ON CHOOSING A BASE COVERAGE LEVEL FOR MULTIPLE PERIL CROP INSURANCE CONTRACTS

For multiple peril crop insurance, the U.S. Department of Agriculture'Â’s Risk Management Agency estimates the premium rate for a base coverage level and then uses multiplicative adjustment factors to recover rates at other coverage levels. Given this methodology, accurate estimation of the base coverage level from 65% to 50%. The purpose of this analysis was to provide some insight into whether such a change should or should not be carried out. Not surprisingly, our findings indicate that the higher coverage level should be maintained as the base.Risk and Uncertainty,

Investigating within-canopy variation of functional traits and cellular structure of sugar maple (Acer saccharum) leaves

Patterns of increasing leaf mass per area (LMA), area-based leaf nitrogen (Narea), and carbon isotope composition (δ13C) with increasing height in the canopy have been attributed to light gradients or hydraulic limitation in tall trees. Theoretical optimal distributions of LMA and Narea that scale with light maximize canopy photosynthesis; however, sub-optimal distributions are often observed due to hydraulic constraints on leaf development. Using observational, experimental, and modeling approaches, we investigated the response of leaf functional traits (LMA, density, thickness, and leaf nitrogen), leaf carbon isotope composition (δ13C), and cellular structure to light availability, height, and leaf water potential (Ψl) in an Acer saccharum forest to tease apart the influence of light and hydraulic limitations. LMA, leaf and palisade layer thickness, and leaf density were greater at greater light availability but similar heights, highlighting the strong control of light on leaf morphology and cellular structure. Experimental shading decreased both LMA and area-based leaf nitrogen (Narea) and revealed that LMA and Narea were more strongly correlated with height earlier in the growing season and with light later in the growing season. The supply of CO2 to leaves at higher heights appeared to be constrained by stomatal sensitivity to vapor pressure deficit (VPD) or midday leaf water potential, as indicated by increasing δ13C and VPD and decreasing midday Ψl with height. Model simulations showed that daily canopy photosynthesis was biased during the early growing season when seasonality was not accounted for, and was biased throughout the growing season when vertical gradients in LMA and Narea were not accounted for. Overall, our results suggest that leaves acclimate to light soon after leaf expansion, through an accumulation of leaf carbon, thickening of palisade layers and increased LMA, and reduction in stomatal sensitivity to Ψl or VPD. This period of light acclimation in leaves appears to optimize leaf function over time, despite height-related constraints early in the growing season. Our results imply that vertical gradients in leaf functional traits and leaf acclimation to light should be incorporated in canopy function models in order to refine estimates of canopy photosynthesis

A New Site Index Model for Intensively Managed Loblolly Pine (Pinus taeda) Plantations in the West Gulf Coastal Plain

Site index (SI) estimation for loblolly pine (Pinus taeda L.) plantations is important for the successful management of this important commercial tree species in the West Gulf Coastal Plain of the United States. This study evaluated various SI models for intensively managed loblolly plantations in the West Gulf Coastal Plain using data collected from permanent plots installed in intensively managed loblolly pine plantations across east Texas and western Louisiana. Six commonly used SI models (Cieszewski GADA model, both Chapman-Richards ADA and GADA models, both Schumacher ADA and GADA models, and McDill-Amateis GADA model) were fit to the data and compared. The Chapman-Richards GADA model and the McDill-Amateis GADA model were similar and best in their fit statistics. These two models were further compared to the existing models (Diéguez-Aranda et al. 2006 (DA2006), Coble and Lee 2010 (CL2010)) commonly used in the region. Both the Chapman-Richards GADA and the McDill-Amateis GADA models consistently predicted greater heights up to age 25 than the models of DA2006 and CL2010, with larger height differences for the higher quality sites, but predicted shorter heights thereafter. Ultimately, the McDill-Amateis GADA model was chosen as the best model for its consistency in predicting reasonable heights extrapolated beyond the range of the data. Foresters can use this model to make more informed silvicultural prescriptions for intensively managed loblolly pine plantations in the West Gulf Coastal Plain

The effects of policy expectations on crop supply, with an application to base updating

We develop a dynamic model to assess the effects of policy expectations on crop supply and illustrate the approach with estimates of the effects of base updating in U.S. crop programs. For corn and soybeans in the Corn Belt, the effect of base updating is relatively small because relevant crop alternatives are subject to similar policies and the alternatives are substitutes in production. Increasing acreage of one program crop to capture future payments from base updating reduces future payments from the alternative crop. We also use our model to assess the effect of base updating on acreage response to prices

