PARENT SESSION
Oral Session #3: Plant Population Ecology. Presiding: N. Fetcher.
Monday, August 6, 2001. 8:00 AM to 11:30 AM. Hall of Ideas L&M.

Consequences of resourse pulse use in an herbaceous desert perennial.

Peek, Michael¹, Forseth, Irwin¹, ¹

ABSTRACT- We have a wealth of knowledge concerning how, when, and what resource pulses plants exploit. There is also increasing understanding of the spatial and temporal distribution of resources. However, our understanding of what a plant does with acquired resources that come in pulses is still lagging. We addressed this question by measuring growth, reproduction, and survivorship on an herbaceous desert perennial, Cryptantha flava. We picked experimental plants based on size (large or small) and reproductive status (flowering or non-flowering) and treated plants with a one time application of urea nitrogen, simulating a Mule deer excretion. We used stage-structured transition models to evaluate three years of demographic data. In years following treatment, growth and flowering of plants increased significantly over that of controls, while mortality was not affected. More than 80% of small and 90% of large, non-flowering plants flowered the year after treatment, compared to 50% and 70% for control plants, respectively. A higher number of plants that were flowering at the time of N addition stayed reproductive the following year if treated with urea, compared to controls. We conclude that low nitrogen availability in its native desert habitat places a major constraint on growth and reproduction in C. flava, and that C. flava is able to convert a single pulse of N into increased growth and reproduction over multiple years.

KEY WORDS: Crypthantha flava, Nitrogen pulses, Resource use, Demography