Fallow Sites Research Articles

Productivity of vegetation and carbon stock in meadow steppe on fallow areas in the Bashkir Cis‐Urals (Southern Urals region), Russia

Aim. Data collection and analysis of the composition and productivity of vegetation and assessment of carbon sequestration by vegetation and soil in meadow steppe at a fallow site in the Bashkir Cis‐Urals, Russia. Material and Methods. The work is based on a survey of vegetation and soils of meadow steppe located in fallow areas, where post‐agrogenic restoration succession has been going on for more than 20 years. Results. The plant cover of the area studied is close to natural rich‐forb meadow steppes but differs in lower indicators of species richness and saturation, as well as the presence of weedy segetal species. The total plant biomass on the plot studied was estimated at 11.35 t/ha (including live aboveground biomass 2.98 t/ha, mortmass 3.11 t/ha, root weight 5.25 t/ha). The average stock of carbon in the plant biomass is 427.6 g/m2, and the total carbon stock in plant matter within the site is 36.88 tons. The soil cover of the area studied is Chernozem Calcic. The average levels of carbon stocks in short‐thickness soil at the 0–90 cm layer is 308 t/ha, while in medium‐thick soil it is 378 t/ha. Conclusions. A feature of the communities surveyed is a poor floristic composition, low productivity and low proportion of roots (47 % of the total plant biomass), which is caused by incomplete recovering of steppe vegetation and low thickness of the humus horizon. The soils of the site are close to virgin steppe lands in terms of carbon content and reserves.

Integration of the social dimension in urban wastelands reconversion projects: Case of the Guelma railway station, Algeria

The railway station of Guelma (city located in the Northeast of Algeria) is an imposing building, built by the French colonization, which is closed now after so many years of prosperity. The development of the city and the urban sprawl have meant that after having been located for a long time on the periphery, this station now occupies a central position, where the city is now made. However, the future of this station is so far unclear since it will no longer be operational, given that the new Guelma’s railway station will be located on the outskirts of the city. What would be the fate of this architectural good left to itself? By preserving the memory of the station by offering it a new permanent use, this architectural jewel with its fallow site is a real opportunity for urban regeneration for the city. Therefore, the purpose of this paper is to try to give new life to Guelma station, through a new global approach that would channel the useful and sustainable reuse of the site from its immediate environment and the current executive context. The questionnaire was used as an investigative tool intended for residents living near the station, in total, 40 respondents have been surveyed, to find out their opinions and expectations relating to the future of this lost part of the city. The data from the study were descriptively analyzed, using percentages. Results revealed that the inhabitants are aware of the importance of the reconquest of the station, which will constitute for them a real opportunity for urban and economic development for the region. A reconquest that wants to be sustainable by adopting a socio-spatial approach, which will integrate socio-economic and environmental aspects. Keywords: industrial heritage, railway station, reconversion, sustainability, urban wasteland.

Passive regeneration of subtropical grassland vegetation in a chronosequence of ex‐cultivated fields in Australia

AbstractAimIn Australia, natural grasslands largely occur on fertile clay soils and have consequently been extensively cultivated since European settlement. Other studies have demonstrated that passive restoration of subtropical grassland is possible in environments where there is substantial native remnant vegetation in the surrounding landscape. This study examined a chronosequence of abandoned fields to investigate the recovery of fragmented grassland in a matrix of cultivated land with significant exotic species that may impede succession.LocationDarling Downs, Queensland, Australia.MethodsIn this study we surveyed a chronosequence of ex‐cultivated subtropical grasslands in Queensland's Darling Downs, where only 1% of the original grasslands remain. Floristic surveys were carried out in 80 fallow sites up to 51 years old, and data were compared with 16 previously surveyed remnant grasslands on the same land type.ResultsRichness of native species increased with time since cultivation and approached, but did not reach, that of remnant grasslands after 51 years, whereas the richness of exotics declined with time since cultivation. Rainfall and grazing positively and negatively affected exotic plant abundance respectively and these factors had no significant direct or indirect effect on the native species richness. In terms of composition, fallow grasslands supported 54% of the native plant species from remnant grasslands after 51 years. The native perennial grasses Dichanthium sericeum and Aristida leptopoda were the only dominant species in the remnants that were present in more than 60% of the fallow grasslands. Of the species from remnants that were “missing” from fallow sites, most were native perennial forbs and grasses. Compositional dissimilarity of fallow grassland to remnant grasslands remained high after 51 years (78%). Grassland species that are uncommon in nearby hill woodlands were preferentially absent in fallow grassland and this partly explains the slow compositional recovery.ConclusionIn a highly fragmented landscape, passive restoration is only partially effective. The restoration of grassland is probably enhanced by repositories of native seeds from hill woodlands that are too rocky to cultivate. However, some species may have to be actively reintroduced to achieve complete recovery. In this landscape, where grazing is a dominant land use, exotic species do not seem to impede succession.

