Abandoned Cropland Research Articles

Abandoned cropland mapping and its influencing factors analysis: A case study in the Beijing-Tianjin-Hebei region

Abandoned cropland (AC) is one of the important types of land cover and land use change that poses a threat to food security, nature conservation, and ecosystem protection. Despite its significance, detailed spatial distribution patterns of AC across expansive geographic regions remain under-explored. Therefore, this study 1) proposes a novel framework designed to precisely determine the timing and extent of AC, and evaluates its effectiveness in the Beijing-Tianjin-Hebei region from 2000 to 2020; 2) analyses the spatial and temporal evolution of AC; 3) investigates the relationship between AC and both physical geographic and socio-economic factors. The proposed AC recognition framework integrates the method of change detection. Initially, regions changing are pinpointed, followed by categorizing pre- and post-change images to ascertain the magnitude and timing of these shifts, enabling the pinpointing of AC locations and their temporal onset. The results showed that the accuracy of land cover classification mapping ranged from 80.83% to 99.08%. Specifically, the user's accuracy of the proposed method varied between 79.29% and 89.38%. We discerned that AC was mainly distributed in the northwest water conservation belt, adopting an inverted “L” pattern. Additionally, physical geographic factors predominantly influenced AC. The use of remote sensing plays a crucial role in assessing AC, which is of great significance for understanding the evolution of abandoned landscapes and analyzing the relationship between abandonment and geology, environment, and socio-economy.

Grain-for-green accelerates functional restoration of rodent-mediated seed dispersal

The Grain-for-Green Program in China is one of the largest payments for ecosystem services programs, and it is regarded as effective for protecting the ecological environment and mitigating disasters. However, research into the effects of revegetation on seed dispersal as an ecosystem service remains limited. Thus, we compared the effects of different types of vegetation restoration (i.e., natural forest (NF), Grain-for-Green forest (GG), and abandoned cropland (AC)) in the Taihang Mountains on the rodent abundance, seed dispersal, and seedling recruitment in Quercus variabilis forest and the pathways involved. The results showed that NF and GG clearly had similar effects on the rodent composition and abundance, but the seed removal rate, seed dispersal distance, and scatter-hoarded proportion were higher under GG than AC, thereby indicating that GG may provide a similar seed dispersal service compared to NF. By contrast, the scatter-hoarding acorn proportions and dispersal distance were significantly lower under AC than NF. Therefore, GG stands could supply an equivalent seed dispersal service to NF, as well as increasing the rodent composition and abundance, and improving the seed dispersal services and capacity for plant movement, thereby contributing to accelerated vegetation restoration at the landscape scale, with significant implications for conserving biodiversity.

Vegetation restoration of abandoned cropland improves soil ecosystem multifunctionality through alleviating nitrogen-limitation in the China Danxia.

The microbial requirement for nutrient resources can be estimated by soil extracellular enzyme stoichiometry (EES) and their stoichiometries. Implementing the Grain for Green Program has significantly impacted land use and soil nutrient management in the China Danxia. However, drivers of soil microbial nutrient limitation changes in abandoned cropland (AC) remained unclear after vegetation restoration. Here, according to vector analysis, we evaluated microbial nutrient limitation by studying soil EES across vegetation restoration types (naturally restored secondary forests (NF) and artificially planted forests (AF)) with AC as a control. Results showed both NF and AF soils averaged higher C- and P- acquiring enzyme, indicating rapid C and P turnover rates after vegetation restoration. However, vegetation restoration resulted in higher C requirement for microorganisms with higher enzyme C:N and vector length. In addition, microorganisms shifted from N- (< 45°) to P-limited (> 45°) conditions with enzyme N:P less than 1 after vegetation restoration, and NF exacerbated microbial P limitation compared to AF. Decreased N limitation following vegetation restoration could be contributed to improving soil ecosystem multifunctionality. The greater variation of EES was explained by the interaction of pH, soil nutrient, and microbial biomass than by any one of these factors alone, suggesting that both abiotic and biotic factors regulate microbial nutrient limitation and microbial process. Overall, our results revealed vegetation restoration could alleviate N limitation in the China Danxia, and thus enhance soil ecosystem by regulating lower microbial N limitation, which provide insight into nutrient management strategies under ecological restoration of degraded areas.

