Paired Plots Research Articles

Seed Yield Increase in Niger Crop in to Relation to Honeybee and Other Pollinators

AbstractNiger (Guizotia abyssinicaCass) is an important minor oilseed crop of hilly and tribal regions and it is used for oil as well as for various other purposes only by the tribal people. Therefore, a systematic study was arranged to document about the increase in the seed yield of niger crop in relation to honeybees (Aphis mellifera), as a pollinator in niger crop with paired plot technique at the Niger Research Station (NRS) at Navsari Agricultural University (NAU) and at farmer’s field, Vanarasi, Navsari, Gujarat (India) and also studied its relation in terms of cost benefit ratio (CB). The trial was conducted at Niger Research Station (NRS), Vanarasi for 3 years (2013-14, 2014-15 and 2015-16) and also at farmer's field to ascertain the role and involvement of honey bees (Aphis mellifera) in swelling the seed yield of niger crop (due to pollination) and its effect on income due to increase in the niger seed yield. Significant differences were observed for number of capitula/plant, number of seeds/capitula, 1000 seed weight and seed yield in both the location for the consecutive 3 years. However, the seed yield and gross returns were considerably higher in first location of T1Natural plot/open pollinated with beehive (Aphis mellifera)in all the 3 years data with the maximum seed yield with the gross return was obtained in this treatment.

Community‐weighted means and functional dispersion of plant functional traits along environmental gradients on Mount Kilimanjaro

AbstractQuestionsHow do community‐weighted means of traits (CWM) and functional dispersion (FDis), a measure of trait variability, change in response to gradients of temperature, precipitation, soil nutrients and disturbance? Is the decrease in trait similarity between plots continuous or discontinuous? Is species turnover between plots linked to trait turnover?LocationMount Kilimanjaro, Tanzania, Africa.MethodsSixty plots were established in 12 major vegetation types on Mount Kilimanjaro, covering large gradients of temperature, precipitation, soil nutrients and anthropogenic disturbance representing the dominant ecosystems in East Africa. Environmental data, plant abundances and plant traits were recorded for each plot. Trait CWM and FDis were related to environmental factors with partial least squares regressions. Trait similarity between pairs of plots was assessed with a null model approach.ResultsBoth CWM and FDis of most traits responded strongly to environmental factors, particularly to precipitation and disturbance. FDis of traits associated with growth and reproduction mostly increased with temperature and precipitation, and decreased with disturbance. Pair‐wise plot comparisons revealed an inverse relationship of trait similarity with differences in temperature, precipitation and anthropogenic disturbance. However, changes in similarity were often discontinuous rather than continuous. Several vegetation types differed strongly in species composition but not in traits.ConclusionsTrait dispersion indicating functional niches increased with productivity and temperature. Conversely, low‐productivity conditions were characterized by trait convergence. Discontinuous changes in trait similarity between plots suggested tipping points at which trait expressions change strongly to adjust to environmental conditions. Large sections of the temperature gradient were characterized by species turnover with only minor changes in traits, indicating that the functional composition may be resilient to gradual environmental changes until a tipping point is reached.

Comparative accuracy of CT perfusion in diagnosing acute ischemic stroke: A systematic review of 27 trials.

ObjectiveTo systematically evaluate and compare the diagnostic accuracy of CT perfusion (CTP), non-enhanced computed tomography (NCCT) and computed tomography angiography (CTA) in detecting acute ischemic stroke.MethodsWe searched seven databases and screened the reference lists of the included studies. The risk of bias in the study quality was assessed using QUADASII. We produced paired forest plots in RevMan to show the variation of the sensitivity and specificity estimates together with their 95% CI. We used a hierarchical summary ROC model to summarize the sensitivity and specificity of CTP in detecting ischemic stroke.ResultsWe identified 27 studies with a total of 2168 patients. The pooled sensitivity of CTP for acute ischemic stroke was 82% (95% CI 75–88%), and the specificity was 96% (95% CI 89–99%). CTP was more sensitive than NCCT and had a similar accuracy with CTA. There were no statistically significant differences in the sensitivity and specificity between patients who underwent CTP within 6 hours of symptom onset and beyond 6 hours after symptom onset. No adverse events were reported in the included studies.ConclusionsCTP is more accurate than NCCT and has similar accuracy to CTA in detecting acute ischemic stroke. However, the evidence is not strong. There is potential benefit of using CTP to select stroke patients for treatment, but more high-quality evidence is needed to confirm this result.

