Ex-arable Land Research Articles

Effects of fertilizer levels and drought conditions on species assembly and biomass production in the restoration of a mesic temperate grassland on ex-arable land

The restoration of degraded arable land to species-rich and functional grasslands by sowing native species has been tested successfully, while studies on restoration considering land use interest and climate change challenges are underrepresented. In this five-year study, we focused on the process of restoring grassland biodiversity and biomass production under different fertilizer levels in the face of several years of under-averaged precipitation. In 2017, we sowed a species and forb-rich native seed mixture to establish a submontane Arrhenatherion grassland. We applied fertilizer treatments (0, 60, 120 kg N ha-1 y-1, combined with and without P and K fertilizing) in order to meet local farmers' demands on biomass for hay production with nature conservation goals that aim to promote a highly species-rich and functional grassland community. Our results show that sowing a high-diverse and forbs-rich mixture not only leads to a high species richness, but also to usable aboveground biomass production for animal feeding, even with below-average precipitation. However, the slight decline in species number and cover of sown forbs following the dry period in the first year after sowing indicates the sensitivity of less drought-resistant forbs. Due to the priority effects of sown species, no undesirable species have invaded the sward. The nitrogen treatments shifted the grass-forb ratio, with grasses dominating in the nitrogen enrichment treatments due to their increased competition ability, while forbs dominating in the non-nitrogen enrichment treatments. Biomass production was higher at the first cut than at the second, and non-nitrogen fertilized treatments had a lower biomass production compared to nitrogen fertilized treatments. Both grasses and forbs contributed to drought resilience related to biomass production, but forbs contributed relatively more in the first cut under moderate or no nitrogen fertilization and in the second cut only without nitrogen application. Biomass production was strongly determined by year, and thus precipitation. Under drought conditions, species-rich stands produced sufficient biomass even without nitrogen fertilization. In order to establish and maintain species and forb-rich grasslands on ex-arable land, nitrogen fertilization should be moderate at most. Six of the 44 sown species, namely Arrhenatherum elatius, Alopecurus pratensis, Dactylis glomerata, Poa pratensis, Centaurea jacea, and Trifolium pratense, contributed significantly to the biomass and could act as matrix species in climate-adapted high-diverse native seed mixtures for our study region.

Native Microbes Amplify Native Seedling Establishment and Diversity While Inhibiting a Non-Native Grass.

Although several studies have shown increased native plant establishment with native microbe soil amendments, few studies have investigated how microbes can alter seedling recruitment and establishment in the presence of a non-native competitor. In this study, the effect of microbial communities on seedling biomass and diversity was assessed by seeding pots with both native prairie seeds and a non-native grass that commonly invades US grassland restorations, Setaria faberi. Soil in the pots was inoculated with whole soil collections from ex-arable land, late successional arbuscular mycorrhizal (AM) fungi isolated from a nearby tallgrass prairie, with both prairie AM fungi and ex-arable whole soil, or with a sterile soil (control). We hypothesized (1) late successional plants would benefit from native AM fungi, (2) that non-native plants would outcompete native plants in ex-arable soils, and (3) early successional plants would be unresponsive to microbes. Overall, native plant abundance, late successional plant abundance, and total diversity were greatest in the native AM fungi+ ex-arable soil treatment. These increases led to decreased abundance of the non-native grass S. faberi. These results highlight the importance of late successional native microbes on native seed establishment and demonstrate that microbes can be harnessed to improve both plant community diversity and resistance to invasion during the nascent stages of restoration.

