Simple strategies for increasing the power of soil moisture measurements to explain ecological patterns across the landscape

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Presenter/Primary Author: 
Michael Duniway

Primary production in arid and semiarid systems is predominantly limited by water availability. Precipitation is a strong predictor of primary production at broad scales in these systems. However, due to local variability in soil-water availability associated with landscape position, soil characteristics, and species composition, precipitation can be a pore predictor of production at finer scales. Thus, measured soil moisture content should provide a better predictor of primary production at fine scales. Differences in soil texture, both within a soil due to horizon development and across the landscape due to variation in soil forming factors, can greatly affect the availability of soil water for plant growth thereby limiting our ability to integrate soil moisture measures across soil horizons and types. If water retention characteristics of study soils are know or can be estimated, field measured soil water contents can be adjusted to reflect the amount of water that is readily available for plant growth, referred to as plant available water (PAW). This is a strategy is commonly employed in agricultural studies but is not often used in ecology. We use long term soil moisture and net primary production (NPP) data coupled with soil property data from the Jornada Long Term Ecological Research site to provide examples of how using PAW can greatly increase the amount of variability in NPP explained by soil moisture when compared to using total measured soil water content. Results indicate adjusting measured soil water contents to reflect the availability of moisture should be especially important for explaining ecological patterns across diverse soil systems.