Andreas Zingg

Comparison between the productivity of pure and mixed stands of Norway spruce and European beech along an ecological gradient

Abstract• Existing growth and yield plots of pure and mixed stands of Norway spruce (Picea abies (L.) H. Karst.) and European beech (Fagus sylvatica L.) were aggregated in order to unify the somewhat scattered sources of information currently available, as well as to develop a sound working hypothesis about mixing effects. The database contains information from 23 long-term plots, covering an ecological gradient from nutrient poor and dry to nutrient rich and moist sites throughout Central Europe.• An empirically formed interaction model showed, that depending on the site conditions, dry mass growth in mixed stands can range from −46% to +138 % of the growth yielded by a scaled combination of pure stands at equal mixing proportions.• Drawing from the interaction model, overyielding of the mixed stands appears to be triggered by two separate mechanisms. On poor sites, where significant overyielding is commonly found, facilitation by beech offsets nutrient-related growth limitations in spruce. In contrast, overyielding of mixed stands occurs less frequently on rich sites, and appears to be based on an admixture effect, with spruce reducing the severe intra-specific competition common in pure beech stands.• It was concluded that silviculture can accelerate growth of spruce by beech admixtures on poor sites, while growth of beech can be promoted by admixture of spruce, particularly on excellent sites.

Effectiveness of structure improvement thinning on stand structure in subalpine Norway spruce (Picea abies (L.) Karst.) stands

Abstract In the Swiss mountains there are numerous Norway spruce stands which have never or have not received silvicultural treatment for a long time. It is feared that the stand structures and, therefore, stand stability, i.e. resistance against storms and snow loads, will decline to such a degree that their protective function against natural hazards will be reduced. In this study, such stands, which local forest services consider having unsatisfactory structures and being unstable and with little regeneration, were subjected to a first thinning operation. Selected silvicultural treatments to maintain and improve the mechanical stability of the stands with the long-term goal of transforming them into mountain selection forests are presented. The subsequent development of the stands will be monitored and analysed. The effects of the treatments on structure and stand stability will be examined in the long-term by comparisons to adjacent stands with similar structures and similar stability which have received no treatment. First results concerning the effectiveness of the applied silvicultural measures regarding stand structure are analysed. It seems that the variables h / d ratio, spatial distribution and the stand density index (SDI) are the best indicators of the effectiveness of the silvicultural treatment.

Estimating growth in beech forests: a study based on long term experiments in Switzerland

Abstract• This contribution presents a dynamic stand growth model for Beech (Fagus sylvatica L.) forests, based on a dataset provided by the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf. The dataset includes 143 research plots, covering a wide range of growing sites and providing up to 16 interval measurements per research plot.• The objective of this research is to complement the range of existing beech growth models by bridging the gap between the historical yield tables and the single tree growth models. The specific aim is to develop transition functions which will project three state variables (dominant height, basal area and number of trees per hectare) at any particular time, in response to any arbitrary silvicultural treatment.• Two of the transition functions were derived using the generalized algebraic difference approach (GADA), the third one was derived with the algebraic difference approach (ADA). All the functions were fitted simultaneously using iterative seemingly unrelated regression and a base-age-invariant method. The influence of thinnings on basal area growth was included by fitting different transition functions for thinned and unthinned stands.• The overall model provides satisfactory predictions for time intervals up to 20 years. The new model is robust and its relatively simple structure makes it suitable for economic analysis and decision support.Résumé• Cette contribution présente un modèle dynamique de croissance des peuplements de hêtres (Fagus sylvatica L.), basé sur un ensemble de données fournies par l’Institut Fédéral Suisse de Recherche sur la Forêt, la Neige et le Paysage, WSL à Birmensdorf. L’ensemble des données comprend 143 parcelles de recherche, couvrant un large éventail de sites et fournissant jusqu’à 16 intervalles de mesures par parcelle de recherche.• L’objectif de cette recherche est de compléter la gamme de modèles de croissance du hêtre existants, en jetant un pont entre les tables de production historiques et les modèles de croissance d’arbre. L’objectif spécifique est de développer des fonctions de transition qui projeterons trois variables d’état (hauteur dominante, surface terrière et nombre d’arbres par hectare) à n’importe quel moment déterminé, en réponse à n’importe quel traitement sylvicole arbitraire.• Deux des fonctions de transition ont été calculées en utilisant l’approche différence algébrique généralisée (GADA), la troisième a été dérivée de l’approche différence algébrique (ADA). Toutes les fonctions ont été ajustées en utilisant simultanément une régression itérative sans lien apparent et une méthode basée sur l’invariance de l’âge. L’influence des éclaircies sur la croissance de la surface terrière a été inclue en ajustant différentes fonctions de transition pour les peuplements éclaircis et les peuplements non éclaircis.• Le modèle général fournit des prédictions satisfaisantes pour des intervalles de temps jusqu’à 20 ans. Le nouveau modèle est robuste et sa structure relativement simple fait qu’il est convient pour l’analyse économique et l’aide à la décision.