Characterization of rhizosphere bacterial microbiota under Robinia pseudoacacia plantations during long-term vegetation restoration on ex-arable land

Rhizosphere microbiota are intimately linked with plant growth and defense, but the microbial response to long-term vegetation restoration remains unclear. Here, soil samples were collected from Robinia pseudoacacia stands of different ages (7–35 years old) and a wheat field (control) for a comparative study of rhizosphere bacterial microbiota. The potential influencing factors were identified using principal coordinate analysis, partial least squares discriminant analysis, and partial least squares path modeling. Afforestation influenced soil environmental conditions and bacterial microbiome structure. Microbiota differentiation was mainly explained by niche compartments at the horizontal level. Age-related differences in the rhizosphere microbiota were not prominent, whereas soil samples of different niche compartments were clustered separately. The rhizosphere microbiota exhibited remarkable convergence with increasing stand age. The rhizosphere microbiota dynamics were inconsistent with those of the bulk soil microbiota. Soil organic carbon and available phosphorus contents were the major environmental factors influencing rhizosphere bacterial richness. Accordingly, rhizosphere niche predominantly drove microbiota differentiation along horizontal gradients depending on the soil environment. Growth of R. pseudoacacia trees played a non-significant role in the structuring of rhizosphere microbiota in the restored ecosystem. Results of this study enable a broader understanding of how rhizosphere microbiota respond to long-term afforestation, which could facilitate vegetation restoration.

Co-seeding grasses and forbs supports restoration of species-rich grasslands and improves weed control in ex-arable land.

Sowing is widely used for the restoration of species-rich grasslands but still there are knowledge gaps regarding the most suitable application of different seed mixtures. We tested the effect of seed mixtures application timing on the establishment of sown forbs and weed control. 36 experimental plots with nine sowing treatments were established in an abandoned cropland in Hungary. Grass-seeds, diverse forb seed mixture and the combination of the two were applied: diverse forb mixture was sown simultaneously or 1, 2 or 3years after grass sowing, in plots sown previously with grass or in empty plots (fallows). All sowing treatments supported the rapid establishment of the sown species in large cover and hampered weed encroachment. Forbs performed better when sown into fallows than in grass-matrix and forbs establishment was worse in older fallows than in younger ones. Grasses expressed a strong priority effect, especially when forbs were sown at least two years later than grasses. We also investigated the relation between seed germinability, weather parameters and establishment success. Germination rate in the greenhouse could not predict the establishment success of forbs in the field and showed great differences between years, hence we recommend sowing target forbs in multiple years.

Natural and Managed Grasslands Productivity during Multiyear in Ex-Arable Lands (in the Context of Climate Change)

Ex-arable land-use change is a global issue with significant implications for climate change and impact for phytocenosis productivity and soil quality. In temperate humid grassland, we examined the impact of climate variability and changes of soil properties on 23 years of grass productivity after conversion of ex-arable soil to abandoned land (AL), unfertilized, and fertilized managed grassland (MGunfert and MGfert, respectively). This study aimed to investigate the changes between phytocenosis dry matter (DM) yield and rainfall amount in May–June and changes of organic carbon (Corg) stocks in soil. It was found that from 1995 to 2019, rainfall in May–June tended to decrease. The more resistant to rainfall variation were plants recovered in AL. The average DM yield of MGfert was 3.0 times higher compared to that in the AL. The DM yields of AL and MG were also influenced by the long-term change of soil properties. Our results showed that Corg sequestration in AL was faster (0.455 Mg ha−1 year−1) than that in MGfert (0.321 Mg ha−1 year−1). These studies will be important in Arenosol for selecting the method for transforming low-productivity arable land into MG.

The legacy of initial sowing after 20years of ex-arable land colonisation.

Priority effects provide an advantage to early establishing species and are thought to significantly affect the course of succession. We conducted a 20-year long experiment sowing high- and low-diversity mixtures in an ex-arable field. We ask how long the effect of sowing persists and which sown species affect the course of succession. The experiment was established in the Czech Republic in five replicate blocks, each containing three random 10 × 10m plots with three treatments: natural colonisation, sowing low- and high-diversity seed mixtures. The species cover was annually estimated in 12 permanent 1m2 quadrates within each plot. To identify the effects of sowing, we used an innovative method analysing the data separately for each year using Redundancy analysis (RDA) with identity of sown species as explanatory variables. In the first year, the effect of sowing was small; the peak of explained variability occurred between third and fifth year. The legacy of sowing was detectable in the natural colonisers for 18years and in the sown species for the whole 20-year period. For some species, the difference between the plots where they were and were not sown remained significant for the whole 20-year period (e.g. Lathyrus pratensis) although the plots were adjacent and the area was mown with the same machine. Other ones (e.g. Trisetum flavescens) colonised all the plots evenly. The long-lasting effect of the initial sowing confirms contingency of successional pathway on the propagule pressure in the time of start of succession due to the priority effects.

