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Although high elevation meadows are often considered to be primarily temperature-limited, aboveground net primary production (ANPP) is influenced by both growing season length (GSL) and soil moisture (SM). Progress in understanding these responses comes from studies at individual sites that are often focused on single abiotic drivers, so little is known about how climatic constraints relate to one another and limit ANPP at larger scales. We examined the independent and combined effects of these two key climate drivers (GSL and SM) across a suite of high elevation meadows from two continents. We also sampled gradients of each variable at a single site to explore mechanisms for SM and GSL limitations. Here, we show that high elevation meadows are limited by both GSL and SM levels. GSL constrained maximum ANPP by approximately 4 g m d whereas average daily ANPP beneath this constraint was significantly influenced by SM. Carbon isotope and plant/soil nitrogen data suggest that SM influenced ANPP through its impact on nitrogen availability. Increases in GSL can increase ANPP unless those increases are accompanied by SM decreases. These interactive effects can produce distinct ecological patterns and must be considered when predicting high elevation meadow responses to future climate changes. [ABSTRACT FROM AUTHOR]