Soil nitrogen transformation in different land use and implications for karst soil nitrogen loss controlling

A large amount of cropland in the Southwestern (SW) China karst area has been abandoned since the implementation of the Grain for Green project at the end of the last century, which significantly impacted the biogeochemistry cycle in soil. However, the effect of cropland abandonment on the soil nitrogen (N) cycle and the N loss process is still little understood. N content and isotope analysis were used to assess karst soil’s N fate and explore the N loss process in SW China. Soil samples were collected from four land uses, cropland (CR), abandoned CR (AC), shrubland and grassland (SG), and secondary forest (SF), by seasonal in a typically mixed land-use karst catchment at six soil depths. The results showed that the average soil particulate organic N (PON) content increased from 1.58 ± 0.49 g kg−1 to 2.70 ± 1.82 g kg−1, whereas average dissolved nitrate (NO3–-N) content decreased from 10.77 ± 8.87 mg kg−1 to 1.72 ± 1.84 mg kg−1 during revegetation. There was a decreasing amount of PON and dissolved N (NH4+-N、NO3–-N、TDN) content from surface to the bottom of the soil profile and large variation mainly occurred in 0 – 30 cm in the soil profiles of four different land uses, which suggests N transformation mainly occurred in topsoil (<30 cm). Mineralization was the major nitrogen transformation process that affected PON content and δ15N-PON values. The highest δ15N-PON fractionation (-5.0‰) in the soil profiles of the four types of land use caused by mineralization was detected in SF. Variation of N content and isotope values in soil profiles after cropland abandonment suggested that the loss of NO3–-N in karst catchment mainly came from the topsoil of cropland. Overall, N loss from the topsoil of cropland should pay more attention, while cropland abandonment can effectively reduce the loss of dissolved N from the thin karst soil layer.

Rapid improvement in soil health following the conversion of abandoned farm fields to annual or perennial agroecosystems

Incorporating perennial crops into agroecosystems has been shown to mitigate soil degradation and improve soil health by enhancing soil aggregation and soil organic carbon (SOC) accrual. However, our understanding of the ability and timeframe for perennial crop systems to build soil health within the context of conversion from abandoned crop land remains limited. Here, we examined changes in soil health in the first year following the conversion of an abandoned crop field into an agroecosystem planted with various treatments, including: novel perennial grain (intermediate wheatgrass, IWG; Thinopyrum intermedium), IWG/ alfalfa biculture, forage grass, tallgrass prairie, or annual wheat. We analyzed factors considered central to the concept of mitigating soil degradation to improve soil health (soil aggregation, aggregate organic carbon (OC), bulk SOC) and their soil biological and physicochemical correlates throughout the first growing season. Comparisons between treatments showed that both annual and perennial treatments rapidly and significantly improved soil health metrics including aggregation, aggregate stability, and OC levels compared to pre-conversion conditions. Such increases were positively correlated with the abundance of arbuscular mycorrhizal fungi (AMF hyphae, root colonization), labile SOC and microbial activity. Notably, IWG/ alfalfa biculture resulted in significantly higher levels of macroaggregate OC in comparison to other treatments, including tallgrass prairie, supporting the potential of perennial grasses to contribute to soil carbon gains. Overall, the conversion of this abandoned land to an agroecosystem produced rapid and substantial increases in soil health in the first year after planting.

