Years Of Low Precipitation Research Articles

Assessing recent declines in Upper Rio Grande runoff efficiency from a paleoclimate perspective

AbstractRecent decades have seen strong trends in hydroclimate over the American Southwest, with major river basins such as the Rio Grande exhibiting intermittent drought and declining runoff efficiencies. The extent to which these observed trends are exceptional has implications for current water management and seasonal streamflow forecasting practices. We present a new reconstruction of runoff ratio for the Upper Rio Grande basin back to 1571 C.E., which provides evidence that the declining trend in runoff ratio from the 1980s to present day is unprecedented in context of the last 445 years. Though runoff ratio is found to vary primarily in proportion to precipitation, the reconstructions suggest a secondary influence of temperature. In years of low precipitation, very low runoff ratios are made 2.5–3 times more likely by high temperatures. This temperature sensitivity appears to have strengthened in recent decades, implying future water management vulnerability should recent warming trends in the region continue.

Interacting effects of climate and landscape physiography on piñon pine growth using an individual‐based approach

AbstractForest and woodland ecosystems play a crucial role in the global carbon cycle and may be strongly affected by changing climate. Here, we use an individual‐based approach to model piñon pine (Pinus edulis) radial growth responses to climate across gradients of environmental stress. We sampled piñon pine trees at 24 sites across southwestern Colorado that varied in soil available water capacity (AWC), elevation, and latitude, obtaining a total of 552 piñon pine tree ring series. We used linear mixed‐effect models to assess piñon pine growth responses to climate and site‐level environmental stress (30‐year mean cumulative climatic water deficit [CWD] and soil AWC). Using a similar modeling approach, we also determined long‐term growth trends across our gradients of environmental stress. Piñon pine growth was strongly positively associated with winter precipitation. Summer vapor pressure deficit (VPD) was strongly negatively associated with piñon pine growth during years of low winter precipitation, whereas summer VPD had no effect on piñon pine growth during years of high winter precipitation. The strength of the relationship between the annual climatic variables (winter precipitation and summer VPD) and piñon pine growth was also influenced by site‐level environmental stress, suggesting that the sensitivity of woodland ecosystems to changing climate will vary across the landscape due to differences in local physiographic conditions. Trees at sites with lower CWDs were more responsive to summer VPD, showing greater reductions in growth rates during warmer years. Trees at sites with greater soil AWC were more responsive to winter precipitation, showing higher growth rates during years of high precipitation. Piñon pine growth rates declined moderately over the past century across our study area, suggesting that recent increases in aridity have resulted in long‐term growth declines.

Understanding Dominant Factors for Precipitation over the Great Lakes Region

Statistical modeling of local precipitation involves understanding local, regional and global factors informative of precipitation variability in a region. Modern machine learning methods for feature selection can potentially be explored for identifying statistically significant features from pool of potential predictors of precipitation. In this work, we consider sparse regression, which simultaneously performs feature selection and regression, followed by random permutation tests for selecting dominant factors. We consider average winter precipitation over Great Lakes Region in order to identify its dominant influencing factors.Experiments show that global climate indices, computed at different temporal lags, offer predictive information for winter precipitation. Further, among the dominant factors identified using randomized permutation tests, multiple climate indices indicate the influence of geopotential height patterns on winter precipitation.Using composite analysis, we illustrate that certain patterns are indeed typical in high and low precipitation years, and offer plausible scientific reasons for variations in precipitation.Thus, feature selection methods can be useful in identifying influential climate processes and variables, and thereby provide useful hypotheses over physical mechanisms affecting local precipitation.

