, Volume 141, Issue 2, pp 194–210 | Cite as

Modifying the ‘pulse–reserve’ paradigm for deserts of North America: precipitation pulses, soil water, and plant responses

  • James F. Reynolds
  • Paul R. Kemp
  • Kiona Ogle
  • Roberto J. Fernández
Pulse Events and Arid Ecosystems


The ‘pulse–reserve’ conceptual model—arguably one of the most-cited paradigms in aridland ecology—depicts a simple, direct relationship between rainfall, which triggers pulses of plant growth, and reserves of carbon and energy. While the heuristics of ‘pulses’, ‘triggers’ and ‘reserves’ are intuitive and thus appealing, the value of the paradigm is limited, both as a conceptual model of how pulsed water inputs are translated into primary production and as a framework for developing quantitative models. To overcome these limitations, we propose a revision of the pulse–reserve model that emphasizes the following: (1) what explicitly constitutes a biologically significant ‘rainfall pulse’, (2) how do rainfall pulses translate into usable ‘soil moisture pulses’, and (3) how are soil moisture pulses differentially utilized by various plant functional types (FTs) in terms of growth? We explore these questions using the patch arid lands simulation (PALS) model for sites in the Mojave, Sonoran, and Chihuahuan deserts of North America. Our analyses indicate that rainfall variability is best understood in terms of sequences of rainfall events that produce biologically-significant ‘pulses’ of soil moisture recharge, as opposed to individual rain events. In the desert regions investigated, biologically significant pulses of soil moisture occur in either winter (October–March) or summer (July–September), as determined by the period of activity of the plant FTs. Nevertheless, it is difficult to make generalizations regarding specific growth responses to moisture pulses, because of the strong effects of and interactions between precipitation, antecedent soil moisture, and plant FT responses, all of which vary among deserts and seasons. Our results further suggest that, in most soil types and in most seasons, there is little separation of soil water with depth. Thus, coexistence of plant FTs in a single patch as examined in this PALS study is likely to be fostered by factors that promote: (1) separation of water use over time (seasonal differences in growth), (2) relative differences in the utilization of water in the upper soil layers, or (3) separation in the responses of plant FTs as a function of preceding conditions, i.e., the physiological and morphological readiness of the plant for water-uptake and growth. Finally, the high seasonal and annual variability in soil water recharge and plant growth, which result from the complex interactions that occur as a result of rainfall variability, antecedent soil moisture conditions, nutrient availability, and plant FT composition and cover, call into question the use of simplified vegetation models in forecasting potential impacts of climate change in the arid zones in North America.


Antecedent soil moisture Storms Simulation model Primary production 



The authors thank John Anderson for his assistance in accessing the Jornada LTER datasets. Susanne Schwinning, Osvaldo Sala, and an anonymous reviewer provided very helpful comments and suggestions. This research was supported by USDA Specific Cooperative Agreement 58-1270-3-070, NSF-SBR-95-21914 and NSF-DEB-02-12123. K.O. acknowledges support from the NASA Earth System Science Fellowship NGT5-30355 and R.J.F. from UBA and IAI-SGP008. This paper is a contribution to the Jornada Basin LTER.


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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • James F. Reynolds
    • 1
    • 2
  • Paul R. Kemp
    • 3
  • Kiona Ogle
    • 1
    • 5
  • Roberto J. Fernández
    • 4
  1. 1.Department of Biology, Nicholas School of the Environment & Earth ScienceDuke UniversityDurhamUSA
  2. 2.Division of Environmental Science and Policy, Nicholas School of the Environment & Earth ScienceDuke UniversityDurhamUSA
  3. 3.Department of BiologyUniversity of San DiegoSan DiegoUSA
  4. 4.IFEVA-Ecología, CONICET/Facultad de AgronomíaUniversidad de Buenos AiresBuenos AiresArgentina
  5. 5.Department of Ecology and Evolutionary BiologyPrinceton UniversityPrincetonUSA

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