Species indicators for naturally-regenerating and old calcareous grassland in southern England

Habitat restoration requires realistic goals. To naturally regenerate European lowland calcareous grassland, whose extent has severely declined, over a century may be required for vegetation to become indistinguishable from that of old calcareous grassland. Progress of natural regeneration can be characterized using member species of the reference vegetation as indicators of favourable site condition. Chronosequence studies have suggested that calcareous-grassland species differ predictably in their ability to colonize ex-arable land, with some usually colonizing early on, and others in later stages. If such patterns are affected by gradually-attenuating establishment limitation, this would have important implications for restoration practice and indication of progress. Particularly, late-colonizing species might be better indicators of favourable site conditions than early colonizers.To explore these aspects, we have reanalysed chronosequence data previously used to investigate causal mechanisms affecting calcareous-grassland restoration progress. We carried out an indicator species analysis to determine which species are indicative of particular stages of natural regeneration. Using correlation analyses, we tested whether species colonization patterns matched those found by previous chronosequence studies that were geographically more limited or relied on more informal approaches to determine species order of colonization. Correlation analyses were also used to test whether order of colonization could be explained by establishment limitation or by dispersal limitation, or by established plant strategies that underlie such limitations.We identified 30 species as indicative of particular stages of natural regeneration, including nine that specifically indicate old calcareous grassland. Correlation results confirmed high congruence with species order of colonization in previous chronosequence studies, and indicated that establishment limitation plays a role in shaping species order of colonization, potentially mediated through differential stress tolerance. We failed to demonstrate a role of dispersal limitation in shaping order of colonization. Based on our results, we derived three categories of indicator species for passively-restored calcareous grassland, mirroring the regeneration stage during which these species usually colonize. This includes a category labelled by us as ‘old-grassland indicators’ that achieve notable abundance only in old grassland. We conclude by discussing how such a categorization can benefit the measurement of restoration progress, the tentative identification of old grassland and its conservation, e.g. through linking agri-environment payments to the occurrence of old-grassland indicators, thus fostering positive change in farmer attitudes towards old grassland.

Grassland restoration on ex-arable land by transfer of brush-harvested propagules and green hay

Effective restoration of meadows requires seeds of local provenance to preserve not only the species diversity but also the genetic identity of plant communities. We compared three different methods of seed harvesting from local meadow communities and assessed their efficiency in meadow restoration on ex-arable land. These methods were: brush harvesting once only, brush harvesting three times during a season, and green hay transfer. We observed the composition of species and functional traits of seed source meadows, sampled the three harvested seed mixtures and monitored plant communities restored on ex-arable land with this seed over the five following years. Green hay transfer was the method producing the highest amount of seeds (expressed as mass) and the highest number of species per unit of source-meadow area, followed by brush harvesting three times during one season and once only, respectively. This resulted in the highest establishment rate of species on ex-arable land in the green hay transfer method, followed by brush harvesting three times during one season and once only, respectively. Across all methods, species abundant in the seed mixture, having a low specific leaf area and a low capacity for lateral clonal spread, were the most successfully harvested and established ones. In the restored communities, mainly species number and cover of legumes but also of target meadow species increased with time, while ruderal weedy species decreased. Concerning species number and composition as well as trait spectrum, green hay transfer was the most successful method of restoration, resulting in a community most similar to the seed source meadow.