Evaluation of the forest growth model SILVA along an elevational gradient in Switzerland

The semi-empirical single-tree model SILVA 2.2 has been developed and parameterised using forest research and inventory data from Germany that range from the colline to the montane zone. The focus of the model evaluation presented in this study was to test the applicability of the model for the main Swiss forest types and at elevations ranging from the colline to the upper subalpine zone. To this end, SILVA was initialized using data from long-term forest yield research plots. The results at the end of the 30-year simulation were compared with observed data. The analysis of the results at each test site showed that there were no significant differences in model performance between forest types. However, the deviation between simulated and observed growth depended strongly on the elevational zone, i.e., on climate. As expected, the best results were found in the colline zone, for which the model had been calibrated, whereas the upper subalpine sites revealed the strongest differences. The quality of the data regarding forest structure that were available for model initialization had a strong impact on the simulation results, mainly at high-elevation zones (i.e., supalpine and upper subalpine). We conclude that SILVA 2.2 is a suitable tool to estimate the development of single trees and standing volume for a large fraction of the forests in Switzerland. However, extreme climate conditions should be avoided with the model, and the availability of detailed stand structure information is a key priority that has a strong effect on the quality of the simulation results.

Evaluation of permanent sample surveys for growth and yield studies : a Swiss example

Abstract This paper compares experimental growth and yield study plots with sample plots from forest inventories. The difference in research objectives leads to a situation where sample plots are available that are representative of the total population, but give only limited information on site conditions and management history. However, detailed information on site condition and management history is available for growth and yield plots, but does not represent the total population. As an example, Swiss growth and yield plots are compared with survey plots in terms of species distribution, stem form, slope class and elevation. A critical review is given of the two most common sampling designs for regional forest surveys. Continuous forest inventory is recommended over the more efficient but more complex sampling with partial replacement design for use in conjunction with growth and yield studies. The limitations of both growth and yield plots and sample plots are discussed. Recommendations for linking both types of plots to close information gaps are given to improve both forest surveys and growth and yield studies.

A decade of irrigation transforms the soil microbiome of a semi-arid pine forest

The impact of climate change on the soil microbiome potentially alters the biogeochemical cycle of terrestrial ecosystems. In semi‐arid environments, water availability is a major constraint on biogeochemical cycles due to the combination of high summer temperatures and low rainfall. Here, we explored how 10 years of irrigation of a water‐limited pine forest in the central European Alps altered the soil microbiome and associated ecosystem functioning. A decade of irrigation stimulated tree growth, resulting in higher crown cover, larger yearly increments of tree biomass, increased litter fall and greater root biomass. Greater amounts of plant‐derived inputs associated with increased primary production in the irrigated forest stands stimulated soil microbial activity coupled with pronounced shifts in the microbiome from largely oligotrophic to more copiotrophic lifestyles. Microbial groups benefitting from increased resource availabilities (litter, rhizodeposits) thrived under irrigation, leading to enhanced soil organic matter mineralization and carbon respired from irrigated soils. This unique long‐term study provides new insights into the impact of precipitation changes on the soil microbiome and associated ecosystem functioning in a water‐limited pine forest ecosystem and improves our understanding of the persistency of long‐term soil carbon stocks in a changing climate.

Improving estimations of maximal stand density by combining Reineke’s size-density rule and the yield level, using the example of spruce (Picea abies (L.) Karst.) and European Beech (Fagus sylvatica L.)

