So how did they survive the Medieval Optimum and the Little Ice Age?
From a Purdue University media release:
Warmer, drier summers and extreme weather events considered possible as the climate changes would be especially troublesome – possibly fatal – for walnut trees, according to research at Purdue University…
“Walnut is really restricted to sites not too wet or dry. It has an extremely narrow range,” said Jacobs, whose findings were published in the December issue of Annals of Forest Science.
“We suspect and predict that climate change is going to have a real impact on walnuts. We may see some type of decline of the species.”
Specifically, walnuts would have difficulty tolerating droughts that could be associated with a changing climate.
“Changes in moisture could restrict its ability to survive without irrigation,” Jacobs said. “Almost all climate change models predict that climates will become drier.”
Walnuts are also sensitive to cold, so much so that they have developed a defense mechanism against late frosts. Jacobs said walnut trees don’t begin sprouting leaves until almost a month after other trees in the spring.
That defense mechanism could be compromised by extreme weather events associated with climate change scenarios. Late spring frosts after walnuts have developed leaves could kill trees.
“That, on top of the increase in temperatures, would be a problem for walnut,” Gauthier said. “The trees would basically shut down”…
Our guess is that Walnut trees — and all flora and fauna, generally — are hardier than alarmists would have us believe. Otherwise, what would have survived that last 1,000 years of climate fluctuation?