Thirty years of vegetation change in the coastal Santa Cruz Mountains of Northern California detected using landsat satellite image analysis

The Santa Cruz Mountains is a coastal landscape with a history of extensive forest logging, and a future with projected climate warming that may alter vegetation cover and surface water runoff in new ways. Results from Landsat satellite image time-series analysis since 1983 of this study area showed gradual, statistically significant increases in the normalized difference vegetation index (NDVI) in more than 90 % of the (predominantly second-growth) evergreen forest locations sampled. The cumulative distribution of NDVI values in 2013 was significantly different and higher overall from the cumulative distribution of NDVI values in 1983. The extreme drought year of 2013 (and other previous years of low precipitation) did not affect average NDVI growth rates in most drainage basins of the study area, with the exception of four relatively small basins that had less than 30 % forested land cover. Notably different patterns of NDVI change were detected in areas burned by wildfires in recent years. Within the perimeters of the 2008 Summit Fire and the 2009 Lockheed Fire, NDVI showed notable declines from pre-fire levels to those calculated in 2013 Landsat imagery. In contrast to these recent fires, the burned area from the 1985 Lexington Fire showed the highest rate of NDVI increase (over 27 years of regrowth) of any relatively large contiguous area within the Santa Cruz Mountains.

Anthropogenic warming has increased drought risk in California

California is currently in the midst of a record-setting drought. The drought began in 2012 and now includes the lowest calendar-year and 12-mo precipitation, the highest annual temperature, and the most extreme drought indicators on record. The extremely warm and dry conditions have led to acute water shortages, groundwater overdraft, critically low streamflow, and enhanced wildfire risk. Analyzing historical climate observations from California, we find that precipitation deficits in California were more than twice as likely to yield drought years if they occurred when conditions were warm. We find that although there has not been a substantial change in the probability of either negative or moderately negative precipitation anomalies in recent decades, the occurrence of drought years has been greater in the past two decades than in the preceding century. In addition, the probability that precipitation deficits co-occur with warm conditions and the probability that precipitation deficits produce drought have both increased. Climate model experiments with and without anthropogenic forcings reveal that human activities have increased the probability that dry precipitation years are also warm. Further, a large ensemble of climate model realizations reveals that additional global warming over the next few decades is very likely to create ∼ 100% probability that any annual-scale dry period is also extremely warm. We therefore conclude that anthropogenic warming is increasing the probability of co-occurring warm-dry conditions like those that have created the acute human and ecosystem impacts associated with the "exceptional" 2012-2014 drought in California.

Water balance along a chain of tundra lakes: A 20-year isotopic perspective

Summary Stable isotope measurements and isotope mass balance (IMB) calculations are presented in support of an unprecedented 20-year water balance assessment for a tailings pond and a chain of downstream lakes at the Salmita–Tundra mine site, situated near Courageous Lake, Northwest Territories, Canada (65°03′N; 111°11′W). The method is shown to provide a comprehensive annual and interannual perspective of water balance fluxes along a chain of lakes during the period 1991–2010, without the need for continuous streamflow gauging, and reveals important lake-order-dependent patterns of land-surface runoff, discharge accumulation, and several key diagnostic ratios, i.e., evaporation/inflow, evaporation/evapotranspiration, land-surface-runoff/precipitation and discharge/ precipitation. Lake evaporation is found to be a significant component of the water balance, accounting for between 26% and 32% of inflow to natural lakes and between 72% and 100% of inflow to mine-tailings ponds. Evaporation/evapotranspiration averages between 7% and 22% and is found to be higher in low-precipitation years, and in watersheds with a higher proportion of lakes. Runoff ratios for land-surface drainages and runoff ratios for watersheds (including lakes) ranged between 14–47% and 20–47%, respectively, and were higher in low precipitation years, in watersheds with a higher proportion of lakes, and in watersheds less affected by mining development. We propose that in general these two runoff ratios will likely converge as lake order increases and as land cover conditions become regionally representative. Notably, the study demonstrates application of IMB, validated with streamflow measurements, to constrain local water balance in a remote low-arctic region. For IMB chain-of-lakes applications, it underlines the importance of accounting for evaporatively-enriched upstream sources to avoid overestimation of evaporation losses.