Abstract• The Reineke Stand density rule relating stem numbers to the quadratic mean diameter is generally used as a reference for modelling maximal stand density.• The linearity of this relationship after double logarithmic transformation is generally assumed, but it must be questioned for untouched stands and stands with a conventional thinning regime. Curvilinearity is demonstrated for some spruce and beech stands in Switzerland and shown to be statistically representative. This relationship is independent of the site index. It can be interpreted as a change in mortality in young stages mainly due to competition and in older stages more to ageing.• A more accurate estimation of the maximal stand density needs to take into account the important variation around the mean course, known as the yield level. A simple method to assess the yield level of any stand regardless of whether it is thinned or not is presented, based on estimating the effect of a stand opening on the basal area.Résumé• La loi de Reineke reliant le nombre de tiges au diamètre quadratique moyen est généralement utilisée comme référence pour la modélisation de la densité maximale de peuplements.• On remet en question la linéarité d’une telle relation dans l’espace logarithmique, dans le cas des peuplements non traités aussi bien que pour ceux traités par des interventions conventionnelles. La curvilinéarité de cette relation est démontrée pour quelques peuplements purs d’épicéa et de hêtre en Suisse et dans sa représentativité statistique. La relation est indépendante de l’indice de fertilité et interprétée comme modification du type de mortalité au cours du développement, due pendant le jeune âge à la seule compétition, puis s’y ajoute celle due au vieillissement.• Une estimation appropriée de la densité maximale des peuplements doit tenir compte des variations importantes autour de la courbe moyenne connue comme niveau de production. Une méthode simple de détermination du niveau de production dans tous les cas de traitement antérieur est présentée, fondée sur une estimation de l’effet de l’ouverture du couvert sur la surface terrière.

Tree size distribution and abundance explain structural complexity differentially within stands of even-aged and uneven-aged structure types

Abstract Characterizations of physical structural complexity are an important surrogate for the potential of forested stands to provide desired ecosystem services such as biodiversity. Distinguishing between stands with different structural conditions is not only a necessary feature of useful structural metrics and indices, but how such measures vary among stands can reveal clues to the ecological processes driving structure. We used stand inventory metrics and indices of structural complexity to differentiate between even-aged and uneven-aged structure types using 10 stem-mapped coniferous stands of each type distributed across Switzerland. Within each structure type, we further explored relationships among stand inventory metrics and structural indices over a roughly 10-year period of management intervention. The even-aged and uneven-aged structure types were clearly differentiated using both stand inventory metrics and spatially explicit structural complexity indices. Overall, structural complexity within even-aged stands was strongly related to, and best predicted by, metrics including the distribution of basal area among canopy layers, while complexity in the uneven-aged stands was most strongly related to, and best predicted by, metrics including measures of abundance. Although predictive models could be developed for canopy position mixture, diameter differentiation, and small-scale structural complexity (but not spatial aggregation) using only stand inventory metrics, the prediction success after only a single management intervention was lower than expected. These results indicate that research to explore small-scale structural complexity requires detailed spatially explicit inventory data and that management to enhance structural complexity may require the manipulation of different attributes in stands of even-aged (diameter distribution) and uneven-aged (total abundance) structure types.

A Comparison of Analytical Approaches for Detecting Diameter Growth Trends: Case Studies from Switzerland

Growth patterns in forests can be monitored using three approaches: assessments on permanent growth and yield plots, tree ring and stem analyses and forest inventories. Each of the three approaches has distinct advantages and disadvantages. To evaluate the effects of the three approaches on the detection and description of growth trends, they are applied to three identical areas: Switzerland, the Toppwald region in the Canton of Berne and the selection forests in the Toppwald region. The results of the case studies are discussed and the specific contribution of each approach for monitoring forest growth is highlighted. The data presented show a clear increase in growth rates in the last decades. However, these growth rates cannot be related to site productivity alone; confounding factors are very likely.

Der Binding Waldpreis – Auslöser für waldbaulich-ertragskundliche Forschung | The Binding Forest Award initiates silvicultural and yield research

Between 1995 and 2008 the granting of the Binding Forest Award led to fresh cooperation between forest owners and research on silviculture, growth and yield at the Swiss Federal Institute for Forest, Snow and Landscape Research. Various topics were treated: a study of the beech coppices in Rothenfluh rapidly made it clear that very little was known about this formerly widespread type of forest management and its consequences. The same was true to a lesser extent for the conversion of rather uniform high forest into selection forest (in Plasselb), and for the selective management of light demanding tree species, such as the oak, in Rheinau. In Boudry, cooperation between practice and research already existed: the prize award here led to new approaches in the production of high quality oak, whilst taking ecological values into account. All these new projects are still in their earliest stages and will call for a great deal of “sustainability”, in both senses of the word, from all those involved. Considering...