Carbon loss from a deforested and drained tropical peatland over four years as assessed from peat stratigraphy

Deforested, drained, and converted tropical peat forest is common in Southeast Asia, and these areas have become a major source of carbon (C) emissions. In this study, measurements of peat properties, i.e., peat thickness, organic matter (OM), bulk density (BD), total organic C (TOC), and total nitrogen (TN), were taken four years apart (2012–2016) at 24 sites in a previously deforested and drained tropical peat in West Kalimantan, Indonesia. We calculated that the average peat subsides at a rate of 3.8 ± 1.2 cm yr−1. The estimated net change in C stock ranged from −8 to −41 Mg C ha−1 yr−1, with an average of −31 Mg C ha−1 yr−1. C loss varied by peat depth and land use. C loss was four times faster on shallow peat (50–100 cm) than deep (>300 cm) peat sites. Fallow sites (bush fern and secondary forest) subsided and lost C faster than oil palm plantations, likely due to land-clearing fires. Percent C and C/N ratio declined significantly in the upper 150 cm of peat, especially in the fallow sites, indicating oxidation within the peat profile. No change occurred in bulk density, showing little effect of compaction, though the density profile migrated downward with subsidence. The current peat topography, modeled from satellite LiDAR data, reflects past peat-loss patterns and confirms the coring results. C loss in this region continues at a high rate since its original deforestation in the early 1970s. This study concludes that C loss due to anthropogenic disturbances on tropical peat is larger than the 2013 Tier 1-IPCC CO2 emission factor for Acacia and oil palms on drained tropical peats, which are 20 and 11 Mg CO2-eq ha−1 yr−1, respectively.

The use of Shanon Weiners diversity index in the assessment of floral diversity and equitability of Neni–Nimo Watershed in Anaocha L.G.A. of Anambra State, Nigeria

The study on the floral diversity of Neni-Nimo watershed in Anaocha L.G.A. of Anambra State was conducted between November 2009 and July 2020. The aim of the study was to find out the species richness and the floral biodiversity of the watershed. In this study, the watershed was divided into three sites, the forested site, the fallow site and the current usage site. The experiment was laid out in a Randomized Complete Block Design. The ecological methods used in this study are the Point Centred Plotless Count sampling technique for areas dominated by trees while the Plot Count technique using quadrats were used for sampling the areas dominated by forbs, shrubs, climbers and grasses. The vegetation data collected was used to estimate the species richness of the different plant growth forms, the diversity and equitability of the various growth forms encountered were calculated using Shanon Weiners diversity index. The Shanno Weiners diversity index shows that the forested areas had the highest floral biodiversity than the fallow and current usage area. Regression analysis shows that a significant relationship exists between species abundance and floral biodiversity at a p-value of <0.05 for all plant growth forms in the watershed except for grasses and as abundance increases, diversity also increases.

