Temporal Variability Of Productivity Research Articles

Effects of Soil Moisture and Atmospheric Vapor Pressure Deficit on the Temporal Variability of Productivity in Eurasian Grasslands

Effects of Soil Moisture and Atmospheric Vapor Pressure Deficit on the Temporal Variability of Productivity in Eurasian Grasslands

Environmental heterogeneity modulates the effect of plant diversity on the spatial variability of grassland biomass

Plant productivity varies due to environmental heterogeneity, and theory suggests that plant diversity can reduce this variation. While there is strong evidence of diversity effects on temporal variability of productivity, whether this mechanism extends to variability across space remains elusive. Here we determine the relationship between plant diversity and spatial variability of productivity in 83 grasslands, and quantify the effect of experimentally increased spatial heterogeneity in environmental conditions on this relationship. We found that communities with higher plant species richness (alpha and gamma diversity) have lower spatial variability of productivity as reduced abundance of some species can be compensated for by increased abundance of other species. In contrast, high species dissimilarity among local communities (beta diversity) is positively associated with spatial variability of productivity, suggesting that changes in species composition can scale up to affect productivity. Experimentally increased spatial environmental heterogeneity weakens the effect of plant alpha and gamma diversity, and reveals that beta diversity can simultaneously decrease and increase spatial variability of productivity. Our findings unveil the generality of the diversity-stability theory across space, and suggest that reduced local diversity and biotic homogenization can affect the spatial reliability of key ecosystem functions.

Sustainable Food Supply by Peri-Urban Diversified Farms of the Agri-Food Region of Central Córdoba, Argentina

Peri-urban vegetable cropping areas, such as horticultural farms, provide several ecosystem services, such as the provision of fresh food. However, food supply must be estimated on the basis of the current and potential demand of future populations, taking into account the landscape carrying capacity towards sustainable agricultural planning. From this perspective, the study aimed at estimating the resilience of the “Agri-food Region of Central Córdoba” (ARCC) and its role in supporting the provisioning of ecosystem services, such as proximal services, provided by the diversified agricultural landscape in the peri-urban area of Córdoba (Argentina). A direct field survey has been carried out to collect data on the main species and types of crops, the annual productivity, and the area covered by each species and type of horticultural crops. The data have been statistically elaborated to test the spatial and temporal variability of productivity as well as the spatial autocorrelation. In relation to crop diversification, a total of 30 vegetable species have been recorded in the diversified farms under study, with 15 species identified as the most frequent crops as on the basis of the area dedicated to each vegetable species sampled in the farms (in %). The productivity of 30 species has been integrated into a single value of “vegetable crop productivity mean” (kg/m2), proposed and measured in this study, which has been 3.46 kg/m2. It can be a useful monitoring indicator in diversified production contexts. The estimated food supply (ton/year) of vegetable crops for the 170 farmlands has been 72,881 ton/year. An accurate measurement of the biomass harvested on a given surface area can be useful to assign productivity data to the pixel of each land use/cover class, providing accurate input data for remotely sensed-based models supporting decision-making on food provision in peri-urban systems. In this sense, the paper proposes a methodological framework that can be useful worldwide when up-to-date official productivity data are not available, but they are a necessary basis for planning, decision-making, and the implementation of public policies. Thus, diversity in farming systems can combine high ecological and socio-economic benefits, in terms of ecosystem service provision and sustainable food production.

Diel Measurements of Oxygen‐ and Carbon‐Based Ocean Metabolism Across a Trophic Gradient in the North Pacific