Soil microbiomes with distinct assemblies through vertical soil profiles drive the cycling of multiple nutrients in reforested ecosystems

BackgroundSoil microbiomes play an important role in the services and functioning of terrestrial ecosystems. However, little is known of their vertical responses to restoration process and their contributions to soil nutrient cycling in the subsurface profiles. Here, we investigated the community assembly of soil bacteria, archaea, and fungi along vertical (i.e., soil depths of 0–300 cm) and horizontal (i.e., distance from trees of 30–90 cm) profiles in a chronosequence of reforestation sites that represent over 30 years of restoration.ResultsIn the superficial layers (0–80 cm), bacterial and fungal diversity decreased, whereas archaeal diversity increased with increasing soil depth. As reforestation proceeded over time, the vertical spatial variation in bacterial communities decreased, while that in archaeal and fungal communities increased. Vertical distributions of the soil microbiomes were more related to the variation in soil properties, while their horizontal distributions may be driven by a gradient effect of roots extending from the tree. Bacterial and archaeal beta-diversity were strongly related to multi-nutrient cycling in the soil, respectively, playing major roles in deep and superficial layers.ConclusionsTaken together, these results reveal a new perspective on the vertical and horizontal spatial variation in soil microbiomes at the fine scale of single trees. Distinct response patterns underpinned the contributions of soil bacteria, archaea, and fungi as a function of subsurface nutrient cycling during the reforestation of ex-arable land.

Soil multifunctionality and drought resistance are determined by plant structural traits in restoring grassland.

It is increasingly recognized that belowground responses to vegetation change are closely linked to plant functional traits. However, our understanding is limited concerning the relative importance of different plant traits for soil functions and of the mechanisms by which traits influence soil properties in the real world. Here we test the hypothesis that taller species, or those with complex rooting structures, are associated with high rates of nutrient and carbon (C) cycling in grassland. We further hypothesized that communities dominated by species with deeper roots may be more resilient to drought. These hypotheses were tested in a 3‐yr grassland restoration experiment on degraded ex‐arable land in southern England. We sowed three trait‐based plant functional groups, assembled using database derived values of plant traits, and their combinations into bare soil. This formed a range of plant trait syndromes onto which we superimposed a simulated drought 2 yr after initial establishment. We found strong evidence that community weighted mean (CWM) of plant height is negatively associated with soil nitrogen cycling and availability and soil multifunctionality. We propose that this was due to an exploitative resource capture strategy that was inappropriate in shallow chalk soils. Further, complexity of root architecture was positively related to soil multifunctionality throughout the season, with fine fibrous roots being associated with greater rates of nutrient cycling. Drought resistance of soil functions including ecosystem respiration, mineralization, and nitrification were positively related to functional divergence of rooting depth, indicating that, in shallow chalk soils, a range of water capture strategies is necessary to maintain functions. Finally, after 3 yr of the experiment, we did not detect any links between the plant traits and microbial communities, supporting the finding that traits based on plant structure and resource foraging capacity are the main variables driving soil function in the early years of grassland conversion. We suggest that screening recently restored grassland communities for potential soil multifunctionality and drought resilience may be possible based on rooting architecture and plant height. These results indicate that informed assembly of plant communities based on plant traits could aid in the restoration of functioning in degraded soil.

Vegetation development after a large scale restoration of species-rich grasslands in a Central European floodplain

Large scale restoration using local high-diversity seed mixture combined with turf transfer was applied on ex-arable land in the Morava River floodplain in the western Slovakia in the years 1999–2012. The post-restoration vegetation development was recorded during 12 years after the restoration using floristic records per restored polygons with cover estimation in simple 3-degree scale. Temporal changes in species composition were evaluated by gradient analysis and number of characteristic grassland and ruderal species on restored sites was analysed by general linear models. Species composition changed gradually towards the species composition typical for species-rich floodplain grasslands, but the trajectory was not straightforward and several irregularities were observed. They were probably induced by extreme weather events (drought, floods). The decrease in ruderal species and increase in the number of typical floodplain grassland species were observed, when floodplain grassland species permanently outcompeted ruderal species since 8th year after the restoration. However the development in large scale was slower, than expected from previous small-scale experiments, it is evident, that combination of local seed mixture sowing with a turf transfer is a feasible method for the restoration of species-rich floodplain grasslands from arable land.