Effects of low precipitation periods on the herbage yield of mesic semi-natural grasslands under different cutting regimes

Climatic changes have led to extreme weather events, with longer dry periods affecting forage production in mesic grasslands. The effects of grassland management and years with periods of low precipitation on herbage dry matter (DM) yield were studied in two-long term grassland experiments with different cutting and fertilization regimes for the period 2000–2012. In both experiments, the annual herbage DM yields had high correlations with the amount of precipitation. The correlation was stronger in frequent cuttings regimes. The management type and the year significantly affected the herbage DM yield in both experiments. There was also a significant management × year interaction. On average, over the whole observation period, the herbage DM yield of equally fertilized treatments in experiment I was higher in treatments with two cuts per season than in treatments with more cuts. Furthermore, longer periods of low precipitation exerted fewer effects on the DM yield of the two cuts treatments compared to higher cutting frequencies. However, the increase in herbage productivity in years following seasons with low precipitation was higher in the treatments with higher cutting frequencies than in those with two cuts per season. When the treatment, cut four times per year, received a higher amount of fertilizer than the treatment, cut twice per year (experiment II), the long-term average annual herbage DM yield was higher and the yield was less decreased by longer periods of low precipitation than the two cuts per year treatment. Despite the fact that the effects of different treatments were proved in both experiments, the differences in the DM yields among the treatments in low precipitation years were not high enough to recommend best-management practices for forage production on mesic grasslands in areas subject to increasing periods of low precipitation.

Regulation of soil moisture dynamics in agricultural fields using strips of native prairie vegetation

There is a growing interest in the use of native prairie vegetation to restore the hydrologic balance in agricultural watersheds. The objectives of this study were to investigate the effects of establishing strips of native prairie vegetation (SNPV) in agricultural fields (CROP) on soil water dynamics and assess the potential value of SNPV as an agricultural conservation practice to regulate soil water dynamics. Soil water storage (SWS) was monitored biweekly at four soil depth intervals (0–30, 30–60, 0–60, 0–100) during the growing seasons of 2007, 2008, 2009 and 2010 at the Neal Smith National Wildlife Refuge, Prairie City, Iowa. The influence of land cover (SNPV, CROP), topographic position (summit, sideslope footslope), season, and precipitation on SWS was analyzed. Results indicated that SWS was higher under prairie vegetation than CROP the year the SNPV was established (2007), while a reverse pattern was observed for the following three post-treatment years. More pronounced differences among land covers were observed in the first 30cm of soil. Overall, June–July had the highest SWS and August–September the lowest, but the trend varied within years. In 2009 and 2010, years of low and high precipitation, respectively, the differences in SWS among land covers were minimal and no statistical differences were observed. Overall, results indicate that the introduction of SNPV can contribute to the regulation of the water balance in agricultural watersheds by increasing water holding capacity, and hence, reducing runoff during high rainfall events.

No cumulative effect of 10 years of elevated [CO2] on perennial plant biomass components in the Mojave Desert

Elevated atmospheric CO2 concentrations ([CO2 ]) generally increase primary production of terrestrial ecosystems. Production responses to elevated [CO2 ] may be particularly large in deserts, but information on their long-term response is unknown. We evaluated the cumulative effects of elevated [CO2 ] on primary production at the Nevada Desert FACE (free-air carbon dioxide enrichment) Facility. Aboveground and belowground perennial plant biomass was harvested in an intact Mojave Desert ecosystem at the end of a 10-year elevated [CO2 ] experiment. We measured community standing biomass, biomass allocation, canopy cover, leaf area index (LAI), carbon and nitrogen content, and isotopic composition of plant tissues for five to eight dominant species. We provide the first long-term results of elevated [CO2 ] on biomass components of a desert ecosystem and offer information on understudied Mojave Desert species. In contrast to initial expectations, 10 years of elevated [CO2 ] had no significant effect on standing biomass, biomass allocation, canopy cover, and C : N ratios of above- and belowground components. However, elevated [CO2 ] increased short-term responses, including leaf water-use efficiency (WUE) as measured by carbon isotope discrimination and increased plot-level LAI. Standing biomass, biomass allocation, canopy cover, and C : N ratios of above- and belowground pools significantly differed among dominant species, but responses to elevated [CO2 ] did not vary among species, photosynthetic pathway (C3 vs. C4 ), or growth form (drought-deciduous shrub vs. evergreen shrub vs. grass). Thus, even though previous and current results occasionally show increased leaf-level photosynthetic rates, WUE, LAI, and plant growth under elevated [CO2 ] during the 10-year experiment, most responses were in wet years and did not lead to sustained increases in community biomass. We presume that the lack of sustained biomass responses to elevated [CO2 ] is explained by inter-annual differences in water availability. Therefore, the high frequency of low precipitation years may constrain cumulative biomass responses to elevated [CO2 ] in desert environments.

