Ecological Modelling 279 (2014) 100–113 Contents lists available at ScienceDirect Ecological Modelling j ourna l h omepa ge: www.elsevier.com/locate/ecolmodel ForestMAS – A single tree based secondary succession model employing Ellenberg indicator values Simon Kolmaniˇ c a,∗ , Nikola Guid a , Jurij Diaci b a University of Maribor, Faculty of Electrical Engineering and Computer Science, Smetanova 17, SI-2000 Maribor, Slovenia b University of Ljubljana, Biotechnical Faculty, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia a r t i c l e i n f o Article history: Received 23 October 2013 Received in revised form 13 February 2014 Accepted 18 February 2014 Keywords: Abandoned agricultural land Secondary succession Ellenberg indicator values Ecological neighbourhood Species composition Individual-based model a b s t r a c t Over recent decades farmland abandonment has affected large areas of the landscape. To better predict the changes associated with this process, we developed a secondary succession model based on Ellenberg indicator values describing the ecological niche of a tree along environmental gradients. These values are compared with local ecological factors dependent on terrain conditions. The terrain is represented by a Digital Terrain Model, where the local conditions are represented by a light availability model, climate data, soil properties, and a combination of a water flow model and average annual rainfall data. Each tree in our model is associated with its immediate circular ecological neighbourhood and is treated individually from the seedling stage through to its decay. Each year, tree heights, actual vigour, and neighbourhood radii were calculated. When two radii intersected, the vigour of both trees was compared. The weaker of the two became dominated, leading to stress-related mortality. When a tree reached the adult stage, it produced seeds that established new seedlings that competed for light and nutrition. To start the simulation, the initial amount of seed was planted on bare ground. It was possible to monitor the succession phases either visually or statistically. 3D tree models were used to visualize a tree at any age, generating realistic landscape images useful for demonstrating long-term changes in the cultural landscape to non-experts. The results were compared with those from previous field studies in various areas of Slovenia. Apart from predicting landscape changes after farmland abandonment, the model can be used for forecasting the regeneration process after clearcutting or natural disasters. © 2014 Elsevier B.V. All rights reserved. 1. Introduction In the late 1940s, entire villages were abandoned in Slovenia. The affected regions became economically unimportant and have remained so. In recent decades a similar process has been occur- ring in Slovenia and in the Balkans. It is occurring at a much slower rate and for different reasons, but with similar consequences. Farm- land with higher production costs is being abandoned and is slowly being colonized by forest. Since this process is gradual, people are mostly unaware of it. To prevent the stagnation of the affected regions, there is a need for appropriate tools, firstly to point out the necessity for new policies by highlighting the long-term changes in the cultural landscape, and secondly to support the decision making process. One possibility to better understand the process would be the use of forest growth simulators, gap models, or ∗ Corresponding author. Tel.: +386 2 220 7475; fax: +386 2 220 7272. E-mail addresses: simon.kolmanic@uni-mb.si, simon.kolmanic@gmail.com (S. Kolmaniˇ c). similar tools. Thorough overviews of these simulators are given in Liu and Ashton (1995), Bugmann (2001), and Pretzsch et al. (2008). Although these simulators are very impressive, they were created to support decisions aligned with forest management and are mainly focused on the annual biomass and volume increment of existing stands. Growth models are based on the long-term mea- surements of increments in tree diameters and heights taken at predefined time intervals, usually every five years. The oldest mea- surements used in the SILVA growth model (Pretzsch et al., 2002), for example, even date all the way back to 1870. Because these measurements were used to predict timber production in particu- lar stands, only economically important tree species, such as Picea abies (L.) H. Karst., Abies alba Mill., Pinus sylvestris L., Fagus syl- vatica L., and Quercus petraea (Mattuschka) Liebl., were included. Other trees of little economic value, but of high ecological impor- tance, such as Betula pendula Roth, Salix caprea L., Carpinus betulus L., and Alnus glutinosa (L.) Gaertn., were left out. From a compu- tational point of view, forest gap models such as JABOWA (Botkin et al., 1972), ForClim (Bugmann, 1996), and many others (Bugmann, 2001) are very interesting since the forest is abstracted as a http://dx.doi.org/10.1016/j.ecolmodel.2014.02.016 0304-3800/© 2014 Elsevier B.V. All rights reserved.