Abstract:

The objectives of this study were to (i) determine the importance of soil moisture and soil nitrogen availability as resource requirements for the establishment of Stipa pulchra, (ii) to examine how changes in slope within a local habitat can affect the accumulation of soil moisture and soil nitrogen and (iii) to measure the physiological responses of S. pulchra among such slope locations.

The field experiment occurred in the San José Hills of Southern California on the California State Polytechnic University, Pomona campus. Plots were established within three different slope locations (shallow, moderate and steep) within four separate canyons. Three nitrogen treatments (ambient, addition and removal) were replicated within each slope location for all four canyons, and five S. pulchra plants were planted in each plot. Soil nitrogen accumulation and soil moisture, as well as other abiotic variables, were measured across the varied slope locations and nitrogen treatments. We measured the cover, stress, and reproduction of S. pulchra plants for 2 years and used a mesocosm experiment to determine how S. pulchra responds to varying water and nitrogen availability.

Stipa pulchra had a strong positive response to the wettest watering treatment and a weak response to nitrogen addition in the mesocosm experiment. In the field experiment, S. pulchra responded positively in moderate slope locations and did not respond to nitrogen treatments, possibly due to drought. Field patterns of soil moisture were driven by slope, soil compaction and solar radiation. Soil nitrogen accumulation did not vary among slope locations. For restoration of S. pulchra, priority should be placed on managing soil moisture availability and determining suitable edaphic factors.

Key words: establishment, ecophysiology, slope, soil moisture, soil properties, nitrogen deposition