Fire in a sub-humid woodland: The balance of carbon sequestration and habitat conservation

Public lands are often tasked with ecosystem restoration that may include fire as a management tool in order to foster the return of ecosystem composition, structure, or function to a previous state. In some ecosystems, such as woodlands, the role of fire is poorly understood because mixed-fire regimes complicate assessment of landscape level fire return intervals and successional pathways. Management of these public woodlands may be difficult due to the need to accomplish multiple objectives such as carbon (C) sequestration and wildlife conservation on properties with marginal productivity. To assess the role of fire in affecting various ecological processes and offer information for future wildland management decision-making, we measured C storage, vegetation composition, and habitat suitability for an endangered bird species (golden-cheeked warbler, Dendroica chrysoparia) in juniper-oak woodlands with documented past surface fires within Balcones Canyonlands National Wildlife Refuge. We found significantly different total aboveground biomass C with average values of 5.25, 6.86, and 9.18kgm−2 of C for 60 plots grouped into recent (<40year), old (⩾40year), and no fire treatments, respectively. Interpretation of fire for each plot was based on fire scar data derived from a previous tree-ring study for the refuge. We found fire significantly reduced site C primarily due to reduced tree density. We also found increased oak recruitment associated with fires that occurred in low summer precipitation years. Calculated habitat suitability index values for the golden-cheeked warbler did not significantly differ between groups. However, fire may have a dual effect on habitat suitability. While catastrophic wildfire can damage potential habitat and significantly reduce regional carbon storage, our study showed that moderate intensity fires in dense young juniper stands promotes tree species diversity, favorable for future habitat formation. We conclude that fire as a management focus, including use of prescribed burning and fuel treatments to reduce wildfire risk, may be implemented on a single conservation property to achieve multiple expected outcomes. However, this requires detailed ecological information regarding woody species composition and population structure to help assess legacy conditions that influence the interpretation of present woodland conditions and future projections given restoration efforts.

The use of NDVI and its Derivatives for Monitoring Lake Victoria’s Water Level and Drought Conditions

Normalized Difference Vegetation Index (NDVI), which is a measure of vegetation vigour, and lake water levels respond variably to precipitation and its deficiency. For a given lake catchment, NDVI may have the ability to depict localized natural variability in water levels in response to weather patterns. This information may be used to decipher natural from unnatural variations of a given lake’s surface. This study evaluates the potential of using NDVI and its associated derivatives (VCI (vegetation condition index), SVI (standardised vegetation index), AINDVI (annually integrated NDVI), green vegetation function (F g ), and NDVIA (NDVI anomaly)) to depict Lake Victoria’s water levels. Thirty years of monthly mean water levels and a portion of the Global Inventory Modelling and Mapping Studies (GIMMS) AVHRR (Advanced Very High Resolution Radiometer) NDVI datasets were used. Their aggregate data structures and temporal co-variabilities were analysed using GIS/spatial analysis tools. Locally, NDVI was found to be more sensitive to drought (i.e., responded more strongly to reduced precipitation) than to water levels. It showed a good ability to depict water levels one-month in advance, especially in moderate to low precipitation years. SVI and SWL (standardized water levels) used in association with AINDVI and AMWLA (annual mean water levels anomaly) readily identified high precipitation years, which are also when NDVI has a low ability to depict water levels. NDVI also appears to be able to highlight unnatural variations in water levels. We propose an iterative approach for the better use of NDVI, which may be useful in developing an early warning mechanisms for the management of lake Victoria and other Lakes with similar characteristics.