How land-use change affects soil respiration in an alpine agro-pastoral ecotone

Land-use change alters soil carbon (C) storage in terrestrial ecosystem through affecting soil respirations (Rs). However, the long-term effects of land-use change on Rs are poorly understood. We undertook a field experiment to examine the effects of long-term land-use change on Rs. The land-use types included grazed grassland (GGL), enclosed grassland (EGL), continuous cropland (CCL), rotation cropland (RCL) and abandoned cropland (ACL) in an alpine agro-pastoral ecotone in Qinghai-Tibetan Plateau in China. Our results showed that the accumulative Rs was shown a decreasing order of EGL > CCL > RCL > GGL > ACL, with the highest value of 12.2 t CO2 ha−1 and the lowest value of 5.3 t CO2 ha−1. Soil bulk density, moisture, pH and C/N ratio were the key factors regulating Rs with land-use change in Tianzhu alpine agro-pastoral ecotone. Soil pH and C/N ratio regulated Rs indirectly by affecting bacterial diversity, while soil moisture had indirect impacts on Rs mainly by regulating microbial biomass. The net effects of soil bulk density on Rs was mainly through the direct pathway. Considering the soil C stocks showed an increasing order of ACL < RCL < CCL < GGL < EGL, even though ACL had the lowest Rs, grasslands probably the favorable land-use type in alpine agro-pastoral ecotone. Our findings highlight the importance of the land-use change on Rs, which may need to be incorporated into regional and global models for better predicting C-climate feedbacks.

Effect of Different Grain for Green Approaches on Soil Bacterial Community in a Karst Region.

Soil bacteria participate in nutrient cycling above and below ground to promote ecosystem stability and health. However, the relationship of soil bacteria and environmental factors following the Grain for Green (GfG) program remains poorly understood in southwest China. Soil samples were collected from seven Grain for Green sites that had been revegetated for 15 years. Four of these sites were afforested with a different tree species: Zenia insignis (ZI), Toona sinensis (TS), Castanea mollissima (CM), and Citrus reticulate (CR). One site was revegetated with Zenia insignis and Guimu-1 elephant grass (ZG), and one with only Guimu-1 elephant grass (GM). The remaining site, abandoned cropland (AC), was left to regenerate naturally. Here, we used Illumina sequencing of 16S rRNA genes to explore how the Grain for Green project affected soil bacterial community. We found that Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were the dominant phyla in these soils. The dominant genera at each revegetation site were also different. The CM, ZI, TS, and AC sites were dominated by Micromonospora, ZG was dominated by Streptomyces, and CR and GM were dominated by Subgroup 6. The bacterial structure was most similar in AC and TS. Correlation analysis showed that the ratio of C:P had positive effects on KD4-96, Intrasporangiaceae, and Gaiella. The ratio of soil N:P was significantly positively correlated with Cupriavidus and Kribbella. The combination of planting Zenia insignis and Guimu-1 elephant grass had the best edaphic benefits, and the approach of planting Citrus reticulate and Toona sinensis needs to be improved. Redundancy analysis (RDA) revealed that plant Simpson index, and soil N:P contributed to 16 and 15.7% of the total variations in the soil bacterial community composition, respectively. Our results suggested that plant diversity (Simpson index) and soil stoichiometric ratio (N:P) were the important factors affecting the bacterial community, and phosphorus was the limiting factor of the bacterial community in the Grain for Green karst region. In the future, revegetation should be accompanied with phosphorus fertilizer and polycultures should be considered.

Spatiotemporal variations in cropland abandonment in the Guizhou–Guangxi karst mountain area, China

