Andreas Fischlin

Dynamical effects of plant quality and parasitism on population cycles of larch budmoth

Population cycles have been remarkably resistant to explanation, in part because crucial experiments are rarely possible on appropriate spatial and temporal scales. Here we show how new approaches to nonlinear time-series analysis can distinguish between competing hypotheses for population cycles of larch budmoth in the Swiss Alps: delayed effects of budmoth density on food quality, and budmoth-parasitoid interactions. We re- examined data on budmoth density, plant quality, and parasitism rates. Our results suggest that the effect of plant quality on budmoth density is weak. By contrast, a simple model of budmoth-parasitoid interaction accounts for 90% of the variance in budmoth population growth rates. Thus, contrary to previous studies, we find that parasitoid-budmoth interaction

The Larch Budmoth in the Alps

During the late 1940s, immediately after World War II, the lush green forests of the Engadine Valley, high in the Swiss Alps, turned an ugly red-brown in the midst of the tourist season. This was due to a spectacular outbreak of the larch budmoth, Zeiraphera diniana Guenee (Lepidoptera: Tortricidae). Preparing for a revival of the tourist industry, and having the new insecticide DDT at hand, it seemed only appropriate that the tourist office urge the forest service to control the pest. This was the beginning of what was to become a 34-year study of the population dynamics of the larch budmoth (Fig. 1).

Sensitivity of a forest ecosystem model to climate parametrization schemes

An analysis of the climate parametrization scheme adopted by conventional forest gap models revealed that most models assume a constant climate and are difficult to calibrate consistently. Tree growth showed unrealistically sensitive threshold effects along ecological gradients of temperature and precipitation. A new parametrization was compared with its predecessors in terms of the models capability to predict realistic steady state species compositions at three test sites in the Alps. Applying the new model variant ForClim to some climate-change scenarios suggests that forest gap models are highly sensitive to climate pametrizations, regardless of the realism with which they simulate forests for the current climate. Moreover, the precision of climate scenarios based on General Circulation Models (GCM), for example, falls short of ForClims sensitivity. Climate-dependent processes in forest gap models should be rehearsed before these models are used in impact studies of climatic change.

Assessing impacts of climatic change on forests in the Alps

This paper presents a method to project quantitatively the possible impacts of climatic change on mountain forests at high temporal (annual cycle), spatial, and qualitative resolution. It allows linkage from global scenarios simulated by climate models through local climatic scenarios to stand-specific forest models. The method was applied to four representative sites in the Alps using the CCC-GCMII climate model, a statistical procedure to downscale GCM-output to the regional scale, and the forest patch model FORCLIM. Sharply contrasting forest responses were observed within short distances under the same 2xC0, scenario of radiative forcing. While some forest simulations produced only small changes in tree species

The response of the carbon cycle in undisturbed forest ecosystems to climate change: a review of plant-soil models

We compared six plant-soil models from the literature which describe the C-dynamics in forests and include climatic forcing explicitly. Our selection included the two physiological models FOREST-BGC and TCX, the ecosystem/population model FORCLIM, two ecosystem/ tissue models, MBL-GEM and CENTURY Forest and the global model TEM. The review revealed a multitude of differences with respect to the model structure, the incorpor- ation of particular processes and the coupling with the abiotic environment. We made an assessment of what kind of questions the models can be best applied to and how well they are suited for studying the response of the C

Untangling a Holocene pollen record with forest model simulations and independent climate data.

