Drought and cool temperature cue general flowering synergistically in the aseasonal tropical forests of Southeast Asia

Abstract

The family Dipterocarpaceae, along with species from many other families, flower synchronously at irregular intervals of several years in the extensive humid forests of Southeast Asia. The intermittent mast seeding in these forests satiates seed predators whose populations remain low due to starvation in non masting periods, effectively increasing seed survival and seedling recruitment. A previous study demonstrated that a synergistic interaction between drought and cool temperatures, instead of either climate factor alone, best explains the occurrence of general flowering events observed over 14 years at the Pasoh Research Forest, Malaysia. However, several measures of drought were proposed and which drought measure should be used to explain general flowering remains untested. Here we examined the relationship between flowering of five Shorea species and three drought indices, the difference between the mean daily accumulation of precipitation and a threshold level of precipitation, water deficit and antecedent precipitation index. Our analyses confirmed that for most of Shorea species we studied the synergistic model that considers both cool temperature and drought performs the best regardless of the choice of drought index. In addition, a simplest drought measure using cumulative precipitation is sufficient to explain flowering activities in Shorea species.

Testing the environmental prediction hypothesis for community‐wide mass flowering in South‐East Asia

“…The hypothesis stresses that environmental cues used for flowering (i.e., a proximate factor) impart a significant success on seedling recruitment (i.e., an ultimate factor), suggesting flowering cues are linked to benign environmental conditions suitable for seed germination and seedling establishment. Proximate cues for synchronized flowering of tropical plants include drought (Brearley et al., 2007; Curran et al., 1999; Kobayashi et al., 2013; Sakai et al., 2006; Whitmore, 1984), El Niño Southern Oscillation (ENSO; Cannon et al., 2007; Chechina & Hamann, 2019; Numata et al., 2003; Wich & Van Schaik, 2000), cloud‐free conditions and high solar radiation (Ng, 1977; van Schaik et al., 1993; Wycherley, 1973), a drop or a rise in mean temperature (Appanah, 1985, 1993; Wycherley, 1973), a drop of minimum temperature at night (Ashton et al., 1988; Yasuda et al., 1999), and a synergism of drought and cool temperature (Azmy et al., 2016; Chen et al., 2018; Satake et al., 2019; Ushio et al., 2019). Using drought as a flowering cue should be advantageous in less seasonal climates because drought‐induced mortality and/or leaf shedding of canopy trees increases light levels in the understory, providing favorable regeneration environments for seedlings (Williamson & Ickes, 2002).…”

Tropical phenology: Recent advances and perspectives

“…With new modeling frameworks to test alternative hypotheses, it is possible not only to evaluate the individual cues, but also to examine multiple cues that may work sequentially. In order to investigate climate conditions that trigger flowering, Satake, Chen, and Kosugi () and Wright, Calderón, and Muller‐Landau () construct models to investigate associations between flowering events and climatic conditions. Chen et al () and Satake et al () report that drought and cool temperature variations within a 2–3‐month period synergetically trigger flowering of emergent trees in genus Shorea in a SE Asian rainforest.…”

“…In order to investigate climate conditions that trigger flowering, Satake, Chen, and Kosugi () and Wright, Calderón, and Muller‐Landau () construct models to investigate associations between flowering events and climatic conditions. Chen et al () and Satake et al () report that drought and cool temperature variations within a 2–3‐month period synergetically trigger flowering of emergent trees in genus Shorea in a SE Asian rainforest. Wright et al () conclude that precipitation > 5 mm per day for a few days after a period (~40 day) of dryness triggers flowering of two woody species in a seasonal Neotropical forest.…”

Phenology in the tropics: Physiological controls revealed by long‐term monitoring and predictive models

“…This special collection of papers features recent progresses in the understanding of flowering, leaf flushing, resource allocation revealed by long‐term monitoring and application of new statistical techniques in tropical Asia (Nakagawa, Ushio, Kume, & Nakashizuka, ; Niiyama, Ripin, Yasuda, Sato, & Shar, ; Satake, Chen, & Kosugi, ) and Neotropics (Wright, Calderón, & Muller‐Landau, ). It is complementary to a recent special section in another journal (Morellato, Abernathy, & Mendoza, 2018), which featured papers of similar scope from Neotropics (three papers) and Africa (six papers) (Morellato, Abernathy, & Mendoza, ).…”

“…The most unique phenological feature in SE Asian tropical forests, not found in American or African tropical forests, is supra‐annual flowering and fruiting known as “general flowering” and “community‐wide masting” (Sakai, ). Satake et al () evaluate multiple climate factors and their interactions with a statistical modeling that incorporates threshold and lag time for precipitation and temperature‐related climate indices. Similar to the conclusion by Chen et al (), the results support the view that drought and cool temperature synergistically determine supra‐annual flowering patterns of dominant trees in Dipterocarpaceae.…”