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International audience; AbstractKey messageUsing the three characteristic points of a forest stand, dg (mean quadratic diameter), dmin(diameter of the smallest tree) anddmax (diameter of the largest tree), appears informative enough to determine the parameters of the whole diameter distribution and, hence, the standing volume, with an accuracy of 2–3%. This is related principally with a particular feature of the Weibull distribution function, and the empirical dependency of the main scale parameter α + β from the mean quadratic diameter (dg): This allows the prediction of the parameter β with an unexpectedly high likelihood. This feature could be used for growth modelling as well as inventory purposes, at least for monospecific and even-aged stands and, maybe more, because this feature is proper to the function itself.ContextOne of the most appealing applications of diameter distribution functions is to predict compliant stand diameters without needing to tally all stems, but in determining the function parameters only on the base of simple stand characteristics. This can be applied for yield model construction or inventory purposes.AimsThe aim of this paper is to compare different methods of estimating the Weibull distribution parameters, partly based on parameter recovery method (PRM). They use a remarkable, empiric property of the Weibull function. Their performances are assessed in comparison to real distributions from a wide database of permanent Swiss yield plots repeatedly measured (time series) for Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.).MethodsThe Weibull distribution offers the advantage of simple but reliable estimation procedures. One of these is the main (scale) parameter β being given at a remarkable point of the function free, i.e. independent from the shape parameter γ. Because dg lies very close to this point, it correlates empirically very tightly with this parameter and thus allows for a trustful simple estimation. We compare, with appropriate statistic tests, real distribution with such obtained with the usual maximum likelihood estimation (MLE) of the Weibull parameters and those obtained with these new procedures.ResultsThe results obtained from a set of 800 yield plots of regular spruce stands and 596 of beech in Switzerland illustrate the good performances of the two much simpler procedures. The accuracy of estimating the standing volume is about 1.4% for beech and 2.8% for spruce when the site index (SI) is known.ConclusionThe three considered characteristic stand attributes (dg, dmin and dmax) appear robust enough for determining the diameter distribution with a respectable accuracy. This is enough reason for a revival of the old, but very ingenious, method of angle count sampling of Walter Bitterlich (1947).

International audience; The specific goals of this paper are the following:1. To determine, using beech-dominated pristine forests as anexample,themaindrivingforcesofgenerationrenewal intermsoflifecycledurationandspatialrenewalpatterns; 2. Toillustratecontrastinglightrequirementsduringrenewal by comparing pristine oak and beech forests; 3. To elucidate the lower limits of stocking and canopy openness for silvicultural renewal in small clusters based on pristine forest research; 4. Topresentanapproachforimplementingthesefindingsin a liberal and versatile forest management

In the development of pure beech and pure spruce pristine forests, we assume there should be a continuous transition from full stocking to successive disintegration and, finally, total replacement of the first generational wave at the end of its lifetime, dependent on mortality due to overcrowding as well as ageing, leading newly recruited cohorts to grow up from below. A survey of stem number distribution from permanent plots measured repeatedly in six pristine beech reserves and four spruce reserves, mainly in Slovakia, was considered as well as surveys from yield plots in untouched stands in Switzerland on comparable site conditions. From 64 (54, respectively) surveys in virgin forests, we separated (if necessary) the original regeneration waves from successive waves for calculation of stand density development. Comparison with a previous model for full stand closure according to Reineke’s density rule allowed the risk of stand release to be evaluated and determined. The risk of stand closure release is substantially higher for spruce than for beech because of differences in longevity and in vulnerability to storms. Decay does not seem to be the decisive factor, until advanced ageing is reached. Consequences for the understanding of natural forest dynamics, especially reinitiation through successive waves of regeneration are drawn on the basis of silvicultural expertise from continuous cover systems. The density threshold limit for the accession of a second growth in the upper storey is attained at an age of about 180 years for beech and 140 years for spruce. This corresponds to about 70% or 40% of the life cycle, respectively. Vulnerability to stand release should be considered as a gradual (discrete) rather than a continuous phenomenon that depends on the complex relationship between the collective cohesion within a stand and a propensity for weakening factors. This suggests that the establishment of large disclosure patches could be the driving force in the renewal of these virgin forests.