Features of water regime changes of steppe chernozem in the South-East of Central Chernozem zone in modern conditions

The article presents an analysis of the elements of the water regime of the steppe chernozems of the Stone Steppe of the Central Chernozem Region in the conditions of the dry period from the end of 2019 to the autumn of 2020. The objects of the study were: the mowed fallow land plowing in 1882, the old-growth forest strip of 1903 planting and arable land adjacent to fallow plots. The soil-hydrological constants were calculated (total water capacity, lowest field capacity, permanent wilting point) both in the time interval and down the soil profile to a depth of 2 m. The reserves of productive moisture during the growing season were also studied. The maximum values of productive moisture content was reached on the mowed fallow sites by the beginning of February, the minimum in the forest belt areas, the arable land plots had an intermediate value. By the middle of the growing season (June), 2020, the moisture reserves in the soils of the forest strip, fallow and arable land were 127, 123 and 109 mm, respectively, in the meter thickness. The highest amount of productive moisture in the upper soil horizon (0-20 cm) is observed under the forest belt – 39 mm. However, moisture content under the fallow land in the upper horizon had decreased to rate of the dead moisture reserve by early August. Similar values were found in soil under the forest belt and arable land. Otherwise, moisture profile was formed in underlying carbonate horizons. The forest belt soils in insufficient atmospheric moisture conditions in 2020 were more dried out than soil of fallow and arable land. The estimation was given for nature of soil profile changes of soil moisture profile due to influence of forest belt. The data of productive moisture reserves in soil at different distances from the forest belt were presented. In the meter layer at the edge of the forest belt, moisture reserves were at the level of 94.0 mm, sharply decreasing to 60.3 mm at a distance of 25 m from the forest strip, with a gradual decrease to 34 mm at a distance of 125 m. The results of observations showed a clear downward trend of productive moisture content due to distance from the old-growth forest belt.

The role of fallowing in the restoration of woody species in the Woodlands of Northern Uganda

AbstractThe study sought to determine the extent to which fallowing can lead to recovery towards an historic woody vegetation of Sudanian woodlands in northern Uganda. Fallow sites of three distinct ages were assessed. Plots were established in crop fields that had been under cultivation for over 10 years, sites that had been under fallow for 3–6 years (young fallow) and fallow sites of at least 9 years (old fallow) in three districts. In each plot, all woody plants were enumerated and species composition, diversity and richness assessed. Young fallow plots were dominated by pioneer species such as Piliostigma thonningii and Annona senegalensis, while old fallow by a mix of late and early successional species such as Vachellia hockii (formerly Acacia hockii) and Combretum collinum. Vitellaria paradoxa (Shea butter tree) was the most abundant in all fallow categories. Species composition in crop field was different from young and old fallow. Species richness increased significantly from abandoned Crop field to Young fallow and then to Old fallow. Simpson's Diversity Index showed similar trends. V. paradoxa contributed most to overall similarity among the fallow categories. Fallowing can facilitate restoration of characteristic species of Sudanian woodlands.

Effect of Fallowed and Cultivated Land Use Systems on the Composition and Abundance of Soil Macroinvertebrates Assemblage in Uruk Osung Community, Akwa Ibom State, Nigeria

