Peter Biber

The single tree-based stand simulator SILVA: construction, application and evaluation

Abstract Single tree forest growth simulators have proven to be very flexible tools for predicting forest growth. They are commonly applied in the United States but they are rarely used in European forest management yet. One of the few exceptions is the simulator SILVA, which is presented in this paper. The underlying equations of this simulator are developed from a set of more than 155,000 tree observations, including the species Norway spruce (Picea abies (L.) Karst.), Silver fir (Abies alba Mill.), Scots pine (Pinus sylvestris L.), Common beech (Fagus sylvatica L.) and Sessile oak (Quercus petraea (Mattuschka) Liebl.). These basic model equations are presented together with respective parameter values, derived from the aforesaid data set. The benefits of SILVA for forest practice, research, and education are demonstrated with three exemplary applications. Evaluation in terms of biological plausibility, validation, and practical use of the implemented software is presented, which shows that: (1) biological principles could be represented without explicitly being implemented, and (2) the simulation results are very close to independent observations as far as the range of parameterized site conditions is not exceeded. Furthermore, possible implications of changing conditions or an application of the model across a wider geographical range are discussed with special reference to the ongoing process of parameterization.

Forest stand growth dynamics in Central Europe have accelerated since 1870

Forest ecosystems have been exposed to climate change for more than 100 years, whereas the consequences on forest growth remain elusive. Based on the oldest existing experimental forest plots in Central Europe, we show that, currently, the dominant tree species Norway spruce and European beech exhibit significantly faster tree growth (+32 to 77%), stand volume growth (+10 to 30%) and standing stock accumulation (+6 to 7%) than in 1960. Stands still follow similar general allometric rules, but proceed more rapidly through usual trajectories. As forest stands develop faster, tree numbers are currently 17–20% lower than in past same-aged stands. Self-thinning lines remain constant, while growth rates increase indicating the stock of resources have not changed, while growth velocity and turnover have altered. Statistical analyses of the experimental plots, and application of an ecophysiological model, suggest that mainly the rise in temperature and extended growing seasons contribute to increased growth acceleration, particularly on fertile sites.

Size-symmetric versus size-asymmetric competition and growth partitioning among trees in forest stands along an ecological gradient in central Europe

Current individual tree growth models rarely consider the mode of tree competition, which can be size-asymmetric when growth is limited by light or size-symmetric when belowground resources are scarce. Even with the same competition index, growth reactions may vary considerably due to a prevailing resource limitation, as the dominant trees in a stand benefit disproportionately more on light-limited sites. To scrutinize and model the relationship between mode of competition and site conditions, 34 long-term experiments with 120 plots dating back to 1871 were used. The data cover the dominating tree species in central Europe along a broad range of ecological conditions. For Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and sessile oak (Quercus petrea (Matt.) Liebl.), stronger light competition can be shown on fertile sites compared with sites with poorer conditions. Based on these findings, we constructed an enhanced version of a classic potential modifier growth model. Simulati...

Recommendations for Standardized Documentation and Further Development of Forest Growth Simulators

Summary:The present paper documents the practical applicability of growth simulators, gives an overview of current model approaches, defines standards for the description and evaluation of growth models and growth simulators and indicates research needs. The recommendations aim to give users of growth simulators confidence in the transition to modern prediction systems and to increase the level of acceptance of new information technologies. The recommendations provide developers with guidelines for model description, model evaluation and software development and thus contribute towards efficient co-operation.Zusammenfassung:Der Beitrag dokumentiert die praktische Relevanz von Wachstumssimulatoren, gibt einen Überblick über aktuelle Modellansätze, definiert Standards zur Beschreibung und Evaluierung von Wachstumsmodellen und -simulatoren und weist auf Forschungsbedarf in diesem Bereich hin. Die Empfehlungen sollen Anwendern von Wachstumsmodellen Vertrauen beim Übergang zu zeitgemäßen Prognosesystemen vermitteln und die Akzeptanz neuer Informationstechnologien erhöhen. Indem dieses Papier Modellentwicklern Leitlinien für die Modellbeschreibung, Modellevaluierung und Softwareentwicklung gibt, kann es zu einer effizienten Kooperation aller Beteiligten beitragen.

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.

Change of allometry between coarse root and shoot of Lodgepole pine (Pinus contorta DOUGL. ex. LOUD) along a stress gradient in the sub-boreal forest zone of British Columbia

Abstract This transect study in 41–178 year-old stands of Lodgepole pine (Pinus contorta DOUGL. ex. LOUD.) in the southern boreal forest of British Columbia, Canada, analyses how site conditions modify the coarse root–shoot dynamics of trees. The allometric relationship between diameter growth of coarse roots and trunk is scrutinised for long-term site dependence, and short-term reactions to periodic climate conditions. Along a gradient from poor to rich sites, we analysed 54 trees. The sampling scheme provided two increment cores each from the three main roots and the shoot at breast height per tree. From the year-ring series, we calculated diameter time series for each shoot and each root. With these data, we show (1) that the trees’ coarse root diameter and shoot diameter are linearly related in a double-logarithmic coordinate system, thus representing constant allometry on the long run. Statistical analysis of these long-term trajectories reveals that (2) the relative allocation to coarse roots versus shoot is much higher on poor sites compared to rich sites. A closer look at the short-term reaction to stress events in the period from 1995 to 2000, where several dry years occurred, underpins that (3) a lack of water supply triggers biomass allocation in favour of coarse roots at the expense of shoot growth most pronouncedly on poor sites. Implications of this morphological plasticity for allometric theory, method development, tree and stand dynamics and carbon storage assessment are discussed.