Management of Root Knot Nematode on Tomato through Grafting Root Stock of Solanum sisymbriifolium

The root-knot nematodes (Meloidogyne spp) are difficult to manage once established in the field because of their wide host range, and soil-borne nature. Thus, the aim of the present study was to examine the use of resistant root stock of wild brinjal (Solanum sisymbriifolium) to reduce the loss caused by the nematodes on tomato. For the management of root-knot nematodes, grafted plant with resistant root stock of the wild brinjal was tested under farmers’ field conditions at Hemza of Kaski district. Grafted and non-grafted plants were produced in root-knot nematode-free soil. Around three week-old grafted and non-grafted tomato plants were transplanted in four different plastic tunnels where root-knot nematodes had been reported previously. The plants were planted in diagonal position to each other as a pair plot in 80 × 60 cm2 spacing in an average of 20 × 7 m2 plastic tunnels. Galling Index (GI) was recorded three times in five randomly selected plants in each plot at 60 days intervals. The first observation was recorded two months after transplanting. Total fruit yield was recorded from same plants. In the grafted plants, the root system was totally free from gall whereas in an average of 7.5 GI in 0-10 scale was recorded in the non-grafted plants. Fruits were harvested from time to time and cumulated after final harvest to calculate the total fruit yield. It was estimated that on an average tomato fruit yield was significantly (P>0.05) increased by 37 percent in the grafted plants compared with the non-grafted plants. Grafting technology could be used effectively for cultivation of commonly grown varieties, which are susceptible to root-knot nematodes in disease prone areas. This can be used as an alternative technology for reducing the use of hazardous pesticides for enhancing commercial organic tomato production.Journal of Nepal Agricultural Research Council Vol.3 2017: 27-31

A dominant dwarf shrub increases diversity of herbaceous plant communities in a Trans-Himalayan rangeland

Plant communities are structured by both competition and facilitation. The interplay between the two interactions can vary depending on environmental factors, nature of stress, and plant traits. However, whether positive or negative interactions dominate in regions of high biotic and abiotic stress remains unclear. We studied herbaceous plant communities associated with a dwarf shrub Caragana versicolor in semi-arid, high altitude Trans-Himalayan rangelands of Spiti, India. We surveyed 120 pairs of plots (within and outside shrub canopies) across four watersheds differing in altitude, aspect, and dominant herbivores. Herbaceous communities within shrub canopies had 25% higher species richness, but similar abundance when compared to communities outside the canopy, with the shrub edge having higher diversity than the centre of the canopy. Grasses and erect forbs showed positive associations with the shrub, while prostrate plants occurred at much lower abundance within the canopy. Rare species showed stronger positive associations with Caragana than abundant species. Experimental removal of herbaceous vegetation from within shrub canopies led to 42% increase in flowering in Caragana, indicating a cost to the host shrubs. Our study indicates a robust pattern of a dwarf shrub facilitating local community diversity across this alpine landscape, increasing diversity at the plot level, facilitating rare species, and yet incurring a cost to hosts from the presence of herbaceous plants. Given these large influences of this shrub on the vegetation of these high altitude rangelands, we suggest that the shrub microhabitat be explicitly considered in any analyses of ecosystem health in such rangelands.

Oil Palm and Rubber Tree Water Use Patterns: Effects of Topography and Flooding.