AbstractDaily in situ rates of gross production and community respiration estimated from high‐frequency diel cycles in oxygen (O2) and optically derived particulate carbon from several platforms (both ship based and via profiling floats) were made across an ecological gradient in the North Pacific spanning the high‐nutrient/low‐chlorophyll sub‐Arctic to the oligotrophic subtropical gyre. Both oxygen and carbon‐based gross primary production and respiration rates indicated a ~3× increase between subtropical and subpolar stations. We consistently found that gross production and community respiration rates were in approximate balance at all stations across the full ecological gradient, implying that community respiration is fueled by recently produced organic matter and that recycling efficiency (~90%) is similar along the gradient. We determined that phytoplankton turnover time doubles (from 2 to 4 days) between subtropical and subpolar regimes, whereas biomass increases by approximately tenfold. We found a consistent photosynthetic quotient (1.4 ± 0.2 mol O2 mol C−1), respiratory quotient (1.0 ± 0.2 mol O2 mol C−1), and gross to net production ratio (2.0 ± 0.3) at all stations which underscores the similarity of fundamental ecological characteristics despite the transition f rom nutrient deplete to replete conditions. That the float‐ and ship‐based estimates of in situ production and respiration generally agreed well suggests that float‐based diel O2 and particulate organic carbon measurements have the potential to greatly expand our knowledge of spatial and temporal variability of productivity and respiration in the ocean.

Temporal variability in production is not consistently affected by global change drivers across herbaceous-dominated ecosystems.

Understanding how global change drivers (GCDs) affect aboveground net primary production (ANPP) through time is essential to predicting the reliability and maintenance of ecosystem function and services in the future. While GCDs, such as drought, warming and elevated nutrients, are known to affect mean ANPP, less is known about how they affect inter-annual variability in ANPP. We examined 27 global change experiments located in 11 different herbaceous ecosystems that varied in both abiotic and biotic conditions, to investigate changes in the mean and temporal variability of ANPP (measured as the coefficient of variation) in response to different GCD manipulations, including resource additions, warming, and irrigation. From this comprehensive data synthesis, we found that GCD treatments increased mean ANPP. However, GCD manipulations both increased and decreased temporal variability of ANPP (24% of comparisons), with no net effect overall. These inconsistent effects on temporal variation in ANPP can, in part, be attributed to site characteristics, such as mean annual precipitation and temperature as well as plant community evenness. For example, decreases in temporal variability in ANPP with the GCD treatments occurred in wetter and warmer sites with lower plant community evenness. Further, the addition of several nutrients simultaneously increased the sensitivity of ANPP to interannual variation in precipitation. Based on this analysis, we expect that GCDs will likely affect the magnitude more than the reliability over time of ecosystem production in the future.

Spatially-explicit footprints of agricultural commodities: Mapping carbon emissions embodied in Brazil's soy exports

Reliable estimates of carbon and other environmental footprints of agricultural commodities require capturing a large diversity of conditions along global supply chains. Life Cycle Assessment (LCA) faces limitations when it comes to addressing spatial and temporal variability in production, transportation and manufacturing systems. We present a bottom-up approach for quantifying the greenhouse gas (GHG) emissions embedded in the production and trade of agricultural products with a high spatial resolution, by means of the integration of LCA principles with enhanced physical trade flow analysis. Our approach estimates the carbon footprint (as tonnes of carbon dioxide equivalents per tonne of product) of Brazilian soy exports over the period 2010–2015 based on ~90,000 individual traded flows of beans, oil and protein cake identified from the municipality of origin through international markets. Soy is the most traded agricultural commodity in the world and the main agricultural export crop in Brazil, where it is associated with significant environmental impacts. We detect an extremely large spatial variability in carbon emissions across sourcing areas, countries of import, and sub-stages throughout the supply chain. The largest carbon footprints are associated with municipalities across the MATOPIBA states and Pará, where soy is directly linked to natural vegetation loss. Importing soy from the aforementioned states entailed up to six times greater emissions per unit of product than the Brazilian average (0.69 t t−1). The European Union (EU) had the largest carbon footprint (0.77 t t−1) due to a larger share of emissions from embodied deforestation than for instance in China (0.67 t t−1), the largest soy importer. Total GHG emissions from Brazilian soy exports in 2010–2015 are estimated at 223.46 Mt, of which more than half were imported by China although the EU imported greater emissions from deforestation in absolute terms. Our approach contributes data for enhanced environmental stewardship across supply chains at the local, regional, national and international scales, while informing the debate on global responsibility for the impacts of agricultural production and trade.

