Recent Widespread Tree Growth Decline Despite Increasing Atmospheric CO2

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Deciduous Tree, Czech Republic. Original Image

An often discussed theory has been that increasing atmospheric levels of CO2 should stimulate higher growth levels in plants.  However, this has not proven true.  Lucas C. R. Silva, Madhur Anand, and Mark D. Leithead (Global Ecological Change Laboratory, School of Environmental Sciences, University of Guelph) have published an article titled „Recent Widespread Tree Growth Decline Despite Increasing Atmospheric CO2.“  The abstract to their paper reads:

The synergetic effects of recent rising atmospheric CO2 and temperature are expected to favor tree growth in boreal and temperate forests. However, recent dendrochronological studies have shown site-specific unprecedented growth enhancements or declines. The question of whether either of these trends is caused by changes in the atmosphere remains unanswered because dendrochronology alone has not been able to clarify the physiological basis of such trends.

Methodology/Principal Findings

Here we combined standard dendrochronological methods with carbon isotopic analysis to investigate whether atmospheric changes enhanced water use efficiency (WUE) and growth of two deciduous and two coniferous tree species along a 9° latitudinal gradient across temperate and boreal forests in Ontario, Canada. Our results show that although trees have had around 53% increases in WUE over the past century, growth decline (measured as a decrease in basal area increment – BAI) has been the prevalent response in recent decades irrespective of species identity and latitude. Since the 1950s, tree BAI was predominantly negatively correlated with warmer climates and/or positively correlated with precipitation, suggesting warming induced water stress. However, where growth declines were not explained by climate, WUE and BAI were linearly and positively correlated, showing that declines are not always attributable to warming induced stress and additional stressors may exist.

Conclusions

Our results show an unexpected widespread tree growth decline in temperate and boreal forests due to warming induced stress but are also suggestive of additional stressors. Rising atmospheric CO2 levels during the past century resulted in consistent increases in water use efficiency, but this did not prevent growth decline. These findings challenge current predictions of increasing terrestrial carbon stocks under climate change scenarios.

Read the full article in PDF by clicking here.

Citation: Silva LCR, Anand M, Leithead MD (2010) Recent Widespread Tree Growth Decline Despite Increasing Atmospheric CO2. PLoS ONE 5(7): e11543. doi:10.1371/journal.pone.0011543

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