species, the compromise between the necessary educative steps (shaping of the stem form within tree populations) and closure control function are better in small populations (openings) than in stands with a single tree structure. Because the ultimate aim is to create not one, but several, co‐existing forms of heterogeneity, in the sense of creating varied habitats, modern silviculture should make use of all silvicultural tools. This is a significant challenge for silvicultural expertise. [ABSTRACT FROM AUTHOR]

In the Caspian region of northern Iran, research was carried out into the structure of pure and mixed stands of natural oriental beech (Fagus orientalis Lipsky) and the presence of regeneration in natural gaps of differing sizes. Results showed that beech stands usually occurred naturally in small groups of a similar age, whereas the age structure of larger areas (>1 ha) was more uneven. The total volume of stands investigated ranged from 480 m3 in the pure stand to 600 m3 in the mixed stand. Only one‐third of total trees were classed as large timber (>55 cm diamater at breast height), which in turn accounted for two‐thirds of total stand volume. Although beech regeneration within the large gaps (>0.1 ha) showed the best growth characteristics, more well‐formed saplings were found within medium‐sized gaps (0.02–0.05 ha). From the results, it was concluded that the group selection system, with the removal of two to four main trees, could be a suitable method for managing oriental beech stands. [ABSTRACT FROM AUTHOR]