The BioHolz project in a nutshell - researching biodiversity and ecosystem services of forests to support the implementation of the German National Biodiversity Strategy
Germany is a party to the United Nation’s Convention on Biological Diversity. As such, Germany has developed a National Biodiversity Strategy in order to conserve all levels of biodiversity from genes to ecosystems. Conservation also includes the sustainable use of biodiversity through adaptive management of ecosystem services.
Successful implementation of the goals laid out in the National Biodiversity Strategy requires sufficient knowledge of the various components of biodiversity. It also requires a robust understanding of how biodiversity influences the functioning of ecological systems. The biodiversity strategy thus provides a starting point for the development of applied research questions for interdisciplinary as well as transdisciplinary work.
Forests are an important component of landscapes in Germany. Climatic and soil conditions favour the development of various types of forests across all biogeographic regions in the country. Only on the highest mountains, in some coastal areas, in some types of freshwater wetlands and in a few very dry habitats trees would not dominate under natural conditions. Currently, roughly a third of the total area of Germany is covered by forests, while other areas support agriculture, human settlements and infrastructure.
The vast majority of forests in Germany are managed. Here, species composition, age of trees and stand structure are strongly influenced by the needs of market-oriented as well as subsistence forestry. Finding compromises between the extraction of forest resources such as timber and fuel wood, the needs of visitors who come to forests for recreation and the requirements of biodiversity conservation is the overarching goal of the National Biodiversity Strategy. Because of its transdisciplinary goals, research in support of the Biodiversity Strategy has to include close collaboration between practitioners and scientists as well as contributions from several disciplines including ecological, social and economic sciences.
In the BioHolz project, special attention is given to the role of dead and decaying wood which is scarce in conventionally managed forests compared to natural forests or forests that have been unmanaged for long periods of time. Active enrichment of forest stands with dead wood may be appropriate for supporting the goals of the national Biodiversity Strategy, but forest managers have to be motivated to adopt such measures. Opportunity costs of the measures must be acknowledged, and their economic feasibility needs to be ensured in those cases where the income of forest managers depends on the production of timber.
As part of the BioHolz-Project, several subprojects address different aspects of dead wood in forests. The project encompasses ecological, sociological and economic approaches to scientific analyses of biodiversity and ecosystem services. The research activities are closely linked to applied topics which are relevant for the management of forests.
Ecological dynamics of taxa that strongly depend on dead wood are studied through a series of experimental, observational and model-based studies. The experiments include
- An experiment in which the amount (in terms of volume) and the diversity (in terms of stem or branch diameter ranges and number of tree species) of dead wood vary independently to clarify the role of amount and diversity of dead wood for xylobionts. To also investigate the role of microclimatic conditions on the development of species assemblages of invertebrates and fungi, the treatments were established both in sunny, open locations and in the shade under closed canopies.
- An experiment in which vertical patterns of biodiversity associated with dead wood are investigated by setting standardized bundles of dead wood at diferent heights from ground level to the uppermost crown strata. Colonization of the wood bundles by invertebrates and fungi is measured to elucidate whether the position along the vertical gradient determines species numbers, species composition and abundance. To separate the effect of height from the effect of exposure to direct sunlight, wood bundles at ground level were placed both in open locations and in the shade the canopy.
- An experiment in which contrasting levels of timber extraction have been applied to 50 m x 50 m plots in stands of European beech to create different types of dead wood enrichment. About 20 % of the trees in each plot have been treated by either (a) removing the crown and leaving trunks standing upright, by (b) felling trees and leaving the trunks lying on the ground, by (c) having a combination of both treatments or by (d) felling and removing trunks, so that only the stumps are left. These four treatments were either applied to trees standing next to one another to create a distinct opening in the canopy or to trees distributed across the plot so that only small gaps were created. In each experimental block, a control treatment in which no trees were treated was also established.
- An experiment to test the hypothesis that crowns of harvested trees can be arranged on the ground to create different levels of resistance to movement by large herbivores, and that increasing levels of resistance can enhance natural recruitment of trees. The treatments were established using different tree species in managed forests. Both conifers and deciduous tree species were included. Control plots without added crowns and treatment levels with one crown, two crowns and four crowns were created. Because tree crowns especially of deciduous trees tend to vary stronly in size and branching patterns, the levels of resistance to movement at the levels of zero, one, two and four were established by arranging stems and branches as needed.
The ecological studies are ongoing. Some results have been published in English.
Economic optimization of measures to conserve biodiversity and to provide ecosystem services from forests is the topic of a subproject that uses data from a range of forestry businesses in combination with established models on tree growth.
‚Perception and valuation of ecosystem services derived from forests‘ is the title of a subproject in which questionnaire surveys as well as indirect methods to obtain information on preferences for certain structural characteristics of forests are investigated.
Scenario-based modelling of trends in the provision of ecosystem services is the topic of a BioHolz-subproject that integrates different data sources to evaluate the potential for ecosystem services for different scales. The modelling involves several steps:
- Taking advantage of data from the research platform Biodiversity Exploratories, ecosystem processes are linked to forest structural parameters via ‘production functions’. Those functions are then used to extrapolate ecosystem processes to plots of the German National Forest Inventory. This extrapolation provides a description of the current situation of ecosystem processes for any forested geographic area within Germany.
- Using forest characteristics which are assessed during the German National Forest Inventory, the forests in Bavaria were assigned to eight forest types based on a clustering method. The selection of characteristics used for the clustering were discussed and defined together with forestry experts and stakeholders through a Delphi-study.
- In the same Delphi-study, experts and stakeholders were asked to create scenarios of future forest use and changes in influencing factors. In a second step, the experts and stakeholders translated those scenarios into probabilities of change from one forest type to another. Those probabilities of change are translated into maps of future forest type distribution within each of the developed scenarios with the help of the InVEST Scenario Generator.
- Following the previous steps, the current level of ecosystem processes and information on the forest type is available for each National Forest Inventory point. With this link, the average and variation of ecosystem processes can be calculated for each of the eight forest types. Based on the change in forest type distribution within each of the scenarios, possible future distribution of the ecosystem processes can be modelled.
In addition to the ecosystem processes measured in the Biodiversity Exploratories, ecosystem processes related to aboveground and belowground animal activity were measured within one of the deadwood experiments (third experiment described above): seed removal, predation of caterpillars, activity of belowground micro-arthropods and litter decomposition. Those processes will be analyzed together with assessments of scenic beauty and costs of deadwood enrichment to investigate potential trade-offs between different supporting, provisioning and cultural ecosystem services.
In order to test empirically which options for action are feasible to enhance biodiversity and ecosystem services within the context of different stakeholders, measures are tested by implementation partners. Objectives for forest management may differ according to business models and world views held by stakeholders.