ILAND · A framework for individual-based forest landscape modeling under changing climate and disturbance regimes

A framework for individual-based forest landscape modeling under changing climate and disturbance regimes

Project context Disturbance regimes have been intensifying significantly in European forest ecosystems in recent decades. This trend towards more frequent and severe natural disturbances (i.e. abrupt events of premature tree mortality caused, for example, by strong wind, insect outbreaks, or wildfires) will likely continue under a changing climate in the future. Intensifying disturbance regimes and their potentially detrimental impacts on ecosystem goods and services thus pose a major challenge to the sustainable management of forest ecosystems. A prerequisite for addressing this challenge and making management more robust with regard to changing climate and disturbance regimes is a better (and more quantitative) understanding of disturbance regimes. This is complicated by at least two aspects: first, the fact that disturbance processes affect forest ecosystems across a range of spatial scales (from individual tree resistance to landscape-scale disturbance spread), and secondly, the complex nature of disturbance regimes, in which different agents (e.g. wind, bark beetles) interact in space and time. Project objectives The objectives of the project were thus to develop a process-based model that consistently scales from individual trees to forest landscapes, and integrates a variety of different disturbance agents and their interactions explicitly. In particular, the project aimed at designing and implementing a scalable, individual-based simulation platform, and evaluating this novel tool against observations from a wide range of ecosystems in both Europe and the USA. Furthermore, in order to facilitate a better understanding of disturbance dynamics as a prerequisite for advancing simulation modelling, an additional objective was to empirically explore interactions between climate, vegetation and disturbances across large scales. Project results A key result of the project was the individual-based forest landscape and disturbance model "iLand". iLand explicitly simulates the principal adaptive agents in forest ecosystems, i.e. individual trees over areas of several thousands of hectares. It is based on physiological principles and explicitly considers spatial interactions (e.g. tree competition, disturbance spread through the landscape). The model has been successfully tested against empirical data from a variety of forest ecosystems in Oregon, USA and Austria. iLand is a fully functional software suite developed in C++ (currently >25 000 lines of code), and was developed with a flexible graphical user interface to facilitate the use of the model by peers. It includes a >100 page online model documentation and is distributed under the GNU general public licence. A further key result was a major advance in understanding drivers and impacts of natural disturbances in forest ecosystems. In a continental scale analysis conducted within the project, the interacting drivers of intensifying disturbance regimes in Europe could be disentangled for the first time. This analysis showed that both climate change and changes in the forest structure and composition have contributed in the same order of magnitude to intensifying disturbance regimes. In a subsequent analysis focusing on disturbance impact, the project showed that disturbances such as wind not only affect ecosystem structure (through mortality) but also ecosystem functioning (via changing key ecosystem processes). Finding a large and persistent growth reduction after wind disturbance documented to date widely neglected impact of wind disturbance that has high relevance in the context of ecosystem services such as, for instance, forest carbon storage. These findings highlight the importance of an integrated approach to disturbance assessment and modelling, accounting for dynamic interactions between climate, vegetation and disturbance across scales. Such an approach was taken up in developing and integrating disturbances into the iLand simulation framework via a flexible modular interface for disturbance agents. Currently, iLand incorporates process-based modules for wildfire, wind and drought, which have all been evaluated against independent empirical data. Interactions between these agents (e.g. through changes in forest structure, fuel load, etc.) are dynamically simulated by the model. Project impacts iLand's novel and innovative approach to tackling the central issue of scale and scaling in ecosystem modelling, as well as its ecological generality, suggests that it will have a substantial impact on the ecosystem modelling community in the coming years. Furthermore, its open and modular architecture allows peers to adapt, use and further develop the model, suggesting considerable potential to become a major landscape simulation platform in the near future. The number of model downloads since its release in March 2012 supports this suggestion. The development of iLand also contributes substantially to the current tools available to assess the resilience of forest ecosystems to changing climate and disturbance regimes. It will thus have an impact on the community of applied researchers concerned with assessing disturbance impacts, understanding ecosystem functioning, and sustainably managing forest resources. For example, the model has already been applied in collaborative projects funded by the EC under FP7 - see http://www.fundiveurope.eu/ - and is also used to assess disturbance and climate change impacts in the context of the US Long-term Ecological Research network: see http://tinyurl.com/andrewsforest for details. As regards the wider societal impacts of the project, the recent call for "urgent action [ ] to minimise risks of damage from events such as storms, floods, fire, drought, pests and diseases in order to protect European forests and their functions", issued by the European Ministerial Conference on the Protection of Forests in Europe (Oslo Ministerial Decision 2011), highlights the importance of this issue for Europe and European forestry. The project has delivered the improved understanding required to heed this call and has contributed tools to making forest ecosystem management in Europe more resilient. Project website: http://iland.boku.ac.at

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