Transformation of ex-arable land to permanent grassland promotes pore rigidity and mechanical soil resilience

The conversion of degraded arable land to permanent grassland is widely presumed to be amendatory and is therefore proposed as a climate-smart agriculture strategy, which may rapidly restore soil quality. However, the rate and extent of soil repair will largely depend, on the management practices, deployed in the permanent grassland. In this study, our objective was to assess the effects of no-till and no-renovation management, on aggregation, internal soil strength parameters and pore system dynamics of permanent grassland, established from degraded arable land. Also, we analysed the time dependence of these changes on the some functions of the soil. Undisturbed samples were collected at 3 depths: 0–10cm, 10–25cm and 25–40cm, from permanent grassland, aged 1, 8 and 19-years, and were used to determine water retention and saturated hydraulic conductivity for each sward age. Moreover, compression properties and shear stress parameters at these depths and sward-ages were determined. The results indicated remarkable improvement in pore structure in relation to the age of each sward, which resulted in improved water retention, air and water fluxes with the age of the grassland. The shear parameters and precompression stress data showed differences in the structural recovery timeline at the various depths, highlighting the difference in ecological engineering processes as a function of the time since the grassland was established and the depth considered. Our results indicate that permanent grassland management will contribute to a substantial recovery of pore functions, coinciding with enhanced pore rigidity and increased soil strength which may also influence sequestration potential in the grassland.

Soil inoculation steers restoration of terrestrial ecosystems.

Many natural ecosystems have been degraded because of human activities(1,2) and need to be restored so that biodiversity is protected. However, restoration can take decades and restoration activities are often unsuccessful(3) because of abiotic constraints (for example, eutrophication, acidification) and unfavourable biotic conditions (for example, competition or adverse soil community composition). A key question is what manageable factors prevent transition from degraded to restored ecosystems and what interventions are required for successful restoration(2,4). Experiments have shown that the soil community is an important driver of plant community development(5-8), suggesting that manipulation of the soil community is key to successful restoration of terrestrial ecosystems(3,9). Here we examine a large-scale, six-year-old field experiment on ex-arable land and show that application of soil inocula not only promotes ecosystem restoration, but that different origins of soil inocula can steer the plant community development towards different target communities, varying from grassland to heathland vegetation. The impact of soil inoculation on plant and soil community composition was most pronounced when the topsoil layer was removed, whereas effects were less strong, but still significant, when the soil inocula were introduced into intact topsoil. Therefore, soil inoculation is a powerful tool to both restore disturbed terrestrial ecosystems and steer plant community development.

A tool for easily predicting short-term phosphorus mobilization from flooded soils

The construction and restoration of riparian (temporarily flooded) wetlands as water storage and flood protection areas plays a central role in climate-adaptive water management. In general, arable and ex-arable lands are used for this type of water storage. However, inundation may lead to problems, as excess phosphorus (P) stored in these soils may be released and result in the eutrophication of the overlying surface waters. Clearly, water and nature managers need to be able to determine for which areas temporary water storage would be a feasible option without causing eutrophication problems. Here, using a controlled experimental approach, a simple predictive tool for the P mobilization rates from soils upon short-term inundation has been developed. A large suite of soil characteristics and P mobilization rates were determined during flooding for different soil types (peat and sand), at two different depths to mimic topsoil removal (topsoils and soils from −30 to −60cm below ground level), and at two temperatures to test seasonal influence (8°C and 18°C). Increasing the temperature from 8 to 18°C almost tripled P mobilization rates, but the variation could not be linked to any of the soil characteristics measured – average Q10 (temperature coefficient) values were 2.8 (2.9 for peaty soils, 2.6 for sandy soils). Although P mobilization was related to P saturation of amorphic Fe, water-extractable P was found to be by far the best predictor for short-term P mobilization rates, explaining 86.9% of the variation. The predictive tool for P mobilization after short-term rewetting is simple, low-cost and widely applicable, and can support water managers during their decision-making processes concerning the optimal location for the construction of water storage areas, the restoration of riparian wetlands, and the combinational use of different ecosystem services.

