Dynamics of Community Biomass and Soil Nutrients in the Process of Vegetation Succession of Abandoned Farmland in the Loess Plateau

The interaction between vegetation and soil is important for vegetation restoration and reconstruction during the succession of abandoned farmland. We chose four kinds of abandoned farmlands with the time of 1, 6, 12, and 22 years to experiment in the Loess Plateau. The community composition, community biomass, and soil nutrients of the four kinds of abandoned farmlands were studied by the method of temporal–spatial alternation, and the interaction effects among vegetation, biomass, soil nutrients, and abandonment time were analyzed. The results showed there were 33 species belonging to 13 families during the succession and 15 species of Gramineae and Compositae, accounting for 47% of the total community species. The succession trend of abandoned farmland was as follows: The vegetation was the weed community of Heteropappus altaicus + Artemisia capillaris in the beginning of the abandonment stage and became the weed community of Tragus racemosus + Enneapogon borealis after 6 years of abandonment. Then, Leymus secalinus became the dominant population in the community after 12 years of abandonment. When the succession lasted for 22 years, the vegetation became a common advantageous community of Stipa breviflora and Cleistogenes songorica. Soil moisture (SM) was positively correlated with soil nutrients and negatively correlated with abandonment time and community biomass. Soil organic matter (SOM), soil total nitrogen (STN), and alkali hydrolyzable nitrogen (AHN) were the highest in 0–10 cm soil layer, showing obvious surface accumulation. The three decreased with the soil layer, and there was a positive correlation among them. The abandonment time had a positive effect on the above-ground biomass (AGB) and below-ground biomass (BGB) and a negative effect on the SOM, STN, and AHN. The root/shoot ratio (R/S) was positively correlated with SOM and negatively correlated with abandonment time. With the progress of succession, the hierarchical differentiation of the community was gradually obvious, and the community structure begun to complicate. The community better adapted to the arid environment and toward the local top community succession.

Analysis of the Spatial and Temporal Pattern of Changes in Abandoned Farmland Based on Long Time Series of Remote Sensing Data

With the rapid increase in the costs of rural labour and the adjustment of planting structures, the phenomenon of farmland abandonment has appeared in China. It is of great significance to promptly and accurately grasp the information on dynamic temporal and spatial changes in abandoned farmland to ensure national food security and the sustainable use of cultivated land. Luquan District in Hebei, China was selected as the research area based on multispectral images from Sentinel-2A, Landsat-7, and Landsat-8 combined with methods of random forest (RF) classification and vegetation index change detection. Rules for the identification of abandoned farmland were also developed, and remote sensing monitoring of the abandonment status of the cultivated land was also carried out in the study area. We also obtained the spatial distribution of abandoned and reclaimed farmland and analysed the frequency of farmland abandonment. The results show that the overall accuracy of the land-use time-series map ranged from 90.20% to 96.92% for the study period of 2010–2020. The average rate of farmland abandonment in the study area was 10.62%, with the lowest rate (5.83%) in 2020 and the highest (14.09%) in 2012. From 2011 to 2020, the maximum farmland abandonment area was 3906.02 hm2, and the minimum area was 1618.74 hm2. The farmland abandonment area showed a trend of first increasing and then decreasing. From 2012 to 2020, the maximum area of reclaimed farmland was 291.49 hm2, and the highest rate of reclamation was 14.26%. The overall reclamation rate was low. The abandonment frequency of most of the abandoned farmland was 1–3 years, covering an area of 8193.73 hm2, which comprised 79% of the total area of abandoned farmland. The frequency of abandonment was inversely proportional to the area of abandoned farmland. Farmland abandonment mainly occurred in hilly areas. We expect that our results can provide case studies for long time series in farmland abandonment research and can provide a reference for studying the driving factors, risk assessment, and policymaking with respect to abandoned farmland.

