The American quaking aspen (Populus tremuloides Michx.) and its close relative, the Eurasian quaking aspen (Populus tremula L.), cover a realm that is perhaps the most expansive of all tree species in the world. In North America, sudden aspen decline (SAD) is a growing concern that marks the rapid decline of quaking aspen trees leading to mortality at the stand and landscape scale. Research suggests that drought and water stress are the primary causes of SAD. Predisposing factors (age, structure, and landscape position), as well as associated stressors (i.e., pests and pathogens), have been linked to mortality in affected stands. The conflation of multiple interacting factors across the aspen’s broad geographic range in North America has produced significant debate over the classification of SAD as a disease and the proper management of affected stands. Interestingly, no such effects have been reported for the Eurasian aspen. We here review and synthesize the growing body of literature for North America and suggest that SAD is a novel decline disease resulting from multiple inciting and interacting factors related to climate, land-use history, and successional dynamics. We suggest that the range of aspen observed at the onset of the 21st Century was bolstered by a wet period in western North America that coincided with widespread regional cutting and clearing of late-successional forests for timber and grazing. No comparable land-use history, successional status, or age-class structure is apparent or linked for Eurasian forests. Eurasian aspen is either absent or young in managed forests, or old and decadent in parks in Fenno-Scandinavia, or it grows more intimately with a more diverse mixture of tree species that have arisen from a longer period of frequent timber cutting in Russia. Based on these insights we provide recommendations for practical management techniques that can promote stand resilience and recovery across a range of stand conditions in North America. Managers should attempt to identify SAD-prone stands using the presence of predisposing conditions and focus treatments such as coppice or prescribed fire on stands with suitable topographies, elevations, and climates. We conclude that SAD will persist throughout the coming decades, given the enormity of past cutting history, fire exclusion, and current changes in climate until a more active restoration agenda is implemented.

rect samples of the lunar mantle, has led to widely different estimates of the "water" content of the lunar mantle. The Apollo 12 basalt samples contain some of the most useful clues to understanding lunar mare volcanism and lunar mantle geochemistry. A subset of the Apollo 12 samples, the olivine basalts, picrites, and gabbros, likely formed by the differentiation and eruption of a single magma body (Kushiro and Haramura, 1971; Walker et al., 1976a, b); thus they permit us to track the evolution of the volatile components in a mare basaltic magma body through its cooling history (Greenwood et al., 2014). Petrological analysis of the suite led Walker et al. (1976a) to propose that the Apollo 12 olivine basalts sampled ~35 m of the basal portion of a magma body, such as a sill, lava flow, or pond that differentiated primarily by olivine settling (Fig. 1). Olivine vitrophyre 12009, which has skeletal olivine and the smallest plagioclase grains, may have formed at the chill margin of this magma body (Walker et al., 1976a). With increasing depth in the putative magma body, normative olivine increases due to olivine accumulation, and plagioclase grain size increases due to slower cooling (Fig. 1; Walker et al., 1976a). In this work, we studied hydrogen and D/H of three of the

Earth. High volatile abundances in lunar samples are also problematic for our basic understanding of the Moon, such as its formation in a giant impact event and the crystallization of a lunar-wide magma ocean. The giant impact event provides the necessary energy for melting a large portion of the Moon, but a severe depletion of the most volatile elements is generally an expectation of this fantastic event (Albaréde et al., 2015). Crystallization of the lunar magma ocean (LMO) predicts that the last liquids would be enriched in incompatible elements, such as K, REEs, and P (KREEP) (Warren and Wasson, 1979). Volatile elements are also incompatible in the anhydrous minerals expected to crystallize from the magma ocean, and thus water, fluorine, and chlorine should have been highly enriched in the original KREEP component (urKREEP). If water contents were 1000 ppm in the lunar magma ocean, such as found in olivine hosted melt inclusions of 74220 (Hauri et al., 2011), this would lead to 5 wt.% H 2 O in urKREEP (Elkins-Tanton and Grove, 2011). This much water would lead to water saturation at the base of the lunar crust (a likely place for the KREEP liquid to reside at the end of LMO crystallization). To prevent extensive water in the KREEP liquid, water contents of the initial magma ocean likely should have 100 ppm water or far less (Elkins-Tanton and Grove, 2011).

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