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Ontogenic changes rather than difference in temperature cause understory trees to leaf out earlier
1Institute of Botany, University of Basle, 4056, Basle, Switzerland.
The New Phytologist
|January 26, 2013
Summary
Canopy trees exhibit later leaf emergence than understory trees due to ontogenic changes, not microclimate. This finding impacts predictions of forest phenology in response to climate warming.
Area of Science:
- Forest Ecology
- Plant Phenology
- Climate Change Biology
Background:
- Understory trees leaf out earlier than canopy trees in temperate climates, but the underlying causes are not fully understood.
- Potential explanations include ontogenic changes (age-related development) or microclimatic variations within the forest.
- Understanding this discrepancy is crucial for predicting forest responses to climate change.
Purpose of the Study:
- To investigate whether the difference in leaf-out timing between understory and canopy trees is driven by ontogenic changes or microclimatic factors.
- To compare leaf development in seedlings and adult trees at different forest heights.
- To assess the influence of microclimate on leaf emergence timing.
Main Methods:
- Five deciduous tree species seedlings were grown at understory and canopy levels (45m) in a Swiss Jura Mountains forest.
- Leaf development of seedlings was compared with conspecific adults.
- Microclimatic conditions, including temperature, were monitored at both understory and canopy heights.
Main Results:
- Seedlings at canopy level exhibited leaf unfolding 10-40 days earlier than conspecific adults.
- Understory seedlings flushed approximately 6 days later than canopy-height seedlings, correlated with slightly cooler temperatures at lower heights.
- The study indicates ontogenic changes, not vertical thermal profiles, are the primary drivers of the observed leaf emergence differences.
Conclusions:
- Later leaf emergence in canopy trees compared to understory trees is primarily due to ontogenic changes, not microclimatic differences.
- Assumptions that phenological data from juvenile trees in controlled experiments can predict forest-wide responses to climate warming may be flawed.
- Further research is needed to refine models predicting forest phenology under changing climatic conditions.
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