Conditions and Trends of Sky Island Forests in Big Bend National Park

A Sky Island is an isolated mountain range that rises above the surrounding lowland “sea.” In Big Bend National Park, the sky island forests, which occur in the Chisos Mountains, are surrounded by a “sea” of desert. Located at the northern end of the Chihuahuan Desert, only 2% of the park is woodland. But what beautiful and ecologically important woodlands they are.

Forests and woodlands throughout the world are threatened by environmental change, and the forests of Big Bend are no exception. Some of the main stressors driving change in forests are increased temperature, intensified drought, greater pest outbreaks, and hotter and larger wildfires—all related to human-induced climate change. Long-term changes in factors affecting forests, as well as specific weather events in 2011—an extended freeze followed by the most acute one-year drought on record—led the National Park Service, under the Natural Resource Condition Assessment Program, and its partners to evaluate the status and trends of the sky island forests in Big Bend.

We’ll share a few of the study’s results here, but to learn more AND see some beautiful photos and informative maps, see the authors’ story map for the project.

The authors found that:

• From 2003 to 2019 there was significant, recent tree mortality, shifts in forest stand structure, and increases in dead fuel loads across the Chisos Mountains.
• Tree mortality was most extreme in the Mexican pinyon pine, the dominant pine species throughout the mountain range.
• The five-day freeze in February of 2011 and the following drought were key in the forest changes observed.
• The results of the study and climate projections suggest a high probability of continued change in the forests and woodlands of the Chisos Mountains and mortality risk of drought sensitive tree species.

Active Processes:

Some of the sites sampled for this work will be resampled in 2022/2023 as part of a separate project. A wildfire burned through the Chisos Mountains high country in April 2021, and the new sampling effort will study the effects of the fire. Having conducted the previous work allows the researchers to differentiate the effects of the drought (and freeze) and the fire on forest structure.

The story map and information in this article are based on Barton, A., and H. Poulos. 2021. Evaluating Conditions and Trends for Sky Island Forests in the Chisos Mountains, Big Bend National Park: Focused Condition Assessment Report. Natural Resource Report. NPS/BIBE/NRR–2021/2290. National Park Service, Fort Collins, Colorado.

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