Abstract Since 2000, vast areas of cropland in the rural mountain areas of China have been abandoned for reasons including labor loss and rapid urbanization, although the spatiotemporal patterns and causes of abandoned cropland (ACL) are not fully understood. We investigated changes in cropland abandonment in the Guizhou–Guangxi karst mountain area (GGKMA). We used the Moderate Resolution Imaging Spectroradiometer normalized difference vegetation index in conjunction with phenology metrics to obtain the land-use trajectory from 2001 to 2015, and then mapped the extent of cropland abandonment based on this land-use trajectory and local crop rotation cycle. We found that 10.45% (2.24 × 104 km2) of cropland in the GGKMA has been abandoned since 2001. In three sub-periods (2001–2005, 2005–2010, and 2011–2015), the overall trend showed an initial increase and then a slight decrease in the cropland abandonment rate (CAR) of 11.55%, 19.29%, and 17.17%, respectively. We explored the effects of environmental and socioeconomic factors on differences in the CAR by applying a multi-level model approach. About 26% and 16% of the variances in CAR were explained at the county and small watershed levels. At the small watershed level, spatiotemporal changes in CAR were primarily influenced by farming and soil conditions, while the severity of soil hydraulic erosion was a key factor in determining the distribution of CAR. Rural depopulation, the decline of agricultural activity, and low levels of education had significant positive effects on the increasing CAR, while the “feminization” of agriculture had the opposite effect on CAR at the county level. The results of this study implied that the spatial variation of abandonment may be influenced by environmental constraints, while socio-economic changes were the direct cause of the temporal trend of abandonment. Government should encourage farmers to increase the vegetation cover rather than continually undertake unsustainable agricultural activities in the areas with steep slopes and eroded soil, as well as strive to reduce the production costs associated with scattered plots, poor agricultural infrastructure, and the rising opportunity cost of labor. This could include conducting land consolidation and transfer, and providing agricultural subsidies.

A new exploration for accurately quantifying the effect of afforestation on soil moisture: A case study of artificial Robinia pseudoacacia in the Loess Plateau (China)

Soil moisture is crucial for the sustainable development of artificial forests in arid and semi-arid regions, and an accurate quantification of the influence of artificial vegetation on soil moisture has profound implications in the assessment of the ecological effects of artificial vegetation in arid and semi-arid regions. This study analyzed the variations in the soil moisture content (SMC) following the conversion of croplands into forests with Robinia pseudoacacia (RP) at different vegetation ages (5, 20, and 40 years) in the Loess Plateau and attempted to regard abandoned cropland (AL) with different restoration years (5, 20, and 40 years) as control samples to accurately quantify soil moisture depletion in the absence of RP at different ages. The results showed that the SMC of the 0–500-cm soil profile, which the zone that supports the whole growth processes for RP in the study area, was in a state of depletion, with an average water depletion of 40.75% and a maximum water depletion of 68.39%. RP mainly consumes shallow soil moisture (0–100 cm) during the early stage of afforestation, and with increases in forest age, RP mainly consumes soil moisture at increasingly deeper layers (100–500 cm). The largest soil water consumption in the presence of RP was observed at 150–180 cm. As RP forests grow, the water demand increases and shifts from the upper to deeper soil layers, and when the deeper soil water consumption reaches a certain level, the water consumption shifts upward. This phenomenon results in different degrees of drying between surface and deep soil layers over time. Abandoned cropland has a decreased influence on the SMC of the whole profile and appears to benefit water conservation at deeper soil layers in the mid-recovery period. Therefore, the vegetation succession in control plots should be considered to enhance the accuracy of the findings in future soil moisture research and afforestation practice. To maintain the sustainability of afforestation, succession should progress from less to more advanced plants (grasses-shrubs-forests), and the cultivation of shallow-rooted herbaceous plants (the main herb species in abandoned croplands) and natural restoration should be prioritized. Moreover, the ecological importance of natural restoration should be considered, the degree of blind artificial transformation should be reduced, and the strong adaptability and evolutionary ability of tree species to survive should receive proper attention.

Soil organic carbon variation in relation to land use changes: the case of Birr watershed, upper Blue Nile River Basin, Ethiopia

BackgroundThis study investigated the variation of soil organic carbon in four land cover types: natural and mixed forest, cultivated land, Eucalyptus plantation and open bush land. The study was conducted in the Birr watershed of the upper Blue Nile (‘Abbay’) river basin.MethodsThe data was subjected to a two-way of ANOVA analysis using the general linear model (GLM) procedures of SAS. Pairwise comparison method was also used to assess the mean difference of the land uses and depth levels depending on soil properties. Total of 148 soil samples were collected from two depth layers: 0–10 and 10–20 cm.ResultsThe results showed that overall mean soil organic carbon stock was higher under natural and mixed forest land use compared with other land use types and at all depths (29.62 ± 1.95 Mg C ha− 1), which was 36.14, 28.36, and 27.63% more than in cultivated land, open bush land, and Eucalyptus plantation, respectively. This could be due to greater inputs of vegetation and reduced decomposition of organic matter. On the other hand, the lowest soil organic carbon stock under cultivated land could be due to reduced inputs of organic matter and frequent tillage which encouraged oxidation of organic matter. ConclusionsHence, carbon concentrations and stocks under natural and mixed forest and Eucalyptus plantation were higher than other land use types suggesting that two management strategies for improving soil conditions in the watershed: to maintain and preserve the forest in order to maintain carbon storage in the future and to recover abandoned crop land and degraded lands by establishing tree plantations to avoid overharvesting in natural forests.