The influence of floods and precipitation on Tamarix establishment in Grand Canyon, Arizona: consequences for flow regime restoration

Decoupling of climate and hydrology combined with introduction of non-native species creates novel abiotic and biotic conditions along highly regulated rivers. Tamarix, a non-native shrub, dominates riparian assemblages along many waterways in the American Southwest, including the Colorado River through Grand Canyon. We conducted a tree-ring study to determine the relative influences of climate and hydrology on Tamarix establishment in Grand Canyon. Riparian vegetation was sparse and annually scoured by large floods until completion of Glen Canyon Dam, which allowed pioneer species, including Tamarix, to expand. Post-dam floods in the mid-1980s were associated with high Tamarix mortality but also initiated a large establishment event. Subsequent establishment has been low but continuous with some exceptions. From 1984 to 2006 establishment increased during years of high, late-summer flows followed by years of low precipitation. This combination provided moist surfaces for Tamarix establishment and may have caused reduced erosion of seedlings or reduced competition from native plants. Attempts to mimic pre-dam floods for ecosystem restoration through planned flood releases also have affected Tamarix establishment. Early (March 1996) and late (November 2004) restoration floods limited establishment, but a small restoration flood in May 2000 followed by steady summer flows permitted widespread establishment. Flood restoration is not expected to prevent Tamarix spread in this system because historic flood timing in May–July coincides with seed release. To decrease future Tamarix establishment, river managers should avoid floods during peak Tamarix seed release, which encompasses the historic spring and early summer flooding period. Tamarix dominance may be reduced by early spring floods that initiate asexual reproduction of clonal shrubs (e.g., Salix exigua, Pluchea sericea).

Carbon isotope variation in shrub willow (Salix spp.) ring-wood as an indicator of long-term water status, growth and survival

Abstract Quantifying interannual change in water status of woody plants using stable carbon isotopes provides insight on long-term plant ecophysiology and potential success in variable environments, including under-utilized agricultural land for biomass production and highly disturbed sites for phytoremediation applications. We analyzed δ 13 C values in annual ring-wood of four shrub willow varieties used for biomass production and phytoremediation at three sites in central New York State (U.S.A). We tested a cost-effective sampling method for estimating whole-shrub water status by comparing δ 13 C values of the plant’s largest stem against a composite sample of all stems. The largest stem showed 0.3‰ 13 C enrichment (range −0.7–1.1‰) compared to the whole-plant, making it a more sensitive indicator of water status than the composite sample. Growing season precipitation exerted a strong negative influence on wood tissue chemistry, with an average 0.26‰ 13 C depletion per 100 mm increase in precipitation. An average annual 0.28‰ 13 C enrichment was also observed with increased plant age; this pattern was consistent among all four willow varieties and across sites. Finally, increased 13 C enrichment in wood tissue was positively associated with plant size at the individual plant level, and associated negatively and more variably survival at the plot scale. These results have important implications for the design and management of biomass production and phytoremediation systems. Increased sensitivity of older plants suggests that longer rotations may experience growth limitations and/or lower survival in low-precipitation years, resulting in reduced yields of biomass crops and loss of effectiveness in phytoremediation applications.

Comment on “Characteristics and trends in various forms of the Palmer Drought Severity Index (PDSI) during 1900–2008” by Aiguo Dai

] Dai [2011] (henceforth D11) reported that the PalmerDrought Severity Index (PDSI) is superior to other statisti-cally based drought indices including the StandardizedPrecipitation Index (SPI) and the Standardized PrecipitationEvapotranspiration Index (SPEI). D11 argued that given thephysical character of the PDSI water balance model, theindex provides robust estimates of drought severity becauseit takes the preceding conditions into account, in contrast toother drought indices that are based purely on past statisticsof particular climate variable(s). However, D11 has over-estimated the ability of the PDSI to realistically simulate thedistributed soil water balance at large spatial scales, andignored the inherent complexity and multiscalar character ofdrought phenomena, which are related to more than themoisture conditions of the soil. In this comment we discussthe complex characteristics of droughts and the limitationsof the PDSI to quantify drought conditions in a variety ofhydrological systems. We describe the advantages of statis-tically based drought indices including the SPI and the SPEI.ThefactthattheSPIandtheSPEIarenot(anddonotintendtobe) physically based indices is more liberating than con-straining, especially when the physical basis of PDSI can beseriously questioned.[

