Abstract
AbstractIn semi‐arid mountainous regions across the western United States, the distribution of upland aspen (Populus tremuloides) is often related to heterogeneous soil moisture subsidies resulting from redistributed snow. As temperatures increase, interactions between decreasing snowpack and future trends in the net primary productivity (NPP) of aspen forests remain uncertain. This study characterizes the importance of heterogeneously distributed snow water to aspen communities in the Reynolds Creek Critical Zone Observatory located in southwestern Idaho, USA. Net primary productivity of three aspen stands was simulated at sites spanning elevational and precipitation gradients using the biogeochemical process model Biome‐BGC and precipitation data adjusted to account for drifting snow. Compared to a spatially homogeneous precipitation distribution, Biome‐BGC simulations accounting for redistributed precipitation were in better agreement with previous simulations of snow accumulation and soil moisture field measurements. During drought years, simulations below the largest drifts that included wind‐redistributed snow resulted in NPP values nearly 77% higher than simulations assuming uniform precipitation. However, during wet years (and at sites with higher total precipitation), increased effective precipitation resulting from drifting snow did not have a significant role in aspen productivity. In these cases, soil moisture was found to be non‐limiting even in the absence of redistributed snow. Increased water availability from snow drifts often exceeded the storage capacity of the soil and contributed little to plant available water used later in the growing season.
Highlights
In mountainous ecosystems, interactions between hydrological and ecological processes can have profound impacts on the distribution and vigor of vegetation
Measured Srz across all sites tended to follow similar seasonal trends throughout the year, where peak soil moisture storage occurred during the late winter and early spring following peak snowmelt
As soil moisture became increasingly limited in the region measured by soil moisture sensors, measured Srz began to plateau either as plant water use decreased or soil moisture was withdrawn at depths extending beyond the measured profile (Fig. 2)
Summary
Interactions between hydrological and ecological processes can have profound impacts on the distribution and vigor of vegetation. Upland aspen communities are highly productive relative to many other adjacent plant communities, are characterized by relatively high understory biodiversity (Kuhn et al 2011), and provide important, isolated habitats for many different avian and mammalian species (DeByle 1985, Griffis-Kyle and Beier 2003), yet their tolerance to decreases in water availability via changes in precipitation regime remains largely unknown Since these upland aspen communities currently act as important habitat, understanding how future shifts in precipitation phase impact vegetation productivity is increasingly important when identifying response thresholds and managing resilient habitat refugia as temperatures continue to increase with climate change (Keppel et al 2012)
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