Oil palm and rubber plantations extend over large areas and encompass heterogeneous site conditions. In periods of high rainfall, plants in valleys and at riparian sites are more prone to flooding than plants at elevated topographic positions. We asked to what extent topographic position and flooding affect oil palm and rubber tree water use patterns and thereby influence spatial and temporal heterogeneity of transpiration. In an undulating terrain in the lowlands of Jambi, Indonesia, plantations of the two species were studied in plot pairs consisting of upland and adjacent valley plots. All upland plots were non-flooded, whereas the corresponding valley plots included non-flooded, long-term flooded, and short-term flooded conditions. Within each plot pair, sap flux densities in palms or trees were monitored simultaneously with thermal dissipation probes. In plot pairs with non-flooded valleys, sap flux densities of oil palms were only slightly different between the topographic positions, whereas sap flux densities of rubber trees were higher in the valley than at the according upland site. In pairs with long-term flooded valleys, sap flux densities in valleys were lower than at upland plots for both species, but the reduction was far less pronounced in oil palms than in rubber trees (-22 and -45% in maximum sap flux density, respectively). At these long-term flooded valley plots palm and tree water use also responded less sensitively to fluctuations in micrometeorological variables than at upland plots. In short-term flooded valley plots, sap flux densities of oil palm were hardly affected by flooding, but sap flux densities of rubber trees were reduced considerably. Topographic position and flooding thus affected water use patterns in both oil palms and rubber trees, but the changes in rubber trees were much more pronounced: compared to non-flooded upland sites, the different flooding conditions at valley sites amplified the observed heterogeneity of plot mean water use by a factor of 2.4 in oil palm and by a factor of 4.2 in rubber plantations. Such strong differences between species as well as the pronounced heterogeneity of water use across space and time may be of relevance for eco-hydrological assessments of tropical plantation landscapes.

A correlation radius estimate between in-panel faults and high-stress areas using Monte Carlo simulation and point process statistics

Since quantitative correlation association between in-panel faults and high-stress areas have not been well understood, we propose a workflow to quantitatively estimate this spatial association through Monte Carlo simulations and point process statistics using measured fault traces and tomographic seismic velocities as inputs. According to different distribution scenarios of fault traces and high-stress areas based on in situ characteristics, we build three different spatial statistical models: a no spatial correlation model, an anti-correlation model and a correlation model to analyze and compare with the observed data. By estimating and cross plotting RHA (Ratio of High-stress Areas over total area) and RFL (Ratio of included Fault-trace Length over total fault-trace length) pairs for Monte Carlo realizations of those models, we generate a template to estimate the correlation association between in-panel faults and high-stress areas for the study panel. After comparing the observed cross plots of RHA vs. RFL pairs with the template, we find that the in-panel faults and high-stress areas have positive correlation association and yield an estimate of correlation radius for the study panel. This result is in accordance with previous geological analysis. However, the estimated correlation radius can be affected by velocity artifacts and inaccurate interpreted faults. Considering the influence of velocity artifacts, we achieve a calibrated template to better estimate the correlation radius between in-panel faults and high-stress areas. This estimate could be a practical parameter to optimize mining methods and to minimize stress related rock failures.

Using resistance distance from circuit theory to model dispersal through habitat corridors

Resistance distance (RD), based on circuit theory, is a promising metric for modelling effects of landscape configuration on dispersal of organisms and the resulting population and community patterns. The values of RD reflect the likelihood of a random walker to reach from a source to a certain destination in the landscape. Although it has successfully been used to model genetic structures of animal populations, where it most often outperforms other isolation metrics, there are hardly any applications to plants and, in particular, to plant community data. Our aims were to test if RD was a suitable metric for studying dispersal processes of plants in narrow habitat corridors (linear landscape elements [LLE]). This would be the case, if dispersal processes (seed dispersal and migration) resembled random walks. Further, we compared the model performance of RD against least-cost distance (LCD) and Euclidean distance (ED). Finally, we tested the suitability of different cost surfaces for calculations of LCD and RD. We used data from 50 vegetation plots located on semi-natural LLE (field margins, ditches, road verges) in eight agricultural landscapes of Northwest Germany. We mapped LLE, including hedges and tree rows, from aerial images in a Geographic Information System, converted the maps into raster layers, and assigned resistance values to the raster cells, where all cells outside of LLE received infinite resistance and, thus, represented barriers to dispersal. For all pairs of plots within study areas, we calculated Jaccard similarity assuming that it was a proxy (or correlate) of dispersal events between plots. Further, we calculated RD and LCD of the network of LLE and ED between the plots. We modelled the effects of distance metrics on community similarity using binomial generalized linear mixed models. ED was clearly the least suitable isolation metrics. Further, we found that RD performed better than LCD at modelling Jaccard similarity. Predictions varied markedly between the two distance metrics suggesting that RD comprises additional information about the landscape beyond spatial distance, such as the possible presence of multiple pathways between plots. Cost surfaces with equal cell-level resistances for all types of LLE performed better than more complex ones with habitat-specific resistances. We conclude that RD is a highly suitable measure of isolation or, inversely, connectivity for studying dispersal processes of plants within habitat corridors. It is likely also suitable for assessing landscape permeability in other landscape types with areal habitats instead of narrow corridors. RD holds the potential to improve assessments of isolation (or connectivity) for models of regional population and meta-community dynamics.

