Biology ETDs

Publication Date

Summer 7-28-2017


The Southwestern United States is currently experiencing severe drought, resulting in the mortality of many tree species. Piñon-juniper woodlands are an extensive biome in the Southwest, and are highly vulnerable to extended periods of drought that lead to tree mortality. Specifically, Pinus edulis populations are decreasing due to increasingly arid conditions. I used dendrochronology to investigate how tree growth rings of Pinus edulis reflect severe drought in living and dead trees. I also investigated how severe drought affects Pinus edulis along an altitudinal gradient. Tree core samples were taken from currently living and dead trees, as well as from trees at three elevations separated by 100 m in elevation. Growth rings were cross-dated and measured, and widths were statistically compared between all living and dead trees to find years where growth may have differed. Widths were also compared between the three elevation sites. I sought to differentiate between two mortality-related hypotheses: 1) trees that died had a lifetime of underperforming compared to surviving trees and lacked the resources to deal with severe drought, or 2) trees that died consistently outperformed surviving trees and in doing so were closer to physiological limitations when stressed. I also hypothesized that, across elevations, trees at lower elevations would exhibit less growth and greater variability in growth compared to higher elevations. My results indicate that trees that died began to experience decreased growth compared to surviving trees following the drought of the 1950s, and that they had a higher variability in growth that was highly correlated with precipitation. I also found that trees at higher elevations had a higher variability in their growth, while trees at lower elevations may not be able to tolerate severe drought and may periodically die and then re-establish. Using tree rings offers the chance to compare growth patterns to known climate events and see the response of a tree. This knowledge is important for understanding how tree mortality will affect piñon-juniper woodlands in the future, and how to best predict ecosystem shifts.




drought, pinyon pine, dendrochronology, tree mortality, elevation gradient

Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Committee Member (Chair)

William Pockman

Second Committee Member

Marcy Litvak

Third Committee Member

Valerie Trouet