Adaptation potential of forests to rapid climatic changes can be assessed from vegetation dynamics during past climatic changes as preserved in fossil pollen data. However, pollen data reflect the integrated effects of climate and biotic processes, such as establishment, survival, competition, and migration. To disentangle these processes, we compared an annually laminated late Wurm and Holocene pollen record from the Central Swiss Plateau with simulations of a dynamic forest patch model. All input data used in the simulations were largely independent from pollen data; i.e. the presented analysis is non-circular. Temperature and precipitation scenarios were based on reconstructions from pollen-independent sources. The earliest arrival times of the species at the study site after the last glacial were inferred from pollen maps. We ran a series of simulations under different combinations of climate and immigration scenarios. In addition, the sensitivity of the simulated presence/absence of four major species to changes in the climate scenario was examined. The pattern of the pollen record could partly be explained by the used climate scenario, mostly by temperature. However, some features, in particular the absence of most species during the late Wurm could only be simulated if the winter temperature anomalies of the used scenario were decreased considerably. Consequently, we had to assume in the simulations, that most species immigrated during or after the Younger Dryas (12 000 years BP), Abies and Fagus even later. Given the timing of tree species immigration, the vegetation was in equilibrium with climate during long periods, but responded with lags at the time-scale of centuries to millennia caused by a secondary succession after rapid climatic changes such as at the end of Younger Dryas, or immigration of dominant taxa. Climate influenced the tree taxa both directly and indirectly by changing inter-specific competition. We concluded, that also during the present fast climatic change, species migration might be an important process, particularly if geographic barriers, such as the Alps are in the migrational path.

Simulating forest dynamics in a complex topography using gridded climatic data

The forest model ForClim was used to evaluate the applicability of gap models in complex topography when the climatic input data is provided by a global database of 0.5° resolution. The analysis was based on 12 grid cells along an altitudinal gradient in the European Alps. Forest dynamics were studied both under current climate as well as under four prescribed 2 × CO2 scenarios of climatic change obtained from General Circulation Models, which allowed to assess the sensitivity of mountainous forests to climatic change.Under current climate, ForClim produces plausible patterns of species composition in space and time, although the results for single grid cells sometimes are not representative of reality due to the limited precision of the climatic input data.Under the scenarios of climatic change, three responses of the vegetation are observed, i.e., afforestation, gradual changes of the species composition, and dieback of todays forest. In some cases widely differing species compositions are obtained depending on the climate scenario used, suggesting that mountainous forests are quite sensitive to climatic change. Some of the new forests have analogs on the modern landscape, but in other cases non-analog communities are formed, pointing at the importance of the individualistic response of species to climate.The applicability of gap models on a regular grid in a complex topography is discussed. It is concluded that for their application on a continental scale, it would be desirable to replace the species in the models by plant functional types. It is suggested that simulation studies like the present one must not be interpreted as predictions of the future fate of forests, but as means to assess their sensitivity to climatic change.

Calculating temperature dependence over long time periods: derivation of methods

Abstract Rates of ecological processes are usually influenced by temperature. For simplicity and efficiency of ecosystem models it is often necessary to summarize information about temperature dependence from short, e.g., hourly, time intervals over longer, e.g. monthly, time periods, i.e. to calculate long term expected values of dependence functions. This aim can seldom be achieved by applying the temperature function to the mean temperature, because temperature dependencies are in many cases nonlinear. Therefore, we derived seven new, general methods for a temporal aggregation of temperature dependence. The methods determine the expected value interpreting either hourly temperature, daily temperature mean, or daily temperature mean and amplitude as random variables. The dependence function is approximated by a piecewise linear function. Some methods use a triangle as approximation for the daily temperature course, some a parabola as approximation for the density function of the normal distribution. The resulting methods cover a range of temperature data resolutions: monthly mean and standard deviation of hourly temperatures; daily temperature extrema; daily temperature means; and amplitudes, or daily temperature means alone. The methods can be applied to all types of dependence functions, in particular to nonlinear ones.

Ecological Processes in Forest Gap Models — Analysis and Improvement

In the last two decades, forest succession models of the JABOWA/FORET type (“gap models”) have grown to rather complex models. This complexity makes simulation studies tedious, not the least because of the long simulation times and the inflexibility in experimenting with model modifications. As a result, only little could be learned about the relative importance of the numerous ecological processes built into the models and about their mathematical properties from a systems theoretical viewpoint.

Simulation and Computer Aided Control System Design in Engineering Education

Abstract A wide range of possibilities exists for the use of computers in the teaching of control system design and simulation. Several approaches such as the use of program packages, single purpose programs or complete environments are described in the paper. Experience gained from teaching with these methods is summarized, and recommendations for forther improvements are given.