Effect of Hummock-Forming Vegetation on Methane Emissions from a Temperate Sedge-Grass Marsh

Plants affect CH4 emissions from wetlands by providing routes for CH4 ventilation from the soil and its re-oxidation, the outcome depending on the vertical distribution of the plant ventilating structures as related to water level. This study investigated the effect of elevated hummocks on CH4 emissions in a temperate wetland dominated by a hummock-forming sedge, Carex acuta L. Comparative measurements of CH4 fluxes from paired plots with or without hummocks revealed a prevailing positive difference interpreted as plant-mediated fluxes. All types of CH4 fluxes responded positively to water level with a hysteresis related to its recent dynamics. Seasonal medians of CH4 emissions from the ecosystem, based on fluxes from both types of plots, were 15.09 and 0.11 mg m−2 day−1 in the wet year 2012 and the dry year 2014, respectively. This relatively low magnitude of CH4 emissions, compared to values from similar habitats within the same range of water levels, is ascribed to the presence of hummocks. At water levels near the soil surface, hummocks extend above the water table and serve as aerobic micro-habitats in which plant structures avoid anaerobic stress and CH4 produced in the bulk soil and vented via deep roots can be re-oxidized.

Fungal adaptation to contemporary fungicide applications: the case of Botrytis cinerea populations from Champagne vineyards (France).

In addition to being one of the most acute problems impeding chemical control of fungal diseases, the evolution of fungicide resistance is an emblematic case of local adaptation to spatially heterogeneous and temporally variable selection pressures. Here we dissected the adaptation of Botrytis cinerea (the causal agent of grey mould) populations on grapes to several fungicides. We carried out a 2-year survey (four collection dates) on three treated/untreated pairs of plots from vineyards in Champagne (France) and monitored the frequency of four resistant phenotypes that are unambiguously associated with four distinct genotypes. For two loci under selection by currently used fungicides (MDR1 and MDR2), the frequencies of resistant mutations at vintage were greater in treated plots compared to untreated plots, showing that the effect of selection is detectable even at the plot scale. This effect was not detectable for two other loci under selection by previously used fungicides (BenR1 and ImiR1). We also found that treatment with currently used fungicides reduced B.cinerea effective population size, leading to a significant decrease in genic diversity and allelic richness in treated vs. untreated plots. We further highlight that even under ample drift and migration, fungal populations can present an efficient response to selection. Finally, for the four studied loci, the costs of fungicide resistance were estimated by modelling the decrease in the frequency of resistant mutations in the absence of treatment. We discuss the importance of these estimates for defining strategies for limiting or counteracting the local adaptation of pests to fungicides.