Water use and yields of no-till managed dryland grasspea and yellow pea under different planting configurations

Grasspea (GP) ( Lathyrus sativus) is a drought-tolerant legume that can be grown for forage and grain. It has potential value to be used as a nitrogen-fixing crop in dryland rotations with non-legume grain crops. However, the agronomy of GP for the Central Great Plains region have not been investigated. The objective of this research was to compare the grain and biomass yield, as well as N accumulation of GP relative to field pea (FP) in two planting configurations. We carried out a 3-year field experiment to compare dryland GP with Admiral yellow field pea ( Pisum sativum) in two configurations: (1) a wide row spacing with lower population (WL) with 76-cm rows with 75 kg seeds planted per ha, and (2) a narrower row spacing with a higher population (NH) with 19-cm rows with 136 kg seeds planted per ha. We measured the biomass, grain yield, N content, and soil water use. Our results show that the NH treatment out-yielded the WL treatment in both pea species. The GP had higher yield than FP on the lowest yielding year, while FP yielded better when overall yields were higher. Biomass production was also higher for the NH configuration, and GP was a higher biomass producer than FP over the 3-year study. The GP had higher N concentration in shoots and seed compared to FP, indicating higher N-fixing capacity. The FP matured faster than GP, and had marginally higher grain water use efficiency than GP. Our results show that GP is a viable alternative legume for the Central Great Plains, with comparable yields in low precipitation years. However, the longer growing season required by GP to mature has water use implications in years with reduced water availability in mid to late summer.

Population Demographics and Dynamics of Colonizing Elk in a Desert Grassland–Scrubland

AbstractElk Cervus elaphus are rare in Southwestern desert grassland and desert-scrub habitats, and these habitats are anecdotally considered unsuitable for elk. We studied a colonizing herd in a Southwestern desert grassland–scrubland in northwestern New Mexico to determine the condition and population dynamics of elk in this habitat type. We radiotracked ≤ 24 adult (1.5 y and older) cows and ≤ 8 calves annually, 2003–2006; the sample of radiocollared cows in this study was very close to a census of the entire population for 2004–2006 based on repeated surveys and monitoring. Mean body fat of lactating cows in autumn was 10.6–13.2% in 2003–2004, indicating that lactating elk were acquiring high moderate–low good nutrition, but dropped to 5.6% in 2005 and 6.8% in 2006, indicating poor nutrition for these years of low precipitation. We found adult female survival of 0.94–1.00 and calf survival of 0.38–1.00. Calf survival was related to maternal size, maternal condition, and cumulative annual precipitation through parturition; all calf mortality occurred at or near parturition. Pregnancy rates averaged 0.33 for yearling cows and 0.86 for ≥ 2.5-y-olds, 2003–2006, and pregnancy was positively related to body mass for ≥ 2.5-y-old adults. Lactation rates of ≥ 2.5-y-olds averaged 0.59, 2003–2005, but dropped to 0.30 in 2006, due to poor maternal condition and low precipitation. Since colonization, elk have increased from about 20 to ≥ 53 individuals, a mean rate of increase of 18%/y prior to 2006, but decreasing to ≤ 4% in 2006. The high sustained rate of increase (with few exceptions) indicates that desert grassland–scrubland habitats are suitable for elk and merit consideration in elk management plans of Southwestern agencies.

