Southwestern Tree Degradations Continue, Extremes of Weather Killing on Both Wet & Dry Sides

Alex Wierbinski's picture

By Alex Wierbinski - Posted on 03 October 2019



Semi-Arid Forest Dilemma
Semi-Arid Forest Dilemma, long-term declines in tree growth, even with no change in average precipitation, Deborah Lee Soltesz/CC 1.0 Universal.
In the semi-arid forests of the western U.S., increases in rainfall extremes – wetter wet years and drier dry years – can lead to long-term declines in tree growth, even with no change in average precipitation. (Deborah Lee Soltesz/CC 1.0 Universal)


Tree Degradations Continue, Extremes of Weather Killing on Both Wet & Dry Sides

Increasing Precipitation Extremes Driving Tree Growth Reductions Across Southwest,
University of Arizona, October 2, 2019.


"In many parts of the United States, tree growth responds more strongly and consistently to dry years than it does to wet years, so increases in growth during wet years does not completely offset reductions in growth during drought."

Increasing Rain & Tree Death
"Because of this, increases in rainfall extremes can lead to long-term declines in tree growth, even with no change in average precipitation. This is particularly true for forests of the Southwest."

"...analyzed long-term tree-ring records for more than 1,300 sites across the United States. Tree rings document yearly tree growth in response to seasonal climate changes for the full life span of the tree, providing a window into tree growth hundreds of years into the past."

"By looking at how tree growth responded to climate in the past, we were able to investigate how changing precipitation extremes are likely to affect our forests."

The Search
"The authors used tree-ring data to identify species vulnerable to degradation, or potentially even large-scale mortality, if rainfall extremes continue to increase."

Found Southwest Degradation
"...surprised to find most of the major tree species of the U.S. Southwest - a region where precipitation extremes are changing most rapidly - showed clear evidence of strong negative growth responses to precipitation extremes."

Regional Classics in Decline
"The Southwest's iconic ponderosa pine, Douglas-fir, and piñon pine were particularly affected, as were the bur oak in the upper Midwest, each seeing significantly reduced growth during dry years that wasn't balanced by the growth spurred by wetter years."

"Key Southwest tree species may be at risk as precipitation extremes intensify. The loss of these important species could have profound negative consequences for society, including large reductions in regional ecosystem carbon storage."




The increasing temperatures are fueling increased tropical flows in Southern Latitudes, while turning snow into rain at higher latitudes. Desert trees are evolved for a specific climate. Changes in the timing and temperatures of the rain can push them out of their preferred range of climate conditions, even if those changes consist of more rain. More rain will create ideal conditions for different species that those now dominant.

August 2019
Global Warming Driving Increase in Numbers and Intensity of Southwestern US Monsoons

What the study above failed to account for is the extreme damage the increasing heat is doing by driving longer, hotter dry seasons that not only fry the deserts, but also replace snow with rain in the Colorado watersheds, which brings even less water to make up for the longer, hotter, and drier Summers.

Too Big Not to Fail
The increased tropical flows across our Southwest Deserts are a symptom of our climate dysfunction, not a solution. The vast, ever-increasing populations of the already brutally overpopulated megacities of the Southwest, being primarily composed of LA, Phoenix, and Tuscon, are going to find themselves increasingly short of water to cover their basic needs for their existing native populations, let alone provide resources for any additional irresponsible growth, as this century progresses.

Growth Cycle of Doom
The vast populations we so unwisely let sneak into the the Southwest of the US will be forced to shrink to stay below available water supplies, likely by 2050 at the very latest. We are growing vast populations into drying deserts that are warming and drying further and faster in direct response to our relentless population expansions.

We are accelerating towards disaster...



The Southwestern United States

Jan 2019
Our current drought is worse than most megadroughts, new study says


Dec 2018
Another Tree Ring Survey
Observing the Decline of the Doomed Forests in the Southwestern US


Sept 2018
Colorado River Flows Drop By 15 Percent Over Last 100 Years


March 2018
Climate Change News: Whole Southwest of US Undergoing Aridification


Nov 2017
Tree News, Widespread Pinyon Pine Mortality Throughout Much of the Southwestern U.S.


April 2007
Permanent Drought for Southwest
Permanent drought predicted for Southwest,



Plant & Tree News & Reseach, Summer and Fall of 2019


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