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Global Warming doesn’t actually benefit Plants

Global warming signs

Things are heating up. It’s no secret that the mercury is rising and we are to blame. Sure, there is a lot of uncertainty, for example how long we have until we simply cannot reverse global warming, or worse, how long we have before we cannot survive on the planet. That would be a good question to answer; maybe it will get the people who can actually do something to fix it, to make a change.

The planet works in sometimes-unforeseen ways, sometimes that is good and sometimes that is bad. The hope was that global warming might be offset – if only for a short time – by the increased energy in the system [meaning longer warm periods], which would increase the growing season. It is unfortunate then, that this turns out not to be the case.

Whether air temperature or day-length is the dominant factor determining the date of leaf-out is actually known for very few of the thousands of species of trees and shrubs, so the assumption was made based only on that data.

Some 16,000-plant species from diverse climate zones are cultivated in the Garden, and researchers took advantage of this resource to monitor the timing of leaf-out in nearly 500 different species of woody plants.

“Such a comprehensive phenological study has never been undertaken before,” said Renner Director of Munich’s Botanic Garden.

Temperature and day-length are the primary triggers of leaf development, and selective forces during the course of evolution have determined which signal is actually used in a given species. The results of this new study show that, in many woody plants that thrive in warmer southern climes, day-length acts as a safety barrier so that these trees don’t risk having their leaves damaged by late frosts – and increased temperature does not, unfortunately, override this barrier.

 “This evolutionary adaptation is particularly striking in the case of beech trees, in which leaf-out occurs relatively late in the year,” Renner adds. “The beech in Central Europe is a relic of the warmer temperatures that prevailed during the Tertiary Period; leaf emergence requires 13 hours of daylight, regardless of whether the spring was warm or cool and moist.”

For example, southern species develop their first leaves up to a month later than plants from a temperate climate and the more of these thermophilic species expand their range northwards as temperatures rise, the more late flushers we could have. Moreover, species that are already adapted to the [normal] northerly climates are unlikely to undergo leaf-out at ever-earlier times, because they require prior exposure to a certain number of chilly days to prime the process.

The bottom line is that while nature might save itself — after all it is arrogant to think nothing can survive on the planet just because we cannot – we need to start thinking about how we can change what we’re doing for our own good. If we cannot, then well… at least we won’t die cold.

Zohner, C., & Renner, S. (2014). Common garden comparison of the leaf-out phenology of woody species from different native climates, combined with herbarium records, forecasts long-term change Ecology Letters DOI: 10.1111/ele.12308

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