September 11, 2012

Pinyon Pine Trees Are Dying In The American Southwest

Michael Harper for — Your Universe Online

The Pinyon Pine trees of the American southwest are dying off in large numbers, and many researchers have already guessed what is to blame: the heat.

Well, and pine beetles.

While it may seem like common sense to blame the death of thousands of trees and other forms of vegetation on extreme heat and dry conditions, some researchers at the University of Arizona are looking past the cause and into the effect. Namely, what will happen to the area if the climate continues to get warmer and the trees continue to die?

“We know the climate in the Southwest is getting warmer, but we wanted to investigate how the higher temperatures might interact with the highly variable precipitation typical of the region,” said lead author Jeremy Weiss, a senior research specialist in the University of Arizona Department of Geosciences in a statement.

To study this interaction, Weiss and his team used weather data to understand how well plants grew during times of drought.

“The approach we took allows us to model and map potential plant responses to droughts under past, present and future conditions across the whole region,” said U.S. Geological Survey senior scientist Julio Betancourt. Betancourt co-authored the paper with Weiss, along with Jonathan Overpeck, co-director of the University of Arizona Institute of the Environment.

“Our study helps pinpoint how vegetation might respond to future droughts, assuming milder winters and hotter summers, across the complex and mountainous terrain of the Southwest.”

To conduct this study, Weiss and team utilized a growing season index, which is composed of measurements such as day length, cold temperature limits and vapor pressure deficits. With this data, the team analyzed the plant life´s response to the droughts of 1953-1956 and 2000-2003.

The difference between how much moisture the air can hold when it´s fully saturated and how much moisture is actually present in the air is called the vapor pressure deficit. According to Weiss and team´s research, this deficit was a major source of plant life stress in the area. When the atmosphere is warmer, the air can hold more moisture. Therefore, in times of extreme drought, the air can soak up all the moisture from the ground and even plant life, such as the Pinyon Trees.

In analyzing the data, the researchers discovered that during both droughts, these trees suffered in staggering numbers. By studying the difference between the two droughts, however, the team will be able to determine how much drying and warming affects the plant growth. With this information, the researchers hope to be able to better predict how badly plants will suffer in future times of drought.

“When warmer temperatures combine with drought, relatively stressful growing conditions for a plant become even more stressful,” said Weiss.

“You could say drought makes that atmospheric sponge thirstier, and as the drought progresses, there is increasingly less moisture that can be evaporated from soil and vegetation to fill and cool the dry air.”

Sadly, says Weiss, this continuation of drying and warming can work in a vicious circle, causing the Pinyon Trees to die off rapidly.

“Our concern is that vegetation will experience even more extreme growing conditions as anticipated further warming exacerbates the impacts of future droughts.”

According to Betancourt, the data the team has compiled will create a “roadmap,” allowing them to predict future rough patches for the vegetation.

“The next step will be to start planning, determine the scale of intervention and figure out what can be done to direct or engineer the outcomes of vegetation change in a warmer world.”