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A seasonally occurring summer hypoxic (low oxygen) zone in the northern Gulf of Mexico is the second largest in the world. Reductions in nutrients from agricultural cropland in its watershed are needed to reduce the hypoxic zone size to the national policy goal of 5,000 km 2 (as a 5-y running average) set by the national Gulf of Mexico Task Force's Action Plan. We develop an integrated assessment model linking the water quality effects of cropland conservation investment decisions on the more than 550 agricultural subwatersheds that deliver nutrients into the Gulf with a hypoxic zone model. We use this integrated assessment model to identify the most cost-effective subwatersheds to target for cropland conservation investments. We consider targeting of the location (which subwatersheds to treat) and the extent of conservation investment to undertake (how much cropland within a subwatershed to treat). We use process models to simulate the dynamics of the effects of cropland conservation investments on nutrient delivery to the Gulf and use an evolutionary algorithm to solve the optimization problem. Model results suggest that by targeting cropland conservation investments to the most cost-effective location and extent of coverage, the Action Plan goal of 5,000 km 2 can be achieved at a cost of $2.7 billion annually. A large set of costhypoxia tradeoffs is developed, ranging from the baseline to the nontargeted adoption of the most aggressive cropland conservation investments in all subwatersheds (estimated to reduce the hypoxic zone to less than 3,000 km 2 at a cost of $5.6 billion annually).waters are proliferating worldwide, impacting more than 400 coastal marine systems (1, 2). A major cause of their formation and persistence is nutrient pollution (from agricultural, urban, and other sources) delivered from their watersheds. Excess nutrients threaten not only coastal waters (3), but also pose problems within the watersheds (4), diminishing the quantity and quality of the ecosystem services they provide (5-7). For example, 55 percent of US streams are in "poor" condition (4), drinking water supplies are compromised by high nitrate concentrations, harmful algal blooms risk human health, and commercial fisheries are threatened. The second-largest hypoxic zone in the global ocean is in the northern Gulf of Mexico and covers an area averaging more than 14,500 km 2 in the summers of 2004 through 2013 (8). The documentation of this pervasive phenomenon led to the 2008 Action Plan for Reducing, Mitigating, and Controlling Hypoxia in the northern Gulf of Mexico (9). The Action Plan, a joint federal-state effort, set the goal of reducing the size of Gulf hypoxia to less than 5,000 km 2 over a 5-y period.Current analysis of the sources of nutrient loads from the Mississippi-Atchafalaya River Basin (hereafter referred to as the Mississippi Basin) into the Gulf indicate that agricultural sources in the watershed contribute 80% of the delivered nitrogen (N) and more than 60% of the delivered phosphorus (P) (10).A number of cr...

The first part of the chapter reviews the genetic systems of Populus and Salix and how they form the basis for the various domestication and conservation options available today. The second part of the chapter provides a description of the rich diversity of programmes focused on Populus and Salix genetics around the globe. The chapter includes a listing of the world's leading Populus and Salix geneticists and breeders who have contributed material.

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