This study was to assess the effect of fallowed and cultivated land-use systems on the abundance of soil macroinvertebrates assemblage. Collections of soil samples were carried out fortnightly twice a month for four months. The extraction of soil macroinvertebrates was carried out using Berlese-Tullgren funnel extractor, and elutriation technique. The mean values of 6.93+/-0.25 were recorded for pH, 32.08+/-0.52oC for temperature, 15.60+/-1.22 for moisture content, were recorded for fallowed soil, and 4.43+/-0.16 (pH), 30.95+/-0.19oC (temperature) were recorded for cultivated soil. A total of 17 soil macroinvertebrates species comprising of 11 orders, from four classes were encountered. Out of the 517 individual soil macroinvertebrates encountered, 327 individuals representing four classes were present in the fallow land while 190 individuals representing three classes were present in the cultivated land. The most dominant species in terms of abundance in the fallowed land site included; Cryptotermes sp 67(20.49%) > Blatta sp 56(17.12%) with Hogna sp 1(0.0.30%) the least; while Cryptotermes sp. 79(41.58%) >Lasius sp 30(15.79%) > Lumbricus terrestris 21(11.05%) represents the dominant species in the cultivated soil with Paraponera sp 1(0.53%) the least. Soil temperature showed positive correlation with the abundance of Clitellata (r = 0.851; p < 0.05) and Insecta (r = 0.826; p < 0.05) and Soil pH showed positive correlation with the abundance of Diplopoda (r = 0.911; p ≤ 0.05). In conclusion, it could be deduced from the study that human activities in the cultivated site perturb soil macroinvertebrates community structure which is reflected in the relative abundance of soil macroinvertebrate from the two sampling sites. The results obtained in this study could be a piece of pointing information for the conservation and management of the soil macroinvertebrates giving their functions in balancing agroecosystems.

Impact of biochar on nutrient supply, crop yield and microbial respiration on sandy soils of northern Germany

AbstractThe application of biochar to agricultural soils to increase nutrient availability, crop production and carbon sequestration has gained increasing interest but data from field experiments on temperate, marginal soils are still under‐represented. In the current study, biochar, produced from organic residues (digestates) from a biogas plant, was applied with and without digestates at low (3.4 t ha−1) and intermediate (17.1 t ha−1) rates to two acidic and sandy soils in northern Germany that are used for corn (Zea mays L.) production. Soil nutrient availability, crop yields, microbial biomass and carbon dioxide (CO2) emissions from heterotrophic respiration were measured over two consecutive years. The effects of biochar application depended on the intrinsic properties of the two tested soils and the biochar application rates. Although the soils at the fallow site, with initially low nutrient concentrations, showed a significant increase in pH, soil nutrients and crop yield after low biochar application rates, a similar response was found at the cornfield site only after application of substantially larger amounts of biochar. The effect of a single dose of biochar at the beginning of the experiment diminished over time but was still detectable after 2 years. Whereas plant available nutrient concentrations increased after biochar application, the availability of potentially phytotoxic trace elements (Zn, Pb, Cd, Cr) decreased significantly, and although slight increases in microbial biomass carbon and heterotrophic CO2 fluxes were observed after biochar application, they were mostly not significant. The results indicate that the application of relatively small amounts of biochar could have positive effects on plant available nutrients and crop yields of marginal arable soils and may decrease the need for mineral fertilizers while simultaneously increasing the sequestration of soil organic carbon.Highlights A low rate of biochar increased plant available nutrients and crop yield on marginal soils. Biochar application reduced the availability of potentially harmful trace elements. Heterotrophic respiration showed no clear response to biochar application. Biochar application may reduce fertilizer need and increase carbon sequestration on marginal soils.

Soil organic carbon stocks maintained despite intensification of shifting cultivation

Shifting cultivation systems of Southeast Asia are rapidly intensifying, especially through shortening of the fallow periods. It is typically assumed that intensification will result in a depletion of soil organic carbon (SOC) stocks, but existing estimates of carbon stocks in these systems are variable, and there is little certainty about the carbon outcomes of intensification. We investigated the effects of intensification on SOC stocks of a shifting cultivation system in northern Laos. Volume-specific soil samples were collected from 20 sites representing: i) various rotation intensities (fallow periods of 3–4 years and 7–10 years), ii) various stages of the rotation cycle (fallows and active fields) and iii) reference plots (old regrowth of 25–30 years). Samples were analyzed for SOC, soil texture, pH, Total Nitrogen and permanganate oxidizable carbon (POXC) – an active carbon fraction that has been suggested as an easily measured early indicator of land use induced changes in soil quality and SOC. There were no significant differences between SOC concentrations or stocks of any of the sites under shifting cultivation and the reference sites. However, the SOC stock under fallows in the intensive rotation category was significantly larger than the SOC stock under fallows in the extensive rotation category. This is likely because inputs of dead root biomass from the slashed vegetation provides an important input to the SOC pool. Fallow sites under intensive rotation had significantly higher contents of POXC in the topsoil than the active fields, which suggests that POXC captures the immediate effect of the decreased input of litter to the topsoil during the cultivation period. We conclude that in this study there is no evidence that intensification of shifting cultivation leads to a decline in total soil carbon stock, or to a decline in the more active carbon fraction measured by POXC. Therefore, narratives of shifting cultivation leading to a decline in soil carbon stocks need to be revisited, and land use policies related to the system should not uncritically be based on this incorrect assumption.