Aboveground Biomass Estimation for Three Common Woody Species in the Post Oak Savannah of Texas

The Post Oak Savannah occupies about 3.4 million hectares of gently rolling to hilly lands in east central Texas. Large post oak (Quercus stellata Wangenh.) blackjack oak (Quercus marilandica Munchh.), Eastern redcedar (Juniperus virginiana L.) and honey mesquite (Juniperus virginiana L.) usually form the overstory, often above thickets of yaupon (Ilex vomitoria), winged elm (Ulmus alata), gum bumelia (Sideroxylon lanuginosum Michx. Subsp. Oblongifolium (Nutt) T.D. Penn.), and live oak (Quercus virginiana Mill.). Historically limited to rocky hillsides and draws (Owens and Ansley 1997), these species have migrated over the last several hundred years into bottomlands where grasses once dominated, and the increase in abundance and range has fluctuated due to both the modification of the historic fire regime and overgrazing (Smeins and Fuhlendorf 1997). The primary focus of previous fire studies in the Post Oak Savannah have been ignition time, mortality rate and the effect of burning to the understory vegetation, not standing shrub biomass estimation. Biomass estimation equations developed in different regions may not be applicable to the Post Oak Savannah since these substitutions may result in substantial error (Grier and Milne 1981, Gottfried and Severson 1994). With better prediction equations for this region with an increasing Urban-Wildfire Interface, managers can more accurately estimate the potential severity of wildfires or the effects of prescribed burns (Martin et al. 1978). Biomass estimation methods that involve juniper species have focused on Pinyon-Juniper (Pinus edulis and Juniperus spp.) and overstory-understory interactions in the western states. Schnell (1976) developed biomass prediction equations tables for eastern redcedar in Georgia, Alabama Tennessee and Virginia, that required diameters at breast height (DBH) \u3e 12.7 cm. Clark et al. (1986) and Phillips (1981) developed equations for estimating post oak biomass in North Carolina, South Carolina and Georgia, using DBH and total height; Phillips (1981) also age, but neither included foliage. Common in both studies was a DBH \u3e 15.2 cm and total height as independent variables. There is little biomass estimation information available for gum bumelia, although Bryant and Kothmann (1979) suggested a quadratic equation might work best. The objective of this study was to develop regression models to predict the total above-ground biomass for three species commonly found in Post Oak Savannah plant communities

On the potentials yielding cosmological scaling solutions

In the present work we perform a phase-plane analysis of the complete dynamical system corresponding to a flat FRW cosmological models with a perfect fluid and a self-interacting scalar field and show that every positive and monotonous potential which is asymptotically exponential yields a scaling solution as a global attractor.Comment: RevTeX, 10 pages, no figure

Cosmological dynamics of scalar fields with O(N) symmetry

In this paper, we study the cosmological dynamics of scalar fields with O(N) symmetry in general potentials. We compare the phase space of the dynamical systems of the quintessence and phantom and give the conditions for the existence of various attractors as well as their cosmological implications. We also show that the existence of tracking attractor in O(N) phantom models require the potential with $\Gamma<1/2$, which makes the models with exponential potential possess no tracking attractor.Comment: 9 pages, 4 figures; Replaced with the version to be published in Classical and Quantum Gravity. Reference adde

Changes in understory vegetation of a ponderosa pine forest in northern Arizona 30 years after a Wildfire

Wildland fires can cause shifts in understory species composition and production. Many studies have examined short-term changes in understory vegetation following a wildfire; however, very few long term studies are available. The objective of this study was to examine changes in understory (herb and shrub) species composition and production since the 1972 Rattle Burn wildfire on the Coconino National Forest near Flagstaff, Arizona. Understory species composition and production were originally sampled in 1972, 1974, and 1980 and were re-sampled during July and August of 2002 and 2003 on 30 plots in each of four sites: high severity burn, low severity burn, unburned site prescribed burned in 1977, and an unburned site. Repeated measures analysis was used to test for the effects of fire and time on species production. The effects of fire and time on species composition as well as species production were tested using Multi-Response Permutation Procedures (MRPP). A lingering effect of the Rattle Burn wildfire on the understory plant production and composition was revealed. Burned sites may have greater understory production as compared to unburned sites up to 30 years after a wildfire. However, species composition on burned sites is altered. A significant relationship between tree density and understory species composition and production was found for 1972, but no relationship was found for overstory parameters and understory species production and composition for 2003