College of Behavioral & Social Sciences

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    Environmental and Anthropogenic Degradation of Vegetation in the Sahel from 1982 to 2006
    (MDPI, 2016-11-13) Rishmawi, Khaldoun; Prince, Stephen D.
    There is a great deal of debate on the extent, causes, and even the reality of land degradation in the Sahel. Investigations carried out before approximately 2000 using remote sensing data suggest widespread reductions in biological productivity, while studies extending beyond 2000 consistently reveal a net increase in vegetation production, strongly related to the recovery of rainfall following the extreme droughts of the 1970s and 1980s, and thus challenging the notion of widespread, long-term, subcontinental-scale degradation. Yet, the spatial variations in the rates of vegetation recovery are not fully explained by rainfall trends. It is hypothesized that, in addition to rainfall, other meteorological variables and human land use have contributed to vegetation dynamics. Throughout most of the Sahel, the interannual variability in growing season ΣNDVIgs (measured from satellites, used as a proxy of vegetation productivity) was strongly related to rainfall, humidity, and temperature (mean r2 = 0.67), but with rainfall alone was weaker (mean r2 = 0.41). The mean and upper 95th quantile (UQ) rates of change in ΣNDVIgs in response to climate were used to predict potential ΣNDVIgs—that is, the ΣNDVIgs expected in response to climate variability alone, excluding any anthropogenic effects. The differences between predicted and observed ΣNDVIgs were regressed against time to detect any long-term (positive or negative) trends in vegetation productivity. Over most of the Sahel, the trends did not significantly depart from what is expected from the trends in meteorological variables. However, substantial and spatially contiguous areas (~8% of the total area of the Sahel) were characterized by negative, and, in some areas, positive trends. To explore whether the negative trends were human-induced, they were compared with the available data of population density, land use, and land biophysical properties that are known to affect the susceptibility of land to degradation. The spatial variations in the trends of the residuals were partly related to soils and tree cover, but also to several anthropogenic pressures.
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    Unplanned Natural Experiments: The Case of Remote Sensing of Primary Production and Its Environmental Correlations in the Negev
    (MDPI, 2020-10-31) Prince, Stephen D.; Jackson, Hasan
    Studies of the correlations of environmental factors with vegetation growth using remotely sensed measurements are necessarily made against a background of biophysical and anthropogenic factors, such as local fertility, microclimate, and the effects of human land use, in addition to the factors of interest. This is an inevitable outcome of a natural (unplanned) design where the effects of the factors of interest are confounded with other, often unknown factors, possibly rendering the results inaccurate or poorly-constrained. The problems associated with a natural design would be reduced if sites could be identified in which uncontrolled variables had no impact. However, rarely are such sites known a priori. Here, a component of the net primary production (NPP) local scaling (LNS) method was used to estimate the potential NPP in the absence of confounding factors. Subsequent analyses of the effects of the selected environmental variables were carried out using the potential NPP. The method was tested in relation to NPP along the transitional ecotone from desert to semiarid conditions in the northern Negev, Israel. The effects of four environmental factors were tested: precipitation, topography, land cover, and interannual variability. While precipitation is generally the only environmental variable that is considered in drylands, the other factors were found to be significant. The results provided unambiguous evidence of the value of the method.
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    Regulation, Institutions, and Productivity Growth
    (2006-08-24) Oviedo Silva, Ana Maria; Haltiwanger, John C; Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation investigates how the investment climate affects firm dynamics, productivity, and macroeconomic performance across countries. The first chapter provides an empirical analysis of the macroeconomic impact of business regulation. It characterizes the stylized facts on regulation across the world, using a set of comprehensive indicators of regulation in a large number of countries. These indicators are used to study the effects of regulation on growth and volatility employing cross-country regression analysis. The analysis allows for the effects of regulation to vary with the country's level of institutional development, and it also controls for the likely endogeneity of regulation with respect to macroeconomic performance. Results show that a heavier regulatory burden reduces growth and increases volatility, although these effects are smaller the higher the quality of the overall institutional framework. The second chapter focuses on the mechanism through which regulation impacts on macroeconomic outcomes, and assesses the role of firm entry and exit as channel of transmission of the effects of regulation on productivity growth. We use sector and manufacturing-wide productivity and firm turnover data derived from firm-level information for OECD and Latin American countries to explore the effects of various types of regulations following a two-step approach. The first step examines the impact of regulation on firm turnover. The second assesses the effects of firm turnover on productivity growth. Results provide partial evidence that regulation, particularly product market regulation, hampers productivity growth by deterring firm entry and exit. The third chapter investigates the effects of regulation uncertainty on the innovative behavior of firms, and on the efficiency of the Schumpeterian "creative destruction" process. It argues that regulation uncertainty, caused by a poor institutional environment, distorts the selection process of firms and leads to high observed reallocation, but low productivity. Following Hopenhayn (1992), an industry is modeled where firms engage in innovative investment and face an uncertain innovation cost. The analysis centers on the entry and exit decision of firms, their innovative behavior, and the subsequent industry evolution. In equilibrium, a more uncertain cost creates distortions in the reallocation process that lead to lower average productivity, size, and innovative investments, having similar effects as an increase in the magnitude of the cost. This indicates that, in addition to the level of regulation, unpredictability of regulation is an important source of inefficiency in the reallocation process.