Can seed production and restricted dispersal limit recruitment in Pinus pinaster Aiton from the Spanish Northern Plateau?

Natural regeneration faces increasing difficulties in dry forests from the Mediterranean basin, including for normally well-regenerating species such as maritime pine (Pinus pinaster Aiton). In this paper, we studied female fertility, seed dispersal and spread rates in P. pinaster from the Spanish Northern Plateau, where natural regeneration failure is a main concern for forest managers. For this purpose we periodically collected data from seed traps and trees located at two core locations across several years. We found significant variation in interannual cone production, with the best seed trees being the same across years. In addition, we found highly skewed distributions of female reproductive effort and large fertility differences across stands located few kilometres away. Annual seed dispersal kernels fitted lognormal or 2Dt models depending on the stand analysed, with median dispersal distances between 14 and 25m. Kernels fitted for maximum dispersal periods showed an outstanding intraseasonal variation of median dispersal distances, from 10 to 54m, in association to variable patterns of rainfall and maximum wind speed. The amount of seed produced appeared to be enough to guarantee the natural regeneration of the stands during the typical 20-year regeneration period. Colonisation simulations concluded that Mediterranean maritime pine has a notable dispersion capacity, which is strongly influenced by levels of fecundity and, especially, by the number and frequency of long-distance dispersal events. The latter play a key role in tree dispersion processes through enlarging the occupied area and fostering the invasion of abandoned crop land.

Establishment of Native Grasses with Biosolids on Abandoned Croplands in Chihuahua, Mexico

The objective of the work was to evaluate establishment and forage production of native grasses with application of biosolids, a byproduct of waste-water treatment, at an abandoned field, in Ejido Nuevo Delicias, Chihuahua, Mexico. Four biosolids rates from 0 (control) to 30 dry Mg ha−1and two methods of application, surface applied (BioSur) and soil incorporated (BioInc), were evaluated. Seedbed preparation included plowing and harrowing before rainfall. Field plots of 5 × 5 m were manually sown with a mix of blue grama (Bouteloua gracilis) (50%) and green sprangletop (Leptochloa dubia) (50%) in early August 2005. Experimental design was a randomized block with a split plot arrangement. Grass density, height, and forage production were estimated for three years. Data were analyzed with mixed linear models and repeated measures. Green sprangletop density increased under all biosolids rates regardless of method of application, while blue grama density slightly decreased. Biosolids were more beneficial for green sprangletop height than for blue grama height. Blue grama forage production slightly increased, while green sprangletop forage production increased the most at 10 Mg ha−1biosolids rate under BioSur method. It was concluded that BioSur application at 10 and 20 Mg ha−1rates had positive effects on the establishment and forage production of native grasses, especially green sprangletop.

Datos corológicos y morfológicos de las especies del género "Ambrosia" L. ("Compositae") presentes en la Península Ibérica

A chorological study of the species of the genus Ambrosia L. (Compositae) present on the Iberian Peninsula has been performed. The species were Ambrosia maritima L., A. tomentosa Nutt., A. trifida L., A. artemisiifolia L., A. psilostachya DC. and A. tenuifolia Spreng. Additionally, using material from the herbarium and samples collected by the authors, we carried out a morphological and micromorphological study of the leaves and fruits of the species examined, in the latter case using a scanning electron microscope. The data obtained allowed the elaboration of two keys for the determination of these species; one based on leaf characteristics and the other on floral and carpological aspects. The corological study revealed that the penetration of the neophyte plants occurs through the Mediterranean and Atlantic littoral areas, first colonizing habitats altered by human activity, such as roadsides, railway lines, maritime dunes, abandoned crop lands and the banks of rivers and streams.

