, Volume 141, Issue 2, pp 282–294 | Cite as

Plant responses to precipitation in desert ecosystems: integrating functional types, pulses, thresholds, and delays

  • Kiona OgleEmail author
  • James F. Reynolds
Pulse Events and Arid Ecosystems


The ‘two-layer’ and ‘pulse-reserve’ hypotheses were developed 30 years ago and continue to serve as the standard for many experiments and modeling studies that examine relationships between primary productivity and rainfall variability in aridlands. The two-layer hypothesis considers two important plant functional types (FTs) and predicts that woody and herbaceous plants are able to co-exist in savannas because they utilize water from different soil layers (or depths). The pulse-reserve model addresses the response of individual plants to precipitation and predicts that there are ‘biologically important’ rain events that stimulate plant growth and reproduction. These pulses of precipitation may play a key role in long-term plant function and survival (as compared to seasonal or annual rainfall totals as per the two-layer model). In this paper, we re-evaluate these paradigms in terms of their generality, strengths, and limitations. We suggest that while seasonality and resource partitioning (key to the two-layer model) and biologically important precipitation events (key to the pulse-reserve model) are critical to understanding plant responses to precipitation in aridlands, both paradigms have significant limitations. Neither account for plasticity in rooting habits of woody plants, potential delayed responses of plants to rainfall, explicit precipitation thresholds, or vagaries in plant phenology. To address these limitations, we integrate the ideas of precipitation thresholds and plant delays, resource partitioning, and plant FT strategies into a simple ‘threshold-delay’ model. The model contains six basic parameters that capture the nonlinear nature of plant responses to pulse precipitation. We review the literature within the context of our threshold-delay model to: (i) develop testable hypotheses about how different plant FTs respond to pulses; (ii) identify weaknesses in the current state-of-knowledge; and (iii) suggest future research directions that will provide insight into how the timing, frequency, and magnitude of rainfall in deserts affect plants, plant communities, and ecosystems.


Pulse-reserve Walter’s two-layer model Resource partitioning Soil water Root distributions 



Susanne Schwinning, Michael Loik, Travis Huxman, David Tissue and two anonymous reviewers provided helpful comments and suggestions on earlier drafts. This work was stimulated by the “Workshop on Resource Pulse Use in Arid Ecosystems” held at the University of Arizona, Tucson (2002). This research was supported by a NASA Earth System Science Fellowship (#NGT5–30355) to K.O. and by USDA Specific Cooperative Agreement #58–1270–3-070 and NSF-DEB-02–12123. This paper is a contribution to the Jornada Basin LTER.


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© Springer-Verlag 2004

Authors and Affiliations

  1. 1.Department of BiologyDuke UniversityDurhamUSA
  2. 2.Division of Environmental Science and Policy, Nicholas School of the Environment & Earth ScienceDuke UniversityDurhamUSA
  3. 3.Department of Ecology and Evolutionary BiologyPrinceton UniversityPrincetonUSA

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