Natural Colour? How are the colours of New England in the fall changing?

New England is known for the colours of the trees in autumn. The leaves turn a striking red. However, research in PLOS One suggests that global warming could alter the appearance of autumn colours.

There are a few things that could turn the colour of leaves. The days becoming shorter could be a signal to prepare for winter. It could be a turn in temperature or a change in precipitation. A study in PLOS One: Predicting Climate Change Impacts on the Amount and Duration of Autumn Colors in a New England Forest by Marco Anchetti et al. has studied long term records of hardwood forests in New England and found a correlation between variation in temperature and precipitation with the colours of leaves.

As a general rule they predict that autumn colours will last longer if temperatures rise broadly with IPCC predictions. There are some problems with the model and this is easy to spot because the authors have included helpful phrases like: Indeed, we found that when run under future climate scenarios, the MLR predictions were sometimes not reliable: ‘crossing-over’ commonly occurred, for some species as early as 2020 or 2030, so that (for example) f₅₀ was predicted to occur before f₂₅. In English, this means that 50% of the leaves were predicted to have fallen before 25% of the leaves. Clearly that’s a problem for the MLR model.

What makes the paper interesting isn’t the hope that you can set your watch by the colour of canopy, but rather that it presents some simple demonstrations of the problems of modelling the effects of climate change and how you can take steps to reality-check your predictions instead of simply announcing a computer said it, so it must be true. Even with their preferred CDD/P model they note:

This approach also predicted dubious patterns in the case of Fraxinus americana, for which e.g. c₉₀ (90% canopy coloration) was predicted to occur after f₉₀ (90% leaf fall) originating from the inability of the CDD/P model to describe the current interannual variations of leaf fall in this sole species.

There’s clearly no simple linear function you can apply to predict the future, but Anchetti et al‘s modelling raises interesting possibilities for the changing ecology of hardwood forests. The change in fall could also have biological impacts elsewhere.

Archetti M., Richardson A.D., O’Keefe J. & Delpierre N. (2013). Predicting Climate Change Impacts on the Amount and Duration of Autumn Colors in a New England Forest, PLOS One, 8 (3) e57373. DOI: 10.1371/journal.pone.0057373

Photo: 365/274 Finally a real Fall day by Rachel (justmakeit) / Flickr. [cc]by-nc[/cc]