Proposing the solar wind-energy-flux hypothesis as a driver of interannual variation in tropical tree reproductive effort tropical tree reproduction

Abstract

A growing body of research documents how the El Niño Southern Oscillation (ENSO) results in short-term changes in terrestrial environmental conditions, with the potential to drive ecosystem processes as the duration and severity of ENSO events increases with anthropogenic climate change. An ENSO positive phase results in anomalous patterns of rainfall and temperature throughout the tropics that coincide with leaf flush and increased fruit production in tropical forests worldwide. However, our understanding of possible mechanisms underlying this natural phenomenon is limited. Furthermore, flowering in tropical trees anticipates ENSO development, motivating the continued search for a global phenological cue for tropical angiosperm reproduction. We propose the solar energy flux hypothesis: that a physical energy influx in the Earth’s upper atmosphere and magnetosphere generated by a positive anomaly in the solar wind preceding ENSO development, cues tropical trees to increase allocation of resources to reproduction. We show that from 1994-2013, the solar wind energy flux into the Earth’s magnetosphere (Ein) is more strongly correlated with the number of trees in fruit or flower in a Puerto Rican wet forest than the Niño 3.4 climate index, despite Niño 3.4 being a previously identified driver of interannual increases in reproduction. We discuss the idea that changes in the global magnetosphere and thermosphere conditions via solar wind-effects on global atmospheric circulation, principally a weaker Walker circulation, cue interannual increases tropical tree reproduction. This may be a mechanism that synchronizes the reproductive output of the tropical trees to changes in environmental conditions that coincide with ENSO. Thus, space weather patterns may help explain terrestrial biological phenomena that occur at quasi-decadal scales.

Climate-growth relations of congeneric tree species vary across a tropical vegetation gradient in Brazil

“…These characteristics can favor carbon gain, reduce water stress caused by drought and modulate growth (Estrada-Medina et al, 2013). Tradeoffs between reproduction and growth may also be under influence of ENSO events (Brodribb et al, 2020;Hogan et al, 2019) and may thus also drive these differences between species. Differences in growth responses between sites may relate to soil differences: savannah Entisols (sandy) and dry-forest litholic soils (FAO, 2014;Santos et al, 2011Santos et al, , 2018 show different water retention capacities.…”

Variações estruturais, químicas e de crescimento do lenho de espécies distribuídas ao longo de um gradiente de vegetação neotropical sazonal (floresta sempre verde-savana-floresta seca) e suas relações com as mudanças climáticas

“…Essas características podem favorecer o ganho de carbono, reduzir o estresse hídrico causado pela seca e modular o crescimento(Estrada-Medina et al, 2013). As compensações entre reprodução e crescimento também podem estar sob influência de eventos ENSOHogan et al, 2019) e, portanto, também podem impulsionar essas diferenças entre as espécies. Diferenças nas respostas de crescimento entre os locais podem estar relacionadas a diferenças de solo:…”