We know from scientific studies there have been 66 prolonged droughts in the last millennium. Studies have shown that of all those dry periods, only three were similar to the present drought in the western U.S. in the past 1,200 years.
In a story reported in Digital Journal in December 2014, scientists using precipitation data and tree ring history were able to determine the present California drought is the worst in the past 1,200 years. But what makes this drought different is the heat, coupled with the lack of precipitation, making it an example of “consequential climate change.”
William Anderegg is a biologist at Princeton University who studies forests and climate change. “The droughts of the future look to be more frequent and more severe,” Anderegg said this week at the annual fall meeting of the American Geophysical Union.in San Francisco, California.
The Legacy effect
Anderegg explained that it’s been demonstrated that droughts have a “legacy effect” on trees. In other words, the damage done to a tree during a drought will have an effect on the tree long after a drought is over, lasting, at least, four years and sometimes longer, resulting in serious implications for the Earth’s climate.
Why is this? Quite simply, scientists think of forests as natural “carbon sinks,” absorbing and trapping carbon dioxide, helping to reduce greenhouse gas emissions in the atmosphere, Up until this past year, no one really had any idea just how many trees we had on this planet, and until recently, it was assumed there were about 400 billion trees on Earth. Now we know there are a whopping 3.04 trillion of them.
With trees being an important part of our natural world helping to mitigate the effects of climate change, it was all the more important to understand how trees recover from drought conditions and if there would be any lasting damage to the tree. And drought can kill a tree in a number of ways, from making it more susceptible to bark beetles, to setting up conditions that could cause wildfires capable of burning down a whole forest, said Anderegg,
A tree’s hydraulic factors at play
Plants suck up water through their xylem, a vascular system much like our blood vessels, that winds its way through the tree’s roots and branches, creating a pressure gradient. The less water there is in the soil, the harder the trees have to suck to get water.
“At a certain point, which varies by species and tissue, we start to get air bubbles pulled into these xylem elements,” Anderegg said. Just like in humans, when enough of these air bubbles get into the xylem, they cause an “air embolism.” The embolism blocks the flow of water and nutrients, causing “hydraulic failure.” Anderegg says this problem is the one we need to fully understand to predict tree mortality, according to the Washington Post.
In follow-up studies, Anderegg and his colleagues discovered differences in plant hydraulics seemed to differ, even among trees in the same forest, while some tree species such as the trembling aspen (Populus tremuloides) would die off altogether if hotter conditions continued.
The loss of our forests due to drought mitigated climate change is something we must take very seriously. In a new study, published Thursday in the journal Science, Anderegg and his fellow researchers demonstrate that legacy effects actually do exist
The study, Pervasive drought legacies in forest ecosystems and their implications for carbon cycle models, was published in the journal Science.