Potential of temperate agricultural soils for carbon sequestration: A meta-analysis of land-use effects

Restoring depleted soil organic carbon (SOC) stocks of arable land to remove carbon from the atmosphere and offset fossil fuel emissions is a promising strategy for the mitigation of climate change. In agroecosystems conservational tillage practices and the abandonment of formerly plowed fields (ex-arable land) are shown to have the highest potential to sequester SOC. Nevertheless reported sequestration rates vary and the effects of environmental site conditions remain poorly understood. Our results are based on a meta-analysis of 273 paired SOC estimates from 65 publications which included only mineral soils from the temperate zone. SOC stocks of ex-arable grasslands with an average of 14years since abandonment were 18% larger compared to the SOC of arable land. Likewise, SOC stocks of never-plowed grassland plots were 11% larger than the SOC stocks of abandoned fields. The average sequestration rate was 0.72t Cha−1yr−1. Semi-arid and sub-humid climate as well as low initial SOC stocks positively affected proportional SOC gains suggesting that the recovery of carbon stocks is not limited by low primary production. Therefore, the northward shift of cultivation areas in the temperate zone will lead to the abandonment of soils with high SOC recovery potential. However, if native soils are opened up elsewhere to compensate for yield losses due to abandonment the surplus of SOC in ex-arable land can easily be overcompensated by cultivation losses.

Post-Soviet recovery of grassland vegetation on abandoned fields in the forest steppe zone of Western Siberia

Following the collapse of the Soviet Union in 1991 around 45 million hectares of arable land became abandoned across Russia. Our study focused on the recovery potential and conservation value of grassland vegetation on ex-arable land in the Tyumen region of the Western Siberian grain belt. We compared ex-arable grasslands of different successional stages with ancient grasslands as reference for the final stage of succession along a climatic gradient from the pre-taiga to the forest steppe zone. Plant community composition and species richness of ex-arable land clearly developed towards reference sites over time, but even after 24 years of abandonment, the grassland vegetation had not totally recovered. The γ-diversity of vascular plants was slightly higher on ex-arable land than in ancient grasslands but the mean α-diversity was still moderately lower. A significant proportion of the vegetation of ex-arable land still consisted of ruderal and mesic grassland species and the number and cover of meadow-steppe species was significantly lower than in ancient grasslands. Grazing and time since abandonment positively affected the reestablishment of target grassland species, whereas it was negatively affected by the cover of grasses. In contrast to ex-arable land, the conservation value of arable land is only modest. Therefore, future intensification of land use is most likely less harmful if directed to existing arable land. Re-cultivation of ex-arable land and grassland improvement operations such as seeding of competitive grass species are major threats for the biodiversity of secondary grasslands on ex-arable land in the forest steppe zone of Western Siberia.

Can the Stepping Stone Enhance the Establishment, Competition and Distribution of Sown Grassland Species during Recovery on Ex-Arable Lands?

Most diversity restoration projects are not to improve diversity per se, but rather to enhance the presence and abundance of species that are characteristic of reference or target community. The use of Bromus inermis suppresses annual noxious grasses and increases the control of other-forb group these species are also noxious weeds; these may be substituted with another perennial species of the same functional group all through the whole experimental period, as it occurs with other perennial-forb Carduus tenuifolius. A field experiment was conducted on abandoned arable land with sown low and high diversity treatments and natural colonization following typical farming practice for the site. Experimental plots were installed on former agricultural land that had been cropped with (a rotation of) monocultures until the end of 1995. The experiment was organized according to a block design with five replicate blocks. An opposite trend was performed among the colonizer species, because the colonizer grasses were relegated by the high dominance of sown grasses. But at the same time, the sown grasses facilitated the dominance of other colonizer-forbs species; therefore its functional replacement in the community due to sown effect was again tested. However, in natural conditions the other-forbs group was the dominant group, without taking into account the stepping-stone treatment and there was also a functional change of dominance. Our study has demonstrated the restoration effectiveness of species richness at abandoned arable land and may be enhanced by sowing late successional species.