Effect of human disturbance on the structure and regeneration of forests in the Nevado de Toluca National Park, Mexico

Sample plots were established in the principal forest types in the the Nevado de Toluca National Park, Mexico including those dominated by Pinus hartwegii, Abies religiosa, Quercus laurina and Alnus jorullensis. The vertical structure was defined by three strata in the coniferous forests and two strata in the broadleaved forests. Timber harvesting in Abies religiosa and Quercus laurina forests and fires generated by humans in Pinus hartwegii forests impeded the recruitment of saplings. Mature trees were also heavily impacted by logging in Pinus hartwegii forests. On the contrary, Alnus jorullensis forests were increasing due to the disturbance of Pinus and Quercus forests, as well abandoned crop lands within the park. A combination of logging, uncontrolled fire, and grazing appears to be compromising the recruitment of important tree species in this national park. These factors, together with human settlements, have also increased the proportion of early successional species. Changes in forest structure from human disturbance indicate a need to control these activities if conservation goals are not to be compromised.

Naturally regenerated English oak (Quercus robur L.) stands on abandoned agricultural lands in Rilate valley (Piedmont Region, NW Italy)

The present study was carried out in 14 sites located in Rilate valley, a hilly area in the south-east Piedmont (NW Italy) within the Monferrato district. Sites were selected where naturally regenerated forest communities are developing on abandoned crop lands. Altitude ranges from 190 to 240 m a.s.l., while the abandonment period varied from 1 to 50 years at the time of the surveys (year 2007). The presence of younger stands (i.e., stands with age < 12 yrs) demonstrates a rapid invasion of abandoned farmlands by forest communities dominated by English oak mixed with other hardwoods, such as wild cherry and common elm. Observations conducted in older stands (i.e., stands with age ranging between 20 and 50 yrs) confirm the ability of English oak to generate well structured woodlands in the study area. In these environmental conditions previous cropping and exposure seem to play a significant influence on stand characteristics. Other noble hardwoods, such as wild cherry and common elm, are frequently associated with the oak. These stands showed a mean annual increment varying from 4 to 6 m3 ha-1 year-1 at the age of 45-50 yrs. At the present, black locust is only sporadic in the uppermost canopy layer and generally confined in the understory. The rapid colonization by Q. robur is favoured by the presence of adult oak trees in the field edges, providing abundant acorns efficiently dispersed by small rodents and birds. Oak stands observed in this study are worthy of notice in the light of the current decline of many adult oak communities in northern Italy, as well as for their potential to produce lumber and veneer logs. Therefore, these stands should be preserved avoiding coppicing or other irrational cuts. Further studies would be needed to analyze the contribution of soil characteristics to the colonization processes.

Soil Seed Bank and Standing Vegetation of Abandoned Croplands on Chinese Loess Plateau: Implications for Restoration

Vegetation succession depends on the availability of suitable propagules in the soils, and an understanding of soil seed banks is important for effective vegetation restoration of abandoned croplands. Aims of this study were to identify characteristics of soil seed bank, relationship with standing vegetation, and potential significance of soil seed bank for vegetation restoration in abandoned croplands on the hilly-gullied Loess Plateau. Results of field survey, germination, and correspondence analysis showed that density of soil seed bank ranged from almost 900 through almost 6470 seeds m−2 at 0–5 cm depth and almost 120 through almost 2470 seeds m−2 at 5–10 cm depth, with species richness of 7–14. Early successional species dominated soil seed bank, while later successional species occurred only at low densities. Similarity between soil seed bank and standing vegetation was low (with an average of 0.261). Most important variables contributing to the variation of the standing vegetaion included soil water, extractable P, soil seed bank density, and aspect. Soil seed bank alone explained 32% of vegetation community variation. Potential for vegetation restoration from soil seed banks is limited, and it is recommended to transplant some later successional species into abandoned croplands to accelerate succession.

