Modifying the ‘pulse-reserve’ paradigm for deserts of North America: precipitation pulses, soil water and plant responses
Abstract
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.
Type
Journal articleSubject
WaterSoil
Ecosystem
Biomass
Desert Climate
Rain
Seasons
Species Specificity
Models, Theoretical
Computer Simulation
North America
Plant Development
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https://hdl.handle.net/10161/24242Published Version (Please cite this version)
10.1007/s00442-004-1524-4Publication Info
REYNOLDS; James, F; Kemp, PR; Ogle, K; & Fernández, RJ (2004). Modifying the ‘pulse-reserve’ paradigm for deserts of North America: precipitation
pulses, soil water and plant responses. Oecologia, 141(2). pp. 194-210. 10.1007/s00442-004-1524-4. Retrieved from https://hdl.handle.net/10161/24242.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Show full item recordScholars@Duke
James F. Reynolds
Professor Emeritus
Integrated assessment of complex human-environmental systems; Land degradation and
desertification in global drylands; Conceptual frameworks and models to advance the
science of dryland development

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