Long-term woodland restoration on lowland farmland through passive rewilding

Natural succession of vegetation on abandoned farmland provides opportunities for passive rewilding to re-establish native woodlands, but in Western Europe the patterns and outcomes of vegetation colonisation are poorly known. We combine time series of field surveys and remote sensing (lidar and photogrammetry) to study woodland development on two farmland fields in England over 24 and 59 years respectively: the New Wilderness (2.1 ha) abandoned in 1996, and the Old Wilderness (3.9 ha) abandoned in 1961, both adjacent to ancient woodland. Woody vegetation colonisation of the New Wilderness was rapid, with 86% vegetation cover averaging 2.9 m tall after 23 years post-abandonment. The Old Wilderness had 100% woody cover averaging 13.1 m tall after 53 years, with an overstorey tree-canopy (≥ 8 m tall) covering 91%. By this stage, the structural characteristics of the Old Wilderness were approaching those of neighbouring ancient woodlands. The woody species composition of both Wildernesses differed from ancient woodland, being dominated by animal-dispersed pedunculate oak Quercus robur and berry-bearing shrubs. Tree colonisation was spatially clustered, with wind-dispersed common ash Fraxinus excelsior mostly occurring near seed sources in adjacent woodland and hedgerows, and clusters of oaks probably resulting from acorn hoarding by birds and rodents. After 24 years the density of live trees in the New Wilderness was 132/ha (57% oak), with 390/ha (52% oak) in the Old Wilderness after 59 years; deadwood accounted for 8% of tree stems in the former and 14% in the latter. Passive rewilding of these ‘Wilderness’ sites shows that closed-canopy woodland readily re-established on abandoned farmland close to existing woodland, it was resilient to the presence of herbivores and variable weather, and approached the height structure of older woods within approximately 50 years. This study provides valuable long-term reference data in temperate Europe, helping to inform predictions of the potential outcomes of widespread abandonment of agricultural land in this region.

Estimation of Determinants of Farmland Abandonment and Its Data Problems

Abandoned farmland is particularly problematic in developed countries where agriculture has a comparative disadvantage in terms of effective use of land resources invested over time. While many studies have estimated the causes of these problems, few have discussed in detail the impact of data characteristics and accuracy on the estimation results. In this study, issues related to the underlying data and the estimation of the determinants of farmland abandonment were examined. Most previous studies on farmland abandonment in Japan have used census data as the basis of their analyses. However, census data are recorded subjectively by farmers. To address this, surveys of abandoned farmland are being conducted by a third party, and the results are compiled into a geographic information system (GIS) database. Two types of datasets (subjective census data and objective GIS data) were examined for their estimation performance. Although the two sets of data are correlated, there are considerable differences between them. Subjective variables are compatible with subjective data, and objective variables are compatible with objective data (meaning that parameters are easily identified). Original data for analysis, such as policy variables, are compatible with objective data. In policy evaluation research, attention should be paid to objective data collection.

Evaluation of Soil Physicochemical Properties, Soil Seed Bank and Species Density of Five Plant Communities in Awka Anambra State

The research study investigated the physicochemical properties of the soil in five different locations around Nnamdi Azikiwe University Awka campus for their above ground and seed bank status with regards to their germination rate and species density. The study areas were located at Cattle grazed field at gariki Amansea, abandoned farmland near Chisco Transportation and Engineering workshop, frequently mowed lawn at Unizik e-library, a Savanna woodland behind the banking plaza Unizik and tropical lowland forest at Botanical garden Unizik. The seed bank investigation was conducted from September 2016 to March, 2017. Analysis of variance was used to test significant differences between seed bank densities among experimental plots at different soil horizons. The soil physiochemical parameters among the experimental plots were also analyzed by one-way analysis of variance. Significant differences were tested at P= 0.05 at 95% confidence intervals. Results revealed the highest value for above ground species was found in tropical lowland forest (53.67±6.11) while the lowest was in cattle grazed field (8.00±0.82). Meanwhile the highest value for seed bank was in the frequently mowed lawn Unizik e-library (93.00±18.00) and the lowest was in the forest (6.50±4.95). The comparison of the two groups using T-test revealed that there was a significant difference between the above ground and seed bank values of the tropical lowland forest P=0.003 and also between the above ground and seed bank values of the frequently moved lawn, Unzik e-library P=0.001. More so, the Savanna above ground values and seed bank species value were not significant at P=0.006, as well as cattle grazed field (8.00 ± 0.82) and (50.00± 19.31) at P=0.006. Also, the Savanna plot comparison of above ground (44.50±3.54) and the seed bank (14.00±5.20) revealed significant differences between the two groups at P=0.006. Electrical conductivity was highest in the cattle grazed field (40.00+1.08) and the highest pH value was found in the Unizik e-library (6.19+0.22). Sorensen’s coefficient index revealed the highest similarity between above ground and seed bank species occurred in the cattle-grazed field followed by the frequently mowed lawn Unizik e-library (0.196), then the abandoned farmland (0.074), the Savanna (0.060) and the forest (0.025) respectively. Since the similarity is measured between 0 and 1, it means therefore that there is a weak similarity (0.276) between above ground vegetation and the seed bank in the cattle grazed field while the frequently mowed lawn (0.196) above ground similarity with seed bank was very weak. There is no similarity (0.025) between the above ground vegetation and the seed bank in the tropical forest. This seed bank investigation showed that the number of plant species in the seed bank does not reflect the total number of species in the above ground and the soil properties have an impact on the species density of the areas.