Effects of disturbance and drought on the forests and hydrology of the Southern Rocky Mountains

Statement of Problem:

Western mountains, including the Southern Rocky Mountains of northern New Mexico, are increasingly subject to accelerating and transformative changes in forest landscape processes driven by climate-forced alterations in water and ecosystem dynamics. Warming temperatures across western North America are driving earlier snowmelt and increasing proportions of rain versus snow, along with increases in atmospheric vapor pressure deficit, resulting in: a) altered and diminished water resources, ranging from snowpacks and stream flows to glaciers and lakes; b) decreasing plant-available-water, increasing forest drought-stress, tree growth declines, extensive insect outbreaks, and forest die-offs; and c) larger and more severe fires that affect vegetation, watersheds, and society (Stevens et al., 2017).  This project addresses these emergent changes in forest and hydrological patterns and processes in response to climate variability in Southern Rocky Mountain landscapes.

Why this Research is Important: 

Forests sequester the majority of the terrestrial biosphere’s carbon, making them key components of the global carbon cycle and potentially strong contributors of biogenic feedbacks to climatic change.  Additionally, forests provide humans with economically important and often irreplaceable ecosystem goods and services, such as carbon sequestration, clean water, wood products, biodiversity, and recreational opportunities.  Yet society’s ability to understand, predict, and respond to the effects of climatic changes on forests are limited by (1) lack of information on ongoing forest changes and their diverse causes, (2) our surprisingly poor understanding of many of the basic processes (particularly disturbances like drought-kill, insect outbreaks, fire) that drive forest dynamics, hampering our ability to forecast future changes, and (3) lack of science-based adaptation options.  Our work helps fill these gaps.  

Objective(s): 

The overall objective of this project is to investigate effects of climate variability and changing land use on long-term ecosystem dynamics, changing disturbance regimes, and related ecohydrology issues in forests of the Southern Rocky Mountains.  Our collective research will improve the understanding of the interactions between climate variability, disturbance, and forest ecosystems.  This enhanced understanding will inform effective management of these landscapes for long-term resilience and ecosystem services.

Methods:

To accomplish our objective, we will build upon our unique, long-term, place-based data sets from forested landscapes of northern New Mexico that are part of larger networks of similar data.  Specifically, we will:

1. Develop multi-century to millennial-length tree-ring chronologies for reconstruction of climate variability, including the North American Monsoon.  Tree rings provide multi-century to millennial-scale records of climate at annual to sub-annual resolution that are vital to understanding long-term patterns and drivers of climate variability.
2. Investigate drivers and patterns of long-term changes in forest structure, composition, and fire regimes.  Changing land use has altered fire regimes and forest structure and composition in many dry conifer forests across western North America. 
3. Continue and expand long-term measurements of forest plots across environmental gradients to monitor for changing ecosystem processes in response to climate variability and disturbance.  Long-term monitoring of forest plots provides critical data for assessing patterns and processes of ecosystem change. 
4. Continue long-term monitoring in Bandelier National Monument of tree growth and cellular-level xylogenesis analyses to investigate environmental drivers of tree physiological processes and monitor for emerging trends.
5. Continue multi-disciplinary research on changing tree mortality patterns, trends, and drivers at local, regional, and global scales.
6. Analyze drivers, patterns, and trends of contemporary fire in the Southwest.  We will use remotely-sensed burn severity products and new algorithms for analyzing patch characteristics to assess trends in forest fire severity characteristics in Arizona and New Mexico over the past 38 years, identifying key climatic, weather, and land management drivers of variation in fire severity.
7. Investigate how recent wildfires are impacting winter snowpack in montane forests.  We will build on existing research using remotely-sensed and field-based measurements to document snowpack depth across a gradient of fire severity in the Jemez Mountains, and assess whether there is an optimal gap size in post-fire landscapes that can maximize snowpack retention.