Exploring the effect of changes in land use on soil quality on the eastern slope of the Cofre de Perote Volcano (Mexico)

Changes in land use on the eastern slope of the Cofre de Perote Volcano (Mexico) appear to have a negative effect on soil quality. In this study, we use a multivariate data set to research whether the change in land use has affected soil quality and to identify the indicators that best represent variability of the original data set. An elevation transect was identified as follows: upper segment (US), middle segment (MS) and lower segment (LS). The following nondisturbed areas and farm fields were sampled: US: pinus forest (PF), corn cropland (CP), and abandoned cropland (AC); MS: tropical cloud forest (TF), corn cropland (CC), and grassland (GL); LS: oak forest (OF) and sugarcane (SG). Sixteen soil chemical, physical, and biological attributes were measured on each site of interest. It was shown that the change in land use caused a reduction in organic material content, especially on MS and LS. The highest acidity was recorded in nondisturbed soils and abandoned cropland. Microbial biomass- C ( C m) and the microbial quotient ( C m/ C) were altered the most on MS and LS. C m and mineralized N (Nm) decreased from US to LS. Bulk density (BD) increased with the change in land use, especially on LS. Principal component analysis was used to analyze soil quality overall. The first principal component (PC1) explained 46% of the total variance of the data set, and seven soil attributes had significant loadings. C, N, and total porosity (TP) were negatively weighted and were contrasted with Mg, ECEC, BD, and C m/ C. The second principal component (PC2) explained 16% and had significant positive loadings on Ca, inorganic nitrogen (Ni), and C m. LS soils had the highest PC1 scores and US soils the lowest. The positively high PC1 scores recorded for LS soils revealed a greater sensitivity to changes in land use. In US, there were no significant effects on PC1 caused by land use change, while in the MS, positively high PC1 scores obtained in the CC soil were related to greater microbial activity and a decrease in C and N. In LS, SG soil had significantly higher PC1 scores than OF soil, indicating an increase in microbial activity.

Oribatid mite (Acari) community structure in steppic habitats of Burgos Province, central northern Spain

This work is a study of the communities of oribatid mites in steppic areas of Burgos Province, central northern Spain, in relation to different habitat types belonging to natural or disturbed ecosystems. The primary objective was to find the relationship between anthropogenic use of land and several diversity indices. Parameters such as abundance, species richness, real diversity (H′) and equitability (J′) of the mite communities were calculated in 20 soil plots, sampled in spring and autumn 2000, belonging to the predominant habitat types of this area: (1) cultivated lands, (2) abandoned crop lands, (3) grasslands/pastures, and (4) natural oak forests or a pine plantation. The most widespread species in the area as well as the most abundant taxa overall are documented, together with the faunistic checklist of oribatid mites identified in the study. The results show a general decline in the composition of the oribatid community, in terms of species diversity and abundance, from non‐disturbed soils to cultivated lands. The number of species (richness) was usually higher in forest soils than in disturbed ecosystems, in which the most degraded soils showed the lowest number of species. The community analysis shows the differences due to habitat type and ubiquitous bioindicator species.

