Rough wave-like heaped overburden promotes establishment of woody vegetation while leveling promotes grasses during unassisted post mining site development

The effects of surface heterogeneity on erosion and sedimentation and their implications for of soil properties at postmining sites

Erosion is often mentioned as a serious problem namely in vegetation free areas such as post mining soils. Much less attention has been paid to the role of erosion and deposition on habitat formation. Study describes the effect of erosion and deposition on soil chemical and physical properties in sites with various topography using an array of artificial postmining catchments located near Sokolov (Czech Republic). All the study sites are formed by the deposition of postmining overburden consisting of clays impregnated with carbonates. Falcon was established in 2019 and allows a detailed assessment of the first stages of ecosystem development. It consists of four parallel catchments (0.25 ha each); two are rehabilitated, and two are not. The reclaimed areas are leveled and planted with alders, whereas the unreclaimed sites created longitudinal terrain waves to mimic the situation after heaping. Detailed surface change studies by means of erosion pins and 3D terrain models created with the help of drones revealed that the surface elevation rises in the flat catchments and decreased in the wave-like catchments. In contrast, sediment loss through surface runoff shows no difference between the flat and wave-like areas. Considerable heterogeneity in the erosion process is observed in wave-like areas; the upper part of the terrain waves is heavily eroded, while eroded material accumulates in the depression. The depressions contain more silt and clay material and have higher water retention rates and lower infiltration rates, whereas the opposite is true for elevated wave tops. Study show that erosion and deposition play key role in microhabitat formation, which can be crucial in future ecosystem development.

Topographic heterogeneity triggers complementary cascades that enhance ecosystem multifunctionality

Topographic heterogeneity sets the stage for community assembly, but its effects on ecosystem functioning remain poorly understood. Here, we test the hypothesis that topographic heterogeneity underpins multiple cascading species interactions and functional pathways that indirectly control multifunctionality. To do so, we combined experimental manipulation of a form of topographic heterogeneity on rocky shores (holes of various sizes) with a comprehensive assessment of naturally assembled communities and multifunctionality. Structural equation modeling indicated that heterogeneity: (1) enhanced biodiversity by supporting filter feeder richness; (2) triggered a facilitation cascade via reef-forming (polychaete) and biomass-dominant (macroalga) foundation species, which in turn broadly supported functionally diverse epibiotic and understory assemblages; and (3) inhibited a key consumer (limpet). The model supported that these mechanisms exerted complementary positive effects on individual functions (e.g., water filtration, ecosystem metabolism, nutrient uptake) and, in turn, collectively enhanced multifunctionality. Topographic heterogeneity may therefore serve as a cornerstone physical attribute by initiating multiple cascades that propagate through ecological communities via foundation species, ultimately manifesting disproportionate effects on ecosystem multifunctionality.

Differences in colonization strategies of three common pioneer woody species in post mining heaps

Willow (Salix caprea), birch (Betula pendula) and aspen (Populus tremula) are common pioneer woody species, however little is known about colonization strategies in large-scale disturbances. Here we have compared the strategies of establishment of these pioneer woody species in unreclaimed sites on a large (1957 ha) spoil heap in Czechia. For all species, seedlings numbers peaked in the 17 year old (successional age - time since overburden heaping) plot, suggesting that initial soil development promotes seedling establishment while covering of the surface by litter and organic layers reduces the establishment of pioneer species. The proportion of willow decreased from the edge of the heap and analysis of the age structure suggests that willow establishment was correlated with the presence of older willows in the vicinity of willows of certain ages (13 and 23 years being particularly important). The proportion of birch increased with its distance from the heap edge, and it is correlated with suitable weather conditions in the year of establishment, mainly July rainfall. Aspen proportion does not change significantly with its distance from the heap edge and year of establishment. It correlates with the number of trees in both surrounding and climatic conditions. Detailed analysis of young trees shows that vegetative propagation by root suckers (offspring) is rare in birch. In willow they represent about half of the trees while in aspen all of the young trees were root suckers derived from older aspen trees. This indicates a different colonization strategy of individual species. Birch is capable of long-distance seed transfer, which establishes most of the population, and its establishment is highly influenced by climatic conditions. Willow spreads massively over a short distance, and its establishment is highly influenced by the presence of 21-23 year old willow individuals in the vicinity. Only few scattered trees are able to establish at longer distances, where they can later spread locally by seeds. Aspen spreads over a long distance in low numbers but when some trees are established it spreads massively locally by clones.

Reclaimed Mine Sites: Forests and Plant Diversity

The relationship between vegetation and selected soil characteristics in different monoculture forest types was investigated as part of a landscape restoration project after brown coal mining. Six forest types were selected: alder (Alnus sp.), spruce (Picea sp.), pine (Pinus sp.), larch (Larix sp.), long-term deciduous forest (Quercus robur, Tilia sp.), and forest created by spontaneous succession. These stands were classified into two age categories (younger and older). The soil attributes, C/N, TC, TN, pH, and A horizon depth were assessed. The observed species were categorized into functional groups by life history, life forms according to Raunkiær, and affinity to the forest environment. C/N ratio, humus thickness, and canopy cover were the main soil parameters affecting plant communities. The highest C/N values were recorded in Pinus and Larix stands, which were significantly different from deciduous and succession stands. The highest diversity index was noted in younger stands of Alnus and the lowest in younger stands of Picea. Intermediate values of the diversity index were achieved in successional stands at both age levels and in Larix and Alnus stands. The species belonging to a functional group was not an important factor in these habitat types. The species composition and vegetation change over time in the Alnus, long-life deciduous, and Larix stands show that these species are more suitable for forestry reclamation than spruce or pine. The study also emphasizes the great value of spontaneous succession areas as full-fledged alternatives to forestry reclamation.

