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The analysis presented here was motivated by an objective of describing the interactions between the physical and biological processes governing the responses of tidal wetlands to rising sea level and the ensuing equilibrium elevation. We define equilibrium here as meaning that the elevation of the vegetated surface relative to mean sea level (MSL) remains within the vertical range of tolerance of the vegetation on decadal time scales or longer. The equilibrium is dynamic, and constantly responding to short-term changes in hydrodynamics, sediment supply, and primary productivity. For equilibrium to occur, the magnitude of vertical accretion must be great enough to compensate for change in the rate of sea-level rise (SLR). SLR is defined here as meaning the local rate relative to a benchmark, typically a gauge. Equilibrium is not a given, and SLR can exceed the capacity of a wetland to accrete vertically.
Experimental political science has transformed in the last decade. The use of experiments has dramatically increased throughout the discipline, and technological and sociological changes have altered how political scientists use experiments. We chart the transformation of experiments and discuss new challenges that experimentalists face. We then outline how the contributions to this volume will help scholars and practitioners conduct high-quality experiments.
Experimental political science has changed. In two short decades, it evolved from an emergent method to an accepted method to a primary method. The challenge now is to ensure that experimentalists design sound studies and implement them in ways that illuminate cause and effect. Ethical boundaries must also be respected, results interpreted in a transparent manner, and data and research materials must be shared to ensure others can build on what has been learned. This book explores the application of new designs; the introduction of novel data sources, measurement approaches, and statistical methods; the use of experiments in more substantive domains; and discipline-wide discussions about the robustness, generalizability, and ethics of experiments in political science. By exploring these novel opportunities while also highlighting the concomitant challenges, this volume enables scholars and practitioners to conduct high-quality experiments that will make key contributions to knowledge.
Liben Lark Heteromirafra archeri is a ‘Critically Endangered’ species threatened by the loss and degradation of grassland at the Liben Plain, southern Ethiopia, one of only two known sites for the species. We use field data from nine visits between 2007 and 2019 and satellite imagery to quantify changes over time in the species’ abundance and in the extent and quality of its habitat. We estimate that the population fell from around 279 singing males (95% CL: 182–436) in 2007 to around 51 (14–144) in 2013, after which too few birds were recorded to estimate population size. Arable cultivation first appeared on the plain in the early 1990s and by 2019 more than a third of the plain had been converted to crops. Cultivation was initially confined to the fertile black soils but from 2008 began to spread into the less fertile red soils that cover most of the plain. Liben Larks strongly avoided areas with extensive bare ground or trees and bushes, but the extent of these did not change significantly over the survey period. A plausible explanation for the species’ decline is that grassland degradation, caused before 2007 by continuous high-pressure grazing by livestock, reduced its rates of reproduction or survival to a level that could not support its previous population. Since 2015, communal kalos (grazing exclosures) have been established to generate forage and other resources in the hope of also providing breeding habitat for Liben Larks. Grass height and density within four grassland kalos in 2018 greatly exceeded that in the surrounding grassland, indicating that the plain retains the potential to recover rapidly if appropriately managed. Improvement of grassland structure through the restitution of traditional and sustainable rangeland management regimes and the reversion of cereal agriculture to grassland are urgently needed to avert the species’ extinction.