Pattern of forest recovery and carbon stock following shifting cultivation in Manipur, North-East India.

Shifting cultivation has resulted in large-scale deforestation and forest degradation in the tropics; however the abandoned fallows are known to have high potential for carbon capture. The paper is an attempt to determine the forest recovery patterns following shifting cultivation by evaluating the tree species composition, diversity and abundance with respect to topographical factors in Manipur, India. We also used ordination analysis to understand the change in species composition with regard to environmental variables. The living woody biomass carbon of each fallow was quantified, and the factors affecting the recovery of carbon stock along an increasing fallow gradient was assessed. Our results showed that the species richness and basal area recovered relatively with time since abandonment, and the north-facing lower elevation fallow sites displayed higher species richness and stem density than those in higher elevations. Environmental variables had no impact on the regeneration of Elaeocarpus floribundus Blume and Castanopsis hystrix Hook. f. & Thomson ex A. DC. which suggests that they may be capable of effective restoration of degraded forest areas. As these species appear naturally in the forests, it would facilitate quicker rehabilitation and reinstate the soil nutrients making the soil reusable in a short term. We also found that fallow age plays a vital role in recovering above-ground biomass carbon from living woody species followed by the aspect of the site. The total living woody biomass carbon ranged from 0.98 Mg ha-1 in 5 years fallow to 142.58 Mg ha-1 in 20 years fallow. The above-ground biomass carbon recovery of the oldest fallow was 39% to 40% of the reference undisturbed forest and the estimated time for the shifting cultivation fallows to reach that of the undisturbed forest level was approximately 39 years to 41 years.

Critical connectivity thresholds and the role of temperature in parasite metapopulations

Managing the spread of parasite populations is a ubiquitous challenge for managers of natural and farmed systems. A specific current example are “sea lice”, parasitic marine organisms that live on both wild and farmed Salmon sp., posing a persistent challenge to aquaculture operations in high latitude countries. Lice reproduce with pelagic larvae that spread in the water column, meaning that fish farm sites are connected to one another as a result of their relative location and the response of the organism to the environment. Much work has investigated population connectivity for specific systems, using computational models that link the physical and biological processes affecting larval transport. However, although probability and frequency of dispersal events may be calculated, the specific implications for outbreaks on sites is not entirely clear. We therefore used population models to describe the stage-structured dynamics of connected sea lice population networks, with the goal of establishing the critical connection strength (probability of successful dispersal) for occurrence of an outbreak. Our initial investigation deals with the case of “self-infection” of a single isolated population. Vital rates of life-cycle stages respond to temperature, and as a consequence so does critical connectivity. A dispersal success probability of around 0.01 is required for sea lice population development at the optimal temperature, although this is dependent on parameterisation. The analysis is extended to networks of sites interacting via dispersal, and we show how fallow sites can lead to substantial reductions in population growth rates. Our results provide an important, and to date, missing component in assessment of the environmental impact of marine aquaculture sites. They provide a basis upon which site operators and regional planners can appraise specific developments in the context of their surroundings, and may provide a means for future development of adaptive management strategies.

Rapid recovery of tropical forest diversity and structure after shifting cultivation in the Philippines uplands.

