Introduction

Event Schedule

Contributions

Participants

Publications

Pulse Bibliography

Workshop on Resource Pulse Use in Arid/Semiarid Ecosystems

Held at the University of Arizona, Tucson, AZ, USA on 2-4 August, 2002

This NSF sponsored workshop focused on the effects of precipitation events and event-patterns in arid and semi-arid ecosystems at multiple biological scales. In arid and semi-arid ecosystems, the dominant driver of biological processes across all scales is precipitation. The timing, length and intensity of rainfall events is naturally variable in these ecosystems and is thought to govern the life history strategies of its inhabitants, population dynamics, community change, resilience to invasions, soil nutrient dynamics, and ecosystem fluxes.

As a consequence of global warming, precipitation patterns are expected to change in nearly every arid and semi-arid system worldwide, according to Global Circulation Models. There is a growing awareness that many effects of climate change may assert themselves, not only through a change in average environmental conditions, but also, and perhaps more importantly, through a change in the pattern of environmental variation. For arid and semi-arid ecosystems, this means that climatic shifts, which impact the stochastic characteristics of rainfall events, may have wide-ranging effects across multiple biological scales. The research community is only now beginning to examine such effects by asking how event characteristics, such as event timing and size, modify precipitation effects in water-limited ecosystems.

Over the past few years, researchers have independently begun to investigate rainfall effects on soil processes, plants and animals, populations and communities. Simultaneously, theoretical approaches are being developed to assess the effects of a pulsed, stochastic resource supply on community dynamics and diversity. Neither the experimental results, nor the theoretical investigations have resulted in a clear-cut picture of how rainfall characteristics affect communities and ecosystems in dry regions. This workshop brought scientists together to attempt a synthesis of these issues. Our main objectives for this 3-day workshop were

• Interdisciplinary exchange: to establish a working basis in climate-precipitation interactions, hydrologic, biogeochemic and biologic impacts of rain events. This will be accomplished in the first two days of the workshop in a series of oral and poster presentations.
• Data synthesis: to integrate recent experimental results and resolve apparently conflicting evidence where possible. This will be discussed on the third day of the workshop within smaller working groups. In the following months these groups will formalize their conclusions in contributed chapters to a synthesis volume
• Theory development: to build a framework for an "event-based" approach in experimental ecology and ecological modeling for low-productivity ecosystems. This will also be discussed on the third day of the workshop and brought to conclusion as book chapters.

Three main questions guided workshop activities:

1. How does the timing and size of a rainfall event determine its impact on organisms, communities and ecosystems?
    
2. How are nutrient dynamics coupled to soil moisture pulses?
    
3. What are the consequences of pulsed resource renewal on species interactions (specifically competition), diversity and primary productivity?