A model for field-based evidences of the impact of irrigation on carbonates in the tilled layer of semi-arid Mediterranean soils

Carbonates constitute a significant proportion of the soil mass in many semi-arid soils. Due to their solubility, they can be affected by changes in the soil water regime. This needs to be taken into account when assessing the environmental and agronomical impacts of the adoption of irrigation. To gain knowledge on the importance of the effect of irrigation on carbonates dynamics in the tilled layer (0–20cm) of agricultural soils, we conducted a two-step study embracing field observations and numerical simulation. First, carbonates storage and their size distribution were quantified for two different situations (irrigation and non-irrigation) in three irrigation districts with different time under irrigation (Valtierra (19years), Miranda (5years) and Funes (12years)) in Navarre (Spain). Soil sampling was designed to ensure homogeneous comparisons in the most characteristic soil types at each site (Xeric Haplocalcid, Typic Calcixerept and Xeric Haplocalcid, respectively). Carbonates concentration was systematically lower with irrigation in the finest (<50μm) soil fraction: 22.2±1.4g carbonates 100g−1 fraction without irrigation for 16.1±0.9 with irrigation in Valtierra, 26.7±1.1 for 19.1±3.8 in Miranda and 27.8±2.9 for 22.7±1.5 at Funes1. However, the net annual balance of total carbonates-C between irrigated and non-irrigated condition was neutral at the three sites. This can be explained by agricultural management affecting carbonates in the sand-size fraction, including the addition of carbonates with fertilizers, and coarse carbonate particles brought to the surface by tillage.In a second step, a simplified model was developed for use with easily available data in most irrigation districts, and numerical simulations of the geochemical interactions between the soil, the soil solution and irrigation water were run using actual soil and soil solution data from the tilled layer of another pair of plots in Funes (Funes2). Sensitive analysis was also conducted to investigate the potential impact of water quality and crop types as sources of variability on the model outputs. The modelling results showed annual values of carbonates-C loss in the range between 13.52 and 12.06gm−2year−1 in the studied depth under irrigation, depending on the quality of irrigation water, for 0.46gm−2 without irrigation. These data were within the range of carbonates budgets found in the literature but one order of magnitude lower than the observed results in the fine fraction in the field. Overall, our results showed that irrigation can significantly alter carbonates dynamics in semi-arid Mediterranean land, which implies that human use can significantly alter the mineral phase of these soils in a relatively short time lapse. Simple geochemical models can be a useful approach to evaluate changes in the carbonates balance at the local and regional scale when irrigation is applied, although they have to be improved to account for other factors related to agricultural management and local geochemical conditions.

Impacts of land clearance by fire on spatial variation of mountain cedar pollen concentrations in Texas

Austin, Texas, is one of the worst places with respect to allergies. In winter, mountain cedar (Juniperus ashei) is producing high pollen amounts exerting the so-called cedar fever in individuals allergic to this pollen species. In this study, we evaluated to which extent the effect of prescribed fires in a semi-arid ecosystem decreases pollen concentrations at the local scale.The study was performed on patches characterized by human-induced fire disturbances and unmanaged areas (control sites) in the southwest of Austin. Pollen was sampled on four consecutive days in January 2015 using ten pollen traps installed at 1.5m a.g.l. Microscope slides were inserted every second hour during 8 am and 6 pm. Each station was equipped with meteorological devices to account for influencing factors such as wind speed and direction.Mean cedar pollen concentrations differed across the studied days and plots and ranged between 633 (16th January) and 126,400 pollen grains/m3 (17th January). We determined diurnal patterns with peak values between 2 and 3 pm. Pollen concentrations were on average 15% lower at burnt vs. control plots. Comparing pairs of adjacent plots even revealed a reduction of up to 50%.Therefore, local land management can alter pollen concentrations drastically. A walk across previously burnt areas may trigger less severe symptoms for allergic people during the flowering period of mountain cedar. Our results add to the knowledge about individual cedar pollen exposure in heterogeneous areas and help improving mitigation strategies.