Neue Methoden zur Analyse und Charakterisierung von Bestandesstrukturen

ZusammenfassungSeit langem haben in forstwissenschaftliche Untersuchungen sogenannte Strukturindizes Eingang gefunden, die die räumliche Bestandesstruktur quantifizieren. Namhafte Statistiker haben seit den siebziger Jahren zunächst für außerforstliche Anwendungsgebiete Korrelationsfunktionen entwickelt, mit denen eine Analyse und Charakterisierung von Waldstrukturen möglich ist, die mehr Informationen erschließen. Anhand zweier sehr unterschiedlicher Beispielbestände werden diese beiden Konzepte zur Strukturanalyse gezeigt und gegenübergestellt. Die Ergebnisse zeigen, daß die neuen Methoden zu einem umfassenderen Verständnis von Raumbesetzungsmustern führen und den Weg zu einer genauen künstlichen Erzeugung dieser Muster am Computer ebnen.SummaryFor a considerable time now so-called structure indices which quantify spatial stand structure have been used as an integral part of forest research. In the past three decades renowned statisticians have developed correlation functions — initially for problems not related to forestry — which permit forest stand structures to be analysed and characterised thus giving access to more information. Two very different forest stands are used as examples to explain and compare the two concepts of stand structure analysis. Results demonstrate that the new methods lead to a better understanding of spatial patterns in forest stands and are paving the way towards the exact artificial generation of these structures by computer.

Climate change accelerates growth of urban trees in metropolises worldwide

Despite the importance of urban trees, their growth reaction to climate change and to the urban heat island effect has not yet been investigated with an international scope. While we are well informed about forest growth under recent conditions, it is unclear if this knowledge can be simply transferred to urban environments. Based on tree ring analyses in ten metropolises worldwide, we show that, in general, urban trees have undergone accelerated growth since the 1960s. In addition, urban trees tend to grow more quickly than their counterparts in the rural surroundings. However, our analysis shows that climate change seems to enhance the growth of rural trees more than that of urban trees. The benefits of growing in an urban environment seem to outweigh known negative effects, however, accelerated growth may also mean more rapid ageing and shortened lifetime. Thus, city planners should adapt to the changed dynamics in order to secure the ecosystem services provided by urban trees.

Effect of forest stand management on species composition, structural diversity, and productivity in the temperate zone of Europe

Forests in Central Europe have been used since centuries and were systematically changed by silvicultural practices since the late 1700s. Focusing on possible biodiversity losses, forest stand management primarily impacts on the biodiversity attributes ‘composition, structure and functioning’ that are interlinked and incorporate different organizational and spatial ecosystem levels. Forest stand management can manipulate tree species diversity, which in turn affects stand structure and finally leads to changes in forest functions and services. We used meta-analyses to review 49 papers with 197 comparisons on compositional and structural diversity between unmanaged and managed forests as well as 53 comparisons of biomass productivity between mixed and monoculture forests throughout the temperate biome of Europe. Besides management impacts, for species and structural comparisons, we took time since abandonment of forest stand management into consideration when dealing with unmanaged forests. For species richness and diversity, we could not detect significant management effects; no significant influences of time since abandonment of management could be identified either. Structural attributes partly revealed considerable responses to forest stand management. Importantly, deadwood quantity, the number of microhabitats, and tree size diversity were reduced by forest stand management, while no effect was found for stand basal area and the number of living trees. Some of these effects become more pronounced with increasing time since abandonment. Forest productivity was significantly enhanced by regular moderate thinning compared with untreated stands and by tree species mixing compared with monospecific stands. Based on these results, we discuss the role of direct and indirect silvicultural effects, interactions between biodiversity components, the problem of defining the unmanaged reference state, and perspectives for forest stand management in practice.

The Individual-Tree-Based Stand Simulator SILVA

The forest growth simulator SILVA is single-tree based, tree-position-dependent and age-independent. The model’s core algorithm evaluates the three-dimensional structure of forest stands in order to determine inter-tree competition. SILVA is parameterised with a large amount of data from long-term research plots in pure and mixed species forests, mainly from southern Germany. SILVA covers the tree species Norway spruce, Scots pine, silver fir, Douglas fir, common beech and oak. It includes a regeneration submodel and modules for conducting and visualising large regional scenario analyses based on inventory data.