FG Bodenschutz und Rekultivierung
Ecological multifunctionality quantifies the functional performance of various important plant traits and increases with growing structural habitat heterogeneity, number of plant functional traits, and species richness. However, the successional changes in multifunctionality have not been traced so far. We use quantitative plant samples of 1 m2 plots from the first 6 years of initial vegetation dynamics in a German created catchment to infer the temporal changes in plant functional trait space and multifunctionality. Multifunctionality at the plot level was in all study years lower than expected from a random sample of the local pool of potential colonizers and was lowest at intermediate states of succession. In each year species containing a specific set of traits occurred with limited but focused functionality. The observed average low degree of multifunctionality contrasts with recent models predicting a tendency towards maximum multifunctionality during plant community development. However, variability in multifunctionality among plots increased during succession and the respective multifunctionality distribution among plots was increasingly right skewed indicating an excess of plots with relatively high multifunctionality. This relative excess of plots with high multifunctionality might act as an important trigger of community development paving the way for new species and functions to become established.
Landscapes and ecosystems are complex systems with many feedback mechanisms acting between the various abiotic and biotic components. The knowledge about these interacting processes is mainly derived from mature ecosystems. The initial development of ecosystem complexity may involve state transitions following catastrophic shifts, disturbances, or transgression of thresholds. We propose a conceptual framework of feedback processes in early states of ecosystem development affected by spatiotemporal environmental drivers. To test this concept, we used 10-year time series of hydrological, biological, geomorphological, and soil data from the constructed catchment Chicken Creek.” The 6ha site was left to unrestricted development since 2005 and was intensively monitored. The data showed a very rapid development of the site with an increasing complexity and heterogeneity. In the first years, stochastic signals like the initial substrate conditions and external drivers like extreme weather events were the most important factors resulting in abiotic/abiotic feedback mechanisms shaping the morphology of the site and creating site diversity. Initial abiotic feedback mechanisms between water and substrate were soon followed by abiotic/biotic feedbacks between biological soil crusts, invading vegetation, geomorphology, and hydrology resulting in state transitions of catchment functioning.
Theory on plant succession predicts a temporal increase in the complexity of spatial community structure and of competitive interactions: initially random occurrences of early colonising species shift towards spatially and competitively structured plant associations in later successional stages. Here we use long-term data on early plant succession in a German post mining area to disentangle the importance of random colonisation, habitat filtering, and competition on the temporal and spatial development of plant community structure. We used species co-occurrence analysis and a recently developed method for assessing competitive strength and hierarchies (transitive versus intransitive competitive orders) in multispecies communities. We found that species turnover decreased through time within interaction neighbourhoods, but increased through time outside interaction neighbourhoods. Successional change did not lead to modular community structure. After accounting for species richness effects, the strength of competitive interactions and the proportion of transitive competitive hierarchies increased through time. Although effects of habitat filtering were weak, random colonization and subsequent competitive interactions had strong effects on community structure. Because competitive strength and transitivity were poorly correlated with soil characteristics, there was little evidence for context dependent competitive strength associated with intransitive competitive hierarchies.
An interactive survey panel regarding the effects of mice (Microtus spec.) on a young ecosystem
(2015)
Conclusions
(2011)
The objective of this paper is to present observations, results from monitoring measurements, and preliminary conclusions about the development of patterns and structures during the first 5 years of development of an artificial catchment starting from point zero. We discuss the high relevance of initial system traits and external events for the system development and draw conclusions for further research. These investigations as part of a Collaborative Research Center, aim to disentangle and understand the feedback mechanisms and interrelationships of processes and their co-development with spatial and temporal structures and patterns by studying an initial, probably less complex ecosystem. Therefore, intensive measurements were carried out in the catchment with regard to the development of surface structures, hydrological patterns, vegetation dynamics, water chemistry, and element budgets. During the first 5 years, considerable changes within the catchment were observed. Both internal and external factors could be identified as driving forces for the formation of structures and patterns in the artificial catchment. Initial structures formed by the construction process and initial substrate characteristics were decisive for the distribution and flow of water. External factors like episodic events triggered erosion and dissection during this initial phase, promoted by the low vegetation cover, and the unconsolidated sandy substrate. The transformation of the initial geosystem into areas with evolving terrestrial or aquatic characteristics and from a very episodic to a more permanent stream network and discharge, together with the observed vegetation dynamics increased site diversity and heterogeneity with respect to water and nutrient availability and transformation processes compared with the more homogenous conditions at point zero. The processes and feedback mechanisms in the initial development of a new landscape may deviate in rates, intensity, and dominance from those known from mature ecosystems. It is therefore crucial to understand these early phases of ecosystem development and to disentangle the increasingly complex interactions between the evolving terrestrial and aquatic, biotic, and abiotic compartments of the system. Long-term monitoring of initial ecosystems may provide important data and parameters on processes and the crucial role of spatial and temporal structures and patterns to solve these problems. Artificially created catchments could be a suitable tool to study these initial developments at the landscape scale under known, designed, and defined boundary conditions.
The constructed catchment Chicken Creek was established in 2005 as an experimental landscape laboratory for ecosystem research. The 6 ha area with clearly defined horizontal as well as vertical boundary conditions was left for natural primary succession. All Critical Zone elements are represented at this site, which allows the study of most processes occurring at the interface of bio-, pedo-, geo- and hydrosphere. It provides outstanding opportunities for investigating interactions and feedbacks between different co-evolving compartments. The catchment has been extensively instrumented since 2005. Data are recorded with a high spatial and temporal resolution and include hydrological, geomorphological, pedological, limnological as well as biological parameters in order to detect transition states of the ecosystem. In contrast to other Critical Zone Observatories, this site offers the unique situation of an early stage ecosystem with highly dynamic properties. The first years of development were characterized by a fast formation of geomorphological structures due to massive erosion of the initially non-vegetated surface. Hydrological processes led to the establishment of a local groundwater body within 5 years. In the following years the influence of biological structures like vegetation patterns gained increasing importance. Feedbacks between developing vegetation and e.g. hydrological features became more and more apparent. As a result, different phases of ecosystem development have been distinguished.
The total space of traits covered by the members of plant communities is an important parameter of ecosystem functioning and complexity. We trace the variability of trait space during early plant succession and ask how trait space co-varies with phylogenetic community structure and soil conditions. Particularly, we are interested in the small-scale variability in trait space and the influence of biotic and abiotic filters. We use data on species richness and soil conditions from the first 7 years of initial succession of an artificial catchment in north-eastern Germany. Total functional attribute diversity serves as a proxy to total trait space.
Total trait space steadily increased during succession. We observed high small-scale variability in total trait space that was positively correlated with species richness and phylogenetic segregation and negatively correlated with total plant cover. Trait space increased with soil carbonate content, while pH and the fraction of sandy material behaved indifferently. Our results indicate that during early succession, habitat filtering processes gain importance leading to a lesser increase in trait space than expected from the increase in species richness alone.
During early plant succession, the phylogenetic structure of a community changes in response to important environmental filters and emerging species interactions. We traced the development of temperate-zone plant communities during the first 7 years of primary succession on catchment soils to explore patterns of initial species assembly. We found pronounced small-scale differences in the phylogenetic composition of neighbouring plant assemblages and a large-scale trend towards phylogenetic evenness. This small-scale variability appears to be mediated by soil properties,
particularly carbonate content. Therefore, abiotic environmental conditions might counteract or even supersede the effects of interspecific competition among closely related species, which are usually predicted to exhibit patterns of phylogenetic evenness. We conclude that theories
on phylogenetic community composition need to incorporate effects of small-scale variability of environmental factors.