Abstract
The El Niño–Southern Oscillation (ENSO) is the largest source of interannual climate variability in much of the tropics. We hypothesize that tropical plants exhibit interannual variation in reproduction and resource acquisition strategies driven by ENSO that mirrors their seasonal responses. We analyze the relationship of leaf and seed fall to climate variation over 30 years in a seasonally dry tropical forest in Panama where El Niño brings warm, dry, and sunny conditions. Elevated leaf fall precedes the onset of El Niño, and elevated seed production follows, paralleling associations with dry seasons. Our results provide evidence of a shift in allocation from leafing to fruiting in response to a warming phase of ENSO. This shift may enable plants to take advantage of higher light availability, while coping with higher atmospheric water demand and lower water supply. These findings might be an indicator of adaptive strategies to optimize reproduction and resource acquisition.
Highlights
The El Niño–Southern Oscillation (ENSO) is the largest source of interannual climate variability in much of the tropics
Most tropical plants exhibit distinctive seasonal phenologies driven by the seasonal movements of the Inter Tropical Convergence Zone and associated climate variation, phenologies that are generally interpreted as adaptive[1,2,3,4]
Responses to ENSO have been detected from satellite observations of NDVI, a proxy for leaf phenology[15], with differential responses depending on forest type[16]
Summary
The El Niño–Southern Oscillation (ENSO) is the largest source of interannual climate variability in much of the tropics. We might hypothesize that wind-dispersed species enhance seed production during windy years or that plants prone to embolism reduce leaf area before severe droughts These and similar hypotheses regarding optimal allocation strategies require that plants are able to anticipate future windy conditions or future drought severity at the time of bud formation and differentiation to avoid subsequent fruit abortion or early termination of leaf life. Such anticipation is feasible if plants respond to a predictable interannual climate cycle; for example, by investing in leaves during the wet phase of a large climatic event, when water is not limiting, and trading leaves for fruits during the following phase of the event when drought is likely
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