Monday, September 5, 2016

Study on old trees


The oldest trees in the world are often in the most stressful environments, or so it seems. Yet, there has never been a quantitative attempt to assess tree longevity.

Di Filippo et al. make a first attempt at this by analyzing tree-ring data for broad-leaved deciduous trees in the Northern Hemisphere.

Given the massive impact of humans on old-growth forests, any study like this will have caveats, but the data are interesting.

For example, they report that 300-400 years is a good baseline for tree lifespan (if that concept even applies to trees).  They also report a maximum longevity of 600-700 years for deciduous trees in general.

They also show that the really old trees spent a long time growing slowly. The idea is that mortality rates increase with size, so staying small is a good way to avoid mortal blows like wind throw.

The relationship they show with maximum age for Fagus was interesting. Essentially, in warm places, the maximum age of Fagus was a lot less than in cold places. They cannot answer whether this is a direct or indirect effect, but they did not find the same relationship for Quercus species.

The authors don't believe the evidence assembled indicates a biological limitation to longevity in trees, e.g. meristems senesce after a certain amount of time.

Instead, trees can only roll the dice so many times. And it's hard to roll the dice for more than a few hundred years and not lose.

Di Filippo, A., N. Pederson, M. Baliva, M. Brunetti, A. Dinella, K. Kitamura, H. D. Knapp, B. Schirone, and G. Piovesan. 2015. The longevity of broadleaf deciduous trees in Northern Hemisphere temperate forests: insights from tree-ring series. Frontiers in Ecology and Evolution 3.

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