Primary productivity connects hilsa fishery in the Bay of Bengal

Tropical hilsa shad (Tenualosa ilisha) contributes significantly to the society and economy of Bangladesh, India and Myanmar, but little is known about their habitats across the life cycle and their relationship with environmental drivers. This study describes spatial and temporal variability of productivity in the Bay of Bengal (BoB) relating to hilsa fishery. Decadal data on net primary productivity, nutrients (i.e. nitrate, phosphate and silicate) and zooplankton were collected from Aqua MODIS, world ocean database and COPEPOD respectively with spatial resolution 1°×1°. Moreover, monthly abundance of phytoplankton, hilsa catch and long-term catch dynamics were analyzed to determine the associations between variables. The present study was extended over 3.568 million km2 area, of which 0.131–0.213 million km2 area characterized as the most productive with net primary production of >2,000 mg C/m2/day, 0.373–0.861 million km2 area as moderately productive with 500–2,000 mg C/m2/day, and 2.517–3.040 million km2 area as the least productive with <500 mg C/m2/day which were consistent with field verification data. In case of nutrients, the Ganges-Brahmaputra-Meghna (GBM) delta was rich in nitrate and phosphate than that of the Ayeyarwady delta, while silicate concentration persisted high all over the northern BoB including the deltas. A peak abundance of phytoplankton was observed in GBM delta during the months of August-November, when ~80% of total hilsa are harvested in Bangladesh annually. Variations in seasonal productivity linked with nutrients and phytoplankton abundance are important factors for predicting hilsa habitat and their migration patterns in the deltaic regions and shelf waters of BoB. These results can be useful in forecasting potential responses of the hilsa in BoB ecosystem to changing global ocean productivity.

Testing for changes in biomass dynamics in large-scale forest datasets.

Tropical forest responses to climate and atmospheric change are critical to the future of the global carbon budget. Recent studies have reported increases in estimated above-ground biomass (EAGB) stocks, productivity, and mortality in old-growth tropical forests. These increases could reflect a shift in forest functioning due to global change and/or long-lasting recovery from past disturbance. We introduce a novel approach to disentangle the relative contributions of these mechanisms by decomposing changes in whole-plot biomass fluxes into contributions from changes in the distribution of gap-successional stages and changes in fluxes for a given stage. Using 30years of forest dynamic data at Barro Colorado Island, Panama, we investigated temporal variation in EAGB fluxes as a function of initial EAGB (EAGBi ) in 10×10m quadrats. Productivity and mortality fluxes both increased strongly with initial quadrat EAGB. The distribution of EAGB (and thus EAGBi ) across quadrats hardly varied over 30years (and seven censuses). EAGB fluxes as a function of EAGBi varied largely and significantly among census intervals, with notably higher productivity in 1985-1990 associated with recovery from the 1982-1983 El Niño event. Variation in whole-plot fluxes among census intervals was explained overwhelmingly by variation in fluxes as a function of EAGBi , with essentially no contribution from changes in EAGBi distributions. The high observed temporal variation in productivity and mortality suggests that this forest is very sensitive to climate variability. There was no consistent long-term trend in productivity, mortality, or biomass in this forest over 30years, although the temporal variability in productivity and mortality was so strong that it could well mask a substantial trend. Accurate prediction of future tropical forest carbon budgets will require accounting for disturbance-recovery dynamics and understanding temporal variability in productivity and mortality.

Differential resistance and resilience of functional groups to livestock grazing maintain ecosystem stability in an alpine steppe on the Qinghai-Tibetan Plateau

Ecosystem stability is one of the main factors maintaining ecosystem functioning and is closely related to temporal variability in productivity. Resistance and resilience reflect tolerance and recovering ability, respectively, of a plant community under perturbation, which are important for maintaining the stability of ecosystems. Generally, heavy grazing reduces the stability of grassland ecosystems, causing grassland degradation. However, how livestock grazing affects ecosystem stability is unclear in alpine steppe ecosystems. We conducted a five-year grazing experiment with Tibetan sheep in a semi-arid alpine steppe on the Qinghai-Tibetan Plateau, China. The experimental treatments included no grazing (NG), light grazing (LG, 2.4 sheep per ha), moderate grazing (MG, 3.6 sheep per ha) and heavy grazing (HG, 6.0 sheep ha). We calculated resistance and resilience of three plant functional groups and ecosystem stability under the three grazing intensities using aboveground primary productivity. The results showed that with increasing grazing intensity, aboveground biomass of each functional group significantly decreased. As grazing intensity increased, the resistance of forbs first increased then decreased. The resilience of graminoids in HG was significantly lower than in LG plots, but the resilience of legumes in HG was higher than in LG and MG plots. The resilience of graminoids was significantly higher than legume and forbs under LG and MG treatments. In HG treatments, resilience of legumes was higher than graminoids and forbs. Ecosystem stability did not change under different grazing intensities, because of dissimilar performance of the resilience and resistance of functional groups. Our results highlight how the differential resistance and resilience of different function groups facilitate the tolerance of alpine steppe to grazing under even a heavy intensity. However, the degradation risk of alpine steppe under heavy grazing still needs to be considered in grassland management due to sharp decreases of productivity.