Nitrogen deposition and its impact on forest ecosystems in the Czech Republic - change in soil chemistry and ground vegetation

Abstract: A repeated soil survey (1995 and 2006) on 66 ICP Forests pair plots in the Czech Republic revealed a significant relationship between modeled nitrogen deposition and nitrogen concentration in the soil. Nitrogen deposition was modeled for the years 1995, 2004 and 2006. We found a more significant relationship between deposition data in 2004 and soil data in 2006 than between deposition and soil data from the same year 2006. Concentration of total nitrogen in forest soil increased from 1995 to 2006. Forest soil showed effects of increased nitrogen input from the humus layer to around 20 cm depth of mineral soil. The occurrence and cover of nitrophilous species in the herb layer increased from 1995 to 2006 in 25% of the analyzed plots, which corresponds to the nitrogen increase in forest soil. The results suggest that nitrogen deposition still represents a threat for Czech forest ecosystems.

Accumulation of soil organic carbon after cropland conversion to short‐rotation willow and poplar

AbstractThe demand for bioenergy has increased the interest in short‐rotation woody crops (SRWCs) in temperate zones. With increased litter input and ceased annual soil cultivation, SRWC plantations may become soil carbon sinks for climate change mitigation. A chronosequence of 26 paired plots was used to study the potential for increasing soil organic carbon (SOC) under SRWC willow and poplar after conversion from cropland (CR) on well‐drained soils. We estimated SOC stocks in SRWC stands and adjacent CR and related the difference to time since conversion, energy crop species, SOC stock of the adjacent CR (proxy for initial SOC of SRWC) and the fine soil percentage (&lt;63 μm) (FS). Soil cores to 40 cm depth were sampled and separated by layers of fixed depths (0–5, 5–10, 10–15, 15–25 and 25–40 cm). Additionally, soils were sampled from soil pits by genetic horizons to 100 cm depth. Comparisons of SOC stocks by equivalent soil masses showed that mean SOC stocks in SRWC were 1.7 times higher than those of CR in the top 5 cm of the soil (P &lt; 0.001). The differences between SRWC and CR remained significant for the plough layer (0–25 cm) by a factor of 1.2 (P = 0.003), while no changes were detectable for the 0–40 cm (P = 0.32), or for the entire 0–100 cm soil layer (P = 0.29). The SOC stock ratio, that is the ratio of SOC stock in SRWC relative to CR, did not change significantly with time since conversion, although there was a tendency to an increase over time for the top 40 cm (P = 0.09). The SOC stock ratio was negatively correlated to SOC in CR and FS percentage, but there was no significant difference between willow and poplar at any depth. Our results suggest that SOC stocks in the plough layer increase after conversion to SRWC.

Influence of vegetation cover and other sources of variability on sediment and runoff response in a burned forest in South Korea

Post-fire field measurements of sediment and run off yield were undertaken in natural rainfall event-basis during five rainy months in Korea on a total of 15 small plots: four replica burned unseeded plots, six replica burned seeded plots, and five replica unburned plots. The main aim was to evaluate the effects of vegetation recovery and spatial distribution patterns on sediment and runoff response between and within the treatment replica erosion plots. Six-years after the wildfire, total sediment and runoff yield in the burned unseeded plots with 20%-30% vegetation cover was still 120.8 and 20.6 times higher than in the unburned treatment plots with 100% ground cover, 8.3 and 6.7 times higher than in the burned seeded plots with 70%-80% vegetation cover, while only 1.6 and 2.0 times higher than in the burned seeded plots with 50%-60% vegetation cover, respectively. The differences in sediment and runoff yield between the treatment plots was proportional to total vegetation cover, distance of bare soil to vegetation cover, magnitude of rainfall characteristics and changes in soil properties, but not slope gradient. Three out of the six within-treatment pairs of two replica plots showed large differences in sediment and runoff yield of up to 6.0 and 4.2 times and mean CV of up to 99.1% and 62.2%, respectively. This was due to differences in the spatial distribution patterns of surface cover features, including aggregation of vegetation and litter covers, the distance of bare soil exposed to vegetation cover closer to the plot sediment collector and micro topographic mounds and sinks between pairs of replica plots. Small differences in sediment and runoff of only 0.9-1.4 folds and mean CV of 8.6%-25% were observed where the within-treatment pairs of replica plots had similar slope, total surface cover components and comparable spatial distribution pattern of vegetation and bare soil exposed surface covers. The results indicated that post-fire hillslopes undergoing effective vegetation recovery have the potential to reduce sediment and runoff production nearer to unburned levels within 6-years after burning while wildfire impacts could last more than 6-years on burned unseeded ridge slopes undergoing slow vegetation recovery.

