J. C. Randolph

Changes in Soybean Yields in the Midwestern United States as a Result of Future Changes in Climate, Climate Variability, and CO2 Fertilization

This modeling study addresses the potential impacts of climate change and changing climate variability due to increased atmospheric CO2 concentration on soybean (Glycine max (L.) Merrill) yields in theMidwestern Great Lakes Region. Nine representative farm locations and six future climate scenarios were analyzed using the crop growth model SOYGRO. Under the future climate scenarios earlierplanting dates produced soybean yield increases of up to 120% above current levels in the central and northern areas of the study region. In the southern areas, comparatively small increases (0.1 to 20%) and small decreases (–0.1 to–25%) in yield are found. The decreases in yield occurred under the Hadley Center greenhouse gas run (HadCM2-GHG), representing a greater warming, and the doubled climate variability scenario – a more extreme and variableclimate. Optimum planting dates become later in the southern regions. CO2fertilization effects (555 ppmv) are found to be significant for soybean, increasing yields around 20% under future climate scenarios.For the study region as a whole the climate changes modeled in this research would have an overall beneficial effect, with mean soybean yield increases of 40% over current levels.

Summer Ground Layer Biomass and Nutrient Contribution to Above-Ground Litter in an Indiana Temperate Deciduous Forest

ABSTRACT Eastern deciduous forests of North America have productive ground layers, but information regarding the role of ground layer vegetation in carbon cycling is limited. The ground layer, here defined as all vascular plants ≤1 m in height, contributes most of its biomass and nutrient content annually to the above-ground litter pool. This study assessed the species composition and biomass and nutrient contributions of summer ground layer vegetation to the above-ground litter pool at the AmeriFlux Site in the Morgan-Monroe State Forest, Indiana. Two hundred fifteen 1-m2 subplots were sampled for ground layer species and cover (%). Forty-three of those subplots were harvested for above-ground biomass and tissue nutrient analysis. A 10-cm soil sample was obtained from each harvested subplot and analyzed for pH, organic matter and nutrient content. Boehmeria cylindrica (false nettle), Lindera benzoin (spicebush), Viola spp. (violets), Parthenocissus quinquefolia (Virginia creeper), Polystichum acrostichoides (Christmas fern) and Asplenium spp. (spleenworts) were the most important and abundant ground layer species. Ground layer species were distributed along gradients of weathering and soil organic matter. Mean ground layer cover was 36.7 ± 17.4 % and mean calculated ground layer biomass was 24.7 ± 15.4 g/m2 in the mid- to late-growing season. Ground layer biomass was positively correlated with available soil P. Woody plants accounted for approximately 51% of ground layer biomass followed by non-graminoid herbs (35%) and graminoids (14%). Ground layer litter, comprised of graminoids, non-graminoid herb foliage and stems and woody plant foliage, contributed 26.5 g/m2 and 11.1 g C/m2, or ≤5% of the biomass and C, to the above-ground litter pool in 1999. While the ground layer contributed relatively small quantities of biomass and C to the above-ground litter pool, it provided nutrient-rich tissues with C:N ratios lower than tree leaf litter. With the exception of K, tree leaf litter contributed more nutrients by mass to above-ground litter than did ground layer litter because tree leaf litter comprised 88% of the biomass of above-ground litter.

An Approach to Assess Relative Degradation in Dissimilar Forests: Toward a Comparative Assessment of Institutional Outcomes

A significant challenge in the assessment of forest management outcomes is the limited ability to compare forest conditions quantitatively across ecological zones. We propose an approach for comparing different forest types through the use of reference forests. We tested our idea by drawing a sample of 42 forests from the Midwest USA, Mexico, Guatemala, Honduras, Brazil, Bolivia, Uganda, and Nepal. We grouped these forests by shared characteristics and selected a reference forest to serve as a baseline for each forest type. We developed an index of disturbances using ratios of several forest measurements to assess differences between each study forest and its reference forest. None of the study forests was known to have been impacted by major natural disturbances during the past 50 years. Therefore, the disturbances in these forests appear to be largely related to human activities. The forests most similar to their reference forests have had limited human interventions. Our results indicate the potential of this approach to compare different forest conditions across biomes. We argue that development of this approach could facilitate analyses of forest management institutions, promote reliable indicators to compare management outcomes, and contribute to improved policies for conservation.

Nutrient Encounter by a Generalist Herbivore in a Heterogeneous Landscape

Abstract Most landscapes are heterogeneous in vegetation composition and thus, in the distribution of nutrients required by herbivores for growth and reproduction. Hispid cotton rats (Sigmodon hispdus) inhabit Texas coastal prairies which are characterized by habitat patches dominated by dicots, monocots or both [mixed] plant types. Hispid cotton rats must obtain nutrients necessary for reproduction by ingesting both dicots and monocots, and reproductive females concentrate their activity in mixed patches. Mixed patches may be selected because they have high nutrient contents or because presence of both monocot and dicot food plants lowers cost of foraging movements. Because hispid cotton rats select a nutritionally complete diet and may detect protein by odor and taste cues, we hypothesized that nutrient concentrations may cue position of foraging paths. We used nutrient maps to measure amount of protein, P and Ca encountered during foraging from radiotracked individuals. We compared these values to those obtained from randomly generated foraging paths. Actual and random paths did not differ in amount of protein, P or Ca encountered. Differences in nutient accumulation between seasons were explained by seasonal differences in availability. We conclude that foraging paths do not respond to nutrient content of plants, but that reproductive females likely occupy mixed habitat patches because presence of both dicot and monocot food plants decreases time and energy spent foraging.