Differing Responses to Rainfall Suggest More Than One Functional Type of Grassland in South Africa

Grasslands, which represent around 40% of the terrestrial area, are mostly located in arid and semi-arid zones. Semiarid ecosystems in Africa have been identified as being particularly vulnerable to the impacts of increased human pressure on land, as well as enhanced climate variability. Grasslands are indeed very responsive to variations in precipitation. This study evaluates the sensitivity of the grassland ecosystem to precipitation variability in space and time, by identifying the factors controlling this response, based on monthly precipitation data from Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) and the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) data from the Multi-angle Imaging SpectroRadiometer-High Resolution (MISR-HR) datasets, used as proxy for productivity, at 60 grassland sites in South Africa. Our results show that MISR-HR products adequately capture the spatial and temporal variability in productivity at scales that are relevant to this study, and they are therefore a good tool to study climate change impacts on ecosystem at small spatial scales over large spatial and temporal domains. We show that combining several determinants and accounting for legacies improves our ability to understand patterns, identify areas of vulnerability, and predict the future of grassland productivity. Mean annual precipitation is a good predictor of mean grassland productivity. The grasslands with a mean annual rainfall above about 530 mm have a different functional response to those receiving less than that amount of rain, on average. On the more arid and less fertile soils, large inter-annual variability reduces productivity. Our study suggests that grasslands on the more marginal soils are the most vulnerable to climate change.

Productivity influences trophic structure in a temporally forced aquatic ecosystem

Abstract Previous studies on the relationship between ecosystem productivity, size and food‐chain length have been restricted to comparisons between locations. We examined the effect of temporal variability in productivity on trophic structure of a floodplain ecosystem, hypothesising that during the wet‐flood pulses, the increased resource availability might lead to higher food‐chain lengths. We examined multiple common sampling locations and species during a severe El Niño drought which followed a consecutive series of historically wet La Niña years, comparing trophic position and dietary sources. While carbon stable isotopes showed no significant difference between the two phases, nitrogen stable isotopes indicated that most species were feeding higher in the food chain in the wet phase. The results suggest that oscillations in climate phase‐driven changes have effects on food‐chain lengths through changes in productivity, without the introduction of new sources of carbon or changes to the composition of higher‐order predators.

Global Spatial–Temporal Variability in Terrestrial Productivity and Phenology Regimes between 2000 and 2012

The productivity and phenology of vegetation are spatially and temporally variable ecosystem functions. Monitoring spatial–temporal patterns in these functions can improve our understanding of global change and natural ecosystem variability and inform management actions. Researchers typically focus on temporal changes within or among static regions and omit dynamics of spatial configuration. Our goal was to assess global spatial–temporal variability in productivity and phenology regimes between 2000 and 2012 using a temporally dynamic functional type classification. Fourteen functional types were defined for each year by clustering the annual sum and annual variability (seasonality) of the fraction of photosynthetically active radiation (fPAR)—a biophysical proxy for vegetation greenness or productivity—from the Moderate Resolution Imaging Spectrometer (MODIS). The fourteen functional types ranged from tundra (low cumulative fPAR and highly seasonal) to tropical forests (high cumulative fPAR and low seasonality). Variability in the mean of the fPAR metrics and in two spatial pattern metrics was assessed for each functional type. Many pixels changed from one cluster to another then back again, suggesting considerable short-term variability. Temporal variability in the mean of the fPAR metrics was relatively low, with changes instead primarily manifested in spatial pattern. Spatial pattern was most variable within tundra, grasslands, shrublands, and savannas. A dynamic classification demonstrated the variability in spatial patterns of primary productivity and can be used for future monitoring.