The aim of this study is to scrutinise whether a dynamic equilibrium model based on sustainability of the demography is valid for pure beech plenter forests. Broad-leaved trees in general, and beech in particular react differently to individualisation and to shade than conifers, because of differences in space occupancy and their reaction to shade. Therefore application of the plenter system (or selection system) presents other constraints than for conifers forests. Sustainability must be assessed at stand level, because the plenter system functions without cover interruption and so needs continuous recruitment growing from the stand bottom up. The algorithm used for determination of demographic equilibrium depends on knowledge of the recruitment from below, stem migration over time (dependent on diameter increment), and removal for cultural and harvesting purposes and their dependency from stand density. Data used in this study comes from three permanent research plots in the pure beech plenter forests of Langula (Thuringia basin, Eastern Germany). The determination of the optimal stand density ensuring equilibrium uses an incremental growth model based on a basal area oriented density index (GCUM). It emphasises the phenomenon of growth extinction with increasing stand closure. Equilibrium is gained for a standing volume about 250 m3/ha and Basal area 22 m2/ha. This occurs at a much lower stand density than for classical coniferous plenter forests. The reasons for these differences and the silvicultural consequences are discussed., Modélisation de l'équilibre démographique en futaie jardinée de hêtre en Allemagne de l'Est. L'objectif de cette étude est de vérifier l'applicabilité d'un modèle d'équilibre démographique aux forêts jardinées de feuillus. Les feuillus réagissent différemment des conifères à l'individualisation due à l'irrégularité car ils utilisent différemment l'espace vital et l'ombrage. L'application des principes du jardinage est donc liée à des contraintes limitantes différentes que pour les forêts jardinées classiques de conifères. L'équilibre se détermine au niveau du peuplement, car en futaie jardinée il n'y a jamais interruption de couvert. Il faut donc une continuité du recrutement sous couvert. L'algorithme utilisé pour déterminer l'équilibre démographique se fonde sur la mesure du recrutement, de la migration des tiges dépendant de la croissance radiale et des éliminations à des fins culturales et de récolte, le tout dépendant de la densité des peuplements. Les données proviennent de trois parcelles d'essai de futaies jardinées de hêtre de Langula en Thuringe (Allemagne de l'Est). Le modèle incrémentiel de détermination de la densité optimale de peuplement qui assure l'équilibre démographique utilise un indice de densité variable GCUM fondé sur la surface terrière des plus gros. Il met en évidence un phénomène d'extinction du recrutement avec l'augmentation de la fermeture des peuplements. L'équilibre jardiné s'obtient pour des volumes sur pied de l'ordre de 250 m3/ha et une surface terrière de 22 m2, ce qui est nettement plus bas que dans le cas des forêts jardinées de conifères. On discute les raisons de cette différence et les conséquences sylvicoles.

International audience; This paper outlines the prerequisites for research into natural and opportunistic methods of vegetation control. These methods must be chemical-free and respect naturalness, but must still be acceptable in terms of cost. These alternative regeneration control methods are discussed and illustrated. Firstly, weed control is influenced by the degree of shading during the regeneration process. The principle of antibiosis can also be used by sowing an admixture of herbs: these are invasive enough to flourish but favour the soil's biological activity (or other factors) enough to reduce weed development and so assist the regeneration process. In the long term, natural plant dynamics in temperate Central Europe lead to fairly regular stands, which are composed of relatively poor species, due to natural outmixing processes. This paper examines natural regeneration development in a 0.25 ha gap. Results show that starting from a very heterogeneous mixture of spontaneously regenerated seedlings (20 species), a considerable reduction in tree species in the dominant stand layer has taken place after 15 years. Outmixing differs depending on light conditions. Ash, which is an intolerant species, dominates in the gap centre, and beech, a tolerant species, dominates along the edge of the patch and under the old stand's shelter.; Méthodes opportunistes de contrôle du développement de la végétation de parterre de coupe, inspirées de la dynamique naturelle de la succession végétale avec mention particulière des effets de démélange dans une régénération en trouée. Le présent texte souligne les conditions-cadre de la recherche de méthodes opportunistes de contrôle de la végétation du parterre de coupe. Elles se veulent libres d'intrants chimiques, respectueuses de la naturalité et acceptables en termes de coûts. On présente et illustre de telles méthodes alternatives de contrôle de la végétation. C'est tout d'abord l'utilisation de l'ombrage pendant le processus de régénération qui permet de bien gérer la végétation adventive. D'autres possibilités sont l'utilisation des principes d'antibiose et notamment l'installation par semis dirigé d'un mélange de plantes herbacées suffisamment prospère pour empêcher la prolifération d'autres plantes plus gênantes et pas trop incompatible avec un bon développement des ligneux désirés et ceci tout en agissant de façon favorable sur l'activité biologique du sol. À long terme le développement de la végétation ligneuse aboutit pour les conditions d'Europe centrale tempérée à la constitution de peuplements relativement pauvres en essences à cause de phénomènes de démélange. On présente les résultats du développement d'un rajeunissement naturel dans une trouée moyenne (d'environ 25 ares), constitué au départ de 20 espèces qui après 15 années démontre un effet très significatif de réduction du mélange d'essences dans l'étage dominant. Ce processus de démélange diffère en fonction de l'ombrage. Le frêne espèce héliophile domine les autres essences au centre de la trouée et le hêtre, sciaphile, dans les bords et en lisière.

"Forêts et tempête" Expertise collective sur les tempêtes, la sensibilité des forêts et sur leur reconstitution; National audience

International audience