The Southern Sierra Critical Zone Observatory is a platform for research on critical zone processes, with ongoing investigations and measurements at several sites on the western slope of the southern Sierra Nevada.

Spatial differences along the elevation gradient characterizing our Critical Zone Observatory's field areas - from forest ecology to preciptation phase to bedrock composition - create a natural laboratory to study changes in critical zone characteristics and processes across the landscape. While this elevation transect experiences rapid seasonal changes, from snow cover to wet soil to dry soil in a 1-2 month period, climate warming will shift this transition to an earlier time and a higher elevation. Researchers can also use the gradient then as a substitution of space for time to research how critical zone processes respond to natural and anthropogenic environmental changes, including warmer average temperatures and forest thinning.

Our growing community of critical zone scientists from multiple institutions and areas of research expertise are carrying out investigations in the Sierra National Forest, Kings River Experimental Watershed, San Joaquin Experimental Range, and Sequoia National Park.

Learn more about our field areas and instrumentation -->

Conduct research at our CZO -->

Our integrated research is centered on several interdisciplinary questions and goals:

Critical Zone researchers are currently investigating a tightly linked set of research questions at our Observatory, including:

• How do soil moisture and topographic variability interact to influence soil-formation and weathering?
• How is the response of soil moisture to snowmelt and rainfall controlled by variability across the landscape, and how do these responses both reflect and constrain streamflow and ET?
• How does vegetation, and ecosystem distribution and function (species, plant functional type, production), vary with climate (elevation); and what physiological mechanisms regulate these interactions?
• How does vegetation influence land-atmosphere exchange of water, energy, and CO2?
• How do soil/landscape heterogeneity and water fluxes influence nutrient cycling and retention?
• What is the role of aeolian fluxes in controlling nutrient availability and NPP?

While some research is centered on a single discipline, many questions require a multi-disciplinary approach. Our measurements and monitoring efforts overlap with other observatories in the National Science Foundation's U.S. Critical Zone Observatory Network in order to rapidly improve Earth systems models.

Explore examples of current research topics in detail -->
 

Initial research focus and findings

Since it was initiated in 2007, the Southern Sierra CZO has become a platform for a wide variety of research. Much of the research during the first five years addressed these questions:

• How does landscape variability control how soil moisture, evapotranspiration and stream flow respond to snowmelt and rainfall?
• How is soil moisture linked to topographic variability, soil formation and weathering?
• What physiological mechanisms are controlling how vegetation distribution and function vary with climate
• How do vegetation attributes influence cycling of water, energy, and CO2?
• What is the link between soil heterogeneity, water fluxes and nutrient availability?

Among the many results to date at our CZO, four key findings stand out:

• A strategically distributed measurement suite provides the data needed to close the water balance at multiple scales, providing a foundation for further process research. At the headwater catchment scale our estimates of evapotranspiration (ET) using a water-balance approach are in good agreement with flux-tower measurements. Similarly, our estimate of the water balance across the entire Upper Kings River basin also matches observations.
• Mid-montane forests have a year-round growing season, avoiding summer water-stress shutdown through deep rooting and avoiding winter shutdown cold tolerance, explaining high productivity and biomass in the mid-montane belt.
• In contrast to high rates of evapotranspiration (ET) at mid-elevation, we observed reduced ET and productivity at lower elevations owing to summer moisture stress and at high elevations due to cold stress. This confirms the inverse drought and energy limitation conceptual model, with implications for effects of warming on ET.
• Deep rooting and soil development are important for sustaining high rates of net primary productivity (NPP). At our main instrumented headwater catchment, we found that over one-third of the ET came from depths below 1 m.

For more information on our activities and findings, view our annual reports and publications.