Demographic assessment of a native bunchgrass species for rangeland restoration in the Great Basin

Background/Question/Methods

Altered disturbance regimes are systematically destroying healthy rangeland and directly threatening U.S. agriculture, food security and sustainability. While every major stakeholder group in the West has recognized that restoration is critical to stem the massive and continuous loss of rangeland, establishment of functional plant communities on arid rangeland following disturbance is difficult and failure rates are high.

We seeded out Agropyron desetorum (desert wheatgrass), a native bunchgrass species, in a large-scale, multi-state (Idaho, Oregon, and Nevada) experiment across degraded rangelands to identify key ecological processes limiting demographic transitions. We used integral projection models (IPMs) to determine which life stage transitions most limit seedling recruitment along major ecological gradients (soil moisture and ground cover by the invasive grass Bromus tectorum).

Results/Conclusions

We found that population size of A. desetorum was largely driven by mortality at early life stages, specifically during germination, emergence and establishment. We found that soil dynamics, such as freeze-thaw cycles and soil moisture largely drove limitations of germination while soil physical crusting largely drove limitations of seedling emergence. Finally, we found that spring drought and wind abrasion was most important for seedling establishment success.

Restoring functional plant communities on arid rangeland following disturbance is a long-standing, serious and complex problem. Our results highlight the importance of developing and adopting a systems approach to understanding direct seedling establishment in order to make continuous and measured advancements in rangeland management.