Effect of Fertilization on Native Grass Pastures in Oklahoma

Attempts to improve native grass areas by fertilization have rarely been successful in Oklahoma. Studies by Elder and Murphy (1958) and Murphy (n.d.) have shown that weeds were increased in native grassland by repeated applications of fertilizer. To obtain additional data on the effect of fertilizers on native grass pastures, studies were conducted in 1957 and 1958 in the central cross-timber section of Oklahoma in an area formerly occupied by the Red Plains Conservation Experiment Station (1956). Botanical composition was determined both years on two fertilized and two unfertilized native grass pastures that had been grazed. The land on which these pastures were developed was decribed and designated by Daniel et al. (1943) as two types: 1. virgin, in the sense that it had never been plowed; it had been cleared of timber and scrub brush; 2. eroded and abandoned crop land which had been allowed to return to native grass over a period of 20 years or more. One pasture of each type was fertilized and one was left unfertilized. The unplowed and cleared area had been covered with native grasses and scrubby oaks (Quercus spp.) originally. The oaks were removed in 1935 and 1936 and in 1939 grazing was begun on both areas as a single unit. The fertilized pastures received 300 pounds of superphosphate 0-20-0 per acre in 1952 and again in 1955, and an annual application of 33 pounds of actual nitrogen from ammonium nitrate 33-0-0 per acre applied in late May of each year until the grazing study was terminated at the end of the 1956 season. The four native grass pastures investigated in this study were not grazed in 1957 and 1958. (The pastures will hereafter be referred to by fertility treatment and by land condition on which they were developed.) In August of 1957 and July, 1958, ten samples of vegetation selected at random were obtained from each pasture. The samples collected in 1957 were from plots 30 square feet in size clipped at a height of two inches above the soil surface. The same height of clip was used in 1958, but the plot size was reduced to 18 square feet. Each sample was hand separated into three categories; weeds, grasses and legumes. The composition of each pasture expressed in pounds of oven dry matter per acre is shown in Table 1. Previous treatment of these pastures and experimental grazing results as reported from the Red Plains Conservation Experiment Station (1956) from 1952 through 1956 are given in Tables 2 and 3.

Natural Revegetation of Abandoned Crop Land in the Ponderosa Pine Zone of the Pike's Peak Region in Colorado

Cultivation in the ponderosa pine zone of Colorado has, in many instances, been unprofitable because of the uncertainty of crops and eventual loss of soil fertility. Consequently, many areas have been abandoned, and natural revegetation has resulted in the presence of all stages of the secondary succession, from the initial invasion to almost complete return to the original subclimax grassland community. Some of the more recently abandoned fields have been protected from grazing, while others have been grazed at different rates and different seasons of the year. Therefore, areas representing different periods of abandonment and different types of grazing use are available in the Pike's Peak region for the reconstruction of the abandoned field sere in the ponderosa pine-Douglas fir association. Previous investigations of the rate and manner in which abandoned farm lands in the ponderosa pine zone revert to natural cover are not abundant. Hanson ('24) discussed briefly the secondary succession on abandoned fields in the ponderosa pine zone of northeastern Arizona. He described a first weed stage (Verbesina-Amaranthus associes), a second weed stage (Senecio-Eriogonum associes), a first grass stage (Bouteloua-Agropyron associes), and a subclimax grass stage (Festuca-M uhlenbergia-Blepharoneuron associes). In some instances the subclimax grass stage was omitted, and the succession passed directly from the first grass stage to the ponderosa pine climax. Shantz ('11), and Savage and Runyon ('37) discussed various aspects of the succession that occurs on abandoned farm lands in the central and southern Great Plains. Similar discussions for other areas have been presented by Booth ('41) for Kansas and Oklahoma; Whitman, Hanson, and Loder ('43) for western North Dakota, and Costello ('44) for northeastern Colorado. In general, on the areas where these investigators have worked, there are four distinct associes, beginning with an annual weed type and progressing upward through perennial forb, mixed grass and forb, and, usually, a subclimax grass type-all preceding the final or climax association. Other factors affecting the rate of revegetation of abandoned farm lands have been discussed by various workers. Runyon ('36) evaluated the distribution of the seed supply, Booth ('41) the effect of cultural methods and burning, and Weaver and Albertson ('40) the effects of drought. The present study was made to determine, insofar as possible, the rate of revegetation and the stages of secondary succession on abandoned farm lands in the vicinity of the Manitou Experimental Forest 2 near Woodland Park, Colorado. Detailed studies of ten fields in various stages of succession were initiated in 1936 and were concluded in 1944. The development of the vegetation has been traced only from the initial invasion to the subclimax grass community. It is recognized that the ponderosa pine-Douglas fir association is the potential climax of this area and that the subclimax grass community may eventually be replaced by the conifers.