Discordant response of spider communities to forests disturbed by deer herbivory and changes in prey availability

AbstractDespite the breadth of research on impacts of dense ungulate populations and invasive plants on native vegetation, work involving indirect effects on spider communities is explicitly lacking. Forest spiders depend on palatable insect prey and habitat structure, both of which are affected by herbivory and invasive vegetation. To examine the indirect interactions between spiders and these influential factors, we sampled spider communities, insect prey, and vegetation in paired deer exclusion plots in central Maryland. Spider abundance and richness increased with greater prey density, while increased habitat structure from deer exclusion reduced species richness and the abundance of a dominant web‐building species. Multivariate analyses of spider families also demonstrated the importance of both prey availability and structural complexity to spider community composition. This work identifies the importance of both habitat structure and insect prey in defining the composition, abundance, and richness of forest spider communities. A long history of heavy browsing pressure has resulted in local spider fauna consisting of many species that are able to thrive in low‐growing vegetation and open forest understories. Such changes to vegetative structure from dense deer populations and invasive plants have the potential to affect these important primary predators as well as araneophagic birds and the nutritional dynamics of forest food webs.

Moose directly slow plant regeneration but have limited indirect effects on soil stoichiometry and litter decomposition rates in disturbed maritime boreal forests

Summary Foraging decisions by herbivores are modulated by physiological demands for nutrients and these decisions can influence the biomass, abundance and dynamics of plant species with consequences on key ecosystem processes, such as nutrient cycling and decomposition. Some studies have found that large browser populations can reduce the abundance of nutrient‐rich preferred species, promoting the dominance of nutrient‐poor non‐preferred species. This can have indirect effects on soil nutrient concentrations, soil microbe community composition and above‐ground invertebrates and birds that depend on nutrient‐rich plant species. However, very little research has compared the impact of biotic and abiotic features on nutrient cycling and decomposition in areas of high moose density. We performed a field study to test the generality of moose effects on forest ecosystems observed in iconic study systems such as Isle Royale. Specifically, we used 10 paired moose exclosure and control plots to test the effects of moose on plant community characteristics, litter fall quantity, soil properties and litter decomposition rates in regenerating disturbed forests in Newfoundland, Canada. We found evidence that moose reduce plant height and plant litter biomass, thereby affecting the quantity of carbon, nitrogen and phosphorus available in litter fall with potential indirect effects on soil pH and soil depth. However, we found no evidence that the direct effects of moose lead to indirect effects on soil quality, soil moisture and litter decomposition rates. Disturbance regime and site explained a large portion of the variance in plant community characteristics, litter fall quantity, soil properties and litter decomposition. Our results suggest that while introduced moose in Newfoundland have measurable direct influence on plant regeneration and litter fall biomass, other factors such as disturbance history and climate may be more important predictors of landscape‐scale variation in soil quality and litter decomposition rates. Our study suggests a need for further development of theory to predict the relative contribution of biotic vs. abiotic effects on nutrient cycling in forest ecosystems. A lay summary is available for this article.

Effect of Cassava Mosaic Disease (CMD) on Yield and Profitability of Cassava and Gari Production Enterprises in Sierra Leone

