Tree Mortality Patterns and Processes

Science Center Objects

Natural climatic variability, including episodic droughts, has long been known to trigger accelerated tree mortality in forests worldwide, including in the Southwest U.S. Scientific understanding of the process drivers and spatial patterns of tree mortality is surprisingly limited, constraining our ability to model forest responses to projected climate changes. The onset of regional drought since the late 1990s has resulted in extensive die-off episodes of multiple tree species across millions of acres in the Southwest, fostering substantial collaborative tree mortality research in this region. Ongoing tree mortality research in northern New Mexico includes: reconstruction of historic forest dieback patterns; monitoring of forest and woodland demographies (tree mortality and regeneration); experimental determination of physiological thresholds of drought- and heat-induced tree mortality; relationships between tree growth, drought stress, insects/diseases, and mortality; remote-sensing of landscape-scale patterns of forest stress and die-off; documentation of regional, national, and global patterns of forest die-off; and efforts to improve models of tree mortality processes.

Dead ponderosa pine in Great Basin National Park, Nevada
Dead ponderosa pine in Great Basin National Park, Nevada. Photo by Craig Allen, USGS, 2015. Public domain.
Dead piñon (Pinus edulis), Bandelier National Monument, Jemez Mts., NM
Dead piñon (Pinus edulis), Bandelier National Monument, Jemez Mountains, NM. Trees that died in 2002-2003. Photo by Craig Allen, USGS, 2007. Public domain.
A dramatic display of during piñon pine die-off in New Mexico.
In the summer of 2002, piñon pine (Pinus edulis) began dying en masse from drought stress and an associated bark beetle outbreak. Jemez Mouintains near Los Alamos, NM, October 2002. Credit: Craig Allen, USGS. Public domain.
A dramatic display after piñon pine die-off in New Mexico
The same landscape as above: after the needles dropped, grey skeletons of piñon pine (Pinus edulis) remain, with surviving Jumiperus monosperma still green. Jemez Mountains, NM. May 2004. Photo by: Craig Allen, USGS. Public domain.
Dead ponderosa pine (Pinus ponderosa), Jemez Mts, NM. November, 2013.
Dead ponderosa pine (Pinus ponderosa), Jemez Mts, NM. November, 2013. Photo by: Craig Allen, USGS. Public domain.
Dead ponderosa pines in the Jemez mountains, New Mexico.
Dead ponderosa pines in the Jemez mountains, New Mexico. Photo by: Craig Allen, USGS. Public domain.
Dead white fir (Abies concolor) and Douglas-fir (Pseudotsuga menziesii in the Upper Frijoles mountains, New Mexico, 2003.
Dead white fir (Abies concolor) and Douglas-fir (Pseudotsuga menziesii in the Upper Frijoles mountains, New Mexico, 2003. Photo by: Craig Allen, USGS. Public domain.
Sequoia Nat'l Park, showing mortality of multiple conifer species, particularly ponderosa pine, sugar pine
Sequoia Nationall Park, mortality of multiple conifer species, particularly ponderosa pine (P. ponderosa), sugar pine (Pinus lambertiana), and white fir (Abies concolor). October 2015. Photo by: Craig Allen, USGS. Public domain.
Dead ponderosa pine (P. ponderosa), Yosemite Nat'l Park.
Dead ponderosa pine (P. ponderosa), Yosemite National Park. Nov. 2016. Photo by: Craig Allen, USGS. Public domain.
Dead ponderosa pine (P. ponderosa) and sugar pine (P. lambertiana), Yosemite National Park
Dead ponderosa pine (P. ponderosa) and sugar pine (P. lambertiana), Yosemite National Park. Photo by: Craig Allen, USGS. Public domain.

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