Demographic processes limiting seedling recruitment in arid grassland restoration

Authors: James, Jeremy; Svejcar, Anthony; Rinella, Matthew - Matt

Submitted to: Journal of Applied Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2011
Publication Date: 8/1/2011
Citation: James, J.J., Svejcar, A.J., Rinella, M.J. 2011. Demographic processes limiting seedling recruitment in arid grassland restoration. Journal of Applied Ecology. 48:961-969.

Interpretive Summary: Seeding following fire or other disturbance is an important management tool in arid systems but it is expensive and prone to failure. We examined the demographic processes causing seedings to fail over three years and in four large fire sites seeded by managers. Across years and sites, the transition between a germinated seed to an emerged seedling was the major recruitment bottleneck. Germination across species, years and sites was high, averaging 72%. However, in the experimentally disturbed plots, an average of 85% of the seeds that germinated failed to emerge. For the four fires sown, 98% of the seeds that germinated failed to emerge. Managing ecological processes inhibiting emergence, such as germination timing, soil physical crusting and pathogens may greatly improve restoration success in these systems.

Technical Abstract: Seeding is commonly used in plant community restoration to overcome recruitment limitations. In arid systems, seeding is a particularly important management tool because plant community recovery following disturbance is slow and often inhibited by invasive species. While important in arid systems, seeding is an expensive practice that often fails. Previous research has largely focused on the technical aspects of seeding with little effort directed at identifying demographic processes driving recruitment failures. Understanding demographic stages limiting recruitment is essential for identifying what ecological processes can be managed to improve restoration outcomes. In experimentally disturbed plots, in each of three years, we estimated demographic stage transition probabilities for three species commonly used in sage steppe restoration. We also made similar measurements on seed sown by land managers following four major fires. Across years and sites, the transition between a germinated seed to an emerged seedling was the major recruitment bottleneck. Germination probability across species, years and sites was high, averaging 0.72. However, in the experimentally disturbed plots, an average of 85% of the seeds that germinated failed to emerge. For the four fires sown, 98% of the seeds that germinated failed to emerge. Given the large loss of individuals early in seedling development, variation in survival probabilities for later transitions had little impact on recruitment. Ecological processes occurring later in seedling development, such as spring and summer drought are unlikely to influence restoration outcomes. Processes occurring during emergence, on the other hand, such as freezing and thawing of the seedbed, development of physical soil crusts and pathogen attack on seedlings before they emerge may be large drivers of restoration failures. Managing processes inhibiting emergence and developing seed mixes with higher emergence probabilities may greatly improve restoration outcomes in the sage steppe and similar cold desert systems.