Performance of a new industrial chipper for rural contractors

A new chipper was designed around a versatile wheeled carrier, capable of both in-field and road traffic. This solution reduces relocation cost, and it is especially valuable when dealing with small, scattered fields. At the same time, good off-road mobility allows taking a large industrial operation directly into the field, to the benefit of improved downstream handling. The new machine is especially conceived for use by rural contractors, who must negotiate wood crops established on ex-arable land. Trials were conducted on three sites, representative of the most common conditions encountered by these contractors. Productive potential was very high, averaging 120 m3 loose chips (or 42 tonnes of green chips) per productive machine hour. Such a high productivity may strain the capacity of the chipper support fleet, especially if the latter needs to reach the chipper directly into the field. Therefore, actualizing the potential of the new system requires a good organization, possibly assisted by modern precision control technology.

Exposure to noise in wood chipping operations under the conditions of agro-forestry

An increasing number of agricultural contractors are getting into industrial wood chipping, following the rapid expansion of fiber farms on ex-arable land. Wood chippers are noisy machines and agricultural contractors tend to work long hours, which raises the question about their exposure to noise. The objective of the study was to quantify noise exposure for this occupational group. The Authors selected a representative operation and monitored noise exposure for five full working days, covering the main job types typically encountered in agro-forestry. Noise exposure was highest during chipping time, with 81.8 dB(A). The main source of noise was the powerful diesel engine, followed by the chipper drum: they generated the highest noise levels in the 100–200 Hz and the 20–50 Hz frequency ranges, respectively. Daily noise exposure did not exceed the 80 dB(A) lower action value, and it was similar to the exposure of other workers operating industrial in-wood chippers. However, future optimization measures may lead to increasing the proportion of total time when the machine is under full load, and it generates the highest noise levels. Modeling exposure as a function of efficiency showed that exposure levels may exceed the lower action values, once utilization will increase above 64%. This is a realistic target, which may be achieved in the near future. Fortunately, the problem will materialize only with some specific operation types, which represent a minor component in the wood basket of agro-forestry chipping companies.

From arable land to species-rich semi-natural grasslands: Succession in abandoned fields in a dry region of central Europe

The area of arable land has decreased considerably in Europe over the last decades. Abandoned fields are potential habitats for restoration of species-rich grasslands of high conservation value, but in specific cases it is unclear whether this can be achieved by spontaneous succession or intervention is needed. In dry areas of eastern-central Europe, spontaneous succession of species-rich steppe grasslands was observed on some abandoned fields located close to ancient grasslands. We studied spontaneous succession on ex-arable land in the warm and dry area of the SE Czech Republic using space-for-time substitution. Vegetation was sampled in 175 plots, for which the time since the abandonment (4–71 years) was determined from historical aerial photographs. All plots were close to ancient dry grasslands. Annual weeds were replaced by perennial species in less than four years after abandonment. Perennial grassland was stable over seven decades, but its species composition changed: native dry-grassland species, including Red-List species, gradually increased, and so did the total number of vascular plants, reaching on average of 30–40 species per 16m2 after 40 years. Archaeophytes, including common ruderal species, decreased, while neophytes were insignificant throughout the succession. Scattered shrubs appeared at later stages, but their spread was limited by drought and recently also by nature conservation management. This study suggests that spontaneous succession can be inexpensive yet effective means of dry grassland restoration in dry areas of eastern and central Europe if sources of target species are available in nearby remnants of ancient grasslands.