Estimating methane gas production in peat soils of the Florida Everglades using hydrogeophysical methods

AbstractThe spatial and temporal variability in production and release of greenhouse gases (such as methane) in peat soils remains uncertain, particularly for low‐latitude peatlands like the Everglades. Ground penetrating radar (GPR) is a hydrogeophysical tool that has been successfully used in the last decade to noninvasively investigate carbon dynamics in peat soils; however, application in subtropical systems is almost non‐existent. This study is based on four field sites in the Florida Everglades, where changes in gas content within the soil are monitored using time‐lapse GPR measurements and gas releases are monitored using gas traps. A weekly methane gas production rate is estimated using a mass balance approach, considering gas content estimated from GPR, gas release from gas traps and incorporating rates of diffusion, and methanotrophic consumption from previous studies. Resulting production rates range between 0.02 and 0.47 g CH4 m−2 d−1, falling within the range reported in literature. This study shows the potential of combining GPR with gas traps to monitor gas dynamics in peat soils of the Everglades and estimate methane gas production. We also show the enhanced ability of certain peat soils to store gas when compared to others, suggesting that physical properties control biogenic gas storage in the Everglades peat soils. Better understanding biogenic methane gas dynamics in peat soils has implications regarding the role of wetlands in the global carbon cycle, particularly under a climate change scenario.

Effects of crop residue management on winter durum wheat productivity in a long term experiment in Southern Italy

A long-term experiment comparing different crop residue (CR) managements was established in 1977 in Foggia (Apulia region, southern Italy). The objective of this study was to investigate the long-term effects of different types of crop residue management on main yield response parameters in a continuous cropping system of winter durum wheat. In order to correctly interpret the results, models accounting for spatial error autocorrelation were used and compared with ordinary least square models. Eight crop residue management treatments, based on burning of wheat straw and stubble or their incorporation with or without N fertilization and irrigation, were compared. The experimental design was a complete randomized block with five replicates. Results indicated that the dynamics of yield, grain protein content and hectolitric weight of winter durum wheat did not show any decline as usually expected when a monoculture is carried out for a long time. In addition, the temporal variability of productivity was more affected by meteorological factors, such as air temperature and rainfall, than CR management treatments. Higher wheat grain yields and hectolitric weights quite frequently occurred after burning of wheat straw compared with straw incorporation without nitrogen fertilization and autumn irrigation and this was attributed to temporary mineral N immobilization in the soil. The rate of 50 kg ha−1 of N seemed to counterbalance this negative effect when good condition of soil moisture occurred in the autumn period, so yielding the same productive level of straw burning treatment.

Differences in Late Quaternary primary productivity between the western tropical Pacific and the South China Sea: Evidence from coccoliths

Changes in Late Quaternary oceanic primary productivity in the western tropical Pacific were reconstructed using coccolith counts from the improved SYRACO system in piston core MD01-2386 retrieved from the Halmahera Sea near northwest New Guinea. The calculated primary productivity exhibits cycles on obliquity and precession timescales over the last 192ka. There are marked differences between primary productivity records from the western tropical Pacific and the South China Sea (SCS), with the former being dominated by precession, and the latter showing all three Milankovitch cycles (eccentricity, obliquity and precession). Empirical Orthogonal Function (EOF) analyses reveal two significant EOF modes in the western tropical Pacific and SCS records. EOF-1 accounts for 38% of the total variance and exhibits obvious precessional cycles corresponding to Northern Hemisphere summer insolation, while EOF-2 accounts for 22% of the total variance and exhibits strong 41-kyr periodicity, suggesting different biological responses to hydroclimate changes in the two regions. A more complex hydroclimate regime influenced by the East Asian monsoon and the large contrast in regional topography and circulation during glacial cycles are considered to be the primary drivers of the stronger temporal variability in productivity in the SCS compared to the relatively stable western tropical Pacific.

