Tropical trees shed leaves on internal rhythms, not to capture more sunlight
Tan ZH, Yang LY, Hu YH, Song L, Zeng JY
Phenology
Tropical rainforests you might picture as lush and evergreen actually shed and flush leaves on seasonal schedules, and it turns out those schedules are driven by the trees' own internal clocks, not by a strategy to soak up more sunlight.
Scientists used to think tropical trees shed old leaves and grow new ones at strategic times to capture as much energy from the sun as possible. This study tracked leaf patterns across an entire forest community for 13 years and found that changing the timing of leaves made almost no difference to how much carbon the forest actually absorbed each year. The trees seem to be following built-in rhythms, the way many living things follow internal clocks, rather than fine-tuning their behavior for maximum efficiency.
Key Findings
Seasonal variation in leaf amount and age structure had negligible effects on annual carbon gain across 13 years of community-level data.
The difference in annual carbon uptake between models using fixed versus seasonally-varying photosynthetic capacity was statistically insignificant.
Results support the 'intrinsic rhythm' hypothesis over the 'carbon-gain benefit' hypothesis, suggesting leaf dynamics are governed by internal biological constraints.
chevron_right Technical Summary
A 13-year study of a tropical rainforest in China found that seasonal leaf-dropping and leaf-flushing patterns do not meaningfully boost annual carbon uptake. Trees appear to follow internal biological rhythms rather than timing their leaves to maximize photosynthesis.
Abstract Preview
Original paper
Can Carbon Economy Explain Leaf Dynamic Seasonality in a Tropical Seasonal Rainforest?
AbstractSeasonal leaf dynamics in tropical rainforests directly affect canopy photosynthetic capacity and carbon assimilation. Although hypotheses such as water stress, solar light, and herbivore p...
open_in_new Read full abstractAbstract copyright held by the original publisher.
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