Forest Net Primary Production Resistance Across a Gradient of Moderate Disturbance

The global carbon (C) balance is vulnerable to disturbances that alter terrestrial C uptake and loss. Moderate disturbances that kill or defoliate only a subset of canopy trees such as insect defoliation, drought, and age-related senescence are increasing in extent and frequency; yet, little is known about the effect of moderate disturbance on forest production and the mechanisms sustaining or supporting the recovery of the C cycle across a range of moderate disturbance severities. We used a broad plot-scale gradient of upper canopy tree mortality within a large manipulation of forest disturbance to: 1) quantify how aboveground wood net primary production (ANPPw) responds to a range of moderate disturbance severities and; 2) identify the primary mechanisms supporting ANPPw resistance or resilience following moderate disturbance. We found that ANPPw was highly resistant to moderate disturbance, with production levels sustained following the senescence of 9 to \u3e 60 % of the upper canopy tree basal area. As upper canopy gap fraction increased with rising disturbance severity, greater light availability to the subcanopy enhanced leaf-level C uptake and the growth of this formerly light-limited canopy stratum, compensating for upper canopy production losses. As a result, whole-ecosystem production efficiency (ANPPw/LAI) increased at high levels of disturbance severity and leaf area loss. These findings provide a mechanistic explanation for sustained ANPPw across the disturbance gradient, in which the physiological and growth enhancement of undisturbed vegetation was proportional to the level of disturbance severity. Our results have important ecological and management implications, showing that moderate disturbances may minimally alter ecosystem functions such as C storage

Cue combination for 3D location judgements

Cue combination rules have often been applied to the perception of surface shape but not to judgements of object location. Here, we used immersive virtual reality to explore the relationship between different cues to distance. Participants viewed a virtual scene and judged the change in distance of an object presented in two intervals, where the scene changed in size between intervals (by a factor of between 0.25 and 4). We measured thresholds for detecting a change in object distance when there were only 'physical' (stereo and motion parallax) or 'texture-based' cues (independent of the scale of the scene) and used these to predict biases in a distance matching task. Under a range of conditions, in which the viewing distance and position of the tarte relative to other objects was varied, the ration of 'physical' to 'texture-based' thresholds was a good predictor of biases in the distance matching task. The cue combination approach, which successfully accounts for our data, relies on quite different principles from those underlying geometric reconstruction

Porites superfusa mortality and recovery from a bleaching event at Palmyra Atoll, USA.

BackgroundThe demography of a coral colony is not a binary trajectory of life and death. Based on the flexibility afforded by colonial organization, most reef-building corals employ a variety of dynamic survival strategies, including growth and shrinkage. The demographic flexibility affects coral size, shape and reproductive output, among other factors. It is thus critical to quantify the relative importance of key dynamics of recruitment, mortality, growth and shrinkage in changing the overall cover of coral on a reef.MethodsUsing fixed photographic quadrats, we tracked the patterns of change in the cover of one common central Pacific coral, Porites superfusa, before and after the 2009 ENSO event.ResultsCoral colonies suffered both whole and partial colony mortality, although larger colonies were more likely to survive. In subsequent years, recruitment of new colonies and regrowth of surviving colonies both contributed to the modest recovery of P. superfusa.DiscussionThis study is unique in its quantitative comparisons of coral recruitment versus regrowth during periods of areal expansion. Our data suggest that recovery is not limited simply to the long pathway of settlement, recruitment and early growth of new colonies but is accelerated by means of regrowth of already established colonies having suffered partial mortality

Mitigating confusion: Classification of road subtypes and socioeconomic and environmental impacts of roads in the Amazon

This paper recognizes the disconnect of road terminology present in current road ecology literature. The epistemological methods of First-Order Logic and the Q-Method along with political ecology are utilized to form a working typology of roads and their impacts, specifically centered in the Amazon. Following this, this work briefly discusses three unique cases studies that focus on different road aspects to display real-life examples of subtypes in the typology. The overarching goal of this study is to better organize the field of road ecology and help to mitigate negative environment and socioeconomic impacts in the future. Paper prepared for the Environmental Studies Senior Seminar/Geography Capstone

Biophysical drivers of carbon dioxide and methane fluxes in a restored tidal freshwater wetland

Wetlands store large amounts of carbon (C) in biomass and soils, playing a crucial role in offsetting greenhouse gas (GHG) emissions; however, they also account for 30% of global yearly CH4 emissions. Anthropogenic disturbance has led to the decline of natural wetlands throughout the United States, with a corresponding increase in created and restored wetlands. Studies characterizing biogeochemical processes in restored forested wetlands, particularly those that are both tidal and freshwater, are lacking but essential for informing science- based carbon management

The Science Behind Learning: Practical Applications of Curiosity, Sociality, and Emotion in Communication Center Consultations

How humans learn is a topic explored by many disciplines.  Eyler (2018) synthesized research from diverse fields such as developmental psychology, anthropology, and cognitive neuroscience to identify themes important for understanding the science behind learning. Three of these principles have important relevance for center work: curiosity, sociality, and emotion. This paper explores practical strategies, based on these three principles, that consultants in communication centers can use to enhance learning and better assist students.Keywords: communication centers, consulting, science of learning, curiosity, sociality, emotio