Spatial and temporal aspects of grain accumulation costs for ethanol production: An Australian case study

Ethanol production is increasingly commonplace in many grain-producing regions. This paper uses the grain-producing region of south-western Australia to illustrate spatial and temporal aspects of grain accumulation costs for ethanol production. Specifically, this study examines how price variability of various wheat grades, combined with spatial and temporal variability in production of those grades, affects the costs of grain accumulation. These costs are the main components of an ethanol plant's operating costs so lessening these costs can offer a comparative advantage for a plant owner. Logistics models based on mathematical programming are constructed for a range of plant sizes and locations for ethanol production. Modelling results identify low-cost sites that generate cost savings, in present value terms, of between 5 and 7.5 per cent, depending on plant size, over the 9-year study period. At all locations, small to medium-sized plants offer advantages of lower and less variable costs of grain accumulation. Yet, all locations and all plant sizes are characterised by marked volatility in the cost of grain accumulation. The profitability of ethanol production based on wheat in this region of Australia is particularly exposed to any prolonged period of high grain prices relative to petroleum prices, given current biofuel-policy settings in Australia.

Diversity, productivity and temporal stability in the economies of humans and nature

Recent advances in ecology are of great potential relevance to economists. Here we present two ecological models of mechanisms of competition and coexistence, and use these to derive how the primary productivity of ecosystems, the amount of carbon dioxide removed from the atmosphere and stored by plants, the efficiency of resource use, and the spatial and temporal variability of productivity and resource use should depend on diversity. We then discuss the relevance of these results to (1) ecosystem services and the economic value of diversity and (2) the functioning of any competitive system, including the economy.

Metabolic rate and environmental productivity: well-provisioned animals evolved to run and idle fast.

Even among vertebrate species of the same body mass and higher-level taxonomic group, metabolic rates exhibit substantial differences, for which diverse explanatory factors-such as dietary energy content, latitude, altitude, temperature, and rainfall-have been postulated. A unifying underlying factor could be food availability, in turn controlled by net primary productivity (NPP) of the animal's natural environment. We tested this possibility by studying five North American species of Peromyscus mice, all of them similar in diet (generalist omnivores) and in gut morphology but differing by factors of up to 13 in NPP of their habitat of origin. We maintained breeding colonies of all five species in the laboratory under identical conditions and consuming identical diets. Basal metabolic rate (BMR) and daily ad libitum food intake both increased with NPP, which explained 88% and 90% of their variances, respectively. High-metabolism mouse species from high-NPP environments were behaviorally more active than were low-metabolism species from low-NPP environments. Intestinal glucose uptake capacity also increased with NPP (and with BMR and food intake), because species of high-NPP environments had larger small intestines and higher uptake rates. For metabolic rates of our five species, the driving environmental variable is environmental productivity itself (and hence food availability), rather than temporal variability of productivity. Thus, species that have evolved in the presence of abundant food run their metabolism "fast," both while active and while idling, as compared with species of less productive environments, even when all species are given access to unlimited food.

Molecular characterisation of organic matter in sediments underlying the oxygen minimum zone at the Oman Margin, Arabian Sea

Lipids in replicate sediment cores collected from a transect through the oxygen minimum zone across the Oman Margin continental slope (∼400, 800, 1000 and 1250 m), have been analysed in order to assess the relative contributions of primary and secondary producer-derived material to the sediments. The high abundance of compounds that can be ascribed to primary producers, namely diatoms, dinoflagellates, coccolithophores, Eustigmatophycae and cyanobacteria, reflects the high productivity of surface waters, but there is little direct molecular evidence of zooplankton reworking of organic material, except at the deepest water site (∼1250 m). There is, however, clear evidence of benthic re-working, probably by detritovore megafauna, at one of the sites near the base of the oxygen minimum zone (∼1000 m). The relative abundance of biological markers that can be ascribed to aerobic and anaerobic bacteria in the sediments, namely the hopanoids and branched fatty acids, respectively, mirrors the concentrations of oxygen in overlying water. Considerable intra- and inter-site variability probably results from the spatial and temporal variability in production and from the complexity of sedimentation processes.