Submitted to: Ecohydrology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/29/2014
Publication Date: N/A
Citation: Interpretive Summary: This paper provides a conceptual synthesis of the climatic drivers of plant leaf production strategies in ecosystems characterized by seasonal drought. Regular seasonal droughts occur in many ecosystems, including the U.S. Central Plains grasslands, so this topic has global and local relevance. This paper uses seasonally-dry Mediterranean ecosystems as case studies to demonstrate how a simulation modeling framework can illustrate the costs and benefits of ‘evergreen’, ‘opportunistic’, and ’ scheduled’ leaf flushing strategies. For example, modeling shows that longer dry seasons reduce the advantages of being evergreen, and higher interannual variability in precipitation favors opportunistic species (that flush their leaves only when conditions are favorable) over scheduled species (that flush their leaves in response to a predictable environmental cue, such as photoperiod). This modeling framework thus allows predictions of possible shifts in the composition of vegetation under future climate scenarios.
Technical Abstract: Large areas of tropical and mid-latitude regions are characterized by a pronounced seasonality and extreme inter-annual rainfall variability, which places local ecosystems under unique patterns of water availability, temperature, and irradiance. Despite the importance of these seasonally dry ecosystems (SDEs) in providing food, fiber, and ecosystem services to large populations, and their potential importance for global carbon cycling, a unifying ecohydrological framework to interpret the effects of variability in water availability is still lacking. A synthesis of existing observations suggests that leaf phenological variations, rather than physiological traits, are the most distinguishing plant functional adaptation to seasonally dry climates. Such findings are embedded into a modeling framework to explore the effectiveness of different phenological plant adaptation strategies in coping with intermittent water availability under various climatic regimes. Five illustrative case studies of the hydroclimatic forcing, both from seasonally dry tropical regions (characterized by absence of temperature seasonality) and Mediterranean climates (exhibiting out-of-phase temperature and rainfall seasonal patterns), are examined from a unified ecohydrological perspective. The benefits of leaf phenological strategies in seasonally dry ecosystems are found to depend mostly on the climatic drivers. Longer dry seasons reduce the advantage in terms of carbon gain for evergreen species, while higher inter-annual variability favors species that flush their leaves in response to enhanced water availability (‘opportunistic species’) and penalizes species that flush their leaves in response to other cues such as photoperiod (‘scheduled species’). The predicted climatic change may further stretch the adaptive limits of plants and alter the most beneficial leaf phenological strategy, prompting possible shifts in ecosystem composition.