Nitrogen and Tillage Effects on Wheat Leaf Spot Diseases in the Northern Great Plains

There is a need for management practices in cropping systems that can reduce the impact of plant diseases. Leaf spot diseases on wheat (Triticum aestivum L.) were evaluated for 11 yr to determine the influence of tillage, N fertilization, and cultivar on disease severity in a long‐term cropping system project, which included two cropping systems {spring wheat (SWF)–fallow and annual cropping [spring wheat (SWA)–winter wheat (WWA)–sunflower (Helianthus annuus L.)]}. The major leaf spot diseases were tan spot and Stagonospora nodorum blotch. In low precipitation years, the impacts of management practices on leaf spot disease severity were minimal. No‐till (NT) did not consistently increase the severity of leaf spot diseases. During the drier years, NT had the advantage of conserving soil water while not increasing the risk to leaf spot diseases. When N treatments influenced leaf spot disease severity, higher levels of disease severity were associated with the low‐N fertilizer treatment compared with higher levels of N fertilization. When a tillage × N treatment interaction was significant, disease severity was higher with NT at the low N treatment, but at the high N treatment the differences among tillage treatments were greatly reduced or eliminated. This indicates an advantage of using adequate N fertilizer especially with NT under our environmental conditions. When differences in leaf spot diseases for cultivars were evident, Roughrider winter wheat had higher levels of disease severity compared with Norstar; however, the differences between the spring wheat cultivars Butte86 and Stoa were not consistent for both cropping systems. Producers should integrate a combination of management practices to develop a consistent long‐term strategy for disease management suited to their production system and location.

FREQUENCY AND CORRELATES OF BIRTH-SITE FIDELITY IN PRONGHORNS (ANTILOCAPRA AMERICANA)

Abstract Although a variety of species exhibit birth-site fidelity, examples from ungulate species are rare. We recorded birth-site locations of pronghorns (Antilocapra americana) at the National Bison Range in northwestern Montana during 2000–2004 and found that 82% of females changed locations from the previous year. Females that exhibited birth-site fidelity had successfully weaned more fawns and were less likely to have experienced a fawn mortality event in the previous year than females that changed birth sites. Females that weaned a single fawn or weaned 0 fawns were equally likely to change birth sites. There was a year effect on distribution of birth sites as well as on birth-site fidelity. Dry range conditions in 2003 after multiple years of low precipitation may have caused more females to move their birth sites to areas of greater forage availability. The low observed frequency of birth-site fidelity may be a result of high fawn mortality rates at the National Bison Range. Success in the previo...

Reduced-risk fungicides help manage brown rot and other fungal diseases of stone fruit

New reduced-risk fungicides are highly effective in managing both pre- and postharvest diseases of stone fruit crops in California, and they have replaced most previously registered materials. These fungicides have a low impact on the environment, high specificity to target organisms, and low potential for groundwater contamination and human health risks. In stone fruit, they can be successfully used to manage brown rot blossom blight in a new delayed-bloom fungicide application program for lowprecipitation years. In our studies, we found that fungicide treatments applied 1 to 14 days before harvest were also effective against preharvest brown rot and protected fruit from fungal decays initiated during harvest. Practices such as mixtures and rotations can be implemented to prevent resistance from developing and to ensure the lasting efficacy of these reduced-risk fungicides.

An inexact fuzzy two-stage stochastic model for quantifying the efficiency of nonpoint source effluent trading under uncertainty

Reduction of nonpoint source (NPS) pollution from agricultural lands is a major concern in most countries. One method to reduce NPS pollution is through land retirement programs. This method, however, may result in enormous economic costs especially when large sums of croplands need to be retired. To reduce the cost, effluent trading can be employed to couple with land retirement programs. However, the trading efforts can also become inefficient due to various uncertainties existing in stochastic, interval, and fuzzy formats in agricultural systems. Thus, it is desired to develop improved methods to effectively quantify the efficiency of potential trading efforts by considering those uncertainties. In this respect, this paper presents an inexact fuzzy two-stage stochastic programming model to tackle such problems. The proposed model can facilitate decision-making to implement trading efforts for agricultural NPS pollution reduction through land retirement programs. The applicability of the model is demonstrated through a hypothetical effluent trading program within a subcatchment of the Lake Tai Basin in China. The study results indicate that the efficiency of the trading program is significantly influenced by precipitation amount, agricultural activities, and level of discharge limits of pollutants. The results also show that the trading program will be more effective for low precipitation years and with stricter discharge limits.