Shifting cultivation is a widespread land‐use in the tropics that is considered a major threat to rainforest diversity and structure. In the Philippines, a country with rich biodiversity and high rates of species endemism, shifting cultivation, locally termed as kaingin, is a major land‐use and has been for centuries. Despite the potential impact of shifting cultivation on forests and its importance to many people, it is not clear how biodiversity and forest structure recover after kaingin abandonment in the country, and how well these post‐kaingin secondary forests can complement the old‐growth forests. We investigated parameters of forest diversity and structure along a fallow age gradient in secondary forests regenerating after kaingin abandonment in Leyte Island, the Philippines (elevation range: 445–650 m asl). We first measured the tree diversity and forest structure indices in regenerating secondary forests and old‐growth forest. We then measured the recovery of tree diversity and forest structure parameters in relation to the old‐growth forest. Finally, using linear mixed effect models (LMM), we assessed the effect of different environmental variables on the recovery of forest diversity and structure. We found significantly higher species density in the oldest fallow sites, while Shannon’s index, species evenness, stem number, basal area, and leaf area index were higher in the old‐growth forest. A homogeneous species composition was found across the sites of older fallow age. Multivariate analysis revealed patch size as a strong predictor of tree diversity and forest structure recovery after shifting cultivation. Our study suggests that, secondary forests regenerating after shifting cultivation abandonment can recover rapidly. Although recovery of forest structure was not as rapid as the tree diversity, our older fallow sites contained a similar number of species as the old‐growth forest. Many of these species are also endemic to the Philippines. Novel and emerging ecosystems like tropical secondary forests are of high conservation importance and can act as a refuge for dwindling tropical forest biodiversity.

Temporal change in the spatial distribution of visual organic enrichment indicators at aquaculture sites in Newfoundland, Canada

Growing salmon in sea cages results in the deposition of uneaten feed and wastes which can smother organisms, increase biological oxygen demand, and alter seafloor communities. At some sites with mainly hard-bottom substrates, opportunistic annelids and mat-forming bacteria are used as visual indicators of aquaculture waste and are monitored via drop camera imaging. Additionally, high organic matter sedimentation rates can result in the proliferation of microbes that release gas; this offgassing could also serve as a useful visual enrichment indicator. Little is known of how the distribution of opportunistic annelids, microbial mats, and offgassing might change over time and space, although coverage has important repercussions in some regulatory schemes. Here, we explore spatiotemporal distributions of offgassing, bacterial mats, annelids, and epibenthic taxon richness based on existing video-monitoring data collected along transects at four Newfoundland aquaculture sites in 2011–2012. A high degree of spatial and temporal patchiness was observed at both fallow and production sites, and combinations of time, transect, and distance to cage explained the distribution of bacterial mats, annelids, and taxon richness. Expected successional patterns resulting from organic enrichment or remediation were evident in some patches. Offgassing was observed only at fallow sites and may signal a distinct and persistent phase in organic matter degradation. Results highlight the spatial heterogeneity of benthic organic enrichment indicators across transects at Newfoundland aquaculture sites, with indicators appearing to form a mosaic of patches undergoing different stages of enrichment or recovery.

Honey bee-collected pollen in agro-ecosystems reveals diet diversity, diet quality, and pesticide exposure.

European honey bees Apis mellifera are important commercial pollinators that have suffered greater than normal overwintering losses since 2007 in North America and Europe. Contributing factors likely include a combination of parasites, pesticides, and poor nutrition. We examined diet diversity, diet nutritional quality, and pesticides in honey bee‐collected pollen from commercial colonies in the Canadian Maritime Provinces in spring and summer 2011. We sampled pollen collected by honey bees at colonies in four site types: apple orchards, blueberry fields, cranberry bogs, and fallow fields. Proportion of honey bee‐collected pollen from crop versus noncrop flowers was high in apple, very low in blueberry, and low in cranberry sites. Pollen nutritional value tended to be relatively good from apple and cranberry sites and poor from blueberry and fallow sites. Floral surveys ranked, from highest to lowest in diversity, fallow, cranberry, apple, and blueberry sites. Pesticide diversity in honey bee‐collected pollen was high from apple and blueberry sites and low from cranberry and fallow sites. Four different neonicotinoid pesticides were detected, but neither these nor any other pesticides were at or above LD50 levels. Pollen hazard quotients were highest in apple and blueberry sites and lowest in fallow sites. Pollen hazard quotients were also negatively correlated with the number of flower taxa detected in surveys. Results reveal differences among site types in diet diversity, diet quality, and pesticide exposure that are informative for improving honey bee and land agro‐ecosystem management.