Fibroblasts derived from long-lived insulin receptor substrate 1 null mice are not resistant to multiple forms of stress

Reduced signalling through the insulin/insulin-like growth factor-1 signalling (IIS) pathway is a highly conserved lifespan determinant in model organisms. The precise mechanism underlying the effects of the IIS on lifespan and health is currently unclear, although cellular stress resistance may be important. We have previously demonstrated that mice globally lacking insulin receptor substrate 1 (Irs1−/−) are long-lived and enjoy a greater period of their life free from age-related pathology compared with wild-type (WT) controls. In this study, we show that primary dermal fibroblasts and primary myoblasts derived from Irs1−/− mice are no more resistant to a range of oxidant and nonoxidant chemical stressors than cells derived from WT mice

Essays in Public Finance and Taxation

This dissertation uses administrative tax data to study behavioral responses to taxation and tax enforcement. Chapter I focuses on the two tax penalties associated with Individual Retirement Accounts (IRAs). Chapter II considers the impact of a temporary suspension of tax collection efforts on future tax compliance and income. Chapter III investigates the use of professional tax preparation services by the top 1% of the income distribution. Chapter I, which is co-authored with Victoria Bryant, focuses on tax-benefited retirement savings accounts. These accounts have features designed to encourage retirement savings, including a penalty for withdrawing before age 59.5. Account holders also face a penalty for failing to take required minimum withdrawals after age 72. Using a bunching analysis, we estimate that these penalties cause more than 17% of traditional IRA holders to change their withdrawal timing each year, shifting close to $60 billion of distributions annually. We estimate a dynamic life-cycle model and run counterfactual policy analysis to analyze the effect of changing these penalties. For both penalties, we find alternative combinations of age threshold and penalty rate that lead to increased average welfare and lifetime tax remittances: increasing the age threshold for penalty-free withdrawals while simultaneously lowering the penalty rate, and increasing the age threshold for required withdrawals while leaving the penalty rate unchanged. In chapter II, which is co-authored with William C. Boning, Joel Slemrod, and Alex Turk, we ask whether a temporary suspension of efforts to collect outstanding tax debt ultimately lead to lower or higher tax compliance and income. When economic hardship prevents a tax debtor from paying basic living expenses, the Internal Revenue Service puts debt collection efforts on hold and designates the debt currently not collectible (CNC). This paper uses the quasi-random assignment of IRS Revenue Officers to tax debtors' cases as an instrumental variable to identify the causal effects of suspending debt collection on tax compliance and future income. In contrast to uninstrumented estimates, we find no evidence that putting off attempts to collect debt reduces compliance with future tax obligations or future reported income. Among marginal hardship cases, pausing collection instead increases future income, specifically wages earned by the taxpayer's spouse. Chapter III, which is co-authored with Giacomo Brusco, Yeliz Kacamak, and Mark Payne, considers a recent addition to the conversation about income inequality and the "top 1%:" the extent to which this population avoids and evades its tax liability. As the vast majority of the top 1% of the income distribution use a paid tax preparer, understanding the role of professional tax preparation services among this population is critically important to understanding their tax outcomes. We find that, among the bottom 99% of the income distribution, self-prepared returns have smaller corrections from a random audit relative to paid-prepared returns, but among the top 1%, paid-prepared returns experience smaller corrections relative to self-prepared returns. We then turn to the question of why someone in the top 1% wouldn't use paid tax preparation. We conclude that individuals in the top 1% who are either an accountant or financial advisor, or who have a higher proportion of their income from third-party reported sources such as wages, are less likely to use paid tax preparation services.PHDEconomicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169865/1/stuartem_1.pd

A human factors evaluation of the robotic interface for Space Station Freedom orbital replaceable units

An orbital replaceable unit (ORU) is often defined as any orbital unit aboard Space Station with a wearout life of less than 30 years. The capability of successful changeout of these units by remote manipulation is critical to the ORU to telerobot interface design. A human factors evaluation of the selected interface showed certain inadequacies of the alignment target concept that was part of the interface package. Alternative target concepts which addressed these inadequacies were developed and are presented. Recommendations will be incorporated into NASA requirements documents which ORU suppliers and manufacturers must then build to

Effects of spatially displaced feedback on remote manipulation tasks

Several studies have been performed to determine the effects on computer and direct manipulation task performance when viewing conditions are spatially displaced. Whether results from these studies can be directly applied to remote manipulation tasks is quenstionable. The objective of this evaluation was to determine the effects of reversed, inverted, and inverted/reversed views on remote manipulation task performance using two 3-Degree of Freedom (DOF) hand controllers and a replica position hand controller. Results showed that trials using the inverted viewing condition showed the worst performance, followed by the inverted/reversed view and the reversed view when using the 2x3 DOF. However, these differences were not significant. The inverted and inverted/reversed viewing conditions were significantly worse than the normal and reversed viewing conditions when using the Kraft Replica. A second evaluation was conducted in which additional trials were performed with each viewing condition to determine the long term effects of spatially displaced views on task performance for the hand controllers. Results of the second evaluation indicated that there was more of a difference in performance between the perturbed viewing conditions and the normal viewing condition with the Kraft Replica than with the 2x3 DOF