How High Is the Recreation Value of Successional Forests Growing Spontaneously on Coal Mine Spoil Heaps?

Research highlights: Recreation value increases with the age of replanted as well as successional forests. Successional forests are not systematically less valuable for recreation than replanted forests. Succession may be used as a viable and low-cost reclamation practice of spoil heaps. Background and objectives: Afforestation has been a popular practice in post-mining land reclamation in the Czech Republic. To expand the current evidence on the recreation values of reclaimed forests, we conducted a valuation study for most typical reclaimed forests, as well as for successional forests spontaneously growing on surface coal mine deposit heaps. Using two distinct measurement methods, we also explore whether the estimated recreation value of forests is robust. Materials and Methods: An online survey was conducted in 2016 on a sample of residents living in the vicinity of coal mine deposit heaps, residents of the adjacent region of Karlovy Vary, and a control population from the central Bohemian region. Participants evaluated visual representations of forest stands typical for reclamation and succession, along with commercial spruce forest as a reference type. In the direct measurement, we measured the attractiveness of a respective forest for a walk using a 5-point scale. In the indirect measurement, a hypothetical choice between two forests for a walk was elicited in a discrete choice experiment. Results: Both direct and indirect measurements provide similar results. All reclaimed forests have a lower recreation value than the reference spruce forest. Successional forests are not systematically less valuable for recreation than replanted forests and the recreation value of both types increases with their age. The age, gender, and education of the participants did not affect the recreation value of a forest. Conclusions: We demonstrate that succession may be used as a viable and low-cost reclamation practice of spoil heaps emerging as a by-product of open-cast coal mining. With recreation as only one of many forest uses, our findings need to be interpreted vis-à-vis the objectives and expected results for individual sites and their habitat conditions.

The Effect of Topography on Long-Term Spontaneous Development of Soil and Woody Cover on Graded and Untreated Overburden

We studied the development of soil and soil fauna, as well as selected vegetation parameters important for litter input into soil, in two chronosequences of postmining sites after opencast lignite mining near the town of Most (Czechia). Both chronosequences did not have tree planting. On the first chronosequence, no leveling or any other measures had taken place after heaping, and the site kept the wavelike appearance created by the dumping process. The second chronosequence was formed by sites levelled by earthmoving machinery and in which shallow topsoil layers were spread. Both chronosequences were about 30 years old, and consisted of 8 and 11 sites for wavelike and levelled sites, respectively. In addition, samples were taken from a birch site outside of the heaps. Results showed differences in the development of tree and herb layers in both chronosequences. In the levelled sites, herb and tree cover increased after levelling, and woody cover developed much slower. In ungraded sites, woody cover developed faster, and the herb layer slower. Soil chemistry showed a similar pattern in both sites over time, characterized by a decrease in pH and sodium ion content. Soil macrofauna in levelled sites showed random oscillations, while it gradually increased with time in wavelike sites. The study suggested that site levelling alters long-term ecosystem development in postmining sites. Wavelike sites tend to develop towards pioneer forests, while leveled sites tend to be covered by grass and herb vegetation.

Influence of surface flattening on biodiversity of terrestrial arthropods during early stages of brown coal spoil heap restoration

Heterogeneity of environmental conditions is the crucial factor supporting biodiversity in various habitats, including post-mining sites. The effects of micro-topographic heterogeneity on biodiversity and conservation potential of arthropod communities in post-industrial habitats had not been studied before now. At one of the largest European brown coal spoil heaps, we sampled eight groups of terrestrial arthropods with different life strategies (moths, spiders, ground beetles, ants, orthopteroids, centipedes, millipedes, and woodlice), in successionally young plots (5-18 y), with a heterogeneous wavy surface after heaping, and compared the communities with plots flattened by dozing. A combination of the standardized quantitative sampling, using two different methods, and a paired design of the plot selection enabled a robust analysis. Altogether, we recorded 380 species of the focal arthropods, 15 of them nationally threatened. We revealed the importance of the micro-topographic heterogeneity for the formation of the biodiversity of arthropods in their secondary refuges. The communities with higher biodiversity and conservation value were detected in the plots with heterogeneous surfaces; exceptions were ground beetles and millipedes. The surface flattening, often the first step of technical reclamation projects, thus suppress biodiversity of most terrestrial arthropods during the restoration of post-mining sites. Since the communities of both surface types differed, the proportional presence on both surfaces could be more efficient in supporting the local biodiversity. We suggest reducing the surface dozing for the cases with other concerns only, to achieve a proportional representation of both surface types. Such a combination of different restoration approaches would, thus, efficiently support high biodiversity of groups with various needs.

Flow of CO2 from soil may not correspond with CO2 concentration in soil

The relationship between CO2 flow from soil and soil CO2 concentration was investigated at 72 permanent sampling points at two forested post-mining sites in the northwest of the Czechia. Based on the entire data set (72 points sampled monthly during the growing season), CO2 flow from the soil was positively correlated with soil CO2 concentration. CO2 concentration in deeper soil layers was positively correlated with root biomass and negatively correlated with soil microbial respiration. In individual sampling points relationship between CO2 flow and soil CO2 concentration varied from being significantly positive (30% of points) to significantly negative (7%) but mostly being non-significant (63%). The positive correlation occurred at points with high root biomass in deeper soil layers, while the negative correlation occurred at points with high soil microbial respiration per cm3 of soil. Laboratory experiments showed that the CO2 produced by microbial respiration can reduce microbial respiration but that CO2 produced by root respiration did not reduce root respiration. The results indicate that when soil ventilation is poor, microbial respiration can sufficiently increase soil CO2 concentration so as to reduce microbial respiration, which greatly increases the variability in the relationship between CO2 flow from soil and soil CO2 concentration.