Improving water productivity in moisture-limited rice-based cropping systems through incorporation of maize and mungbean: A modelling approach

Crop and water productivities of rice-based cropping systems and cropping patterns in the irrigated lowlands of Sri Lanka have not been researched to the degree warranted given their significance as critical food sources. In order to reduce this knowledge gap, we simulated the water requirement for rice, maize, and mungbean under rice-based cropping systems in the Dry Zone of Sri Lanka. We evaluated the best combinations of crops for minimum water usage while reaching higher crop and water productivities. We also assessed the risk of cultivating mungbean as the third season/sandwich crop (i.e. rice-mungbean-rice) in different regions in Sri Lanka. In the simulation modelling exercise, APSIM-Oryza (rice), APSIM-maize and APSIM-mungbean modules were parameterised and validated for varieties grown widely in Sri Lanka. Moreover, crop productivities and supplementary irrigation requirement were tested under two management scenarios i.e. Scenario 1: irrigate when plant available water content in soil fell below 25% of maximum, and Scenario 2: irrigate at 7-day intervals (current farmer practice). The parameterised, calibrated and validated model estimated the irrigation water requirement (number of pairs of observations (n)=14, R2>0.9, RMSE=66mmseason−1ha−1), and grain yield of maize (n=37, R2>0.95, RMSE=353kgha−1) and mungbean (n=26, R2>0.98, RMSE=75kgha−1) with a strong fit in comparison with observed data, across years, cultivating seasons, regions, management conditions and varieties. Simulated water requirement during the cropping season reduced in the order of rice (1180–1520mm)>maize and mungbean intercrop=maize sole crop (637–672mm)>mungbean sole crop (345mm). The water productivity of the system (crop yield per unit water) could be increased by over 65% when maize or mungbean extent was increased. The most efficient crop combinations to maximise net return were diversification of the land extent as (i) 50% to rice and 50% to mungbean sole crops, or (ii) 25%, 25% and 50% to rice, maize and mungbean sole crops, respectively. Under situations where water availability is inadequate for rice, land extent could be cultivated to 50% maize and 50% mungbean as sole crops to ensure the maximum net return per unit irrigation water (115 Sri Lankan Rupees ha−1mm−1). Regions with high rainfall during the preceding rice cultivating season are expected to have minimum risk when incorporating a third season mungbean crop. Moisture loss through evapotranspiration from the third season mungbean crop was similar to that of a fallowed site with weeds.

Spatial and temporal changes in epibenthic communities at deep, hard bottom aquaculture sites in Newfoundland

This study explores spatio-temporal changes in epibenthic communities due to salmon aquaculture at deep (>30m), hard-bottom dominated sites in Newfoundland (Canada). Using a drop-camera approach, we followed changes with production at two aquaculture sites, as well as potential recovery processes at two fallow sites, comparing their epibenthic composition with nearby non-production sites. Multivariate analysis revealed that aquaculture production led to rapid changes in epibenthic communities, as evidenced primarily by the presence of two visual indicators: bacterial mats and opportunistic polychaetes. Due to low taxon richness and abundances, as well as variability among sites, no clear intermediate successional stages were apparent. Beggiatoa-like mats and opportunistic polychaetes appeared rapidly once aquaculture production began; these indicators did not increase in spatial extent during the survey and were typically observed up to 100m, and occasionally up to 160m from cages. After 15 months of fallowing, Beggiatoa-like mats and opportunistic polychaetes remained present at sites and were occasionally accompanied by few other taxa, suggesting incomplete recovery.

