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31Theory on plant succession predicts a temporal increase in the complexity of spatial 32 community structure and of competitive interactions: initially random occurrences of early 33 colonising species shift towards spatially and competitively structured plant associations in 34 late successional stages. Here we use long-term data on early plant succession in a German 35 post mining area to disentangle the importance of random colonisation, habitat filtering, and 36 competition on the temporal and spatial development of plant community structure. We used 37 species co-occurrence analysis and a recently developed method for assessing competitive 38 strength and hierarchies (transitive versus intransitive competitive orders) in multispecies 39 communities. We found that species turnover decreased through time within interaction 40 neighbourhoods, but increased through time outside interaction neighbourhoods. Successional 41 change did not lead to modular community structure. After accounting for species richness 42 effects, the strength of competitive interactions and the proportion of transitive competitive 43 hierarchies increased through time. Although effects of habitat filtering were weak, random 44 colonization and subsequent competitive interactions had strong effects on community 45 structure. Because competitive strength and transitivity were poorly correlated with soil 46 characteristics, there was little evidence for context dependent competitive strength associated 47 with intransitive competitive hierarchies. 48 49Running title: Plant community structure in early plant succession 50 51

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Ecosystems are characterized as complex systems with abiotic and biotic processes interacting between the various components that have evolved over long‐term periods. Most ecosystem studies so far have been carried out in mature systems. Only limited knowledge exists on the very initial phase of ecosystem development. Concepts on the development of ecosystems are often based on assumptions and extrapolations with respect to structure–process interactions in the initial stage. To characterize the effect of this initial phase on structure and functioning of ecosystems in later stages, it is necessary to disentangle the close interaction of spatial and temporal patterns of ecosystem structural assemblages with processes of ecosystem development. The study of initial, less complex systems could help to better identify and characterize coupled patterns and processes. This paper gives an overview of concepts for the initial development of different ecosystem compartments and identifies open questions and research gaps. The artificial catchment site “Chicken Creek” is introduced as a new research approach to investigate these patterns and processes of initial ecosystem development under defined boundary conditions. This approach allows to integrate the relevant processes with related pattern and structure development over temporal and spatial scales and to derive thresholds and stages in state and functioning of ecosystems at the catchment level.

An artificial catchment of 6 ha was established in the Lusatian lignite mining district 2 (Germany). A comprehensive monitoring program was launched immediately after the 3 construction was finished in autumn 2005. The setup of the monitoring and first results of the 4 period 2005-2008 are presented in this paper. From the monitoring measurements it is 5 obvious that the establishing ecosystem is highly dynamic. In addition, important components 6 of the artificially created system are governed by characteristic, often seasonal trends. These 7 observations make clear that the performance of the artificial catchment is generally in 8 agreement with naturally formed watersheds but the system is still in a very initial phase of 9 establishment. Especially, soil properties, hydrological behaviour and vegetation succession 10 illustrate that the development of the system started very close to "point zero". Even if the 11 construction of the site itself left different initial structures the starting conditions of the 12 catchment can be characterized in general as relatively homogenous in comparison with other 13 close to "point zero" systems. However, new structures emerging at the surface of the site but 14 also in the subsurface differentiated the system significantly soon after "point zero". 15 16 Keywords 17 artificial catchment, environmental monitoring, ecosystem development, initial ecosystem, 18 ecosystem succession 19 Cottbus (BTU), the Technische Universität München (TUM) and the Swiss Federal Institute 5 of Technology Zurich (ETH). The overall objective of this interdisciplinary project is to 6 elucidate the role of structures and processes during the initial establishment of an ecosystem. 7 The central hypothesis of the project assumes that initial patterns substantially define and 8 shape the development and later stages of an ecosystem. The central objectives of this 9 collaborative project are (1) to reveal which abiotic and biotic structures and processes control 10 the initial phase of ecosystem development; (2) to investigate the interactions existing 11 between both abiotic and biotic processes and patterns in the initial phase; (3) to characterize 12 differences between processes and patterns of initial systems compared to mature ecosystems; 13 (4) to derive and define different stages during this early ecosystem development; and (5) to 14 find indicators that allow the transfer of results to other ecosystems in an initial stage. 15 The project uses an artificially built catchment with defined initial and boundary conditions. 16 This paper describes the setup of the comprehensive ecosystem monitoring that was initiated 17 immediately after the completion of the catchment in autumn 2005 and its first results. 18 19 2. Site description 20 The artificial catchment was constructed in the Lusatian lignite district (Brandenburg, 21 Germany). A general overview of the technical construction works is given by Kendzia et al. 22 (2008). The research site is located close to the city of Cottbus (about 150 km ...

In autumn 2005 the artificial catchment Chicken Creek was completed in an open-cast lignite mine in Lusatia, Germany. The 6 ha area has been constructed as a two-layer system consisting of a clay aquiclude and a sandy aquifer at the top. After construction the site was left to an unrestricted and unmanaged succession. A comprehensive environmental monitoring program started immediately after the site was completed. Time series of essential environmental parameters were recorded with high temporal and spatial resolution. This paper presents selected time series of the past sixyear ecosystem development. Important changes registered in this period allow for the definition of distinctive phases of the still ongoing initial ecosystem evolution. A primary, short but pronounced geo-phasecharacterized by surface runoff, excessive erosion and sedimentation as well as very rapid immigration of biotawas followed by a hydrological dominated phase with processes such as groundwater recharge. At the end of the study period biotic processes became more evident. It can be concluded that the artificial catchment offers unique opportunities for Manuscript Click here to download Manuscript: Elmer_etal_EES_080213_revision.docx Click here to view linked References 2 interdisciplinary research on the establishment of an ecological system with rapidly growing complexity. The highly dynamic development of the Chicken Creek catchment provides the possibility to observe manifold changes within short time and to detect feedbacks and their modifications between different ecosystem compartments.

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