Cassava Mosaic Disease (CMD) seriously affects cassava (Samura et al., 2013; Fargette et al., 1988). There is limited information on tuberous root yield loss and the profitability of growing improved and local varieties infected with the cassava mosaic virus for tuber and gari production in Sierra Leone. The objectives of the study were to determine yield loss associated with cassava mosaic disease and conduct cost benefit analysis (budgets and break-even analysis) on cassava production using two improved varieties (SLICASS 4 and 6) compared against the local susceptible variety Cocoa, for gari production and Cocoa as a poundable enterprises for the boil and eat market. Activity 1 involved the establishment of a yield loss trial using the paired plot technique. Activity 2 assessed productivity of cassava and gari production. Data collected were analysed using the analytical frame work that incorporates the concept of gross margin analysis as describe by Brown (1979). This included cost benefit analysis (CBA), the net social benefit (NSB) or the excess of total benefit over total cost represents the net present value (NPV) and The Internal Rate of Returns (IRR).The yield loss associated with the local variety Cocoa under this system was 4.27 t/ha which is equivalent to 38.92% yield loss resulting from the cassava mosaic disease infection. SLICASS 4 and SLICASS 6 recorded positive returns to production of tubers and gari. The local variety Cocoa enterprises for gari under the same condition recorded a negative returns even in the 6 year. However Cocoa for the boil and eat market had the highest profit level. The implication of this study is that breeding effort should be geared towards high yielding mosaic resistant varieties that are poundable more profitable and suits the cultural and domestic demand of the producers, processors and consumers.

Forest composition and growth in a freshwater forested wetland community across a salinity gradient in South Carolina, USA

Tidal freshwater forested wetlands (TFFW) of the southeastern United States are experiencing increased saltwater intrusion mainly due to sea-level rise. Inter-annual and intra-annual variability in forest productivity along a salinity gradient was studied on established sites. Aboveground net primary productivity (ANPP) of trees was monitored from 2013 to 2015 on three sites within a baldcypress (Taxodium distichum) swamp forest ecosystem in Strawberry Swamp on Hobcaw Barony, Georgetown County, South Carolina. Paired plots (20×25-m) were established along a water salinity gradient (0.8, 2.6, 4.6PSU). Salinity was continuously monitored, litterfall was measured monthly, and growth of overstory trees ⩾10cm diameter at breast height (DBH) was monitored on an annual basis. Annual litterfall and stem wood growth were summed to estimate ANPP. The DBH of live and dead individuals of understory shrubs were measured to calculate density, basal area (BA), and important values (IV). Freshwater forest communities clearly differed in composition, structure, tree size, BA, and productivity across the salinity gradient. The higher salinity plots had decreased numbers of tree species, density, and BA. Higher salinity reduced average ANPP. The dominant tree species and their relative densities did not change along the salinity gradient, but the dominance of the primary tree species differed with increasing salinity. Baldcypress was the predominant tree species with highest density, DBH, BA, IV, and contribution to total ANPP on all sites. Mean growth rate of baldcypress trees decreased with increasing salinity, but exhibited the greatest growth among all tree species. While the overall number of shrub species decreased with increasing salinity, wax myrtle (Morella cerifera) density, DBH, BA, and IV increased with salinity. With rising sea level and increasing salinity levels, low regeneration of baldcypress, and the invasion of wax myrtle, typical successional patterns in TFFW and forest health are likely to change in the future.

A woody plant community and tree-cacti associations change with distance to a water source in a dry Chaco forest of Argentina

In semiarid regions, livestock is concentrated around water sources generating a piosphere pattern (gradients of woody vegetation degradation with increasing proximity to water). Close to the water source, livestock may affect the composition, structure and regeneration strategies of woody vegetation. We used the proximity from a water source as a proxy of grazing pressure. Our objectives were (1) to compare woody vegetation attributes (richness, diversity, species composition, density and basal area) and ground cover between sites at two distances to a water source: near (higher grazing pressure) and far from the water source (lower grazing pressure), and (2) to quantify and compare cases of spatial association among the columnar cacti Stetsonia coryne (Salm-Dyck) Britton and Rose (Cactaceae), and the dominant tree Bulnesia sarmientoi Lorentz ex Griseb. (Zygophyllaceae). We used a paired design with eight pairs of rectangular plots distributed along a large and representative natural water source. We found lower total species richness, plant density and soil cover near than far from water source, and more cases of spatial associations between the two species studied. Our results show evidence of increased livestock impacts around water sources. However, we found no difference in terms of species composition or basal area at near versus far sites. We conclude that grazing pressure might be changing some attributes of the woody plant community, and that the association of young trees with thorny plants (grazing refuge) could be a regeneration mechanism in this semiarid forest with high grazing pressure.