Contrasting response of vascular plant and bryophyte species assemblages to a soil-disturbing ecosystem engineer in calcareous grasslands

Species-rich grasslands are highly threatened by land-use change, including fertilization, land-use intensification and abandonment. These changes evoke a loss of structural heterogeneity. Aside from specific management measures to increase structural heterogeneity, small-scale patches of different vegetation within grasslands are promoted naturally by soil-disturbing ecosystem engineers. The aim of this study is to analyse the importance of Lasius flavus nest mounds for increasing structural and functional diversity in vascular plant and bryophyte assemblages within Central European calcareous grasslands.Our study clearly revealed that the mound-building activity of L. flavus ants in calcareous grasslands alters soil conditions and vegetation structure. Ant mound soil samples had higher potassium and phosphorus levels than control samples in the matrix vegetation. Ant mounds, in general, and the south-facing sides, in particular, represented highly disturbed microsites with open and low-growing vegetation containing high proportions of bare ground. In contrast, the north-facing sides were characterized by transient vegetation between the dense matrix and the open south-facing sides. However, the effects of soil disturbance by ants were different for vascular plant and bryophyte species assemblages. In vascular plants, differences among the three sample groups were less pronounced; in bryophytes, nearly all parameters differed.All in all, the occurrence of L. flavus increases vegetation heterogeneity within grasslands and, therefore, plays an important role in supporting species richness of both plants and animals in calcareous grasslands. This holds true in particular for fallow sites, where ant mounds often represent the only sites of open vegetation.

Tropical secondary forests regenerating after shifting cultivation in the Philippines uplands are important carbon sinks.

In the tropics, shifting cultivation has long been attributed to large scale forest degradation, and remains a major source of uncertainty in forest carbon accounting. In the Philippines, shifting cultivation, locally known as kaingin, is a major land-use in upland areas. We measured the distribution and recovery of aboveground biomass carbon along a fallow gradient in post-kaingin secondary forests in an upland area in the Philippines. We found significantly higher carbon in the aboveground total biomass and living woody biomass in old-growth forest, while coarse dead wood biomass carbon was higher in the new fallow sites. For young through to the oldest fallow secondary forests, there was a progressive recovery of biomass carbon evident. Multivariate analysis indicates patch size as an influential factor in explaining the variation in biomass carbon recovery in secondary forests after shifting cultivation. Our study indicates secondary forests after shifting cultivation are substantial carbon sinks and that this capacity to store carbon increases with abandonment age. Large trees contribute most to aboveground biomass. A better understanding of the relative contribution of different biomass sources in aboveground total forest biomass, however, is necessary to fully capture the value of such landscapes from forest management, restoration and conservation perspectives.

An Undergraduate Student Project to Improve Mechanical Control of Perennial Nutsedges with a Peanut Digger in Organic Crop Production

Yellow and purple nutsedge are common in the southeastern United States, and both perennial species are difficult to control in organic crop-production systems. Tubers are generally confined to the upper portions of the soil profile and are vulnerable to desiccation when brought to the soil surface. A peanut digger is a common implement found in the coastal plain region of the southeastern United States and has shown promise controlling perennial nutsedges in fallow sites. The peanut digger undercuts perennial nutsedges, deposits weeds on the soil surface, and exposes weeds to desiccation. However, rainfall after tillage with the peanut digger allows displaced nutsedges to survive. As part of a senior-level class project, undergraduate mechanical engineering students from Auburn University designed and constructed a cart attached to a peanut digger that collected nutsedges. Key features included a custom hitch that allowed the correct plane of movement and a hydraulic conveyor system that discarded the perennial nutsedges off-site, away from the field. The prototype was tested in a fallow location in the summer of 2014 with a yellow nutsedge infestation averaging 148 plants m−2. One week after the initial field test, tillage using the peanut digger with specialized cart reduced yellow nutsedge densities in the tilled area by > 99%.